Effects of a restricted diet during mid pregnancy of ewes on uterine and fetal growth and lamb birth weight

A moderate below maintenance nutritional restriction was applied to pregnant ewes for 4 weeks commencing at either 79, 87 or 95 days post coitus. Measurements were made after slaughter at the end of each restricted period and at Day 144 of pregnancy on the uterus and fetus of restricted and control ewes. Lambs were weighed at birth. Overall there was no significant difference in the response of ewes to timing of restriction but there was a response to restriction. Dietary restriction reduced fetal growth rate, girth size, crown rump length (CRL) and weight of other fetal tissues. Though reduced, girth size and CRL maintained their normal relationship with fetal weight. Growth rates of fetuses on all treatments were similar during refeeding. The largest effect of nutritional restriction on the reproductive tract occurred in lower fetal membrane weights at 144 days of pregnancy (mean of restricted group 595 g v. 761 g controls). At that time, previously restricted ewes also had an increased number of cotyledons but decreased average weight of cotyledons compared to control ewes. Fetal weight at Day 144 was significantly correlated with girth and CRL (P < 0.01) and placental weight (P < 0.05) but not with weight of fetal membrane or cotyledons. Birth weights of single and twin lambs from the restricted ewes were similar to that of the controls and appeared to be unaffected by the restriction. Small differences in the gestation length of ewes bearing twin lambs may have helped to overcome the deficit in fetal weight observed at Day 144 in ewes bearing single lambs. It was concluded that ewes respond to dietary restriction followed by improved forage availability with changes in maternal and fetal growth patterns that presumably interact to produce viable lambs.