Effects of calcium salts of long-chain fatty acids added to a diet containing choice white grease on lactation performance.

We studied the effect of increased energy density of diets during early lactation on lactational performance of cows injected with bST. Total mixed rations contained 50% forage (DM) and 2.5% choice white grease during the first 14 wk of lactation. Thirty cows were fed diets with grease as the only supplemental fat, and 15 cows were fed grease plus 1.8% calcium salts of long-chain fatty acids. One-half of the cows fed grease and all cows fed grease plus calcium salts of long-chain fatty acids received 640 mg/28 d of sustained-release bST from 6 to 44 wk postpartum. Calcium salts of long-chain fatty acids did not increase milk yield, 3.5% FCM, or DMI during the first 14 wk postpartum or during 15 to 44 wk postpartum. Administration of bST increased milk fat concentration .4% units during the first 14 wk postpartum. Cows receiving bST had higher DMI and produced 18.5% more 3.5% FCM from 15 to 44 wk postpartum than did controls. Calcium salts of long-chain fatty acids or bST injections did not influence body condition score or BW. These data suggest that cows yielding 30 to 35 kg of milk/d during the first 14 wk of lactation may not respond to added fat over 2.5%.