Effects of source and level of fish oil supplementation in late pregnancy on feed intake, colostrum production and lamb output of ewes

Supplementing pregnant ewes with fish oil to enhance the dietary supply of 20:4n-6 and 22:6n-3 has the potential to improve neonatal vigour and increase lamb survival rates. However, dietary fish oil has been shown to reduce colostrum production of ewes which can adversely affect lamb survival. To investigate the effects of source and level of fish oil in this response, 55 twin-bearing ewes were offered grass silage (0.5 kg dry matter per day) plus concentrates (0.5 kg/d) and supplemented with 0, 20 or 40 g/d herring (H) or salmon oil (S) during the final 6 weeks of pregnancy, giving a total of 5 treatments being control, H20, H40, S20 and S40. Salmon oil increased the supply of 18:2n-6 (2.37) and 22:4n-6 (1.98) but reduced the supply of 22:6n-3 (0.84) relative to herring oil. Silage DM intake was marginally lower for S40 ewes (P<0.05) but there were no dietary effects on ewe live weight or body condition score. Plasma non-esterified fatty acids (NEFA) (P<0.05) and urea (P<0.001) concentrations were elevated in ewes fed fish oil. Lambs born to control ewes had higher serum IgG concentrations than those fed herring oil (P<0.01). Colostrum output at 10 h (P<0.01) and total yield of colostrum (P<0.05) were lower for fish oil-supplemented ewes. Concentrations of 10 h IgG (P<0.05), 18 h fat (P<0.001), 18 h total solids (P<0.05) as well as outputs of fat (P<0.05), protein (P<0.01), casein (P<0.05), IgG (P<0.001) and total solids (P<0.05) were reduced by feeding fish oil. Compared with controls, ewes fed herring oil had a higher 10 h lactose concentration (P<0.05) while those fed salmon oil had lower outputs of 18 h protein (P<0.05) and 18 h casein (P<0.05). Offering 20 g/d, but not 40 g/d, fish oil increased the number of lambs weaned (+0.55 lambs/ewe; P=0.06) and the total output of weaned lamb (19.4 kg; P<0.05), but otherwise there were no effects of fish oil level and source on ewe or lamb performance. Results indicate that low levels of crude fish oil supplementation (up to 20 g/d) during late pregnancy improved lamb survival and output at weaning, but these benefits disappeared at higher inclusion rates.