The interaction of nutrition and body condition at mating on ovulation rate and early embryo mortality in Scottish Blackface ewes

Abstract

One hundred and fifty-six Scottish Blackface ewes were differentially group-fed over a 2-month period to achieve three distinct levels of body condition (good, moderate and very poor). Over 5 weeks prior to mating, one group of good-condition ewes was maintained in that condition, one group of good-and one of moderate-condition ewes were brought down in condition by restricted feeding and one group of moderate and the very poor condition ewes were raised in condition by a high level of feeding. Ewes were therefore in good, moderately good or poor condition at mating. After mating, ewes were killed either on return to service or at 25 ± 5 days for counts of corpora lutea and viable embryos.Poor body condition, irrespective of feeding level, was associated with a delay or suppression of oestrus and with a high return-to-service rate. Ovulation rate was positively related to body condition at mating but not to the level of pre-mating food intake at the condition levels studied.Embryo mortality decreased as body condition at mating increased and the interaction between condition and the level of pre-mating food intake had a differential effect on mortality of single-and multiple-shed ova. The lowest rate of embryo mortality was found in ewes in moderately good condition which had been well-fed before mating.reported experiments (source B, Gunn et al. 1972) were randomly allocated to two groups of 62 and In two previous experiments (Gunn, Doney & one group of 32. The ewes in each group were Russel, , 1972 ovulation rate and early within the body condition range of 1-3. Differential embryo survival in Scottish Blackface ewes were supplementary group feeding was then carried out both shown to be positively related to body condi-in small pasture paddocks in such a manner that tion at mating. In one experiment (Gunn et al. by mid-October the majority of ewes in one of the 1969) the level of food intake prior to and at mating large groups were in condition 3, the majority in was shown to have no effect on ovulation rate of the other large group were in condition 2 and the ewes in good condition (score 3, Russel, Doney & majority in the small group were in condition 1. Gunn, 1969) but could possibly have had an effect Oestrus was then synchronized by progestagen on ovulation rate of ewes in poor condition (score pessaries, timed to give the second synchronized 1-5). It was suggested that the level of food intake oestrus in the third week of November. On 13 might only influence ovulation rate when ewes are October the condition-3 and condition-2 groups below a particular level of body condition. The were each randomly divided into two. Ewes in one present experiment was designed to study further of the condition-3 subgroups remained on pasture the effect of different levels of food intake prior to and were managed, with the help of supplementary and at mating on ovulation rate and early embryo feeding, to maintain them in condition 3 (group mortality of Scottish Blackface ewes in different 3/3). Ewes in the other condition-3...

Meiosis and spermatogenesis in bulls heterozygous for a presumptive 1/29 Robertsonian translocation

“…Chapman & Bruère (1975 and Long (1976) have proposed that there was a prezygotic selection of spermatozoa, but it is possible that the gametic products of nondisjunction events formed unbalanced embryos and that these died in the first 12 days of life and were amongst the relatively large proportion (25%) which Long (1976) could not karyotype. This value of 25 % is remarkably close to the expected early embryonic loss in sheep, although this can vary from 9 to 64% in Blackface ewes kept on different feeding regimens (Gunn & Doney, 1975). This large variation in early embryonic loss could explain the observed, apparently normal, fertility of heterozygous sheep for which the theoretical anticipated reduction of fertility may be quite small.…”

Sex-biased maternal expenditure in Rocky Mountain bighorn sheep

“…However, a reasonable explanation for the effect of reproductive effort on return to estrus is that nutrient allocations to reproduction competed with allocations to maintenance and growth. Higher-investing ewes consequently took longer to regain threshold reproductive condition (Sadlier 1969;Mitchell and Lincoln 1973;Gunn and Doney 1975;Frisch 1984).…”

Influence of lambing-to-rebreeding interval on ewe reproductive performance in anestrous season

“…However, when ewes lamb during the anestrous season, Cornu and Cognié (1984) suggest that embryonic survival and/or fertilization rate were lower in ewes mated prior to 80 d PP. Gunn and Doney (1975) noted an influence of BC at mating on embryo mortality. Thus, the mechanisms responsible for reduced fertility following progestagen treatment during PP period are not well understood.…”