مشخصات پژوهش

Experiments were conducted to investigate (a) the timing of ovulation and the associated endocrine changes (progesterone, estrogen and LH) during estrous cycle and (b) the efficacy, with respect to the pregnancy rate, in cycling and anestrus in Murrah buffaloes subjected to the Doublesynch protocol during the low breeding season. In experiment 1, 10 cycling buffaloes were administered PGF2a on day 0 (without regard to the estrous cycle stage), GnRH on day 2, a second PGF2a injection on day 9, and a second GnRH injection on day 11. Transrectal palpation was performed at 2-h intervals after the first and second GnRH treatments until ovulation was detected or for upto 96 h. The plasma progesterone and total estrogen concentrations were determined in blood samples collected at daily intervals starting 2 days before the onset of the protocol and continued until the day of the second detected ovulation. The plasma LH and total estrogen concentrations were measured in blood samples collected at 30-min intervals for 8 h following the first and second GnRH injections and thereafter at 2-h intervals until 2 h after the detection of ovulation. Ovulation occurred in 9/10 buffaloes (90%) at 22.2 ± 1.2 h (mean ± S.E.M.; range 18.0–26.0 h) and 10/10 buffaloes (100%) at 23.2 ± 1.0 h (mean ± S.E.M.; range 20.0–28.0 h) after the first and second GnRH treatments, respectively. The peak LH concentrations of 99.8 ± 28.5 ng/ml (range 37.8–320.0 ng/ ml) and 62.3 ± 11.9 ng/ml (range 20.9–143.9 ng/ml) occurred 2.1 ± 0.3 h (range 1.0–3.5 h) and 2.3 ± 0.3 h (range 0.5–3.0 h) after the first and second GnRH treatments, respectively. The total estrogen concentration gradually increased from the day of both the first and second PGF2a administrations until the LH peak (with great variability) and then gradually declined to the basal level, which was reached at the time ovulation was detected. In experiment 2, 10 cycling and 11 non-lactating anestrus buffaloes were subjected to the Doublesynch pro