Diary Day, 2006; Kansas Agricultural Experiment Station contribution; no. 07-118-S; Report of progress (Kansas State University. Agricultural Experiment Station and Cooperative Extension Service); 965; Dairy; Follicle; Ovsynch; Ovulation; Pregnancy rate


Our objective was to determine whether delaying the PGF2αinjection by 24 or 48 hr after the first GnRH injection in an Ovsynch protocol (from a standard 7 days) altered ovar-ian characteristics in lactating dairy cows. Es-trous cycles were synchronized in 36 Hol-steins after removal of a progesterone-releasing controlled internal drug release (CIDR) insert and injection of PGF2α. On day 6 of the estrous cycle, cows were administered 100 μg of GnRH (81 ± 2 days postpartum) and assigned randomly to receive a treatment in-jection of PGF2α7, 8, or 9 days later. Timed artificial insemination (TAI) was performed at 48 hr after PGF2α, at which time a second in-jection of GnRH was administered. Ovarian structures were mapped by ultrasonography on day 0 (first GnRH injection), on day 2 to de-termine responses to the first GnRH injection, at PGF2αinjection, and daily thereafter through 72 hr after PGF2αto monitor ovula-tion of preovulatory follicles. Blood was col-lected on day 0, day 2, at PGF2αinjection, and at 24 and 48 hr after PGF2α, to monitor serum changes estradiol-17ß and progesterone. On the basis of serum progesterone and ovarian exams, 2 cows were eliminated because of anestrus and their failure ovulate a follicle in response to the first GnRH injection. Two other cows in which luteolysis failed to occur after PGF2αtreatment also were eliminated. Final numbers of cows per treatment were: 7 days (n = 13), 8 days (n = 9), and 9 days (n = 10). Twenty-nine of 32 cows ovulated (90.6%) in response to the first GnRH injec-tion. Despite a 24- or 48-hr delay between first GnRH and PGF2αinjections, the diameter (mm) and volume (mm3) of the ovulatory fol-licle did not differ among treatments. In all 32 cows, at least 1 follicle ovulated after treat-ment, but ovulation rates did not differ. Serum concentrations of estradiol-17ß did not differ among treatments. Two cows in the 7-day treatment and 2 cows in the 8-day treatment were inseminated 24 hr late and were ex-cluded before assessing conception rates: 5/9 (55.6%), 5/9 (55.6%), and 1/10 (10%), respec-tively. We concluded that delaying PGF2αin-jection by 24 hr had little effect on outcomes.; Dairy Day, 2006, Kansas State University, Manhattan, KS, 2006;

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