DAILY CHANGES IN THE CURVED CROWN-RUMP LENGTH OF INDIVIDUAL SHEEP FETUSES DURING THE LAST 60 DAYS OF PREGNANCY AND EFFECTS OF DIFFERENT LEVELS OF MATERNAL NUTRITION

A method is described by which daily changes in the curved crown-rump length (CRL) of individual sheep fetuses were observed during the last 50-60 days of pregnancy. The mean discrepancy between the derived value for CRL and the CRL measured directly in 8 fetuses aged from 100-135 days and in 12 lambs at 143-150 days was 1.5 .+-. 0.2% (mean .+-. SE). In adequately nourished ewes from 100-115 days of gestation, growth rate showed a between-fetus range of 4.2 to 7.5 mm day-1 (n = 16), remained constant within each fetus until about 132 days and then decreased by about 27% (n = 4). Decreases in growth rate of .apprx. 30-44% occurred within 3 days of the introduction of maternal undernutrition at 115 or 120 days of gestation (n = 6), and in 2 other fetuses maternal undernutrition effected an almost complete cessation of growth. The relationship between fetal CRL and weight is described and some physiological implications of the results are discussed.