The effect of the Booroola (Fec(B)) gene on peripheral FSH concentrations and ovulation rates during oestrus, seasonal anoestrus and on FSH concentrations following ovariectomy in Scottish Blackface ewes

Abstract

The aim of this study was to investigate the role of FSH in the control of ovulation rate by the Booroola gene. Three Booroola genotypes (Fec(B)Fec(B), Fec(B)Fec+ and Fec+Fec+) of the F2 population, from a cross between Booroola Merino and Scottish Blackface, and two Booroola genotypes (Fec(B)Fec+ and Fec+Fec+; 25% Booroola Merino and 75% Scottish Blackface), from the backcross of Fec(B)Fec+ sires to Scottish Blackface ewes, were compared. During seasonal anoestrus significant differences (P < 0.05) in hCG-stimulated ovulation rates were obtained between Fec(B)Fec(B) and Fec+Fec+ ewes from the F2 population, and Fec(B)Fec+ ewes were intermediate. No significant difference in hCG-stimulated ovulation rate was observed in the backcross population between Fec(B)Fec+ ewes and Fec+Fec+ ewes. There were no significant differences between genotypes in mean serum FSH concentrations during seasonal anoestrus in either backcross or F2 populations. During the breeding season, two separate experiments confirmed the expected ovulation rate differences between genotypes (Fec(B)Fec(B) > Fec(B)Fec+ > Fec+Fec+). In both experiments, mean peripheral FSH concentrations in the F2 population were similar in Fec(B)Fec+ and Fec+Fec+ ewes, but were significantly higher (P < 0.05) in Fec(B)Fec(B) ewes. In the backcross population, mean peripheral FSH concentrations during the oestrous cycle were not significantly different between Fec(B)Fec+ and Fec+Fec+ ewes, despite significant differences in ovulation rate. Ovariectomy during the breeding season resulted in significantly higher (P < 0.001) mean peripheral FSH concentrations in all three genotypes. After ovariectomy, mean FSH concentrations between Fec(B)Fec+ and Fec+Fec+ ewes, from both the backcross and F2 populations, were not significantly different. However, mean FSH concentrations in the F2 population were significantly higher in Fec(B)Fec(B) ewes than in the other two genotypes. The pattern of differences between genotype in peripheral FSH concentrations and ovulation rates suggest that FSH is not wholly responsible for differences in ovulation rate between genotypes. The results support the hypothesis that the Fec(B) gene is operating both within the ovary and at the level of the hypothalamus and pituitary gland.