Effect of dietary calcium soaps on milk yield, body weight, reproductive hormones, and fertility in first parity and older cows.

The effects were determined of dietary Ca soaps of fatty acids fed to cows to 120 DIM on milk yield, BW, peripheral concentrations of reproductive hormones, and fertility in primiparous and multiparous cows. Milk yield was increased in primiparous and multiparous cows fed Ca soaps, and milk fat and protein yields were enhanced. Body weight losses were greater for all cows fed Ca soaps, and this trend was greater and longer lasting in primiparous cows than in multiparous cows. Plasma triglyceride concentrations were elevated in multiparous cows, but FFA tended to be higher in primiparous cows fed Ca soaps. Conception rate at first AI was lower for primiparous cows fed Ca soaps (33%) than for controls (74%), but differences were not significant for later AI or between multiparous groups. No differences were apparent for plasma progesterone or estradiol in the luteal or follicular phases preceding the first AI, and differences in mean luteinizing hormone concentrations were small in a 6-h window in the follicular phase. The differences in conception rate at first AI in primiparous cows could not be explained on the basis of changes in peripheral hormone concentrations. The enhanced negative energy balance in primiparous cows fed Ca soaps apparently was related to the decrease in their conception rate.