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 thebreeding and non-breeding seasons in the tropics of Queensland. Progesterone profiles andfollicular dynamics were compared over a 21-day period in the non-breeding season andone oestrous cycle in the breeding season. Between September and October, 100% of goatswere 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 duringthe 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 ± 0.05 mm/day vs 0.81 ± 0.05 mm/day, respectively; P < 0.05)and the diameter of the largest follicle measured within follicular waves (6.7 ± 0.1 mm vs7.8 ± 01 mm, respectively; P < 0.05) were less in the non-breeding compared to the breedingseason. During the breeding season the interovulatory interval was 19.7 ± 0.2 days. Totalnumber of small follicles (2–3 mm) and the total number of follicles ≥3 mm from Days 2 to14 of the period of examination were greater (P < 0.05) during the non-breeding comparedto the breeding season. In the breeding season, 35.7% of cycling goats showed large anovula-tory follicles, which persisted and became luteinized. Ovulatory follicles were derived fromthe fourth follicular wave in 71% of goats. These results have described differences in char-acteristics of follicular development in the same Boer goats examined during the breedingand non-breeding seasons. In the non-breeding season, the ovaries remained active andfollicles continued to grow to reach the equivalent size of preovulatory follicles. Folliculardynamics in the breeding season was characterized by the development of larger folliclesand greater follicular growth rates. Short oestrous cycles and follicular cysts may reduceovulation rate in Boer goats in the breeding season.