Maternal-foetal adaptation to mid pregnancy feed restriction in single-bearing ewes

Abstract

In two experiments, restriction of feed to levels below maintenance for periods of up to 4 weeks was imposed on groups of ewes bearing single foetuses at 79, 87 or 95 days post coitus. In the first experiment, carried out at pasture, measurements were made of concentration of ovine placental lactogen (oPL) and progesterone in ewe plasma. Effects on lamb birth weight and gestation length were also examined. The second experiment investigated the effect of maternal feed restriction of (i) feed intake, (ii) maternal oPL, (iii) maternal plasma glucose concentration, (iv) lamb birth weight and (v) gestation length. In the first experiment, there were no significant effects of feed restriction on lamb birth weight or gestation length, although foetal growth rate had been reduced in some treatment groups. There were significant interactions between time of sampling and treatment for oPL and progesterone concentration. Control group ewes had lower oPL (P< 0.001) and progesterone (P < 0.05) concentrations than restricted ewes at the end of feed restriction, but higher oPL (P < 0.001) and progesterone (P <0.05) concentrations at 144 days post coitus. In the second experiment, lamb birth weight and gestation length were not significantly affected by maternal feed restriction (birth weight: restricted 4.94 kg, control 4.87 kg av. s.e.m. 0.17 kg; gestation length: restricted 148.3 days, control 147.0 days, av. s.e.m. 0.76 days). Feed restriction was associated with increased (P < 0.05) oPL and decreased glucose (P < 0.05) concentration in plasma. Maternal feed intake was significantly higher (P <0.05) in the restricted group in the week preceding lambing. These results strongly suggest that continuation of maternal feed intake over the last week of pregnancy is the major contributor to maintenance of 'normal' lamb birth weight in previously feed restricted ewes.