Heterozygous Inverdale ewes show increased ovulation rate sensitivity to pre-mating nutrition

This study aimed to determine whether ewes heterozygous (I+) for the Inverdale mutation of the bone morphogenetic protein-15 (BMP15) gene with high natural ovulation rate (OR) show similar sensitivity to nutritional manipulation as non-carriers (++). Increasing pre-mating nutrition results in OR increases in sheep, but whether this effect occurs in ewes with naturally high OR is unknown. Over 2 years, I+ or ++ ewes were given high (ad libitum) or control (maintenance) pasture allowances for 6 weeks prior to mating at a synchronised oestrus, with OR measured 8 days later. The high group increased in weight compared with controls (+5.84kg; P<0.01), accompanied by increased OR (+19%; P<0.01). As well as having higher OR (+45%; P<0.01), I+ ewes responded to increased feed with a larger proportional increase in OR (+27%; P<0.01) compared with the response in ++ ewes (+11%; P<0.05), suggesting an interaction between BMP15 levels and nutritional signals in the follicle to control OR. Although litter size increases only tended to significance (+12%; P=0.06), extra feed resulted in over 50% of I+ ewes giving birth to more than three lambs, compared with 20-31% of I+ ewes on maintenance rations. This information can guide feed management of prolific Inverdale ewes prior to breeding.