Use of injectable progesterone and hCG for fixed-time artificial insemination during the non-breeding season in goats

Abstract

The objective of this study was to determine the estrous response and the moment of ovulation and fertility after a progesterone (P4) priming plus human chorionic gonadotropin (hCG) administration in multiparous and nulliparous goats. Therefore, two experiments were conducted during non-breeding season (April and May, 26° N) and all the animals received a single injection of 20 mg of P4 and 100 IU of hCG 24 h later. In Experiment 1, 13 multiparous and 9 nulliparous goats were subjected to estrus detection twice a day from P4 administration, and their ovaries were scanned by transrectal ultrasonography every 12 h from the onset of estrus to determine ovulation. The proportion of goats in estrus did not differ between multiparous and nulliparous females. The onset of estrus (60.5 ± 12.4 h vs. 52.0 ± 5.2 h after hCG administration) and the moment of ovulation (91.5 ± 10.3 h vs. 85.3 ± 11.5 h) were also similar in multiparous and nulliparous goats. In Experiment 2, a total of 299 multiparous and nulliparous goats managed under intensive (n = 112 and 41 goats, respectively) or extensive (n = 85 and 61 goats, respectively) production systems were divided to receive a fixed-time artificial insemination (FTAI) with fresh semen at 60 or 72 h after hCG administration. The pregnancy rate did not differ significantly between multiparous and nulliparous goats in both production systems. Nonetheless, in the intensive system pregnancy rate was affected by the moment of insemination (P < 0.05). In this system, the pregnancy rate was higher in goats inseminated at 60 h than in 72 h (55.6%, 44/79 vs. 35.1%, 26/74, respectively; P < 0.05). On the contrary, in the extensive system the pregnancy rate was not affected by the time of insemination (29.4%, 23/78 vs. 22.0%, 15/68). To conclude, both the ovulatory response and the pregnancy rate after a single P4 injection plus hCG was similar between multiparous and nulliparous goats during anovulatory season. Although the pregnancy rate was not affected by the time of insemination in the extensive production system, under intensive conditions FTAI should be performed at 60 h after hCG treatment.

Keywords: Anestrous; Fertility; Follicular dynamics; Gestation; TAI.