PARTITION OF NUTRIENTS IN MODERATELY FAT EWES COMPARED WITH LEAN EWESGIVEN AD-LIBITUM ACCESS TO FEED IN LATE PREGNANCY

The effect of a difference in voluntary feed intake on fetal weight wa s tested in lean v. moderately fat ewes (0.15 v. 0.32 kg/kg fat-free e mpty body weight), by giving them ad libitum access to feed from Day 1 10 to 146 of pregnancy when both had placentas of a similar size (at D ay 146: 437 v. 461 g, s.e.m. = 49.5, P > 0.05). Although the lean ewes ate 29% more than the fatter ewes above their estimated requirements (1258+/-106.9 v. 978+/-105.8 g/ewe.day, P=0.08) fetal weights were not affected (4744 v. 4590 g, s.e.m. = 282.1, P > 0.05). Instead, the lea n ewes partitioned more of their intake into body fat than the fatter ewes (0.13 v. 0.01 kg/kg fat-free empty body weight, P < 0.05). The re sults support the concept that the placenta places an upper limit to t he uptake of nutrients by the fetus.