Genotype,environment and genotype × environment effects on trypsin inhibitor in peas

Four multiparous ruminally canulated cows and four primiparous cows without a ruminal cannula were used in a 4 × 4 Latin square experiment to study the effect of dietary fat source on milk fatty acid composition. Cows were fed a diet containing 550 g lucerne silage and 450 g concentrate kg^?1 dietary DM. The four diets were control and fat supplementation (32 g fat kg^?1 diet DM) as roasted soya beans, calcium salts of palm oil fatty acids (Megalac®). or hydrogenated tallow (Alifet®). Cows fed supplemental fat as roasted soya beans. Megalac®. or Alifet® produced 33.8, 32.6, and 32.5 kg day^?1 of 3.5% FCM. respectively, compared with 31.6 kg day^?1 with no fat supplementation. Addition of fat decreased milk protein percentage. Milk fat percentage was increased with Megalac® and decreased with Alifet® feeding. Dietary fat decreased the proportion of short- and medium-chain fatty acids (C6-C14:0) in milk and increased the proportion of long-chain fatty acids (C16 : 0 and longer). Roasted soya beans were most effective in reducing C16 : 0 and increasing C18 : 1, C18 : 2 and C18 : 3 acids in milk fat. Megalac® did not decrease milk C16 : 0 content, and neither Megalac® nor Alifet® affected C18 : 2 content.