Effects of long term undernutrition of the ewe on the growth rates of individual fetuses during late pregnancy.

Fifteen ewes were fed at between 0.6 and 0.8 times the recommended rates in order to reproduce the liveweight changes observed in Scottish Blackface sheep on hill farms. The curved crown-rump length (CRL) of individual fetuses was measured daily between 90 and 142 days of gestation and fetal dimensions and placental weight were measured at 142 days. Fetal growth rate decreased progressively from about 5.9 mm per day between 90 and 111 days of gestation to about 3.6 mm per day by 130 days. At 142 days of gestation the placental weight and the fetal CRL, girth and weight were all significantly lower than in fetuses of well fed ewes. The mechanisms responsible for the reduction in fetal growth rate after 111 days of gestation and the implications for animals on hill farms are discussed.