Effect of one spontaneous estrus cycle (after synchronization with PGF(2 alpha)) on reproductive performance in dairy cows

The objective of the study was to analyze the effect of a spontaneous estru s cycle after synchronization of estrus with prostaglandin F-2 alpha (PGF(2 alpha)) in dairy cows on the degree of synchronization and reproductive pe rformance. We assigned 557 Holstein cows to two treatment groups. In Group 1 estrus was synchronized by two treatments with 25 mg of Dinoprost-Trometa mol in 14-day intervals. Cows were treated 27 to 33 days postpartum (dpp) a nd 41 to 47 dpp, respectively. Cows in Group 2 were treated with 25 mg of D inoprost-Trometamol three times in 14-day intervals, starting at 34 to 40 d pp. The second and third injections were administered at 48 to 54 dpp and 6 2 to 68 dpp, respectively. All cows were inseminated on observed estrus aft er a voluntary waiting period of 65 days post partum. Thus cows in Group 1 were inseminated on spontaneous estrus and cows in Group 2 on induced estru s. Cows not inseminated at 80 days post partum were palpated per rectum and treated according to a predefined protocol. Herd reproductive performance measures did not differ significantly between groups. The proportion of cow s with low serum progesterone levels was significantly higher 3 days after synchronization than 24 days after synchronization (97% vs 39%). The first- service conception rate was 34.8% in Group 1 and 30.7% in Group 2 (P>0.05). Days open were 113.5 in Group 1 and 110.9 in Group 2 (P>0.05). It is concl uded that postponing artificial insemination for one spontaneous estrus cyc le after synchronization decreased the degree of synchronization. This proc edure, however, had no effect on herd reproductive performance compared to insemination on first observed estrus after synchronization. (C) 2000 by Ei sevier Science Inc.