Effects of treatment of anestrous dairy cows with gonadotropin-releasing hormone, prostaglandin, and progesterone

Cows anestrous at the start of a seasonal breeding period have lesser probability of breeding, lesser conception rates, and a longer interval to conception than cycling herdmates. Historically, treatment included estradiol benzoate, which is no longer available. Consequently, alternative programs are required. Hence, a study was undertaken to assess new treatment regimens for these cows. The presence or absence of a corpus luteum was determined using ultrasonography in cows (n = 2,222 from 12 herds) that were not detected in estrus by 9 d before the start of breeding. Cows were then randomly assigned to one of 4 treatments within each herd. Treatments were (1) 100 mu g of gonadorelin, followed 7 d later by 500 mu g of sodium cloprostenol, followed 54 to 56 h later by 100 mu g of gonadorelin, followed by fixed-time artificial insemination at 13 to 18 h after the final GnRH injection (Ovsynch); (2) as for (1) but with placement of an intravaginal progesterone (P4)-releasing insert between the initial GnRH and PGF(2 alpha) (Ovsynch-56+P4); (3) as for (2) but with the final GnRH treatment delayed until 71 h after PGF(2 alpha) and P4 insert removal with fixed-time artificial insemination 0 to 5 h after GnRH treatment and with insemination of those cows detected in estrus before the second GnRH injection (Cosynch-72+P4); and (4) untreated controls (control). Day 0 was defined as the day of the second GnRH injection. Milk samples were collected from 154 and 152 cows from the Ovsynch and Ovsynch-56+P4 treatments, respectively, at d 0, 7, and 14 for P4 concentration determination. This was to test the hypothesis that inclusion of P4 would result in a greater proportion of cows having normal luteal function after treatment in these 2 groups that differed only in the inclusion of P4 in the Ovsynch-56+P4 treatment. All treatments resulted in shorter intervals from first day of breeding to conception compared with the controls. The Ovsynch-56+P4 treatment resulted in start of breeding to conception intervals 3, 6, and 16 d shorter than those of Cosynch-72+P4, Ovsynch, or controls, respectively, and the positive effect of the Ovsynch-56+P4 treatment occurred both in corpus-luteum-positive and in corpus-luteum-negative cows. The Ovsynch-56+P4 treatment resulted in fewer short interestrus intervals than did Ovsynch (i.e., <18 d; 16 vs. 31%) and more cows with elevated (>1 ng/mL) milk P4 concentrations at d 7 (88 vs. 74%) and d 14 (80 vs. 60%). It was concluded that treatment of anestrous cows before the start of breeding resulted in earlier conception than no treatment but had no effect on the final pregnancy rate. The addition of P4 to the Ovsynch program resulted in earlier conception and in more cows with normal subsequent luteal-phase lengths.