Influence of the Booroola Fec B allele on follicular dynamics

Abstract

Sheep carrying the Booroola Merino fecundity allele (Fec) have increased ovulation rates and litter sizes. Transrectal ultrasonography was used to compare follicular growth patterns between Fec carriers and non-carriers during the estrous cycle. A follicular wave was defined as one or more follicles growing to at least 5 mm in diameter. The day of emergence of a wave was defined as the day when a follicle was 3 mm and grew to at least 5 mm. An ovulatory wave was a wave in which at least one follicle ovulated; all other waves were designated as anovulatory. The ovaries of 23 yr old ewes were scanned daily and the day-to-day identity of follicles maintained. Two groups were compared: carriers (3/4 Rambouillet; 1/4 Booroola Merino with the Fec allele) and non-carriers (3/4 Rambouillet; 1/4 Booroola Merino without the Fec allele). Nine interovulatory intervals were examined in 6 carriers and 12 intervals in 6 non-carriers.