Ovarian follicular development and endocrine function in non-prolific Western White Face ewes with early or late onset of seasonal anestrous

• Published in: Small ruminant research 2002-11, Vol.46 (2), p.191-199
• Main Authors: Huchkowsky, S.L, Bartlewski, P.M, Rawlings, N.C
• Format: Article
• Language: English
• Subjects: Ewe; Follicular dynamics; Seasonal anestrous; Ultrasonography
• ISSN: 0921-4488; 1879-0941
• DOI: 10.1016/S0921-4488(02)00185-2

The aim of this study was to see if there were differences in antral follicle development and endocrine profiles among non-prolific Western White-Faced ewes entering anestrous early (January–February; n=6) or late (March; n=6), using daily transrectal ultrasonography of ovaries and hormone measurements, over a 17-day period during mid-anestrous (May). The ovarian follicles were measured and categorized by size (1-2, 2, 3, 4 and ≥5 mm in diameter). For determination of the patterns of FSH and LH secretion, a 12 h intensive bleed, with blood samples taken every 12 min, was carried out 2 days after the end of the scanning period. A bolus injection of GnRH (250 μg per ewe) was given 6 h into the period of intensive blood collection. The ewes entering anestrous early had significantly lower numbers of 2 and ≥5 mm follicles when compared with ewes entering anestrous late. Similar results were observed for the numbers of all follicles >1 mm in size, total and maximum follicle diameters of all follicles ≥2 mm in size, and the number of ≥5 mm follicles growing by ≥1 mm each day. In contrast, significantly more 4 mm follicles were recorded in ewes entering anestrous early. Daily serum concentrations of FSH and estradiol as well as the peak concentration increases in daily serum FSH concentrations and duration of successive estradiol fluctuations, were greater ( P0.05) between ewes entering anestrous early or late. We concluded that the timing of the onset of seasonal anestrous in Western White-Faced ewes affected the number and size of ovarian antral follicles as well as circulating levels of FSH and estradiol, but not pituitary responsiveness to GnRH at mid-anestrous.