Effect of the Booroola fecundity (FecB) gene on the reproductive performance of ewes under assisted reproduction.

Reproductive traits are important factors in sheep production. The Booroola fecundity (FecB) gene-the first major gene for prolificacy identified in sheep-has a positive effect on ovulation rates and litter size under natural reproductive conditions. However, the effect of the FecB gene on reproductive performance under assisted reproduction, which uses many artificial hormones, remains unclear. In the present study, we evaluated the effect of FecB (BMPR-1B mutation) on reproductive performance under assisted reproduction, and examined offspring body weight at birth and weaning and survival rate at weaning. There were no differences among three genotype groups (homozygous carrier, BB; heterozygous carrier, B+; non-carrier, ++) in terms of estrus detection rate, time to estrus onset, or estrus duration following estrus synchronization (P > 0.05). The pregnancy rates at 60 d were similar among three genotype groups after artificial insemination (P > 0.05). However, the B allele had an additive effect on litter size (one copy resulted in an increase of 0.88 lambs and two copies produced an additional 0.41 lambs; P < 0.01), and increased lambing and fecundity rates (P < 0.01). After multiple ovulation, the average numbers of recovered embryos per ewe were 9.16 ± 0.79, 8.20 ± 0.77, and 8.44 ± 0.61 in the BB, B+, and ++ ewes, respectively (P > 0.05). There were no differences in the fertilization rate or numbers of grade 1-2 embryos among different groups (P > 0.05). The birth and weaning weights of lambs from BB and B+ ewes were lower than those of lambs born from ++ ewes (P < 0.01) owing to the high fecundity. The survival rate of lambs at weaning did not differ among groups (P > 0.05). Our results indicated that the presence of the B allele had an additive effect on litter size after artificial insemination, but it did not influence the parameters of estrus synchronization and multiple ovulation. Furthermore, the higher prolificacy in ewes carrying the B allele was associated with a reduction in offspring body weight at birth and weaning.