Failure of timed inseminations and associated luteal function in dairy cattle after two injections of prostaglandin F 2-alpha

Abstract

Lactating Holstein cows (n = 235) were used to study changes in luteal function after two injections of prostaglandin F 2-alpha (PGF 2-alpha) were administered to induce estrus for timing the first postpartum inseminations. Cows were assigned randomly at parturition to two experimental groups and one control group. Control cows (n = 59) were inseminated at a spontaneous estrus beginning 40 d postpartum. The remaining cows were given two injections of PGF 2-alpha 11 d apart, beginning 40 to 46 d postpartum. After the second injection (0 h), cows were 1) inseminated once at 80 h (n = 119) or 2) inseminated twice at 72 and 96 h (n = 57). Progesterone was measured in blood serum collected from all cows at 0 and 48 h after each injection of PGF 2-alpha and from 48 cows throughout the anticipated luteal phase following the second injection. Conception rates of cows inseminated at 80 h (23%) and at 72 and 96 h (30%) after PGF 2-alpha were lower (P < 0.05) than those of control cows (54%) inseminated according to the a.m. - p.m. rule. When PGF 2-alpha cows were detected in estrus, conception rate of twice-inseminated cows (55%) was similar to that of controls, whereas the rate of once-inseminated cows (38%) tended to be lower (P = 0.09). Lower conception rates after timed inseminations resulted from failure of PGF 2-alpha to induce luteolysis (13% of cows) and the presence of low (<1 ng/ml) concentrations of progesterone in serum (15% of cows) at the time of the second injection of PGF 2-alpha. These results suggest that timed inseminations lowered conception rates after PGF 2-alpha because of poor timing of insemination relative to estrual events, less than expected induced luteolysis, and to lack of anticipated luteal function at the time of the second injection of PGF 2-alpha. The latter appeared to be the result of both prolonged postpartum anestrus and ovulatory failure following a previous injection of PGF 2-alpha.