Mutation in the protease cleavage site of GDF9 increases ovulation rate and litter size in heterozygous ewes and causes infertility in homozygous ewes.

Litter size (LS) in sheep is determined mainly by ovulation rate (OR). Several polymorphisms have been identified in the growth differentiation factor 9 (GDF9) gene that result in an increase in OR and prolificacy of sheep. Screening the databank of the Brazilian Sheep Breeders Association for triplet delivery, we identified flocks of prolific Ile de France ewes. After resequencing of GDF9, a point mutation (c.943C>T) was identified, resulting in a non-conservative amino acid change (p.Arg315Cys) in the cleavage site of the propeptide. This new allele was called Vacaria (FecG(v)). A flock of half-sib ewes was evaluated for OR in the first three breeding seasons, and Vacaria heterozygotes had higher OR (P<0.001), averaging 2.1 +/- 0.1 when compared to 1.2 +/- 0.1 in wild-type ewes. The OR was also influenced by age, increasing in the second and third breeding seasons (P<0.001). In flocks segregating this allele, the LS was higher in mutant sheep (P<0.001), averaging 1.61 +/- 0.07 in heterozygotes and 1.29 +/- 0.03 in wild-type ewes. Analysis of homozygote reproductive tract morphology revealed uterine and ovarian hypoplasia. Ovarian follicles continue to develop up to small antral stages, although with abnormal oocyte morphology and altered arrangement of granulosa cells. After the collapse of the oocyte in most follicles, the remaining cells formed clusters that persisted in the ovary. This SNP is useful to improve selection for dam prolificacy and also as a model to investigate GDF9 post-translation processing and the fate of the follicular cells that remain after the oocyte demise.