Reproduction in Domestic Animals

Reprod Dom Anim 43 (Suppl. 2), 260–267 (2008); doi: 10.1111/j.1439-0531.2008.01171.xISSN 0936-6768Embryonic and Early Foetal Losses in Cattle and Other RuminantsMG Diskin and DG MorrisTeagasc, Animal Production Research Centre, Mellows Campus, Athenry, Co. Galway, IrelandContentsEmbryo survival is a major factor affecting production andeconomic efficiency in all systems of ruminant milk and meatproduction. For heifers, beef and moderate yielding dairycows, does and camelids it appears that fertilization generallylies between 90% and 100%. In high-producing dairy cowsthere is a less substantive body of literature, but it wouldappear that it is somewhat lower and perhaps more variable.In cattle, the major component of embryo loss occurs beforeday 16 following breeding with some evidence of greater lossesbefore day 8 in high-producing dairy cows. In cattle lateembryo loss, while numerically much smaller than earlyembryo mortality loss, nevertheless, causes serious economiclosses to producers because it is often too late to rebreedfemales when they repeat. In multiple ovulating small ruminants,the loss rate is positively related to ovulation rate.Systemic concentrations of progesterone, during both the cyclepreceding and following insemination, affect embryo survivalrate with evidence that too high or indeed too low aconcentration being negatively associated with survival rate.Uterine expression of mRNA for progesterone receptor,oestradiol receptor and retinol-binding protein appears to besensitive to changes in peripheral concentrations of progesteroneduring the first week after artificial insemination. Energybalance and dry matter intake during 4 weeks after calving arecritically important in determining conception rate when cowsare inseminated at 70–100 days post-calving. Concentratesupplementation of cows at pasture during the breeding periodhas minimal effects on conception rates though suddenreductions in dietary intake should be avoided. For all systemsof milk production, more balanced breeding strategies withgreater emphasis on fertility and feed intake and ⁄ or energybalance must be developed. There is sufficient genetic variabilitywithin the Holstein breed for fertility traits. Alternativedairy breeds such as the Jersey or Norwegian Red could alsobe utilized. Genomic technology will not only provide scientistswith an improved understanding of the underlyingbiological processes involved in fertilization and the establishmentof pregnancy, but also, in the future, identify genesresponsible for improved embryo survival. Its incorporationinto breeding objectives would increase the rate of geneticprogress for embryo survival.IntroductionEmbryo mortality is a major cause of economic loss inall systems of ruminant production. Direct effects ofembryonic mortality are reflected in reduced conceptionrates to a service and reduced litter size in litter-bearingspecies. In dairying, the increase in milk yield observedover the past 40 years has been accompanied by adecline in cow fertility both in high input maize-baseddiets and in less intensive, pasture-based systems of milkproduction such as those practised in Ireland (see reviewby Diskin et al. 2006). In litter-bearing species such asthe ewe, death of one or more embryos during theimplantation stage results in the birth of smaller lambs(Rhind et al. 1980) with subsequent adverse consequencesfor their post-natal survival and growth rates.The objective of this article is to review currentinformation on embryonic and early foetal losses incattle and other ruminants and in particular on thefactors that affect their incidence and to proposepotential avenues to embryo and foetal survival rates.Fertilization Rate in CattleThere are a large number of published estimates offertilization rate in heifers and in moderate-yieldingdairy cows (see review by Sreenan and Diskin 1986).Where semen of known high fertility is used in artificialinsemination (AI), fertilization rates are of the order of90–100%. In contrast, for higher producing dairy cowsthere is little quantitative information on fertilizationrate with only three published reports (Wiebold 1988;Ryan et al. 1993; Sartori et al. 2002). Wiebold (1988),using a non-surgical embryo recovery technique on day7 following oestrus, recovered 25 ova ⁄ embryos from 23lactating cows with all recovered ova having beenfertilized. Ryan et al. (1993) in a study on the effectsof ambient temperature on fertilization rate reported noeffect of temperature and quoted fertilization rates of82.4% and 79.5% for high and low temperatures,respectively. Sartori et al. (2002) recorded a low fertilizationrate of 55.6% in lactating dairy cows comparedto 100% for heifers under high ambient temperatures,while in a subsequent study during the cool seasonfertilization rates were 87.8% and 89.5% for lactatingand non-lactating dairy cows, respectively. It appearsthat fertilization rate is similar in high- and moderateproducingdairy cows, at least during the cool season.Fertilization Rates in Small RuminantsThe available evidence is that, like cattle, a fertilizationrate of 90–95% appears to be normal in ewes (Restallet al. 1976; Mitchell et al. 1999), does (see review byNancarrow 1994) and South American camelids (Fernandez-Bacaet al. 1970) under natural mating conditions.There is some suggestion that fertilization is anall-or-none phenomenon in multiple ovulating ewes(Restall et al. 1976), though there is some evidence(Restall et al. 1976; Kleeman et al. 1990) that partialfertilization failure may occur at a low frequency. Thereis some evidence that fertilization rates may be reducedin ewes during both the early (Hulet et al. 1956) andlatter parts of the breeding season, perhaps as aconsequence of suboptimal mating activity in somerams (Colas 1983) or adverse environmental and nutritionalconditions (Mitchell et al. 1996). Yet, when ewesÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag