EFFECTS ON MATERNAL AND FETAL TRAITS OF FEEDING SUPPLEMENT TO GRAZINGPREGNANT EWES

Thirty single-bearing Merino ewes were used to examine the effect of f eeding supplement, from 91 to 140 days of gestation, on changes in che mical composition of the ewes, on the relationships with live weight a nd body condition score and on the foetus. Ewes grazed a perennial rye grass pasture and were offered either no supplement or 500 g per head per day of a concentrate supplement from days 30 to 90 and (or) from d ays 91 to 140 of pregnancy. Maternal carcass and non-carcass component s, uterine wall, foetus and placenta plus cotyledons were chemically a nalysed. Live weight (LW) and body condition score (BCS) on day 140 we re both affected by supplementation during late pregnancy, mobilizatio n of protein and fat being lower in animals receiving supplement. BCS accounted for more variation than LW in the carcass fat depot. Because this depot was the most important source of energy from days 91 to 14 0 of gestation, this suggests that BCS is a useful estimator of mobili zation of maternal fat reserves during this stage of pregnancy. The ab ility to mobilize reserves and protect foetal growth by Merino ewes in southern Europe, where large fluctuations in grass growth rate expose s them to considerable undernutrition as pregnancy proceeds, was confi rmed in this experiment. However, when the nutritional regime is extre me, supplementary feeding to the ewes is recommended, in order to make the whole system economically profitable.