Semen Quality of Rasa Aragonesa Rams Carrying the FecXR Allele of the BMP15 Gene

SIMPLE SUMMARY: It has been demonstrated that the ovine gene BMP15 presents a mutation in the Rasa Aragonesa Spanish sheep breed, which has been called FecXR. In heterozygosis, ewes exhibit a variable increase in the ovulation rate, producing 0.35 additional lambs per birth and, in homozygosis, sterility. Since the importance of carrying this polymorphism in rams has not been studied, sperm quality and fertility of rams carrying the FecXR mutation of the ovine gene BMP15 has been determined, comparing semen quality, testicle characteristics, and fertility rate of rams presenting or not the allele. FecXR rams exhibited a higher masal motility and a higher proportion of rapid sperm than did non-carrier rams; however, no differences in scrotal circumference or testicular length and diameter were found, although FecXR rams produced a higher proportion of pregnant ewes after artificial insemination. Thus, it seems that the FecXR allele creates high-quality semen and improves some sperm parameters in this breed, making these males especially valuable for artificial insemination to produce prolific ewes, when wild-type, non-carrier ewes, are inseminated. ABSTRACT: The FecXR mutation is a variant of the ovine gene BMP15 in the Rasa Aragonesa breed. Information on the physiological importance of carrying the FecX polymorphism in rams is limited. The aim of this study was to compare semen quality, testicle characteristics, and fertility rate of rams that carry the FecXR allele. Rams (n = 15) were either FecXR allele carriers (n = 10) or non-carriers, wild type (++) (n = 5). FecXR rams exhibited higher mass motility (p < 0.05), proportion of rapid sperm (p < 0.05), and a lower proportion of slow sperm (p < 0.0001) than did ++ rams. The presence of the FecXR allele was not associated with mean scrotal circumference or testicular length and diameter, although season had a significant (p < 0.05) effect on these traits. Genotype (p < 0.05) and season (p < 0.01) had a significant effect on mean fertility rate, FecXR rams had a higher proportion of pregnant ewes than did ++ rams (p < 0.05). In conclusion, the FecXR allele produced high-quality semen throughout the year, and corresponded with an improvement in some sperm parameters, particularly, mass motility and the proportion of rapid sperm.