Nutrition of the ewe and embryo growth during early pregnancy

Mature Merino ewes (n = 228) were fed rations at levels of either 5, 10, 15, 20, 30 or 40 g/kg daily from day 1 until day 35 after mating. Embryos were then removed from single ovulating ewes and, after being weighed and measured, were dissected and embryo liver weights were obtained. Plasma samples were taken from all ewes on days 5, 10, 15, 20, 27 and 35 after mating and later analysed for glucose concentrations. During the 35-day treatment period, mean liveweight changes of ewes ranged from -6.9 to 5.5 kg in groups receiving the lowest and highest levels of nutrition respectively. Although there were no significant differences in the percentages of ewes pregnant at day 35 the weight and size of embryos, including embryo liver weight, varied with the level of nutrition. Mean wet weights (+/- s.e.m.) of embryos from ewes receiving rations at the rate of 10 g/kg daily and those receiving 30 g/kg daily were 1.67 +/- 0.04 g and 1.91 +/- 0.04 g respectively (difference significant at P less than 0.01). Plasma glucose concentrations of the ewes increased with increasing level of ration and decreased with time.