High prolificacy in Belle-Ile sheep (Brittany, France): major effects of a putative single gene and the Awh colour gene on ovulation rate and litter size

Ovulation rate (OR) and litter size (LS) were recorded in 72 ewes from a traditional sheep population native to Belle-Ile en Mer, France (BI) from 1986 to 1996. Mean, range and repeatability of OR were: 2.54 +/- 1.1 (n = 494), 1-8 and 0.8, respectively, whereas, for LS, they were: 2.23 +/- 1.0 (n = 146), 1-7 and 0.2, respectively. OR is significantly influenced by age, number of OR, maximum OR in the dam (< or = 3 versus > 3), sire and colour of the fleece (white versus black pattern). OR was also recorded in Charmoise ewes (CH), their F1 progenies with four BI rams and BI ram x F1 backcross ewes (BC). OR range and OR mean in CH ewes, four F1 progenies and BC ewes were: 1-2 and 1.2, 1-2 and 1.2, 1-2 and 1.3, 1-3 and 1.9, 1-4 and 2.3, 1-6 and 2.8, respectively. OR repeatability in CH, F1 and BC were 0.16, 0.45 and 0.71, respectively. The large variation in ovulation rate and litter size combined with high repeatabilities, the familial transmission of a high ovulation rate and the observations in F1 and BC support the hypothesis of a single gene with a large mean effect on ovulation rate and litter size segregating in the population.