Low nutrition of ewes in early pregnancy and the residual effect on the offspring

Abstract

SUMMARYMature Merino ewes (n = 500) were allotted at random to embryo removal (day 35; day 0 = day of oestrus detection), foetal removal (day 90) or lambing groups. These groups were further randomly divided into four single-sire mating groups. From day 1 until day 35 ewes were individually penned and fed either 50 or 150% of a maintenance ration (0·5 M or 1·5 M respectively). At day 35 single embryos were removed from anaesthetized ewes in the embryo removal group and all other ewes were endoscoped to confirm pregnancy. These ewes were then returned to pasture. Plasma samples were taken from all ewes on days 2, 4, 16, 23, 30 and 35 for analysis of glucose concentration. At day 90, ewes allotted to the foetal removal group were anaesthetized and plasma samples were obtained from the ewe's jugular vein and the umbilical arteryand vein. Ewes were then hysterectomized and the foetus was weighed and measured. Functional cotyledons were dissected from the uterus and chorio-allantois and all tissues were weighed. The remaining ewes (lambing group) were supervised at lambing and lambs were identified, weighed and measured.Live-weight changes from weaning and wool production and quality were measured in ewe and ram lambs at their first shearing (11 months of age). Ovulation rates in the first two oestrous seasons of the ewes and wool production at their second shearing (2 years of age) were also measured.During the 35-day treatment period, mean live-weight changes of ewes were –4·9 and + 1·8 kg in the 0·5 M and 1·5 M groups respectively. Pregnancy rates were similar in both groups but embryos from 0·5 M ewes weighed less than those from 1·5 M ewes (1·7 ± 0·04 ν. 1·9 ± 0·05 g; P < 0·005). Foetuses taken at 90 days from 0·5 M ewes were smaller than those from 1·5 M ewes but these differences reached significance (P < 0·025) only in the measurement of chin–crown length (8·0 ± 0·09 ν. 7·6 ± 0·11 cm). Correlations between foetal weight and total cotyledon weight, chorio-allantoic weight and empty uterine weight were all significant. Plasma glucose concentrations of ewes in the 0·5 M group were significantly (P < 0·001) reduced by day 9. Differences between the two nutrition groups in maternal and umbilical plasma glucose concentrations at day 90 were not significant, though foetuses from 0·5 M and 1·5 M ewes removed a mean of 30 and 11% respectively of available glucose from the umbilical vein. Differences in live weight between 1·5 M and 0·5 M animals at weaning and in the post-weaning period were not significant (P > 0·05). Wool production and woolquality were similar for both groups. Spontaneous ovulation rates measured on four occasions during the postpubertal oestrous season and on three occasions the following year were not significant (P > 0·05). Treatment with pregnant mare's serum gonadotrophin (PMSG) increased ovulation rates in the ewes of both groups; however, the differences failed to reach significance (P > 0·05); mean (± S.e.) ovulations per ewe were 4·8 ± 0·61 ν. 4·6 ± 0·60 for 1·5 M and 0·5 M group ewes respectively.