Abstract
The reproductive performance of bulls has a high impact on the beef cattle industry. Scrotal circumference (SC) is the most recorded reproductive trait in beef herds, and is used as a major selection criterion to improve precocity and fertility. The characterization of genomic regions affecting SC can contribute to the identification of diagnostic markers for reproductive performance and uncover molecular mechanisms underlying complex aspects of bovine reproductive biology. In this paper, we report a genome-wide scan for chromosome segments explaining differences in SC, using data of 861 Nellore bulls (Bos indicus) genotyped for over 777,000 single nucleotide polymorphisms. Loci that excel from the genome background were identified on chromosomes 4, 6, 7, 10, 14, 18 and 21. The majority of these regions were previously found to be associated with reproductive and body size traits in cattle. The signal on chromosome 14 replicates the pleiotropic quantitative trait locus encompassing PLAG1 that affects male fertility in cattle and stature in several species. Based on intensive literature mining, SP4, MAGEL2, SH3RF2, PDE5A and SNAI2 are proposed as novel candidate genes for SC, as they affect growth and testicular size in other animal models. These findings contribute to linking reproductive phenotypes to gene functions, and may offer new insights on the molecular biology of male fertility.
Highlights
Reproductive performance has a high economic value in beef cattle, because fertility affects generation intervals, the intensity of selection pressure that can be applied to the population, and the amount of product that can be sent to the market [1]
The ratio between the signal-to-noise coefficients of sliding windows and single single nucleotide polymorphism (SNP) was 2.54, indicating that the smoothing strategy allowed for a 2.54 fold improvement in mapping resolution (Figures 2, S1 and S2)
The human MAGEL2 has been implicated in Prader-Willi Syndrome, a genetic disorder characterized by short stature, low muscle tone, cognitive disabilities, increased food intake, obesity, low levels of insulin and insulin-like growth factor 1 (IGF1), incomplete sexual development, hypogonadism, and male infertility [21,22]
Summary
Reproductive performance has a high economic value in beef cattle, because fertility affects generation intervals, the intensity of selection pressure that can be applied to the population, and the amount of product that can be sent to the market [1]. Domestic cattle are composed by two interfertile species: the humpless taurine cattle (Bos taurus) and the humped indicine or zebu cattle (Bos indicus). Indicine breeds, such as Nellore cattle, form the majority of the beef herds in tropical and subtropical countries. Zebus generally take longer to reach puberty than taurines [2], making the improvement of reproductive performance an impending challenge in the production systems of these regions of the world. SC is used in these programs as a major indicator of precocity and fertility
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