Markers of follicle function in Belclare-cross ewes differing widely in ovulation rate

High prolificacy due to a gene that has a large effect on ovulation rate ha s been noted in Booroola and Inverdale ewes. High prolificacy in the Belcla re breed (a composite developed from stocks selected for very large litter size or high ovulation rate) may be related to the segregation of two genes . The aims of this study were (i) to compare the morphological and function al features of ovulatory follicles from carriers (which could only be heter ozygous for the genes of interest) and non-carriers, and (ii) to identify m arkers of the Belclare genes among secreted or cellular ovarian proteins. B elclare carrier ewes had more ovulatory follicles (4.9 +/- 0.4) than did no n-carrier ewes (2.0 +/- 0.2) (P < 0.001). Ovulatory follicles from carriers were also smaller (4.4 +/- 0.1 mm versus 5.7 +/- 0.2 mm, P < 0.001) and co ntained a significantly reduced number of granulosa cells (P < 0.001). Howe ver, the proportion of proliferating granulosa cells in ovulatory follicles was similar in both groups. The in vitro secretion of steroids per follicl e was only marginally lower in follicles from Belclare carriers compared wi th non-carriers. Furthermore, similar concentrations of steroidogenic enzym es were present in both groups, indicating that steroidogenic potential per granulosa cell is similar between carriers and non-carriers. Possible mark ers of the Belclare genes were identified among cellular proteins of follic ular walls by two-dimensional PAGE and image analysis. Two spots at 78 and 49 kDa were always absent in samples from non-carriers. When secreted prote ins in follicles from carriers were compared with those from non-carriers, two spots at 53 and 41 kDa were restricted to samples from carriers and thr ee spots at 97, 91 and 45 kDa were unique to samples from non-carriers. Int erestingly, the spot at 91 kDa is also affected by the Booroola gene.