Effect of source of supplemental fat in early lactation on productive performance and milk composition

The objective of this research was to evaluate the effects of diets supplemented with rumen inert fat sources on early-lactation performance of dairy cows. Two studies were conducted that varied in total dietary fat level (3.4% of DM for study 1 and 5.1% of DM for study 2). Calcium salts of fatty acids (CSFA) rich in oleic acid versus SFA rich in palmitic acid diets were supplemented to provide 0.9% (study 1) and 1.2% (study 2) of total dietary fatty acids (DM basis). Compared with cows fed the CSFA diet in study 1, cows fed the SFA diet had 0.06 kg/d greater protein yield (P = 0.01) and 0.02 unit greater protein efficiency (P = 0.01) expressed as milk CP/CP intake. In study 2, cows fed the CSFA diet had 0.2 kg/d greater fat yield (P = 0.04), 0.1 unit greater fat efficiency (P = 0.02) expressed as milk fat/fat intake, 3.6 kg/d greater 3.5% FCM (P = 0.04), and 3.3 kg/d greater energy-corrected milk yield (P < 0.05). In conclusion, when cows started at 45 DIM and with a diet fat level of 5.1% (DM), the CSFA diet rich in oleic acid improved milk fat yield, milk fat efficiency, 3.5% FCM, and energy-corrected milk (P < 0.05). However, when cows started at greater than 70 DIM and with a diet fat level of 3.4% (DM), the SFA diet rich in palmitic acid improved lactation performance by improving milk protein yield and protein efficiency (P < 0.05). This study suggests that dietary fatty acids are potentially absorbed and partitioned differently depending on the level of dietary fat and DIM.