Association of a mutation inactivating the myostatin gene with growth, testicular morphology and sperm quality traits measured in Marchigiana young bulls in performance test

Among the Italian autochthonous beef cattle breeds, Marchigiana is particularly important in terms of census and production. In this breed, a SNP inactivating the myostatin gene leads to muscular hypertrophy in the individuals homozygous for the mutated allele while heterozygous individuals have an increased muscle development. The impact of this mutation on growth rate and weight is still under debate. Moreover, there is evidence obtained in mouse that the inactivation of the myostatin gene impairs testicular development. The aim of this work was to investigate whether Marchigiana bulls carrying this mutation differ from the individuals homozygous for the wild allele in terms of production or reproduction traits recorded during the performance test. Eight of the most commercially important production traits, from a dataset of 1074 animals, alongside seven reproduction traits from 298 to 624 animals, were analysed. Statistical analysis showed that heterozygous bulls had increased muscularity compared to their normal counterparts (nominal P-value = 5.42e-24), while average daily gain, live weight, and morphological score were not significantly different. Regarding reproduction phenotypes, scrotal circumference and right testicle length were significantly reduced in heterozygous animals (nominal P-values of 7.87e-05 and 0.0018), right testicle diameter was also significantly reduced, but only at the nominal level (nominal P-value = 0.0354), while sperm volume was increased (nominal P-value = 0.01). Our results highlight the positive effect of this mutation on muscularity, while it does not show an adverse impact on other traits. Thus, the selection of heterozygous bulls in mating plans could be highly beneficial.