LAUSR

This study aimed to evaluate the effects fat supplementation with soybean oil (SO) and calcium salts of fatty acids (CSFA) on mid-lactation dairy cows on feed intake and nutrients digestibility, ruminal fermentation, milk yield and composition, and nitrogen balance. Sixteen multiparous Holstein cows (638 ± 73 kg of body weight and 116 ± 26 days in milk) were used in a 4 × 4 Latin square design for evaluate following diets: CONT) control, without additional fat source; SO) 30 g/kg of soybean oil; CSFA1) inclusion of 30 g/kg of calcium salts of long-chain fatty acids (MEGALAC-E®); and CSFA2) inclusion of 30 g/kg of calcium salts of long-chain fatty acids (LACTOPLUS®) on dry matter basis. Both evaluated CSFA were manufactured using soybean oil. Fat sources addition decreased dry matter intake (23.2 vs 21.7 kg/d) and increased (P<0.001) ether extract intake and digestibility (P<0.001). Ruminal pH, NH3-N, total volatile fatty acid, acetate, propionate and butyrate production were similar among treatments (P≥0.121). Fat supplementation had no effect on milk yield (32.0 kg/d) and composition. However, soybean oil decreased milk fat yield compared to CSFA diets. Dietary addition of fat sources decreased N intake (P < 0.001) without affect on N balance. Inclusion of fat source in the diet, either as free or rumen-protected decreased dry matter intake without affect the ruminal fermentation and performance of mid-lactation dairy cows.