International Dairy Topics — Volume 13 Number 3 17

by Jon Mouncey, WestpointVeterinary Group, Dawes Farm,Bognor Road, Warnham, WestSussex RH12 3SH, UK.

Reproductive efficiency of dairycows can greatly influence theprofitability of dairy farms.

Prolonged intervals from calving topregnancy lead to economic lossesdue to delays in beginning or resum-ing milk production, increased main-tenance costs, a decreased rate ofreplacement and increased depreci-ation costs. These costs have been estimatedto be between approximately £2and £5 per day extension over a 365day calving interval. The variance inthe reported costs are dependenton factors such as milk yield percow, description of lactation curve,milk price, feed costs, calf value andreplacement costs. The actual sumof money per day extended calvingto pregnancy interval is often dis-puted amongst dairy farmers, how-ever most agree that there is asignificant cost.

Critical control points

Two critical control points forimproving reproductive efficiency ondairy farms are:l Optimising calving to first service.l Early diagnosis of non-pregnancyand timely re-insemination there-after. Pregnancy diagnosis is one of themost common and key proceduresperformed by veterinary surgeonsduring routine fertility managementon dairy farms. The purpose of examining cowsand heifers for pregnancy is todetect those cows that are not preg-nant. Detection of the non-pregnantdairy cow or heifer post insemina-tion provides an opportunity toidentify individuals that are not preg-nant and either decrease the intervalbetween inseminations and there-fore reduce the aforementionedcosts of extension of calving to preg-nancy interval; or alternatively atimely management decision can bemade to cull that individual from theherd when economically advanta-

geous. An early accurate diagnosisof non-pregnancy post inseminationfollowed by as short a period oftime possible to re-insemination islikely to be an economically prof-itable strategy for a dairy farm. Fertilisation rates following a cor-rectly timed insemination areapproximately 90%. After enteringthe uterine lumen on approximatelyday five post insemination thebovine embryo signals its presencearound eight days later, 13 days postinsemination. The bovine embryo secretes inter-feron tau from trophoblast cells,preventing regression of the corpusluteum by acting on the mechanismwhich releases prostaglandin F2alpha and return to oestrus does notoccur. In the absence of successfulfertilisation or a viable embryo, nor-mal luteolysis of the corpus luteumwill occur and the cow or heifer willreturn to oestrus 18-24 days afterinsemination.Early embryonic mortality before21 days post-insemination occurs inapproximately 22% of embryos.Embryonic mortality between 21and 42 days post insemination andfoetal loss thereafter occur atapproximately 6% and 5% respec-tively. Therefore early pregnancydiagnosis prior to 21 days post

insemination may be unreliable. Criteria for the ideal pregnancydiagnosis have previously beendescribed and are as follows. Thetest should be as early as possible,identify both pregnant and non-pregnant animals correctly, be inex-pensive, be simple to conduct underfield conditions, determine preg-nancy rapidly at the time the test isperformed and involve as little addi-tional handling as normally requiredof the dairy cow or heifer to admin-ister the test.

Economic benefits

The economic benefits of pregnancydiagnosis depend on the factors out-lined above, such as the time afterinsemination when the diagnosis isperformed, but also its effects onembryonic loss, the efficiency ofoestrus detection, factors that maybe affecting oestrus expression onthe individual dairy unit and themanagement or treatment decisionmade upon finding a non-pregnantindividual. Failure to return to oestrus 18-24days post insemination may indicatethe establishment of pregnancy. Thismethod of oestrus detection is con-sidered to be the most simple, early

and inexpensive method of preg-nancy diagnosis by many farmers.This assumption does not considerearly embryo mortality and isdependent on the efficiency andaccuracy of oestrus detection on thedairy unit. However as labour units per coware declining and oestrus behaviourhas become erratic, short and ofteneven non-existent in Holstein dairyherds, visual observation of oestrushas become particularly difficult.This could lead to the false assump-tion that some cows – which haveeither not been detected in oestrusor have not expressed oestrus –might be pregnant. If oestrus is not detected in thesebarren cows, presumed pregnant,until the point they are expected tore-calve, the individual is likely to beculled, thus increasing the number ofcows culled for failure to conceive.

Culling costs

The cost of culling a dairy cow isestimated to be £750 and total costsdue to fertility culls are likely to bemuch greater than 13% on farmsemploying poor oestrus detectionand depending on return to cyclicityas a means of pregnancy diagnosis.Approximately 6-10% of cowsexhibit behavioural oestrus during anormal pregnancy. Intrauterineinsemination of pregnant cows canresult in termination of pregnancy. In these instances if the cowreturns to oestrus after iatrogenicattrition of pregnancy and at best isre-inseminated and becomes preg-nant within 21 days the incurredcost is estimated to be £94.50,assuming £4.50 per days extensionin calving to pregnancy interval.Equally these 6-10% of cowsexhibiting behavioural oestrus duringa normal pregnancy may be subse-quently culled as barren with greaterassociated costs plus the value of apregnancy. In summary, efficient and accurateoestrus detection in cows andheifers profoundly influences thereproductive performance and prof-itability of dairy herds as one missed

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The use of ultrasonographyin pregnancy diagnosis of dairy cattle

Holsteins in oestrus.

International Dairy Topics — Volume 13 Number 3 19

oestrus event without interventionmay cost approximately £189,assuming £4.50 per days extensionin calving to pregnancy interval;however non-return to oestrus,should be considered an unreliableindicator of pregnancy and preg-nancy loss.

Laboratory testing

Various laboratory tests have beendeveloped for early pregnancy diag-nosis in dairy cattle. These testshave the advantage of being mini-mally invasive as the hormones orproteins they rely on can bedetected in milk, however they dohave some disadvantages. Oestrone sulphate for example,can be detected in plasma and milkin pregnant cows by 105 days, andconcentrations are significantlylower in the non-pregnant animal.However it is not cost effective towait 105 days post-insemination todetermine the pregnancy status of adairy cow and other methods candiagnose pregnancy accurately muchsooner, for example rectal palpationat day 30 post insemination, offeringa potential saving of 70-75 days overoestrone sulphate. Early pregnancy factor (EPF) canbe detected in milk of pregnant cat-tle three days post insemination,although after eight days more accu-rate results can be obtained. This test would enable fertilisationfailure post insemination to be iden-tified within eight days and allowprostaglandin F2a to be adminis-tered resulting in a rapid return tore-insemination, however a dipstickcow side test has to date been toounreliable. Bovine pregnancy specific glyco-protein B (bPSPB) is produced bythe binucleate cells of the tropho-blastic ectoderm thus indicating thepresence of a viable embryo.bPSPB also has the added advan-tage of being detectable in milk at 24days post-insemination, however its

half life is many months and as suchcan be detected after embryonicand foetal death and after normalparturition resulting in a false posi-tive pregnancy diagnosis. Milk progesterone concentrationsare high during dioestrus and preg-nancy and low around the time ofoestrus. The optimum time for sam-pling has been shown to be 24 daysafter service. Milk progesteronesampling has the advantage of beingrelatively cheap, minimally invasive,and can be performed as a cow sidetest. The accuracy of milk proges-terone testing for confirmation ofpregnancy at day 24 post insemina-tion is reported to be 85% and100% for confirmation of non-preg-nancy. However as a single test 24 dayspost insemination there are a num-ber of reasons for false positivepregnancy diagnosis. These includeincorrect timing of insemination,persistent corpus luteum associatedwith endometritis, cystic ovarian dis-ease, short return to oestrus intervaland late embryonic death. The greatest benefit to be gainedin a single test 24 days post insemi-nation is a low progesterone resultas a confident diagnosis of non-preg-nancy can be made. A low proges-terone value indicates only that theanimal is either 2.0-2.5 day’s pre- orpost-oestrus or indeed in oestrus attime of sampling.Milk progesterone sampling hasbeen deemed labour intensive bysome and so less attractive for thepractical farmer. In-line milking parlour biosensors are thereforecurrently being developed for appli-cation in automatic milking systems.

Transrectal palpation

Pregnancy diagnosis by transrectalpalpation of the uterus was reportedto be first recorded in the 19thCentury and is now considered themost widely used method of preg-nancy diagnosis in dairy cattle. This method of diagnosis, althoughinvasive, is relatively cheap and sim-ple to perform once appropriatetraining has been undertaken.

Various structures of the bovinereproductive tract can be palpatedper rectum to assist in pregnancydiagnosis including corpus lutea,amniotic vesicle, chorioallantois, placentomes and the foetus. These various structures can bepalpated at different times frominsemination to pregnancy diagnosis.Accuracy of pregnancy by trans-rectal palpation from day 35 ofgestation has been estimated to be95%, however this will vary betweenoperators. Manual rupture of theamniotic vesicle can cause termina-tion of pregnancy in cattle and thereremains controversy over the risk ofiatrogenic pregnancy loss by examin-ing cows early in gestation by trans-rectal palpation. The viability of the embryo cannotbe assessed by transrectal palpationalone. The risk of pregnancy loss canbe high at 35-42 days of gestationwhen cows are diagnosed pregnantby transrectal palpation and trans-rectal ultrasonography.If most cows within a dairy herdare submitted for pregnancy diagno-sis at this time it may not be possibleto distinguish between spontaneouslosses which might have occurred‘normally’ and those losses whichare iatrogenic. There may also be aninstance when an embryo or foetusmay not be viable or is dead and ispalpated and diagnosed pregnant,with subsequent pregnancy lossthereafter. Although invasive, trans-rectal palpation of the uterus forpregnancy diagnosis remains rela-tively accurate, cheap and simple toperform, with manual skills ratherthan equipment required. It does, however, provide a solidgrounding in the skills of uterine andovarian palpation necessary for transrectal ultrasound for pregnancydiagnosis and ultrasonographicexamination of ovarian structures. It is therefore likely to continue tobe a valued and cost efficient meansof pregnancy diagnosis where acqui-sition of ultrasound technology hasbeen deemed cost prohibitive or isunavailable. The use of real-time B-mode transrectal ultrasonography isnow widely used within the UK forpregnancy diagnosis and in dairy cat-

tle. There are several advantages oftransrectal ultrasonography overtransrectal palpation alone includingthe ability to detect pregnancy andnon-pregnancy earlier, with greateraccuracy and with less iatrogenicpregnancy loss. Furthermore, foetal number, gen-der and viability can be assessed andevaluation can be made in the caseof a non-pregnant diagnosis to aidreproductive management decisions. Although still invasive and rate ofpregnancy loss is significant in stud-ies using ultrasound to assess preg-nancy loss, the technique has notbeen identified as a direct cause ofpregnancy loss and is deemed lessinvasive than transrectal palpation bysome authors, however there is therisk of iatrogenic trauma to the rec-tum by the transducer. The cost of equipment requiredfor transrectal ultrasonography inrecent years has reduced consider-ably and where a source of electric-ity and suitable viewing conditionswere once required, ultrasono-graphic equipment has now becomemore portable, battery operatedand is now commonplace in mostlarge animal veterinary surgeon’svehicles within the UK. Almost all UK veterinary studentsare now taught how to performtransrectal ultrasonography forpregnancy diagnosis as it hasbecome so widespread andexpected by dairy clients, howeverin the author’s opinion uterine andovarian palpation skills remain a cornerstone from which transrectalultrasonography skills grow. Regular routine pregnancy diagno-sis may also allow early identificationof potential costly reproductiveissues. For example if there is a sudden drop of pregnancy rate fromone month’s visit to the next whichmight highlight issues, for example,with insemination technique.

Conclusion

In the author’s opinion, the mostcost effective means of diagnosis ofnon-pregnancy is milk progesteronetesting at days 19 and 24 postinsemination. However, for positivepregnancy diagnosis transrectalultrasonography is cost effectivefrom day 30 post insemination. A re-check diagnosis at day 55-60post insemination is to be recom-mended, given the risk of embryonicdeath after initial pregnancy diagno-sis, with the added advantage thatfoetal sexing (Fig. 1) can be per-formed at this stage. Frustratingly,these results are similar to thatfound by Oletnacu et al. (1990), 20years previously, with the exceptionthat pregnancy diagnosis could beperformed five days earlier usingtransrectal ultrasonography. n

References are available from the author on request.

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Fig. 1. Left, a male foetus and, right, a cystic structure on an ovary.The images were taken with Easi-Scan, BCF.

Portable ultrasound in use.