HAL Id: hal-00889729https://hal.archives-ouvertes.fr/hal-00889729

Submitted on 1 Jan 1998

HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, estdestinée au dépôt et à la diffusion de documentsscientifiques de niveau recherche, publiés ou non,émanant des établissements d’enseignement et derecherche français ou étrangers, des laboratoirespublics ou privés.

Growth promotants in feeding pigs and poultry. III.Alternatives to antibiotic growth promotants

Sigvard Thomke, Klas Elwinger

To cite this version:Sigvard Thomke, Klas Elwinger. Growth promotants in feeding pigs and poultry. III. Alternatives toantibiotic growth promotants. Annales de zootechnie, INRA/EDP Sciences, 1998, 47 (4), pp.245-271.�hal-00889729�

Review

Growth promotants in feeding pigs and poultry.III. Alternatives to antibiotic growth promotants

Sigvard Thomke Klas Elwinger

Department of Animal Nutrition and Management, Sweden Univ Agric Science, P.O. Box 7024,Ultuna, S-750 07 Uppsala, Sweden

(Received 2 December 1997; accepted 27 May 1998)

Abstract - On the basis of improving effects of antibiotic growth promoters in pigs and poultrybeing mediated through their regulating influence on the gastro-intestinal flora, a number of alternativeadditives and feeding strategies are reviewed. Nutrient absorption is facilitated by dietary incorporationof suitable enzyme preparations, thereby decreasing intestinal disorders and upsets. As a result, per-formance is improved, particularly in juveniles. Microbial preparations (probiotics) have also beenclaimed as alternatives to growth promoters of antibiotic type. However, the efficacy of probiotic pre-parations seems to be less consistent than the use of antibiotic-type preparations. Dietary acidifiershave also been proposed. Furthermore, the choice of ingredients and their technological treatmentshould also be considered as a strategy to tailor diets according to the specific capacity and requi-rements of the animal group. Recently, feed induced formation of lectins or peptides has been pro-posed as an efficient method to prevent diarrhoea in pigs by their action on the central regulatingsystem of intestinal fluid secretion. Finally, the environmental and management conditions of the pro-duction systems are of very great importance to secure a safe development of animals. The need formore research in the area of alternatives to antibiotic-type antibiotics is emphasised. (© Elsevier /Inra)

growth promoter / antibiotic / pig / poultry / alternatives to antibiotics

Résumé - Les promoteurs de croissance dans l’alimentation des porcs et des volailles.IIL.Alternatives à l’emploi des antibiotiques. Après un bref rappel du processus de digestion chezles espèces monogastriques, l’article décrit les divers additifs qui peuvent être proposés dans l’ali-mentation des porcs et des volailles comme alternatives à l’emploi des antibiotiques, agents promo-teurs de croissance. L’incorporation d’enzymes peut améliorer, dans des situations définies, les capa-cités digestives des animaux, notamment des plus jeunes. Les enzymes permettent une meilleureutilisation des nutriments en rendant possible leur absorption au niveau du tube digestif. Elles limi-teraient par leur action, l’incidence et la sévérité des déséquilibres intestinaux. Les probiotiques(préparations microbiennes) peuvent aussi affecter avantageusement les performances animales.Cependant, leur efficacité demeure variable et dépend de nombreux facteurs liés à l’état physiologique,

* Correspondence and reprintsTel: (46) 18 67 10 00; fax: (46) 18 67 29 95; e-mail: klas.elwinger@huv.sluse

nutritionnel et sanitaire des animaux ainsi que de facteurs liés à la viabilité et à la stabilité géné-tique des microorganismes qui entrent dans leur composition. Les acidifiants alimentaires ont égalementété proposés comme alternative. Le choix des ingrédients et de leur traitement technologique pour-rait aussi être envisagé comme stratégie pour améliorer les régimes en fonction des capacités etbesoins des animaux. La formation de lectines ou de peptides induite par l’alimentation prévien-drait ainsi les risques de diarrhées chez le porc en agissant sur le système nerveux central de régula-tion de la sécrétion intestinale. Les conditions environnementales et de gestion des systèmes de pro-duction sont également d’une importance majeure pour assurer un développement adéquat desanimaux. (@ Elsevier / Inra)

promoteur de croissance / antibiotique / porc / volaille / additifs

1. INTRODUCTION

As a background to this section, the diges-tive systems and events in pigs and poultryare briefly described. The gut flora has fas-cinated scientists for more than 100 yearsand the importance of its stability for thehealthy development of a species wasobvious before the introduction of the terms

probiosis/probiotic. The nutrient environ-ment is another area that has an impact ongastrointestinal events. Since the supple-mentation of enzymatic preparations becameeconomically feasible, such supplementsmight be tools to improve animal perfor-mance and avoid health disorders. A deepknowledge of interactions between the gas-trointestinal milieu and central mechanisms

regulating gut health opens new ways ofcontrolling animal health by balancing thedietary supply of lectins.

1.1. Digestive system of monogastricanimal species

The digestion of food and feeds involvesa series of processes along the gastrointes-tinal tract, by which dietary components arebroken down into smaller particles to faci-litate solubilisation in order to make absorp-tion possible. This is accomplished by acombination of mechanical and enzymaticalprocesses along the tract. Microorganismsare more or less, and according to animalspecies, involved in digestive activity. The

function of the mouth is chiefly to disinte-grate the ingested feed by mastication, tolubricate it for the process of swallowingand simultaneously to contribute to a regu-lation of the pH of the ingested feed by thesaliva produced in order to control themicrobial activity in the stomach. In themouth, saliva and saliva mucins selectivelyinhibit the binding of food lectins to theteeth and mouth cavity, thereby minimizingagglutination and adherence of bacteria tothe teeth [97]. Poultry have no teeth, theyswallow their feed whole. Any grinding ofthe feed occurs by grit in the gizzard. Thecrop is a semi-batch lactic acid fermenta-tion storage compartment situated craniallyto the gizzard and is specific to birds, as alsois the proventriculus localized between thecrop and the gizzard. This is an enzyme-producing organ, which corresponds to thegastric enzyme and HCI production in thestomach of for example the pig and also ofman. In the proventriculus and the gizzard ofbirds, the pH is very low [8].

The extent of digestive action in the sto-mach varies between animal species. Thepredominant digestive components in thestomach secreted by the gastric mucosa areHCI and pepsin, which are aimed at hydro-lysing protein into polypeptides. In manymonogastric species, carbohydrates are fer-mented into lactic acid and volatile fattyacids by gastric microbial fermentation. Theextent of this microbial action varies greatlybetween species and also reflects feed envi-ronment as a microbial substrate.

As in most other mammals, stomachemptying in the pig is brought about bycontractions passing down the pyloric regioninto the duodenum. Nervous and humoralfeedback mechanisms, largely in the duo-denal region, regulate the ingesta passage.Factors that trigger gastric emptying are thevolume of its content and dietary composi-tion. The rate of ingesta passage throughthe small intestine is very fast and it slowsdown successively along the small tract.Regularly it takes 2.5 h for a given particleto pass the small intestine. At this high speedof digesta passage it would be difficult formicroorganisms to colonize this region. Theepithelial cell layer is continuously regene-rating, therefore microorganisms can colo-nize the small intestine only if their proli-feration rate is faster than the sloughing rate[61].

The small intestine is the primary site forabsorption of amino acids, saccharides,lipids, vitamins and minerals. Carbohydratedigestion occurs mainly as a result ofenzymes produced by the small intestine.The breakdown products absorbed are glu-cose, galactose and fructose. Birds lack thecapacity to break down lactose as they donot produce lactase. In most mammalianspecies, lactase production decreases withthe development of the animal. As mentio-ned earlier, part of the protein digestionoccurs in the stomach. A further digestion ofprotein occurs in the small intestine by theaction of pancreatic trypsin, chymotrypsinand carboxypeptidases forming peptides andamino acids to be absorbed in the smallintestine. Nucleoproteins are digested byintestinal nucleotidases and nucleosidasesformed by the small intestine. Lipids arebroken down by lipase chiefly formed bythe pancreas and are absorbed as fatty acidsand glycerol. Of minor importance is the fatabsorption as glycerides.

Following solubilisation, minerals andvitamins are predominantly absorbed in thesmall intestine.

1.2. Importance of the gut flora

Bacteria are the most important of thesymbiotic organisms breaking down carbo-hydrates and which predominantly occur inthe hind gut of monogastric animal species.This symbiosis, which corresponds to thefermentation processes of cattle, sheep etc.,also gives monogastric animals the advan-tage of breaking-down complex structures,and also to synthesize essential nutrientssuch as vitamins and amino acids. The envi-ronmental conditions in the hindgut are cri-tical for the host animal mainly from twoaspects. In order to optimize the conditions,including those for the microorganisms, withrespect to an appropriate function of the pro-cesses in the hind gut, a certain amount ofnutrients and bulk (indigestible organic mat-ter) is needed, which has to be considered inthe feeding strategy. Secondly, the feedingstrategy has to take into account the enzy-matic capacity of the animal, implying avoi-dance of overloading the digestive systemand the abduction (transfer) of unutilizednutrients from the small intestine into thedistal part of the gastrointestinal tract, i.e.,the caecal and colonic region. An unregu-lated nutrient flow would create uncontrol-led microbial proliferation and overgrowth,causing problems to the host animal, e.g.,in horses developing the most common typeof colic.

2. FEED ADDITIVES WITHENZYMATIC PROPERTIES

Historically, the feed industry has beenreluctant to include barley in broiler diets.The relatively high fibre content associatedwith the high hull content, predominantlyoccurring in winter barleys, has earlier beenclaimed to be one reason. Theoretically, thisshould pose no substantial problem as chic-kens as well as pigs compensate for thelowered dietary energy concentration by anincreased feed intake. Unfortunately, bar-ley, like oats and rye, may contain soluble,

non-digestible carbohydrates, such as (3-glu-cans and arabinoxylans, which create pro-blems in growth performance by their highwater-binding capacity, thereby increasingmorbidity, mortality and wet litter condi-tion in poultry.

2.1. Mode of action by enzymaticpreparations

It has been demonstrated in broiler chic-kens that soluble fibre components decreasefeed intake by lowering the rate of feed pas-sage, thus lowering performance results [ 18,19, 32, 34, 44, 110]. According to theseauthors, impaired water retention in the gas-trointestinal tract results in sticky droppings,followed by impaired litter condition anddecreased hygiene and an increase in mor-tality. Furthermore, high viscosity cerealslower the rate of starch disappearance fromthe small intestine [44], affecting the micro-bial flora in the distal gastrointestinal tract.Another important feature of supplemen-ting enzymes is their capacity of makingnutrients available to the animal, whichotherwise would not be utilized. Further-

more, the improved utilization of feeding-stuffs and lowered excretion of nutrients

following enzyme supplementation hasimplications from the environmental point ofview by limiting nutrient discharge. Quan-titatively, enzymes attacking carbohydrates(carbohydrases) belong to the most impor-tant group of enzymes, compared with pro-teases and lipases. In his thesis Inborr [53]has summarized the mode of action of car-

bohydrate degrading enzymes in pig starterdiets (figure 1 ).

2.2. Impact of cereal bases and enzymesupplementation in pig diets

Nutrient digestibility and performanceresponses in pigs by enzyme preparationshave been reviewed (table 1) in order to exa-mine their quantitative effects and to exem-

plify their potential. With respect to the greatnumber of published data, this table repre-sents only a limited part of the work per-formed in this area. Even though there is avast body of information, details on themode of action are still lacking. Obviously,more research is needed to develop morepotent enzymes and to find efficient com-binations of enzyme preparations suitablefor individual and compounded feedingstuffs. Moreover, methods should be deve-loped in order to protect the potential of thesepreparations until they are expected to act.

By supplementing high viscosity barleywith (3-glucanase, Thomke et al. [1)1] ]improved piglet organic matter digestibilityand animal growth rate. Newman et al. [88]tested bacterial diastase and reported animproved nutrient digestibility of hullessbarley as well as growth performance ingrowing pigs. Administering viscous poly-sacccharides to the diet of pigs was shown toincrease pancreatic exocrine secretion andrate of gastrointestinal feed passage [16].Graham et al. [41 observed improved ilealand total tract digestibility of barley by sup-plementing (3-glucanase/pentosanase whentesting on growing pigs. By supplementinga rye-based diet with pentosanase, Thackeret al. [108] were able to report a tendencytowards an improved average daily growthrate in growing pigs (table n. These authorsconcluded that soluble pentosans did notappear to pose as large a problem for pigs asthey do for poultry.

The effect of enzyme treatment of thecereal part in a piglet diet and the dietarysupplementation of enzymes on growth per-formance and incidence of diarrhoea wasassessed by Inborr and Ogle [57] (table 0.Post weaning daily weight gains wereslightly higher for the diet based on cerealspretreated with carbohydrate degradingenzymes as compared with a negativecontrol. Bedford et al. [11] observed thatp-glucanase supplementation of a pig star-ter diet based on hulless barley significantlyimproved the apparent protein digestibility

over the entire small intestine and tended toreduce ingesta viscosity. A slight, but signi-ficant (P < 0.05), decrease was observed inthe incidence of diarrhoea in the experi-mental group compared with the control. Inone of two piglet performance tests, B6hme[14] demonstrated a significant (P < 0.05)improvement in performance. In both expe-riments, the incidence and severity of diar-rhoea was reduced, indicating that theenzyme supplementation had a beneficialeffect attributable to a stabilizing effect ofthe enzymes included in the piglet diets.

For monitoring the effects of enzymesupplementation the responses in organicmatter and energy digestibility as well as infeed efficiency may be useful measures.Growth rate seems to be inferior since thistrait may be affected by feed intake [ 110].When quantitatively evaluating the infor-mation compiled on pigs in table I, it seemslikely that piglet feed efficiency-responses

are superior to those observed in growing-finishing pigs, which seems plausible withrespect to the development occurring withage in the gastrointestinal tract. In accor-dance with what may be expected, enzymeresponses at the precaecal level to dietaryenzyme supplementation are superior tothose observed for the total tract. For piglets,an average feed efficiency-response byenzymes of approximately 4% may be cal-culated, whereas for growing-finishing pigsthis value averaged about 2% for feed effi-ciency as well as for energy digestibility(GE).

2.3. Impact of cereal bases and enzymesupplementation in poultry diets

The stage of ripeness of barley at harvesthas earlier been demonstrated to affect per-formance of broiler chickens [110]. Thiscondition was demonstrated to be overcome

by supplementation of barley diets with(3-glucanase [45, 46]. The improved perfor-mance results with barley harvested at thestage of full ripeness versus early ripenesswere demonstrated to be related to theextract viscosity of barley as a measure forthe content of p-glucans.

In comparing wheat, rye and three diffe-rent cultivars of triticale as cereal bases inbroiler chicken diets, Pettersson and Aman[94] noticed remarkable differences in birdperformance, with the poorest results on ryeand the best on wheat, with triticale in be-tween (table In. On all cereal bases, thisinvestigation also included a treatment withthe supplementation of an enzyme prepara-tion with pentosanase, (3-glucanase and someother enzyme activities. For the wheat-baseddiet the enzyme effect was limited and sta-

tistically non-significant, whereas for allother cereal bases the overall enzyme sup-plementation effect on performance and feedintake was significant (P < 0.001). ).

Recently, by dietary supplementation ofglucanase, Choct [17] demonstrated animprovement of AME (apparent metaboli-

zable energy) in wheat by 24% and com-mented that it is now generally concededthat the occurrence of low-ME in wheat isdue to an increased level of NSP (non-starchpolysaccarides), and of arabinoxylan in par-ticular. This author also quotes Australianwork according to which 25% of wheatsamples had an AME-value < 13 MJ per kg.Furthermore, by investigating the variationin ME-values in UK wheat samples,McNabb [81] reported a difference of 2 MJper kg DM and suspects that the content ofNSP causes the variation and that this, inturn, is related to the content of arabinoxy-lans in wheat. Therefore, this author expectspositive responses by supplementing wheat-based poultry diets with (3-glucanase andxylanase.

By supplementing a basal broiler chic-ken diet with NSP causing high viscosityin the gastrointestinal tract, Choct et al. [18]tested the effect of an enzyme (glucanase)preparation on bird performance, intestinalingesta viscosity, fatty acid concentrationand microbial activity and dietary AME.NSP inclusion lowered growth performanceand feed efficiency of the birds and dietary

AME. This investigation corroborates earlierwork and demonstrates that increased fer-mentation occurs in the small intestine when

large amounts of viscous NSP are includedin the diet, which is detrimental to the per-formance and well-being of poultry. Theseresults are in line with views put foreward byBedford and Morgan [10] indicating thatenzyme additives mainly act by reducingdigesta viscosity.

Elwinger and Tegl6f [35] demonstratedin one investigation that the incidence ofnecrotic enteritis in broiler chickens could belowered by the dietary inclusion of anenzyme preparation, whereas in a morerecent report by Elwinger et al. [30], cae-cal Clostridium perfringens counts were notaffected. As a side-effect, an improved littercondition with better bird hygiene and lowe-red ammonia emission can be expected [31]. ].

References on nutrient digestibility andperformance responses in poultry by die-tary enzyme supplementation have also beencompiled (table III). There is a tremendousvariation in responses, which demonstratesthe complexity of finding efficient combi-nations of enzymes under the differing cir-cumstances in nutrient supply. An exampleof this may be the Polish work by Alloui etal. [3], in which six lupin varieties were sup-plemented with different enzyme prepara-tions, giving an average enzyme responsein AME of 10%. NDF digestibility of lupinswas significantly improved between 2 and21%. Surprisingly, growth responses in broi-ler chickens fed diets including the samebatches of lupins to enzyme supplementationcould not be observed. Similarly, Austra-lian workers [4] were unable to reveal anyenzyme related responses on performancein broiler chickens fed diets incorporatedwith lupins. Of interest beyond cereals, isthe work by Slominski [104] with rapeseedmeal as the principal feedstuff. Adult birdsresponded to enzyme supplementation withan increase in the AME by 9.7% (table Ill)

An important issue in future diet formu-lation is the inclusion of more specific

enzymes, which is likely to become morecommon, not only in order to solubilizecereal carbohydrtaes, but also NSP (non-starch polysaccharides) of grain legumeslike lupins (with 36% NSP of DM), peas(35%), soyabeans (30%) etc. According toChoct [17] an important portion of thepotential energy of these types of feedstuffshas to be broken down by microbial fer-mentation in monogastric animal species,thereby causing a drop in the efficiency ofenergy turnover, but also risks for upsets inthe digestive tract.

A successful use of proteases has been

reported by Pettersson [93] in diets for earlyweaned piglets.

By evaluating the experimentation intable III on cereals as principal feedstuffsfor broiler chickens and their responses to

enzyme supplementation on feed efficiencyone arrives at an estimated average impro-vement by 4%, which agrees fairly well withthe extensive compilation by Kronseder[66].

In a broiler chicken experiment, Elwingerand Tegl6f [35] tested barley-based dietswithout and with the inclusion of an enzymepreparation and without and with the sup-plementation of virginiamycin. The out-come demonstrated a significantly impro-ved 35-day performance as a result of bothenzyme and virginiamycin supplementation(table IV). The effect of enzyme supple-mentation was greater when testing withoutthe inclusion of virginiamycin than with.By the supplementation with enzyme mor-tality, incidence of sticky droppings and lit-ter condition were greatly improved. Byincluding virginiamycin in the diet the effectof the enzyme preparation was not signifi-cant for growth rate and very limited forfeed efficiency. Nevertheless, there was aneffect on water intake and litter condition.This experiment demonstrates that part ofthe beneficial effects achieved by virginia-mycin could be obtained by the dietaryenzyme inclusion. The interaction observedbetween enzyme and virginiamycin sup-

plementation is corroborated by the resultsof Kronseder [66].

In a wheat-soybean oil diet, Miles et al.[83] tested the effect of enzyme and virgi-niamycin supplementation singly or syner-gistically on broiler chickens. Best perfor-mance results were obtained for the enzymesupplemented singly or in combination withvirginiamycin. The enzyme supplementa-tion also lowered the viscosity of small intes-tine ingesta. There were no health problemsobserved in this experiment, probably as aresult of using wheat as the cereal basis, incontrast to the barley used in the investiga-tion by Elwinger and Tegl6f [34].

Vranjes and Wenk [114] studied theinfluence of an enzyme complex combinedwithout and with antibiotic (flavophospho-lipol) supplementation on nutrient utiliza-tion and performance of laying hens fed adiet based on winter barley (40%). Theenzyme significantly increased dietaryAME, organic matter and NDF digestibi-lity. The antibiotic had no influence onenergy value or nutrient utilization. Therewere no significant treatment effects obser-ved on egg production.

The effects of combining enzyme sup-plementation (combination of 0-glucanaseand pentosanase) with salinomycin on gro-wing pigs fed barley- or rye-based diets has

been investigated by Thacker et al. [109].Neither enzyme nor salinomycin, alone or incombination, significantly improved thegrowth rate or feed efficiency of pigs fedbarley or rye. The digestibility of crude pro-tein was significantly improved by salino-mycin. The lack of, or lower response of,dietary enzyme supplementation on pig per-formance demonstrates a species-relateddifference compared with birds, i.e., poultry,and particularly birds < 3 weeks of agerespond more effectively to enzyme sup-plementation.

2.4. Lactoperoxidase in calves

The above-mentioned enzymes are addedin order to improve nutrient availability inthe gastrointestinal tract. In contrast to theseenzymes, naturally-occurring enzymes withantimicrobial effects may be addressed asalternatives to traditional growth promo-tants. The lactoperoxidase system (LPS) isintimately associated with the antibacterialactivity of bovine milk [99]. By supple-menting LPS to calves in the early stage ofdevelopment, the animals being sensitiveto bacterial and viral infections and often

suffering from diarrhoea, this authordemonstrated significantly improved weightgains of calves as well as lowered incidenceof diarrhoea.

2.5. Environmental implicationsof enzyme supplementation

It has been pointed out in an earlier sec-tion that the effects of enzyme supplemen-tation are generally to enforce the animal’s sown nutrient degrading capacity and/or tocomplement it. This means that a greatershare of the nutrients supplied in the feedthan in the unsupplemented diet is solubili-zed in the gastrointestinal tract and hencemade available for absorption by the ani-mal or to be attacked by microorganismsalong the tract. The animals respond to theimproved nutrient supply by increasedgrowth rate as well as by improved feedefficiency. Simultaneously, the higher rate ofnutrient absorption leads to a lowered outputof these with animal voidings and is, there-fore, also an advantage from an externalenvironment point of view.

In terms of improved digestibility andfeed efficiency a fair estimate for the impro-vement by enzyme supplementation foryoung pigs and poultry according to the lite-rature reviewed above would be approxi-mately 3-4%. Calculating with an averagedigestibility of organic matter in cereal-based diets for these animal species of 80%,one arrives at a decrease in animal nutrient

voidings by 15-20%.

3. PROBIOTICS

3.1. Definition of a probiotic preparation

Originally the term probiotic was intro-duced for a substance secreted by a microor-ganism to stimulate the growth of anotherorganism. It meant the exact opposite of theterm antibiotic. Later, the term has beenwidened to include organisms and sub-stances that contribute to improved animalhealth and intestinal microbial balance. Ful-ler [37] recently redefined probiotic as livemicrobial feed supplement that beneficiallyaffects the host animal by improving itsintestinal microbial balance. Probiotics maycontain one or several strains of microor-

ganisms and may be presented to the ani-mal in the form of solitary microbial addi-tives or mixed with different substances andare distributed to the animal orally as pow-ders (in water or in feed) or directly astablets, granules or pastes. The probioticscan be given as viable organisms in wetform, frozen or freeze-dried. However, theviability of preparations varies greatlydepending on the type of organism, its pre-paration and treatment post-propagation,including feed processing and storage.

The beneficial claims made for probioticsupplementation are numerous and includeimprovement of growth rate of farm ani-mals, improved utilization of the food,improved milk production by dairy cowsand improved egg production. Probioticsmay also directly or indirectly improve ani-mal health [37].

3.2. Gastric and small intestinemicrobial flora

The main areas of microbial interferencein the bird are the crop, the first major sitefor colonization following the ingestion ofmicroorganisms, and the caeca, as the pri-mary colonization site for a number of

pathogens including Salmonella and Cnm-/;’y/!/;’oc?6’r. Corresponding sections of thegastrointestinal tract in the pig are the sto-mach, small intestine and to some extentthe hind gut region.

The foregut (stomach and small intes-tine) of the pig is colonized by a relativelyrich microbial flora and the stomach ingestaof a healthy pig contains 10!-109 bacterialorganisms per g. As the relatively low pH ofthe stomach only has a limited destructiveeffect on its microbial population, bacterialnumbers found in the small intestine are

generally also high. The microbial floraoccurring in the foregut is dominated by lac-tic acid forming bacteria (LAB) Lnctoba-cillu.s and Streptococcus spp. These orga-nisms are found in the digesta and attachedto the epithelium !61]. ].

3.3. Hindgut microbial flora

There is a difference in the compositionof the microbial flora in the caecum and thecolon with Gram-negative dominating theformer and Gram-positive dominating thelatter. There are several circumstances thatenable the LAB microflora to dominatewithin the digestive tract of the pig. The lac-tic acid fermentation in the stomach is faci-litated by a relatively high pH and by theinoculation with the specific flora of theingesta in the pars oesophagea of the sto-mach. Both the lactic acid formed in the sto-mach by microbial fermentation and the lowpH in the pylorus as a result of the HCl-pro-duction in the stomach have been claimed toreduce the number of bacteria passing intothe small intestine. Similarly, in the bird,microorganisms that survive the low pH inthe gizzard generally multiply in the smallintestine. In young animals, the digestiveecosystem is often less stable than in olderanimals, thus in the former class of animalsopportunistic pathogens more easily invadethe digestive tract than in older animals.

The study by Robinson et al. (1981 citedby Stewart and Chesson [ 106 1) revealed thatabout 80% of the cultivable caecal bacteriain the healthy pig were Gram-negative. Therelative proportions of the predominant spe-cies are shown in,figure 2.

3.4. Mode of probiotic action

As modes of action of probiotics it hasbeen suggested that the indigenous micro-flora and the introduced probiotic out-com-pete the pathogen as discussed in terms ofcolonization resistance (Hentges (1992)cited by Conway [20]). The fatty acid meta-bolites, predominantly lactic and acetic acid,produced by the LAB are inhibitory to thegrowth of pathogens. However, the efficacyof these components in controlling patho-gens has been questioned [61] since theacids are inhibitory only in the undissocia-ted state, which occurs at low pH. The pH inthe small intestine of pigs and birds seems tobe too high to allow the fatty acids to beinhibitory at their full potential in vivo.Some microbial probiotic strains have

been shown to produce inhibitory compo-nents other than the short chain fatty acids.This type of larger proteinaceous com-pounds are referred to as bacteriocins(Kleenhammer ( 1988) cited by Conway[20]). However, questions are raised if thesecomponents can be produced and are func-tioning in vivo. There are numerous gut bac-teria which have been shown to have inhi-

bitory effects on E. coli. Similarly, numerousLactobacilli spp. isolated from the gut ofpigs have been demonstrated to producehigh molecular mass components, which

exert inhibitory effects on a range of Gram-negative and Gram-positive pathogens. Aproblem is, however, that strains frequentlylose their capacity to produce these compo-nents [20]. Furthermore, it has been demons-trated that piglet ileal digesta contentscontain heat labile components, which have

growth-inhibiting effects on E. coli. A pre-requisite of intestinal development of patho-gens is their adhesion to the gut wall. It hasbeen shown in vitro that probiotic strainsmay produce metabolites that inhibit theadhesion of the pathogens (Blomberg et al.(1992) cited by Conway [20]), but this hasnot yet been demonstrated in vivo.

3.5. Problems in evaluating probiotics

The type of diet and the amount ofnutrients are important for the developmentof the intestinal microflora. Lactobacilli,having a complex nutrient requirement,seem thus to be more sensitive to the gutnutrient milieu compared with, e.g., E. coli[61]. Starvation survival capacity of Lacto-bacilli spp. of digestive origin in the totalabsence of nutrients seems to be excellent.It is hypothesised that the starvation survivalmechanisms of Lactobacilli have a very lowthreshold for nutrients, beyond whichgrowth is initiated [61 ]. The probiotics canbe supplied to the animal orally, distribu-ted in water or in feed.

The efficacy of probiotics has recentlybeen reviewed for birds [8] and pigs [20, 61,106, 112]. The microbiology of the gut andthe role of probiotics have recently been fur-ther reviewed by Maxwell and Stewart [80].

According to Jonsson and Conway [61 ]assessments of the efficacy of probiotics invivo include studies of:

! influence on the microflora in the digestivetract, including pathogenic bacteria;

! influence on the digestive tract, its functionand morphology;

! performance and health of animals;! various effects where animals are used as

models for humans, e.g., anticholestero-laemic properties, stimulation of theimmune system and anticarcinogenic acti-vity.The type of probiotic preparation and the

time of its introduction and the persistencewould be of importance for effects inducedon the host animal. The active component ofa probiotic concept could be either a pre-formed active antagonistic substance or aviable microorganism culture. The formertype seems to be the easiest concept withrespect to control dosage and monitoringresponses. The efficacy of the latter type ofprobiotic preparations is much more com-plicated since many factors are involved inestablishing the microflora to colonize, e.g.,the viability and genetic stability of the orga-nisms of the preparation as well as theireffects on the gastrointestinal ecosystem.

3.6. Efficacy of probiotics in pigs

As pointed out by Pollman [95] and againrecently by Jonsson and Conway [61 ] whenreviewing the literature on pigs, a great num-ber of microorganisms have been tested asprobiotics (table V), part of which have beenisolated from the indigenous intestinalmicroflora, whereas other organisms repre-sent other origins. Species normally foundin the intestine of the pig are L. acidofilus,L. fermentum, L. reuteri, Enterococcum fae-cium and E. faecalis. Lactobacilli are moresensitive to pelleting and storage than, e.g.,Streptococci and the spore-forming Bacillusspp. There are important differences be-tween strains regarding their characteristicsand ability to colonize.

According to the literature compiled byJonsson and Conway [61], it seems likelythat a number of probiotics in many ins-tances affect the gastrointestinal microbialflora, particularly in cases where the indi-genous digestive tract flora has been dis-turbed. Not always would this balancing bydietary probiotics have an improving effect

on the health and performance of the hostanimal. In cases when this stabilizing cannot be achieved, detrimental effects onhealth and performance could be expected.

The efficacy of administrating probio-tics is dependent on a number of circum-stances, e.g., the physiological or health sta-tus of the animal, environmental factors suchas feed regime and microbial load. Improv-ing effects are more often observed in neo-natal animals and in pre- and post-weaning

piglets. In some herds long-term diarrhoeahas successfully been treated with Strepto-cocci. According to the authors quotedrecently, these circumstances point to thefact that the digestive microflora may befavourably influenced by the dietary inclu-sion of LAB, particularly in young animals.Furthermore, it seems more likely to expectprobiotic response in situations of negativestress of some kind. However, one has toconsider that the indigenous digestive florae

are very potent in preventing other microor-ganisms from colonizing permanently.

In piglets weaned at the age of 2 daysRatcliffe et al. [98] investigated the effectof yoghurt and milk fermented with a por-cine intestinal strain of L. reuteri on per-formance and gastrointestinal flora. Yog-hurt feeding resulted in slightly inferiorpiglet weight gain and significantly poorerfeed efficiency. It also depressed coliformcounts, whereas Lactobacillus counts alongthe tract increased. L. reuteri gave resultssimilar to those obtained with yoghurt, butthe effects did not persist after withdrawal.The authors concluded that the decrease incoliform counts was a result of the low pHproduced by the lactic acid production inall milk diets fed. In commenting theseresults, one has to consider the bactericidaleffect of lactate on intestinal microbial florain addition to the pH effect.

In order to obtain more consistent effectson these two types of probioric preparationsmuch more basic knowledge is required inthe area of our understanding of the inter-actions in the digestive microbial ecosys-tem. As an example, Jonsson and Conway[61] outline in figure 3 the area of interac-tions between animal, diet, microorganisms,digestion and the immune response as beingin need of better understanding.

A summarizing statement by Jonsson andConway [61 ] regarding the efficacy of pro-biotics in pigs may be cited: &dquo;From studiesto date it is feasible to postulate that pro-biotic preparations could contain microbeswith the capacity to improve piglet healthby direct inhibitory effects on the enteropa-thogenic bacteria. The in vitro and in vivodemonstration and characterization of inhi-

bitory components will ensure functionalpreparations. Identifications of adhesionswhich mediate in vivo colonization willallow better predictions if probiotic prepa-rations have the capacity to colonize thedigestive tract. Probiotic strains withdemonstrable direct effects may also func-tion indirectly by stabilizing the digestivemicroflora at times when the ecosystem isstressed. This latter vital role is restricteduntil the complex interactions within thedigestive tract are better understood.&dquo;

3.7. Specific types of phages in pigs

During the past decade bacteriophageshave again been advocated as a novelmethod to control pathogens. By treatmentand prophylaxis, virulent phages have suc-cessfully been demonstrated to controlE. coli infections in mice and enterotoxige-nic E. coli diarrhoea in pigs, calves and

lambs (Smith and Huggins 1982, 1983, citedby Barrow [8]).

3.8. Efficacy of probiotics in poultry

In evaluating the great number of reportson the efficacy of probiotic organisms andsubstances in poultry, Barrow [8] points outa number of difficulties for a critical apprai-sal. The vast majority of results on the effi-cacy of probiotics in poultry is reported asabstracts with essential information lacking,e.g., on the identity of strains used and onexperimental design (e.g., [73]). In manycases, non-avian Lactobacillus strains areused which are known not to colonize. The

implantation in the gastrointestinal tract ofthe strains used is rarely assessed. Themicrobiological results in nutrition-orientedpapers are often poorly interpreted. A furthercomment is that in a number of reports inwhich performance and health could beimproved by probiotics, the general condi-tions seem to have been poor and non-repre-sentative with respect to production leveland morbidity. Moreover, Barrow [8] in hisreview considers that some of the interpre-tations of the results are obviously over opti-mistic and arise mainly from a naive anduncritical acceptance of the data or specu-lations of previous workers.

Probiotic preparations evaluated on broi-ler chickens in Sweden have demonstrated

only inconclusive results [29].

Nguyen et al. [89] reported improvinggrowth performance and feed conversion at42 days of age in broiler chickens fed dietseither unsupplemented (A) or supplementedwith (B) flavomycin; (C) toyocerin (sporesof Bacillus toyoi); (D) paciflor (spores of aBacillus sp. stored at the Institut Pasteur) or(E), a combination of B + D. For treatmentgroups B-E the 42-day average weight gainsof the birds differed significantly (P < 0.01)from the unsupplemented control A

(P < 0.01) by +1.8; +2.0; +2.5 and +2.8%,respectively. Corresponding values for feedconversion (kg feed/weight gain, P < 0.05)

were -2.3, -0.7, -2.3 and -2.7%. Similarimproving results have been reported byKahrs [62] for toyocerin in growing pigs,however, with the greatest promoting effectin the first growing phase compared withthe final phase.

Recently, Mohan et al. [85] reported onthe effects of administering a probiotic mix-ture (L. acidophilus, L. casei, Bifidabacte-rium bifidum, Aspergillus oryzae and Toru-lopsis in descending order of concentration)for broiler chickens with the inclusion of 0,75, 100 and 125 mg/kg diet. Mean weightsat the termination (8 weeks) of the experi-ment were 1204, 1272, 1268 and 1210 g.At ages of 4, 5 and 6 weeks, mean weightsdiffered significantly between control andprobiotic treatments. Feed conversion ratiovaried between 2.31 and 2.26 (kg feed/kgWG). The dietary AME was not affectedby probiotic supplementation. However, inevaluating this experiment, the relativelylimited growth performance in relation tomodern commercial strains with 8 week-LW of more than 2500 g should be consi-dered.

According to Dunham et al. [22], labo-ratory and large-scale field tests havedemonstrated significant benefits from thetreatment of young birds with host speci-fic strains of L. reuteri, particularly whenthe animals are subjected to environmen-tal and/or pathogenic stressors. Treatedflocks consistently exhibited fewer deaths,superior growth rates and improved feedefficiency. These authors state that L. reu-teri treatment confers these benefits throughCE (competitive exclusion) mechanism andby modulating the newborn’s immune res-ponse. In comparison with control birdsthese authors observed: longer ileal villiand deeper crypts, a response associatedwith enhanced T-cell function; suppressedPHA-induced (phytohemagglutenin) epi-dermal DTH (delayed type hypersensiti-vity) reaction and, furthermore, increasedproduction of serum anti-salmonella IgMantibodies.

An example of another type of probioticin a wider sense is the development of liveSalmonella vaccines for chickens. Linde etal. [74] developed a method for optimallyattenuating Salmonella vaccines by usingtwo metabolic drift mutants deficient in the

production of essential enzymes.

According to the overview by Mead [82],there are a number of commercial prepara-tions available that successfully have beenused in the prophylaxis of Clostridium andSalmonella infections in poultry. Recently,Abu-Ruwaida et al. [1] confirmed the poten-tial of this method against Salmonella. AlsoSwedish experimental results when usingthe probiotic BroilactO have been promis-ing, with a significantly lowered mortality inone of the experiments and lowered caecalcounts of C. perfringens [33].

The prophylactic treatment against sal-monellosis is based on the principle of earlyestablishment of an adult intestinal micro-flora in the young bird by supplying a sus-pension or anaerobic cultures of intestinalmaterial to provide necessary organisms inthe gastrointestinal tract thereby competiti-vely excluding pathogen organisms. Youngbirds given this peroral treatment rapidlydevelop protection against a subsequent Sal-monella challenge. Although there are theo-retical risks in using undefined treatmentproducts to combat Salmonella infectionsin poultry, these products, which are widelyspread, are appropriately controlled. How-ever, criteria on which to select pure cul-tures of microorganisms for protective pur-pose are lacking at present and will remainso until more is known about factors influen-

cing Salmonella colonization at the cellu-lar level and the protective mechanism(s)involved [82]. According to this author,future preparations will need to be selectedon a sound scientific basis and be more pro-tective and more stable than those developedso far.

The complexity of Salmonella colonisa-tion is exemplified by the effects of the sup-plementation of the antimicrobial avopar-

cin in Salmonella typhimurium infected chic-kens. Although individual intestinal micro-organisms have been demonstrated to besusceptible to this drug in vitro [7], diffe-rent groups of researchers have reportedincreased and avoparcin-induced Salmo-nella counts at the caecal level or in the

droppings [7, 51, 70]. These findings contra-dict those of Gustafson et al. [43], one expla-nation possibly being differences in the tech-nique of transfer of Salmonella organisms,or interaction with other feed additives

acting antimicrobially. In cases of naturalinfection of the birds, Linton et al. [75] wereunable to observe any influence of avopar-cin or monensin on Salmonella shedding.On providing broiler chickens a dietsupplemented with a combination of avo-parcin and monensin, Holmberg et al. [50] 1and 2 weeks after challenge noticed highercaecal counts and Salmonella infected liversthan straight avoparcin supplementation.

In summarising the literature on probio-tics in poultry, Barrow [8] points to theconsiderable importance of the microbialflora in the avian gastrointestinal tract forperformance and animal health. Any imba-lance in the gut flora could lead to the colo-nisation of pathogens or to a microbial florathat might impair performance. There aresome probiotics (particularly Lactobacillispp.) that have proven beneficial effects onperformance, especially in young birds andwhen stressed by adverse environmentalconditions. Elimination of wet droppingsand occluded vents were also observed insome experiments as a result of dietary Lac-tobacilli administration. However, there arealso reports on uniformly negative resultsof administrating Lactobacillus products onegg production. Supplementation with Strep-tococcus spp. has often been reported togive adverse effects on performance of gro-wing birds. By administering L. acidophilusit seems possible to lower enteric pathogens(E. coli, Salmonella) but not to control themcompletely.

3.9. Specific types of phages in poultry

Phages lytic for Salmonella typhimuriumhave been isolated from poultry feed, excretaand sewage [8]. According to this author,such an approach would be interesting toconsider for Campylobacter and growth-depressing organisms. Recently, Poppe etal. [96] observed 97% of Salmonella strainsisolated from a great number of laying henand broiler herds in Canada to be suscep-tible to the lytic effect of polyvalent bacte-riophages.

4. EFFECTS OF VARYING FEEDINGREDIENTS

4.1. Fermentable carbohydrates

For the survival and the adhesion of the

microbial, including probiotic, flora at thegut cell level the necessity of a suitablenutrient environment in the gastrointestinaltract has been pointed out by several authors(e.g., [8, 61, 82, 106]). By reviewing theliterature on dietary administration of fer-mentable carbohydrates as to manipulatethe normal intestinal flora, Barrow [8] poin-ted out several reports in which the supply(via the feed or via the drinking water) ofe.g., lactose or mannose decreased caecal

pathogen counts (e.g., Salmonella typhimu-rium) by stimulating the lactose fermentingflora inhibiting the growth of pathogenicbacteria and reducing the severity of infec-tion with Eimeria.

In an experiment with broiler chickens,Stanley et al. [105] tested the dietary admix-ture of 0.2% lactose on bird growth rate andcaecal total bacteria coliform counts. In com-

parison with the control diet without incor-poration, the admixture of lactose impro-ved (however, statistically non-significant)the final live weight at 3 weeks of age by6%. The caecal coliform counts were dras-

tically decreased from 5.98 loglo in birdsfed the control diet to 3.8 log 10 by the admix-ture of lactose.

4.2. Dietary acidifiers

In the search for feed additives with gutpH stabilizing effects, organic as well asinorganic acids have been proposed and usedsince the 1950s. Citric acid has widely beenused in piglet diets, so also orto-phospho-ric acid. Even HCI acid has been tested

[101]. Recently, H6hler and Pallauf [47]demonstrated an improved Zn-absorptionby the inclusion of 1 % citric acid in pigletdiet. Broz and Schulze [13] noticed animproved organic matter digestibility byincluding 0.5-2% citric acid in early weanedpiglet diets.

The inclusion of formic acid (FA, at 0,0.6, 1.2, 1.8 and 2.4%) and Ca- or Na-for-miate into piglet diets has been investigatedquite extensively by Kirchgessner and hisgroup. As reported by Roth et al. [100] sto-mach pH and stomach DM content was notaffected, whereas pH in the small intestine,caecum and colon increased in proportionto the dietary FA level. Digesta DM contentincreased distally with the inclusion of FA.At the two highest FA levels the concentra-tion of digesta VFA (volatile fatty acids)decreased. By including 1.25% FA or 1.8%Ca-formiate into piglet diets Bacteroida-ceae spp. and E. coli counts along the smallintestine decreased, whereas simultaneousinclusion of NaHC03 increased the micro-bial counts [65]. As the main active mecha-nism of organic acid supplementation ongut flora microbiology, Eidelsburger et al.[27] point out the anions of the organicacids. These authors tested also HCI (1.4%admixture), but found it to have a depres-sive effect on piglet feed intake and perfor-mance. NH3-fonnation in the stomach, smallintestine and colon was significantly limitedby 0.6 and 1.2% FA [28] and HCI or fuma-ric acid inclusion [101]. In addition to theseeffects, Eckel et al. [24] reported a loweringeffect on caecal digesta concentrations ofcadaverin, putrescin and spermidin. Simi-larly, Mosenthin et al. [87] observed a signi-ficantly lowered caecal digesta cadaverinconcentration when admixing 2% propio-

nic acid in a growing pig diet. These authorsalso observed a significantly improved ilealdigestibility of some essential amino acids asa result of propionic acid admixture. FAlevels > 1.2% have been demonstrated byGrassmann et al. [42] to have adverse meta-bolic effects by changing blood serum andliver aminotransferase activity as well asincreasing blood serum urea concentration.

In a 41-day feeding experiment withpiglets (28-day-old at the start) fed dietsadmixed with either 0 (control), 0.6, 1.2 or1.8% FA, Eckel et al. [25] improved pigletfeed intake (in % over the control) by 14,13 and 4%, respectively, average dailyweight gain by 22, 22 and 5%, respectively,and feed efficiency by 6, 8 and 1 %, respec-tively. The incidence of diarrhoea was signi-ficantly decreased by FA [23]. The highestlevel of 2.4% FA inclusion exerted nega-tive effects on performance.

4.3. Protein sources

In the Swedish pig and poultry industriesthe dietary levels of protein have steadilydecreased during the 1980s in order tominimize intestinal disorders, but also todecrease the external environmental loadvia animal production. This has been pos-sible since several crystalline amino acidsare available at competitive price levels.There have been indications that animal pro-tein sources are more prone to give rise todigestive tract problems than non-animalprotein sources in both pig [38] and poul-try [29] production. Part of these negativeresponses to dietary protein level seems to berelated to gastrointestinal allergic reaction bythe animals to certain protein structures [84].In some of the experiments with broilerchickens, the exclusion of animal proteinfeedstuffs resulted in a lowered incidenceof necrotic enteritis, whereas this was notconsistently observed in subsequent expe-riments [29]. These authors occasionallyfound higher mortality following inclusionof fishmeal than inclusion of meat and bonemeal in broiler diets.

With respect to the dietary cereal supply,Kaldhusdal [63] pointed out that a high levelof maize in broiler chicken diets gave pro-tection against necrotic enteritis, whereasbarley and wheat were identified as risk fac-tors.

Rapeseed meal had earlier been claimedto lower bird gut health [91, 92]. When stu-dying the caecal C. perfringens counts andthe incidence of necrotic enteritis, Elwin-ger et al. [29] were unable to observe anynegative effects. However, in this investi-gation all diets were supplemented with acoccidiostat having antibacterial effects aswell.

4.4. Unmilled wheat

The development of the bird gizzard isinfluenced by the dietary physical structure,implying that also digestive enzyme secre-tion could be affected, thereby triggeringdevelopment of the gastrointestinal flora.Part of the dietary cereals may, therefore,be supplied unmilled without affecting broi-ler chicken performance [35]. No differencesin bird health were observed. However, birdwater intake was significantly lowered bysupplying 20% wheat mixed unmilled withthe crumbled pellets, resulting in an impro-ved litter condition, which might imply asafer and more stable hygienic state for thebirds. To-day, the whole wheat concept inbroiler chicken diets is commonly acceptedin Northern Europe [64]. In Canada, Bennettet al. [12] arrived at a similar conclusionthat pelleting all the wheat in broiler chickenrations is unnecessary, because bird perfor-mance is unaffected by feeding up to 30%whole grain in the finisher diet.

4.5. Fibre and lectins

As mentioned earlier, soluble fibre types(e.g., (3-glucans, arabinoxylans) affect gutfunction and bird health. Elwinger et al. [29]attempted to evaluate the supplementation of

particulate fibres (oat hulls and potato fibreproducts) on gut health of broiler chickens.However, the birds in this experiment suf-fered from an outbreak of necrotic enteritisand therefore had to be treated with anti-biotics. No differences between fibre sup-plementation on the counts of C. perfrin-gens could be observed.

The incidence of post-weaning diarrhoeain pigs has been demonstrated to be relatedto the dietary content of fibrous components[6]. This has been confirmed in Swedishexperiments by G6ransson et al. [39]. A30% decrease in the incidence of post-wea-ning diarrhoea was observed as a result ofthe inclusion of plantago polysaccharidesor beet pulp fibre. However, this might be,at least to some extent, a cosmetic effect.

There is an interrelationship between cer-tain naturally occurring or added feed ingre-dients such as lectins and/or glucoconju-gates (usually of plant origin) and

gastrointestinal health. These constituentsexert their action through competition withthe bacterial adhesions or by changing theexpression of surface composition for bac-terial adhesion, thereby reducing the numberof harmful bacteria to a minimum and pro-moting the proliferation of potentially use-ful strains. As a result of their specificity,other lectins may favour the attachment ofharmful organisms [97]. Certain carbohy-drates may interfere and change the surfacereceptors of the small intestinal brush border.Lectins with the same specificities as bac-teria may prevent the attachment and proli-feration of appropriate species. The forma-tion of feed-induced lectins by dietaryinclusion of certain feed ingredients (sugars,sugar alcohols and amino acids) and theirpotential in preventing post weaning diar-rhoea has been demonstrated by L6nnrothand Lange [76]. Recently, the effects of usingoligosaccharides as feed additives have beenreviewed by Monsan and Paul [86].

The intestinal fluid secretion is regula-ted by an anti-secretory factor (ASF, recentlythe term AF has been used; Gbransson, per-

sonal communication), peptides which aresynthesized in the central nervous systemand accumulated in the anterior part of thepituitary gland [60] and which inhibitspathological secretion induced by entero-toxins [67]. AF seems to be of importance inthe defence against diarrhoeal diseases [40,67,69]. In pigs a very minute amount of AF(only 1 picomole) causes a substantial reduc-tion in enterotoxin-induced intestinal secre-

tion, i.e., induced by verotoxin and E. coliheat labile toxin [69]. The AF is passivelytransferred via sow’s milk to the piglet andis present in nursing piglet blood irrespectiveof a challenge [103]. Soon after weaning,the AF-blood level decreases, but increasesagain following weaning. Piglets sufferingfrom diarrhoea have lower blood plasmaAF-concentrations than healthy littermates[77]. Similarly, the viscosity of droppingsof broiler chicken at slaughter after trans-portation was found to be related to theblood plasma AF-concentration [68].

The efficacy of using AF-inducing dietshas been demonstrated in large commercialunits [40]. AF-induction via drinking wateris an alternative, as demonstrated in a splitlitter experiment with significantly increasedAF plasma-concentrations (table VI; [39]).These authors explain the lower daily weightgains of the control group of piglets in thefirst week post-weaning by postulating sub-clinical intestinal disorder and point to therelationship between performance results inthe first week after weaning and plasma AF-concentrations. In rats and broiler chickens,stress has been demonstrated to rapidlydecrease blood AF-concentrations [68, 77].Gbransson et al. [39] suggest that weaningis a stressful factor that may cause the sud-den drop in blood AF-concentration, leadingto increased susceptibility for gastrointes-tinal disorders.

4.6. Other feed additives

Recently, Devegowda [21 ] reviewed her-bal medicines as potential feed additives

with growth-promoting effects in animals. InIndia 7000 herb species are currently in useas medical preparations for humans. Thisauthor reported on some experiments inwhich minute supplements showed interes-ting results. However, as with other feedadditives, when using herbs beyond thequestion of their efficacy as promotants, thearea of residual levels in foods and long-term effects on resistance have to be eva-luated.

Zinc is a biogenic element and is regu-larly supplemented into compounded feedmixtures for all food-producing animal spe-cies at a level of 50-100 ppm. The inclu-sion may vary beyond this level. In Den-mark in the mid 80s it was observed thatinclusion of high levels (2500 ppm Zn) ofzink oxide in piglet diets had a preventiveand curing effect on E. coli diarrhoea [48].According to this author, E. coli diarrhoea inweaners is no longer a problem for Danishveterinarians. Zinc toxicity in pigs is relati-

vely uncommon. Clinical signs of this disor-der include growth depression, loss of appe-tite and gastroenteritis. Swedish results agreewith the Danish [49]. However, according toEU regulations levels > 250 ppm Zn are not

permitted.The growth promoting effects of chro-

mium provided as picolinate has been inves-tigated by Boleman et al. [15]. A loweredgrowth rate was reported as well as anincreased daily carcass fat accretion.

5. IMPROVEMENT OF ANIMALENVIRONMENT

In the search for methods to improve ani-mal health in modern animal productionsystems, other environmental factors thannutrient supply and feeding strategy haveto be considered. Stocking density, envi-ronmental temperature and hygienic stageare of great importance. The type of bedding

material may affect bird mortality, as hasbeen demonstrated by Elwinger et al. [29] bycomparing straw and wood shavings withsignificantly lowered mortality in the latteralternative. According to these authors, dif-ferences in mortality may also occur as aresult of water supply system. The mixing ofpiglets in connection with their transfer tofattening units may lead to severe strugglesand decreased feed efficiency [36] and isfurther exemplified by a negative correla-tion between the number of received attacksand performance results [78, 102].

6. GENETIC SELECTION

A further alternative to decrease the inci-dence of certain types of diarrhoea in pigletsis selection. For the incidence of diarrhoea

up to 8 weeks post-birth in a Swedish inves-tigation, Stigson [107] reported a heritabilityof 0.26 ± 0.10. A high boar effect on diar-rhoea susceptibility was reported by G6rans-son [38]. By studying the genetic variationin antibody response to E. coli antigens 0149and K88 the heritability for the increase inIgG titres during the first week followingimmunization, Edfors-Lilja [26] arrived atvalues of 0.29 and 0.45, respectively. Lun-deheim [79] investigated the genetic back-ground of respiratory diseases and arrived atheritability values around 0.2, and highervalues for Yorkshire than for Landrace pigs.This research indicates that some of thecommon pig diseases may be controlled bymeans of selection.

7. CONCLUSION

Livestock performance and feed effi-ciency are closely interrelated with the qua-litative and quantitative microbial load ofthe host animal, including load in the ali-mentary tract and in the animal environ-ment. Appropriate nutrient supply andchoice of ingredients and their proper pre-paration with respect to the animal’s diges-

tive capacity will minimize nutrient lossesand overloading, upsets and intestinal over-crowding by often harmful microbial flora.Under given circumstances, supplementingenzymatic preparations may improve thedigestive capacity, particularly in juveniles.Thereby, nutrient utilization in the anteriorpart of the gastrointestinal tract is improvedand the incidence of intestinal perturbationmay be limited, which thus may lead to alimitation of occasions when antimicrobialtreatment of animals has to be used. The

dietary inclusion of enzymes of carbohy-drase type leads to a more efficient use ofnutrients by poultry and pigs, thus decreas-ing nutrient output with urine and faeces inthe range of 15-20%. Organic acids mayhave controlling effects on intestinal micro-bial flora through their specific anion actionson microorganisms.

The probiotic concept is based on eitherpreformed antagonistic agents or on a viablemicroorganism culture with intestinal adhe-sive capacity. In selecting microbial strainswith probiotic potentials, their genetic sta-bility and intestinal colonizing capacity aswell as their stabilizing properties are ofmain concern. Some probiotic preparations(particularly Lactobacilli spp. and yeasttypes) have been demonstrated to improvejuvenile (piglet as well as chicken) perfor-mance and health (e.g., preventing salmo-nellosis in poultry by competitive exclu-sion). However, so far the efficacy ofprobiotics seems to be less consistent thanthe use of antibiotic promotants. In futurecontrol of avian salmonellosis, the poten-tial of bacteriophages has to be investigatedfurther as an alternative to antibiotics.

Another way of achieving withdrawal ofantibiotic promotants is to manipulate cen-tral mechanisms in order to activate the ani-mal’s own defence mechanisms. One

example in porcine production is the anti-secretory factor, a peptide synthesized inthe central nervous system and which isaccumulated in the anterior part of the pitui-tary. This peptide regulates the intestinal

fluid secretion caused by enterotoxins, thuspreventing diarrhoea in pigs.

The withdrawal of antibiotic promotantsmust also be followed by changes and adap-tations in livestock production systems inorder to prevent transfer of pathogenicmicroorganisms and other harmful conta-gious material both between as well aswithin herds. In developing future livestockproduction and housing systems stressfulsituations for the animals have to be avoidedand strict health-care plans have to beapplied.

ACKNOWLEDGMENTS

This review was published in the journal ofthe Royal Swedish Academy of Agriculture andForestry 136 (19) (1997) 37-65. Permission toreprint it was kindly granted by the Royal Swe-dish Academy of Agriculture and Forestry.

REFERENCES

11] i Abu-Ruwaida A.S., Husseini M., Banat LM.,Salmonella exclusion in broiler chicks by thecompetitive action of adult gut microflora,Microbios 83 (1995) 59-69.

[2] ] Albustany Z., The effect of pelleting an enzymesupplemented barley based broiler diet, Anim.Feed Sci. Technol. 58 (1996) 283-288.

[3] Alloui O., Smulikowska S., Chibowska M.,Pastuszewska B., The nutritive value of lupinseeds (L luteus, L augustifolius and L albus) forbroiler chickens as affected by variety andenzyme supplementation, J. Anim. Feed Sci. 3(1994)215-227.

[4] Annison G., Hughes R.J., Choct M., Effects ofenzyme supplementation on the nutritive valueof dehulled lupins, Br. Poultry Sci. 37 (1996)157-172.

[5] Baas T.C., Thacker P.A., Impact of gastric pH ondietary enzyme activity and survivability inswine fed beta glucanase supplemented diets, ’Can. J. Anim. Sci. 76 ( 1996) 245-252.

[6] ] Ball R.O., Aherne F.X., Effect of diet complexityand feed restriction on the incidence and severityof diarrhoea in early weaned pigs, Can. J. Anim.Sci. 62 ( 1987) 907-913.

[7] Barrow P.A., Further observations on the effectof diets containing avoparcin on the excretion ofsalmonellas by experimentally infected chic-kens, Epidemiol. Infect. 102 (1989) 239-252.

[8] Barrow P.A., Probiotics for chickens, in: Ful-ler R. (Ed.), Probiotics - The scientific basis,Chapman & Hall, London, 1992, pp. 225-257.

[9] Barrow P.A., Williams-Smith H., Tucker J.F.,The effects of feeding diets containing avopar-cin on the excretion of salmonellas by chickensexperimentally infected with natural sources ofsalmonella organisms, J. Hygiene 93 (1984)439!44.

[ 10] Bedford M.R., Morgan A.J., The use of enzymesin poultry diets, World’s Poultry Sci. J. 52(1996)61-68.

[111 Bedford M.R., Patience J.F., Classen H.L.,Inborr J., The effects of dietary enzyme supple-mentation of rye-barley-based diets on diges-tion and subsequent performance in weanlingpigs, Can. J. Anim. Sci. 72 (1992) 97-105.

[12] Bennett C.D., Classen H.L., Riddell C., Liveperformance and health of broiler chickens feddiet diluted with whole or crumbled wheat, Can.J. Anim. Sci. 75 (1995) 611-614.

[13] Broz J., Schulze J., Efficacy of citric acid as afeed additive in early weaned piglets, J. Anim.Physiol. Anim. Nutr. 58 (1987) 215-223.

[14] B6hme H., Untersuchungen zur Wirksamkeitvon Enzymzusdtzen in der Ferkelaufzucht. Land-bauforschung Volkenrode 40 (1990) 213-217.

[15] Boleman S.L., Boleman S.J., Bidner T.D., Sou-thern L.L., Ward T.L., Pontif J.E., Pike M.M.,Effect of chromium picolinate on growth, bodycomposition, and tissue accretion in pigs, J.Anim. Sci. 73 (1995) 2033-2042.

[ 16] Cherbut C., Albina E., Champ E., Dublier J.L.,Cannu G., Action of guar gums on the visco-sity of digestive contents and on the gastroin-testinal motor function in pigs, Digestion 46(1990) 205-213.

[ 17] Choct M., The role of feeding enzymes in animalnutrition towards 2000, Proc. World’s PoultrySci. Assoc., Session II-IV, XX World’s Poul-try Congr. New Delhi, India, 1996, pp. 125-133.

[ 18] Choct M., Hughes R.J., Wang J., Bedford M.R.,Morgan A.J., Annison G., Increased small intes-tinal fermentation is partly responsible for theanti nutritive activity of non starch polysaccha-rides in chicken, Br. Poultry Sci. 37 (1996)609-621. 1.

[19] Classen H.L., Campbell G.L., Rossnagel R.G.Bhatty R., Reichert D.R., Studies on the use ofhulless barley in chicken diets: Deleteriouseffects and methods of alleviation, Can. J Amim.Sci. 65 (1985) 725-733.

[20] Conway P.L., Function and regulation of thegastrointestinal microbiota of the pig, Proc. VIthIntern. Symp. on Digestive Physiology in Pigs,Bad Doberan, 1994, pp. 232-240.

[21] Devegowda G., Herbal medicines - an untap-ped treasure in poultry production, Proc. World’sPoultry Sci. Assoc., Session II-IV, XX World’sPoultry Congr., New Dehli, India, 1996,pp. 135-140.

[22] Dunham H.J., Edens F.W., Casas J.A., DobrogosW.J., Efficacy of Lactobacillus reuteri for chic-ken and turkeys, Microbiol. Ecol. Health Dis.7 (1994) 52-53.

[23] Eckel B., Kirchgessner M., Roth F.X., Zum Ein-fluss von Ameisensdure auf tagliche Zunahmen,Futteraufnahme, Futterverwertung und Ver-daulichkeit, 1: Untersuchungen zur nutritivenWirksamkeit von organischen Sduren in der Fer-kelaufzucht, J. Anim. Physiol. Anim. Nutr. 67(1992) 93-100.

[24] Eckel B., Roth F.X., Kirchgessner M., Eidels-burger U., Zum Einfluss von Ameisens5ure aufdie Konzentrationen an Ammoniak und bioge-nen Aminen im Gastrointestinaltrakt, 4: Unter-suchungen zur nutritiven Wirksamkeit von orga-nischen Sauren in der Ferkelaufzucht, J. Anim.Physiol. Anim. Nutr. 67 (1992) 198-205.

[25] Eckel B., Roth F.X., Kirchgessner M., Eidels-burger U., Zum Einfluss von Ameisens5ure aufden pH-Wert, Trockensubstanzgehalt, Konzen-tration fldchtiger Fetts5uren und Milchs5ure imgastrointestinalen Trakt, 3. Untersuchungen zurnutritiven Wirksamkeit von organischen Sau-ren in der Ferkelaufzucht, J. Anim. Physiol.Anim. Nutr. 67 (1992) 148-156.

[26] Edfors-Lilja I., Marker traits of disease resis-tance in the pig. Genetic studies of immune res-ponsiveness and the intestinal receptor for E. coliK88. Diss., Report No. 65, Dept. Animal Bree-ding & Genetics, Swed. Univ. Agric. Sciences,Uppsala, 1985.

[27] Eidelsburger U., Kirchgessner M., Roth F.X.,Zum Einfluss von Fumars5ure, Salzsdure,Natriumformiat, Tylosin und Toyocerin auft5gliche Zunahmen, Futteraufnahme, Futter-verwertung und Verdaulichkeit, 11: Untersu-chungen zur nutritiven Wirksamkeit von orga-nischen S5uren in der Ferkelaufzucht, J. Anim.Physiol. Anim. Nutr. 68 (1992) 82-92.

[28] Eidelsburger U., Roth F.X., Kirchgessner M.,Zum Einfluss von Ameisensdure, Calciumfor-miat und Natriumhydrogencarbonat auf taglicheZunahmen, Futteraufnahme, Futterverwertungund Verdaulichkeit, 7: Untersuchungen zur nutri-tiven Wirksamkeit von organischen Sduren inder Ferkelaufzucht, J. Anim. Physiol. Anim.Nutr. 67 (1992) 258-267.

[29] Elwinger K., Engstr6m B., Berndtson E., Fos-sum B., Tegl6f B., Kycklinguppfodning utanfoderantibiotika. Husdjurskonf. Konferensrap-port, L-fak., SLU Info, Uppsala (in Swedish),1993, pp. 87-93.

[30] Elwinger K., Engstr6m B., Berndtson E., Fos-sum 0., Tegi6f B., Effect of protein level andfeed enzyme addition on the caecal growth ofC. perfringens in broiler chickens, Proc., Word’sPoultry Sci. Assoc., 9th Eur. Poultry Conf., Glas-gow, 1994, pp. 423-424.

[31] Elwinger K., Svensson L., Effects of dietaryprotein content, litter and drinker type on ammo-nia emission from broiler houses, J. Agric.Enging. Res. 64 (1996) 197-208.

[32] Elwinger K., Saterby B., The use of (3-gluca-nase in practical broiler diets containing barleyor oats, Swed. J. Agric. Res. 17 ( 1986) 133-140.

[33] Elwinger K., Schneitz C., Berndtson E., Fos-sum 0., Teglof B., Engstr6m B., Factors affec-ting the incidence of necrotic enteritis, caecalcarriage of C. perfringens and bird performancein broiler chickens, Acta Vet. Scand. 33 (1992)369-278.

[34] Elwinger K., Teglof B., Performance of broilerchickens as influenced by a dietary enzyme com-plex with and without antibiotic supplementa-tion, Arch. GeflUgelk. 55 (1991) 60-73.

[35] Elwinger K., Teglof B., F6rs6k med hel vete tillslaktkycklingar, Fjdderfd 85 (1992) 20-21. 1 .

[36] Friend T.H., Knabe D.A.., Tanksley T.D., Beha-viour and performance of pigs grouped by threedifferent methods at weaning, J. Anim. Sci. 57( 1983) 1404-1411. 1.

[37] Fuller R., History and development of probiotics,in: Fuller E. (Ed.), Probiotics. The scientificbasis, Chapman & Hall, London, 1992, pp. 1-8.

[38] Goransson L., The effect of very restricted fee-ding during late pregnancy on the productionperformance of sows and litters, Diss., ReportNo. 188, Dept. Animal Nutrition & Manage-ment, Swedish Univ. Agric. Sciences. Uppsala,1989.

[39] G6ransson L., Lange S., L6nnroth L, Post-wea-ning diarrhoea: Focus on diet, Pig News Inf. 16 6(1995) 89N-91N.

[40] G6ransson L., Martinsson K., Lange S., L6nn-roth I., Feed-induced lectins in piglets, J. Vet.Med. B 40 (1993) 478-484.

[41] Graham H., Aman P., Lowgren W., Enzymesupplementation of pig diets, Buraczewska L.et al. (Eds.), Proc. 4th Intern. Sem. DigestivePhysiol. of the Pig, Jablonna, Poland, 1988,pp. 371-376.

[42] Grassmann E., Roth F.X., Kirchgessner M.,Imtermediare Effekte durch Einsatz von Amei-sens5ure, 6: Untersuchungen zur nutritivenWirksamkeit von organischen Sauren in der Fer-kelaufzucht, J. Anim. Physiol. Anim. Nutr. 67(1992) 250-257.

[43] Gustafson R.H., Beck J.R., Kohland J.D., Theinfluence of avoparcin on the establishment ofSalmonella in chickens, Zentralbl. Vet. Med. B29 (1982) 119-122.

[44] Hesselman K., Effects of (3-glucanase supple-mentation to barley based diets for broiler chic-kens, Diss., Report No. 112, Dept. Animal Nutri-tion & Management, Swedish Univ. Agric.Sciences, Uppsala, 1983.

[45] Hesselman K., Elwinger K., Nilsson M.,Thomke S., The effect of (3-glucanase supple-mentation, stage of ripeness and storage treat-ment of barley in diets fed to broiler chickens,Poultry Sci. 60 (1981) 2664-2671. 1 .

[46] Hesselman K., Elwinger K., Thomke S.,Influence of increasing levels of (3-glucanaseon the productive value of barley diets for broi-ler chickens, Feed Sci. Technol. 7 (1982)351-358.

[47) H6hler D., Pallauf J., Effekt einer abgestuftenZn-Zufuhr und Zulagen von Citronens5ure zueiner Mais-Soja-Di5t auf Leistungsparameterund Mineralstoffverwertung beim Ferkel, J.Anim. Physiol. Anim. Nutr. 71 ( 1994) 189-199.

[481 Holm A., Zinc oxide in treating E. coli diar-rhoea in pigs after weaning, Compendium,Contin. Educ. for the Practising Veterinarian 18 8Suppl. 28, 1996.

[49] Holmgren N., lnblandning av zinkoxid i sma-

grisfoder som profylax mot avv5njningsdiarr6.Praktiskt inriktade grisforsok. Nr. I, Skara, Swe-den (in Swedish), 1994.

[50] Holmberg T., Wierup M., Engstr6m B., Theeffect of feeding diets containing avoparcin andmonensin on the occurrence of Salmonella incaecum and liver in experimentally infectedchickens, Poultry Sci. 63 (1984) 1144-1148.

[5 I Humbert F., Lalande F., L’Hospitalier R., SalvatG., Bennejean G., Effect of four antibiotic addi-tives on Salmonella contamination of chicks

protected by an adult chicken flora, AvianPathol. 20 ( 1991 ) 577-584.

[52J Inborr J., Feed enzymes. Feed Enzymes in Ani-mal Production, Conference held at Solihull 21 1Sept. 1989, organized by Forum Feeds, 1989,8 p.

[53[ Inborr J., Supplementation of pig starter dietswith carbohydrate-degrading enzymes - stabi-lity, activity and mode of action, Agric. Sci. Fin-land (Suppl. 2) 3 (1994) 1-24.

[54] Inborr J., Gastrointestinal parameters influen-cing performance of pigs fed enzyme-supple-mented barley-based feeds, Anim. Feed Sci.Technol. 71 (1998), in press.

[55J Inborr J., Bedford M.R., Stability of feedenzymes to steam pelleting during feed proces-sing, Anim. Feed Sci. Technol. 46 (1994)179-196.

[56 ! Inborr J., Gronlund A., Stability of feed enzymesin physiological conditions assayed by in vitromethods, Agric. Sci. Finland 2 ( 1992) 125-132.

[57] Inbon-J., Ogle B., Effect of enzyme treatment ofpiglet feeds on performance and post weaningdiarrhoea, Swed. J. Agric. Res. 18 (1988)129-133.

1581 Inborr J., Schmitz M., Aherne F.X., Effect ofadding fibre and starch-degrading enzymes toa barley-wheat based diet on performance andnutrient digestibility in different segments ofthe small intestine of early weaned pigs, Anim.Feed Sci. Technol. 44 ( 1993) I 13-127.

[591 Jamroz D.. Wiliczkiewicz A., Skorupinska J.,Orda J., Volker L., The effect of increased Roxa-zyme G supplement in the broiler fed with triti-cale rich mixtures, Arch. Getliigelk. 60 ( 1996)I65-173.

[60] Johansson E., Lönnroth L, Lange S., Jonson I.,Jennische E., Lbnnroth C., Molecular cloningand expression of pituitary gland protein modu-lating intestinal fluid secretion, J. Biol. Chem.270 ( 1995) 20615-20620.

[61 ] Jonsson E., Conway P., Probiotics for pigs, in:Fuller R. (Ed.), Probiotics. The Scientific Basis,Chapman & Hall, London, 1992, pp. 259-316.

[62] Kahrs D., Toyocerin, ein Weg zur Stabilisie-rung der Darmflora, Kraftfutter 69 (1986)364-370.

[63] Kaldhusdal M., Epedimiological, aetiologicaland morphological studies on necrotic enteritisin broiler chickens, Diss., Norwegian Coll. Vete-rinary Medicine, Oslo, Norway, 1993.

[64] Kiiskinen T., Feeding whole grain with pelleteddiets to growing broiler chickens, Agric. FoodSci. Finland 5 ( 1996) 167-175.

!65] Kirchgessner M., Gedek B., Wiehler S., Bott A.,Eidelsburger U., Roth F.X., Zum Einfluss vonAmeisens5ure, Calciumformiat und Natrium-

hydrogencarbonat auf die Keimzahlen derMikroflora und deren Zusammensetzung in ver-schiedenen Segmenten des Gastrointestinal-traktes, 10: Untersuchungen zur nutritiven Wirk-samkeit von organischen Sduren in der

Ferkelaufzucht, J. Anim. Physiol. Anim. Nutr. 68(1992)73-81. 1 .

[66] Kronseder G., Wirkung und Vertr!glichkeit einerkohlenhydratspaltenden Enzympr5paration(Roxazyme R G) in Broilerrationen, Diss., Lud-wig Maximilians Universit5t, Munchen, Ger-many, 1993, 101 p.

[67] Lange S.. L6nnroth I., Passive transfer of pro-tection against cholera toxin in rat intestine,Microbiol. Lett. 24 (1984) 165-168.

[68J Lange S., Lonnroth L, Martinsson K., Concen-trations of antisecretory factor in eggs and inchicken blood plasma, Br. Poultry Sci. 35 (1994)615-620.

[69] Lange S., L6nnroth L, Skadhauge E., Effect ofanti secretory factor in pigs, Eur. Physiol. (Pflu-gers Arch.) 409 ( 1987) 328-332.

[70] Leuchtenberg W.G., Einfluss antibiotischer Fut-terzus5tze auf die Darmflora von Hdhnerkdkenund auf die Persistenz von Salmonella typhi-murimn-Infektionen, Diss., Tier5rztl. Hoch-schule, Hannover, Germany, 1981, 85 p.

[71J Li S., Sauer W.C., Huang S.X., Gabert V.M.,Effects of beta glucanase supplementation tohulless barley or wheat soybean meal diets onthe digestibilities of energy, protein, ¡3-glucans,and amino acids in young pigs, J. Anim. Sci. 74(1996)1649-1656.

[72] Li S., Sauer W.C.. Mosenthin R.. Kerr B., Effectof ¡3-glucanase supplementation of cereal baseddiets for starter pigs on the apparent digestibili-ties of dry matter, crude protein and energy,Anim. Feed Sci. Technol. 59 (1996) 223-231. 1.

[73] Lin L., Quarles C., Evaluation of Primalacconcentrate on reduction of E. coli in mail broi-

lers, Proc. World’s Poultry Sci. Assoc. SessionII-IV, XX World’s Poultry Congr., New Dehli,India, 1996, pp. 147-151. 1.

[74] Linde K., Hahn I, Vielitz E., Development oflive salmonella vaccines optimally attenuatedfor chickens, Tier5rztl. Umschau 51 (1996)23-28.

[75] Linton A.H., Al-Chalaby Z.A.M., Hinton M.H.,Natural subclinical SalmoneLla infection in chic-kens: A potential model for testing the effects ofvarious procedures on Salmonella shedding,Vet. Rec.l16 (1985) 361-364.

[76] L6nnroth L, Lange S., Purification and charac-terization of the antisecretory factor - a proteinin the central nervous system and in the gutwhich inhibits intestinal hypersecretion indu-ced by cholera toxin, Biochem. Biophys. Acta883 (1986) 138-144.

[77] L6nnroth I., Martinsson K., Lange S., Evidenceof protection against diarrhoea in suckling pigletsby a hormone like protein in sow’s milk, J. Vet.Med. 335 (1988) 628-635.

[78] Lund A., Wallgren P., Rundgren M., Artursson K.,Thomke S., Fossum C., Performance, behaviourand immune capacity of domestic pigs rearedfor slaughter as siblings of transported and rea-red in mixed groups, Acta Agric. Scand. Sect. A,Anim. Sci. 48 (1998) 103-112.

[79] Lundeheim N., Pig progeny station testing ofdisorders and production traits, Diss., ReportNo. 72, Dept. Animal Breeding & Genetics,Swed. Univ. Agric. Sciences, Uppsala, 1986.

[80] Maxwell F.J., Stewart C.S., The microbiology ofthe gut and the role of probiotics, in: VarleyM.A. (Ed.), The Neonatal Pig. Developmentand Survival, CAB International, 1995,pp. 155-186.

[81 ] McNabb J.M., Factors affecting the energy valueof wheat for poultry, World’s Poultry Sci. J. 52( I 996) 69-72.

[82] Mead G.C., Role of probiotics in controllingfoodborne pathogens in poultry, Proc. World’sPoultry Sci. Assoc., 10th European Symp.Poultry Nutrition, Antalya, Turkey, 1995,pp. 226-232.

[83] Miles R.D., Brown R.D., Comer C.W., OelfkeE., Influence of an enzyme and an antibiotic onbroiler performance, J. Appl. Anim. Res. 9(1996)105-117.

[84] Miller R., Newby T.J., Stokes P.D., Hampson D.,Bourne F.J., The role of antigen in the aetio-logy of post weaning diarrhoea, Ann. RechercheVet. 14 (1983) 487-492.

[85! Mohan B., Kadirvel R., Natarajan A., BhaskaranM., Effect of probiotic supplementation ongrowth, nitrogen utilisation and serum choles-terol in broilers, Br. Poultry Sci. 37 (1996)395-401.

[86] Monsan P.F., Paul F., Oligosaccharide feed addi-tives, in: Wallace R.J., Chesson A. (Eds.), Bio-technology in Animal Feeds and Animal Feed-ing, VCH Verlagsgeselischaft mbH, Weinheim,Germany, 1995, pp. 233-245.

[87] Mosenthin R., Sauer W.C., Ahrens F., LangeC.F.M. de, Bornholdt U., Effect of dietary sup-plements of propionic acid, siliceous earth or acombination of these on the energy, protein andamino acid digestibilities and concentrations ofmicrobial metabolites in the digestive tract ofgrowing pigs, Anim. Feed Sci. Techn. 37 ( 1992)245-255.

[88] Newman C.W., Eslick R.F., El-Negoumy A.M.,Bacterial diastase effect on the feed value oftwo hulless barleys for pigs, Nutr. Rep. Int. 28(1983) 139-146.

[89] Nguyen T.H., Eckenfelder B., Levesque A.,Growth promoting efficiency of two probiotics,Toyocerin° and Pacitlor!, in broiler diets, Arch.Gefldgelk. 52 ( 1988) 240-245.

[90] Persson E., Mikrobiellt fytas i foder till v!xandesvin, Master thesis. Report No. 79, Dept. AnimalNutrition & Management, Swed. Univ. Agric.Sciences, Uppsala, Sweden, (in Swedish), 1996,39 p.

[91 1 Petersen V.E., Anti-nutritive stoffer i rapsfro ogderes indflydelse pd slagtekyllinger, Dansk Erh-vervstjerkr! 1 I (1991 ) 243-245 (in Danish).

[92] Petersen V.E., Foderv*rdi af aerter og rapsfrotil slagtekyllinger. Statens Husdyrbrugsforstlg,Medd. 801, Copenhagen, (in Danish), 1991. 1.

[93] Pettersson D., Combining proteases and fibredegrading enzymes, Feed Int. 17 (1996) 59-65.

[94] Pettersson D., Aman P., Effects of enzyme sup-plementation of diets based on wheat, rye or tri-ticale on their productive value for broiler chic-kens, Feed Sci. Technol. 20 ( 1988) 313-324.

[95! Pollman D.S., Probiotics in pig diets, in: Hare-sign W., Cole D.J.A. (Eds.), Recent Advances inAnimal Nutrition, Butterworths, London, 1986,pp.193-205.

[96] Poppe C., McFadden K.A., Demczuk W.H.B.,Drug resistance, plasmids, biotypes and sus-ceptibility to bacteriophages of Salmonella iso-lated from poultry in Canada, Int. J. Food Micro-biol. 30 (1996) 325-344.

[97 ! Pusztai A., Grant G., King T.P., Clarke E.M.W.,Chemical probiosis, in: Haresign W., ColeD.J.A. (Eds.), Recent Advances in Animal Nutri-tion, Butterworths, London, 1990, pp. 47-60.

[98 ! Ratcliffe B., Cole C.B., Fuller R., Newport M.J.,The effect of yoghurt and milk fermented witha porcine intestinal strain of Lactobacillus reu-teri on the performance and gastrointestinal floraof pigs weaned at two days of age, Food Micro-biol. 3 (1986) 203-21 1 .

[99] Reiter B., The lactoperoxidase system in bovinemilk, in: Pruitt K.M., Tenovuo J.O. (Eds.), Thelactoperoxidase system, Marcel Dekker Inc.,New York, 1985, pp. 123-141. 1.

[100] Roth F.X., Eckel B., Kirchgessner M., Eidels-burger U., Zum Einfluss der Ameisensdure aufpH-Wert, Trockenmassegehalt, Konzentratio-nen an fluchtigen Fettsduren und Milchs5ure imGastrointestinaltrakt, 3: Untersuchungen zurnutritiven Wirksamkeit von organischen Sdu-ren in der Ferkelaufzucht, J. Anim. Physiol.Anim. Nutr. 67 ( 1992) 148-156.

[101] Roth F.X., Eidelsburger U., Kirchgessner M.,Zum Einfluss von Fumarsdure, Satzs5ure,Natriumformiat, Tylosin und Toyocerin auf pH-Wert, Trockenmassegehalt, Konzentration anCarbons5uren und Ammoniak in verschiedenen

Segmenten des Gastrointestinaltraktes, 12:Unterzuchungen zur nutritiven Wirksamkeit vonorganischen Sauren in der Ferkelaufzucht, J.Anim. Physiol. Anim. Nutr. 68 ( 1992) 93-103.

! 102] Rundgren M., L6fquist L, Effects on perfor-mance and behaviour of mixing 20 kg pigs fedindividually, Anim. Prod. 49 (1989) 3l 1-315.

[ 103] Sigfridson K., Lange S., Lbnnroth L, Anti-secre-tory protein and feed induced lectines in sowand suckling piglet, Abstract, 46th Ann. MeetingEAAP, Prague, Czech Republic, 1995.

[ 104] Slominski B.A., Campbell L.D., Guenter W.,Enhancement of the feeding value of low-glu-cosinolate rapeseed by the supplementation ofpoultry diets with exogenous enzymes, Proc.19th World’s Poultry Congress, Amsterdam,Netherlands, Vol. 2, 1992, pp. 241-245.

! 105] Stanley V.G., Chukwu H., Gray C., ThompsonD., Effects of lactose and Bio-Mos in dietaryapplication on growth and total coliform bacte-ria reduction in broiler chicks, Proc. Poultry Sci.Assoc. 85th Ann. Meeting, Lousville, Kentucky,75, Suppl. 1, 1996.

[ 106] Stewart C.S., Chesson A., Making sense of pro-biotics, Pig Vet. J. 31 (1993) 11-33.

! 107] Stigson M., Grisningsbeteende och sm5-grisd6dlighet, Swed. Univ. Agric. Sciences,Research Information Centre, Rapporter,Alim5nt 17, Uppsala, Sweden, (in Swedish),1979.

[108] Thacker P.A., Campbell G.L., GrootwassinkJ.W.D., The effect of enzyme supplementationon the nutritive value of rye-based diets forswine, Can. J. Anim. Sci. 71 (1991) 489-496.

[l09] Thacker P.A., Campbell G.L., GrootwassinkJ.W.D., Effects of salinomycin and enzyme sup-plementation on nutrient digestibility and theperformance of pigs fed barley- or rye-baseddiets, Can. J. Anim. Sci. 72 (1992) 117-125.

[110] Thomke S., On the influence of different stagesof ripeness on the productive value of barleyfed to chickens, laying hens, rats and mice, ActaAgric. Scand. 22 (1972) 107-120.

[1)1] Thomke S., Rundgren M., Hesselman K., Theeffect of feeding high-viscosity barley to pigs,Proc. 3 1 st Ann. Meet. EAAP, Munchen, Comm.Animal Nutrition, 1980, 5 p.

[ 1 12] Tuschy D., Verwendung von Probiotika als Leis-tungsf6rderer in der Tierernahrung, Ubers. Tie-rem. 14 ( 1986) 157-178.

[I 13] Vranjes V., Spring M.P., Pfirter H.P., Tricho-derma viride enzyme complex as affected byextrusion of barley based broiler diets: response,Arch. Geflugelk. 60 (1996) 81-87.

[114] Vranjes M.V., Wenk C., Influence of Tricho-derma viride enzyme complex on nutrient utili-zation and performance of laying hens in dietswith and without antibiotic supplementation,Poultry Sci. 75 (1996) 551-555.

[ I I S] Wantia D., Einige Gesichtspunkte zur Wirkungkohlenhydrat-spaltender Futterzusatzenzyme inroggenhaltigen Rationen beim Getlugel, Diss.,Ludwig-Maximilians-Universitdt, Munchen,Germany, 1993, 68 p.

[ l 16] Yalda A.Y., Forbes J.M., Effects of food intake,soaking time, enzyme and cornflour addition onthe digestibility of the diet and performance ofbroilers given wet food, Br. Poultry Sci. 37( 1996) 797-807.