Understanding interactions between forages and concentratesis important for formulating feeding strategies for growingcattle in central Vietnam

P. T. DoyleA, C. R. StockdaleA,C, Nguyen Xuan BaB, Nguyen Huu VanB and Le Duc NgoanB

AFuture Farming Systems Research, Department of Primary Industries, Kyabram Centre,120 Cooma Road, Kyabram, Vic. 3620, Australia.

BFaculty of Animal Sciences, Hue University of Agriculture and Forestry, 102 Phung Hung Street,Hue City, Vietnam.

CCorresponding author. Email: richard.stockdale@dpi.vic.gov.au

Abstract. Three experiments were conducted in Vietnam to measure responses in forage intake and diet digestibility toconcentrate feeding ingrowingcattle.Thebasal diet in all experimentswasgrass (elephant grass,Pennisetumpurpureum, inexperiments 1 and 2; native grass in experiment 3) fed at 1.25% liveweight (DM basis) during the day and rice straw fedad libitum at night. The concentrate in experiment 1 was cassava powder plus urea. In experiments 2 and 3, a formulatedconcentrate comprised ofmaize, rice bran, fishmeal, urea and salt was used. The concentrates were offered at ~0.3, 0.7, 1.3and 2.0% liveweight in each experiment, and a zero concentrate treatment was also included. Effects of the amount ofconcentrate on substitution rate of concentrate for forage and on diet neutral detergent fibre (NDF) digestibility weremeasured to assess interactions between feeds. Substitution rate was high (0.5--0.7 kgDM reduction in forage intake per kgDMsupplement consumed) andnot affectedbyamountof supplement fed inexperiment1. In experiments 2and3, therewasno substitution at the lowest intake of supplement, but it subsequently increasedwith amount of supplement consumed, to ahigh of 0.3--0.5 kg DM reduction in forage intake per kg DM supplement consumed. The cassava powder supplementmarkedly decreased dietary NDF digestibility (from 62 to 41%), whereas the formulated concentrate only reduced NDFdigestibility by 11 and 8%units in experiments 2 and 3, respectively. Itwas calculated that depressions inNDFdigestibilitywould reduce the estimatedmetabolisable energy content of the basal forage by 1--3.6MJ/kg DM at the higher supplementintakes. The importance of these results in making decisions on tactical feeding systems to fatten cattle in central Vietnamis discussed.

Additional keywords: associative effects, substitution.

Introduction

Households in the lowlands of central Vietnam generallygraze their cattle on native grasses during the day and feedrice straw (Oryza sativa) at night (Ba et al. 2005). These lowinput systems lead to low cattle productivity. As the demandfor beef in Vietnam has increased, some rural householdshave implemented confinement feeding systems to finishcattle for market, to increase and diversify their income.The basal diet in these systems includes cut-and-carrynative grass or sown species such as elephant grass(Pennisetum purpureum) (Ba et al. 2005). Supplementssuch as rice bran, maize and cassava powder are available,but they are usually fed in low amounts (average of~1 kg/day), the amount and type of supplement offeredvaries considerably between days, and they are seldommixed. The basal diet of grass and straw meetsmaintenance requirements and can result in liveweight(LW) gains of 0.1 to 0.2 kg/day (Ba et al. 2008a, 2008b).However, the time taken to finish cattle is long, even with theexisting supplementary feeding practices. There is potential toimprove growth rates and efficiency of feed utilisation by

formulating concentrate mixes, implementing more consistentfeeding practices and feeding higher amounts of supplement.

Feed resource planning for ruminant livestock productioninvolves: knowing how much and what type of feeds are likelyto be available; having information on their nutritivecharacteristics; understanding the animal’s nutrientrequirements for particular purposes; and using thisinformation to design feeding strategies. Although feedplanning principles are applied in temperate agriculture, forexample to design diets for confinement production systemsor to set carrying capacity or to decideon calving times in grazingsystems, suchprinciples are poorly understood andnot applied incentral Vietnam. In this region, the number of householdsinvolved in cattle finishing is increasing. Ba et al. (2008b)found local cattle can gain over 50 kg LW in less than2 months when supplemented with a concentrate formulatedfrom locally available feeds at ~2.0% LW/day. Economicanalysis revealed increased profit for farmers compared withtheir traditional practices.

In grazing and forage feeding systems, interactionsbetween basal diet and concentrate supplements occur.

CSIRO PUBLISHING

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� CSIRO 2008 10.1071/EA07417 0816-1089/08/070821

Substitution rates of concentrates for forage in ruminantsgrazing pastures or fed ad libitum on conserved foragesgenerally range between 0 and 1.0 kg DM reduction inforage intake (FI) per kg DM of supplement consumed(Stockdale et al. 1997; Stockdale 2000). The substitutionrate (SR, kg DM/kg DM) is generally higher with increasedconcentrate intake (CI). In addition, associative effects occurwhere the digestibility of the diet may be lower than thatcalculated from the digestibility and amounts of the feedscomprising the diet (Huhtanen 1991). Negative associativeeffects are due to depression in the digestibility of neutraldetergent fibre (NDF) in forageswhen the rumen environmentis altered by feeding concentrates (Mould et al. 1983;Huhtanen 1991). Dixon and Stockdale (1999) havesuggested that reduced NDF digestion is a primary cause ofsubstitution, although other factors are also important(Doyle 1987).

We examined the effects of concentrate supplements given togrowing cattle on the FI and on NDF digestibility in threeexperiments, to determine some of the implications ofsubstitution and associative effects on the formulation offeeding strategies in the central provinces of Vietnam and toimprove understanding of substitution, associative effects andgeneral ration formulation among Vietnamese scientists andextension staff.

Materials and methods

All experiments were conducted at the Hue University ofAgriculture and Forestry (HUAF) farm in Thua Thien HueProvince (16�000 to 16�480N; 107�480 to 108�120E) and eachhad five treatments. In all experiments, the basal diet comprisedfresh grass at 1.25% of LW (DM basis), fed between 0730 and1800 hours, and rice straw fed at 25--50% above the previousday’s intake, from 1830 to 0700 hours. In experiments 1 and 2,the grass was elephant grass with 8--11% DM crude protein and72--82%DMNDF.Native grass,with11%DMcrudeprotein and73% DM NDF, was used in experiment 3. The rice strawscontained crude protein around 5% DM and NDF of 77--84%DM.

The concentrate supplements fed in each experiment wereoffered at ~0.3 (T2), 0.7 (T3), 1.3 (T4) and 2.0% (T5) of LW(DM basis), and there was a zero concentrate treatment (T1) aswell. The amounts of supplement were chosen to cover the rangelikely to be feasible in practice, and were adjusted each week tomaintain the amounts offered in relation toLW.The supplementswere fed in equal amounts, two (for the 0.3 and 0.7% LWtreatments) or three (for the 1.3 and 2.0% LW treatments)times during the day. In experiment 1, the supplementcomprised cassava powder with 2% urea added and had crudeprotein and NDF concentrations of 8 and 8% DM, respectively.The cassava powder contained 37mg hydrogen cyanide/kg DM.In experiments 2 and 3, a formulated concentrate comprised ofrice bran (45% fresh basis), maize (49%), fish meal (3%), urea(2%) and salt (1%) was used. It contained ~17% DM crudeprotein and 33% DM NDF, on average.

Twenty entire male Laisind cattle ~15--18 months of ageand weighing 164 (s.d.� 19.1) kg were used in experiment 1.Laisind cattle are a cross between local Vietnamese yellow

cattle and Red Sindhi. They have a mature LW of ~350 kg.Male Vietnamese yellow cattle were used in experiments 2(n= 20; age 12--15 months; LW 116� 12.3 kg) and 3 (n= 15;age 14--17 months; LW 142� 15.7 kg). These animals have amature LWof 200--250 kg. In each experiment, the animalswereblocked on the basis of LW into groups of five. They were thenallocated at random, within each group, to treatments. The cattlewere adapted to individual stalls and the experimental feedingmanagement for 14 days before each experiment. Each animalhad access to a salt lick and water was freely available from adrinker within each pen.

Measurements, analysis and calculations

Experiments 1, 2 and 3went for 88, 44 and 49 days, respectively.In all experiments, the amounts of all feeds offered and residueswere recorded daily. Subsamples of each feed and of residues(when they occurred) were taken every day for DMdetermination. In experiment 1, total faecal collections weremade during three periods (days 20--26, days 48--54 anddays 76--82). During these periods, subsamples of feeds andfaeces were taken for laboratory analyses. The other twoexperiments included only one period of total collection (days24--30 and 10--16 in experiments 2 and 3, respectively).

Samples of feeds and faeces were analysed for DM andnitrogen (N) according to AOAC (1990) and NDF accordingto Van Soest et al. (1991). Crude protein concentration wascalculated as N� 6.25. Hydrogen cyanide concentrations incassava powder were measured as described by Easley et al.(1970).

Substitution of supplement for forage (kg DM reduction inintake of grass plus rice straw per kgDMconcentrate consumed)was calculated for each animal receiving the concentrate, as:

Substitution rate ¼ FI of control bull� FI of supplemented bull

CI of supplemented bull

As the cattle were grouped on LW before allocation totreatments, the FI without supplement use was from thecontrol animal within the relevant group.

In vivo digestibility of NDF was calculated as intake minusfaecal output, divided by intake and converted to a percentage.Changes in NDF digestibility were used to calculate the likelymagnitude of associative effects on estimated metabolisableenergy (ME, MJ/kg DM) value of the basal forage diet. To dothis, the in vitroDMdigestibility of the basal diet was assumed tobe 60% and this was reduced by the amount that in vivo NDFdigestibility declined at each supplement intake relative to thecontrol treatment. Metabolisable energy of the basal foragediet was estimated using the equation, 0.17� IVDMD � 2.0(Standing Committee on Agriculture 1990).

In all experiments, effects of amount of concentrateconsumed on SR, rice straw and grass intake (i.e. forageintake, FI), and NDF digestibility were examined using linear/quadratic regression analysis in GENSTAT 9 (Lawes AgriculturalTrust, Rothamsted, UK). Residual diagnostics performed aftereach analysis showed the linear or quadratic models fitted thedata well. The effects of dietary treatments on SR and NDFdigestibility in each experiment were also tested using analysisof variance.

822 Australian Journal of Experimental Agriculture P. T. Doyle et al.

Results

Experiment 1

Cattle offered cassava powder at 2.0%LWhad intakes similar tothe 1.3% LW treatment (treatments 4 and 5 in Table 1). Ascassava powder intake (CPI, kgDM/day) increased, the intake ofrice straw (RSI, kg DM/day) declined as follows:

RSI ¼ 1:81 ð�0:086Þ � 0:58 ð�0:058ÞCPIðR2 ¼ 0:849; P< 0:001Þ

Elephant grass intake tended to decrease (P = 0.091), from1.89 to 1.59 kg DM/day, but the effect was biologically small.Therewere no significant effects ofCPI on SR (Table 1), and thisdid not change significantly between the three digestibilityperiods. Digestibility of NDF (Table 1) declined linearly asthe amount of cassava powder consumed increased:

NDF digestibility ¼ 64:5 ð�1:60Þ � 8:9 ð�1:07ÞCPIðR2 ¼ 0:792; P < 0:001Þ

It was estimated that the ME value of the forage could havedeclined by 3.6MJ/kg DM at the highest supplement intakes.

Experiments 2 and 3

Rice straw intake declined linearly with increasing CI in bothexperiments, the relationships being:

Experiment 2: RSI ¼ 1:38 ð�0:077Þ � 0:38 ð�0:062ÞCIðR2 ¼ 0:684; P< 0:001Þ

Experiment 3: RSI ¼ 1:09 ð�0:095Þ � 0:25 ð�0:067ÞCIðR2 ¼ 0:514; P< 0:01Þ:

The intakes of elephant grass (P = 0.273) or native grass(P= 0.218) were not significantly affected by CI. In bothexperiments, the lowest amount of concentrate supplement

increased FI (Table 1), after which substitution rates werepositive and increased with increasing CI. The relationshipsbetween SR and CI, averaged over the whole experiment, aredescribed by:

Experiment 2: SR ¼ �0:59 ð�0:141Þ þ 1:06 ð�0:261ÞCI� 0:27 ð�0:098Þ CI2 ðR2 ¼ 0:796; P< 0:001Þ

Experiment 3: SR ¼ �0:61 ð�0:265Þ þ 0:43 ð�0:166ÞCIðR2 ¼ 0:400; P < 0:027Þ:

DietNDFdigestibility tended to decline as supplement intakeincreased in both experiments (Table 1), but there was only asignificant relationship between NDF digestibility and CI inexperiment 2.

NDF digestibility ¼ 55:1 ð�2:12Þ � 4:2 ð�1:55ÞCIðR2 ¼ 0:287; P ¼ 0:015Þ

It was estimated that the ME value of the forage could havedeclined by 1.8 and 1.2MJ/kg DM at the highest supplementintakes in experiments 2 and 3, respectively.

Discussion

Constraints to adoption of tactical supplementary feeding tofinish cattle for sale at specific times vary between households.They include: the amount of crop residues available, which isinfluenced by areas of cultivated land and crop yields; amount ofsown grass grown or access to native grasses; and availability of,and competing uses for, primary and secondary (those under 17and over 60 years of age) labour. Decisions on when tocommence fattening cattle, how many to feed, what to feedand how much will differ in relation to the household resources,and all ultimately affect profit.

The results presented here indicate much lower substitutionrates of the formulated concentrate compared with cassavapowder, a feed that is high in starch and highly digestible

Table1. Effects of theamountof cassavapowder (experiment1) or formulatedconcentrate (experiments 2and3) consumedbycattle fedbasaldiets ofelephant grass and straw (experiments 1 and 2) or native grass and straw (experiment 3) on substitution rate, diet neutral detergent fibre (NDF)

digestibility and estimated metabolisable energy (ME) content of the basal diet

Concentrate treatment Statistics1 2 3 4 5 s.e.d. P-value

Experiment 1

Intake of cassava powder (kg DM/day) 0 0.55 1.04 2.16 2.21 -- --

Substitution rate (kg DM/kg DM) -- 0.64 0.54 0.69 0.72 0.247 0.894NDF digestibility (%) 62.3 61.3 58.5 46.2 41.3 2.67 <0.001Estimated forage ME (MJ/kg DM) 8.2 8.0 7.6 5.5 4.6 -- --

Experiment 2

Concentrate intake (kg DM/day) 0 0.39 0.80 1.57 2.45 -- --

Substitution rate (kg DM/kg DM) -- --0.20 0.05 0.32 0.48 0.119 <0.001NDF digestibility (%) 56.2 54.4 51.6 45.2 46.4 4.36 0.089Estimated forage ME (MJ/kg DM) 8.2 7.9 7.4 6.3 6.4 -- --

Experiment 3

Concentrate intake (kg DM/day) 0 0.45 0.93 1.80 2.36 -- --

Substitution rate (kg DM/kg DM) -- --0.64 0.06 0.24 0.34 0.330 0.068NDF digestibility (%) 58.0 54.9 54.8 49.8 50.7 4.43 0.051Estimated forage ME (MJ/kg DM) 8.2 7.7 7.7 6.8 7.0 -- --

Forage� concentrate interactions for feeding of cattle Australian Journal of Experimental Agriculture 823

(Tudor andNorton 1982). It is well documented that the amountsof supplement fed and the intake and characteristics of the basediet affect substitution rates (Doyle 1987; Stockdale et al. 1997;Stockdale 2000). The lower substitution rates with theformulated concentrate mean that the basal forages were stillsupplying most of the energy requirements for maintenance,enabling nutrients from the more valuable concentrates to beused for productive purposes. The feeding management used,restricted access to grass during the day and ad libitum feeding ofrice straw at night, may have limited the substitution, and it isimportant that nearly all of the reduction in FI was associatedwith the rice straw component. This means the more valuablegrass is notwasted and that less straw can be offeredwhen higheramounts of supplement are fed, with potential to allocate thesaved straw to other stock. However, because grass intake wasnot affected by feeding the supplements, if a household was tohave more animals, more grass would need to be collectedand fed.

The formulation of the concentrate supplement inexperiments 2 and 3 was not only based on providing readilydigestible energy from locally available concentrates, but alsoprotein and non-protein N. In ruminants fed low quality forages,providing protein or non-protein N to the rumen organisms(Leibholz and Kellaway 1984) or additional amino acids atthe tissue level (Kempton et al. 1979) can increase FI, andpossibly also moderate substitution effects (Doyle 1987).Although both supplements depressed NDF digestion, thehighly digestible, high starch, cassava powder depressed NDFdigestibility by20%units, indicating it should not be fed as a solesupplement in high amounts. Opatpatanakit et al. (1994) rankedcereal grains on their starch degradation characteristics,as follows: wheat > triticale > oats > barley >maize > rice andsorghum. Furthermore, Opatpatanakit et al. (1995) found thatwheat andbarley inhibitedNDFdigestion to a greater extent thanmaize. The slower degradation rates of starch in the maize andrice branmay have limited the negative associative effects of theformulated concentrate onNDFdigestibility, relative to that seenwith cassava powder.Dixon andStockdale (1999) suggested thatreduced NDF digestibility is a primary cause of substitution;thus, combining the supplements available in households wouldseem to be important in maintaining forage consumption and inensuring the efficient use of these forages. The theoreticalcalculations of the implications of associative effects on theME value of the basal forage indicated the energy available tocattle may be reduced by 15--22%, even when using theformulated concentrate at high rates of feeding.

Prior to these experiments, scientists and extension staff incentralVietnamhad little understandingof substitutioneffects ofsupplements for forage in ruminant livestock and no knowledgeof associative effects. The information generated is valuable infeed planning, where achieving target weights in cattle is criticalto farmer profits.

Acknowledgements

The Australian Centre for International Agricultural Research, Departmentof Primary Industries Victoria and Hue University of Agriculture andForestry (HUAF) provided financial support. Technical staff and studentsfrom HUAF provided invaluable support in collecting feed, management ofthe stock and during digestibility collections.

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Manuscript received 18 December 2007, accepted 6 March 2008

824 Australian Journal of Experimental Agriculture P. T. Doyle et al.

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