Effects of digestible undegradable protein (DUP) supply and fish oil supplementation of ewes during late pregnancy on colostrum production and lamb output

Abstract

Studies in pregnant ewes have shown that fish oil supplementation during late pregnancy can increase lamb vigour at birth and may provide a means of reducing neonatal mortality in the sheep flock. However, fish oil also reduces colostrum production by the ewe which could offset the developmental benefits for lamb survival. To counteract the detrimental effects on colostrum, an experiment was carried out to investigate the effects of supplementing late gestation ewes with fish oil and digestible undegradable protein (DUP) on colostrum output and lamb performance. For 6 weeks prior to lambing, 32 twin-bearing ewes were offered grass silage ad libitum plus 550 g/d of one of four concentrates. The concentrates were iso-nitrogenous (195 g crude protein/kg dry-matter) and were formulated to supply 0 or 40 g/ewe/d fish oil and 55 g DUP/kg dry-matter (High, H) or 25 g DUP/kg dry-matter (Low, L) giving a total of four treatments: H0, H40, L0 and L40. Ewes offered fish oil had depressed intakes of silage dry-matter (DM), metabolisable energy (ME) and crude protein (CP) ( P<0.001) and lost on average 3.8 kg more live weight ( P<0.001) between 6 weeks pre-lambing and 24 h post-lambing. Mean plasma concentrations of globulin ( P<0.05) and urea ( P<0.001) during late pregnancy were elevated by fish oil. L40 ewes produced 681 g less colostrum ( P<0.01) and had lower energy ( P<0.001), total solids ( P<0.01), crude protein ( P<0.05) and ash ( P<0.05) outputs in colostrum during the first 18 h after lambing than all other treatments. Total lamb birth weights of ewes were similar for all diets but lamb output at weaning was 16.5 kg lower ( P<0.05) for L40 ewes, due to a reduction in litter size at weaning of 0.51 lambs/ewe ( P<0.05). Despite depressed forage intakes, the results of this study indicate that late gestation ewes can be supplemented with 40 g/d fish oil without detrimental effects on colostrum production or lamb output, providing the intake of metabolisable protein is maintained by increasing the level of DUP in the concentrate portion of the diet.