Direct Evidence on the Contribution of a Missense Mutation in GDF9 to Variation in Ovulation Rate of Finnsheep

The Finnish Landrace (Finnsheep) is a well known high-prolificacy sheep breed and has been used in many countries as a source of genetic material to increase fecundity of local breeds. Analyses to date have indicated that mutations with a large effect on ovulation rate are not responsible for the exceptional prolificacy of Finnsheep. The objectives of this study were to ascertain if: 1) any of 12 known mutations with large effects on ovulation rate in sheep, or 2) any other DNA sequence variants within the candidate genes GDF9 and BMP15 are implicated in the high prolificacy of the Finnish Landrace breed; using material from lines developed by divergent selection on ovulation rate. Genotyping results showed that none of 12 known mutations (FecB(B), FecX(B), FecX(G), FecX(GR), FecX(H), FecX(I), FecX(L), FecX(O), FecX(R), FecG(E), FecG(H), or FecG(T)) were present in a sample of 108 Finnsheep and, thus, do not contribute to the exceptional prolificacy of the breed. However, DNA sequence analysis of GDF9 identified a previously known mutation, V371M, whose frequency differed significantly (P < 0.001) between High and Low ovulation rate lines. While analysis of ovulation rate data for Finnsheep failed to establish a significant association between this trait and V371M, analysis of data on Belclare sheep revealed a significant association between V371M and ovulation rate (P < 0.01). Ewes that were heterozygous for V371M exhibited increased ovulation rate (+ 0.17, s.e. 0.080; P < 0.05) compared to wild type and the effect was non-additive (ovulation rate of heterozygotes was significantly lower (P < 0.01) than the mean of the homozygotes). This finding brings to 13 the number of mutations that have large effects on ovulation rate in sheep and to 5, including FecB(B), FecG(E), FecX(O) and FecX(GR), the number of mutations within the TGF beta superfamily with a positive effect on prolificacy in the homozygous state.