Comparison of follicular dynamics and hormone profiles in Boer goats examined during the breeding and non-breeding seasons in the tropics of Queensland, Australia

Abstract

This study aimed to describe ovarian follicular dynamics in Boer goats (n=14) during the breeding and non-breeding seasons in the tropics of Queensland. Progesterone profiles and follicular dynamics were compared over a 21-day period in the non-breeding season and one oestrous cycle in the breeding season. Between September and October, 100% of goats were in anoestrus while between April and May they were all undergoing ovulatory cycles. The number of follicular waves during a 3-week period of monitoring was greater during the non-breeding compared to the breeding season (4.8±0.1 vs 4.1±0.1, respectively; P<0.05), while the number of codominant follicles (5.6±0.3 vs 6.8±0.3, respectively; P<0.05), growth rate (0.61±0.05mm/day vs 0.81±0.05mm/day, respectively; P<0.05) and the diameter of the largest follicle measured within follicular waves (6.7±0.1mm vs 7.8±01mm, respectively; P<0.05) were less in the non-breeding compared to the breeding season. During the breeding season the interovulatory interval was 19.7±0.2 days. Total number of small follicles (2–3mm) and the total number of follicles ≥3mm from Days 2 to 14 of the period of examination were greater (P<0.05) during the non-breeding compared to the breeding season. In the breeding season, 35.7% of cycling goats showed large anovulatory follicles, which persisted and became luteinized. Ovulatory follicles were derived from the fourth follicular wave in 71% of goats. These results have described differences in characteristics of follicular development in the same Boer goats examined during the breeding and non-breeding seasons. In the non-breeding season, the ovaries remained active and follicles continued to grow to reach the equivalent size of preovulatory follicles. Follicular dynamics in the breeding season was characterized by the development of larger follicles and greater follicular growth rates. Short oestrous cycles and follicular cysts may reduce ovulation rate in Boer goats in the breeding season.