Abstract
Calving in cattle is affected by calf morphology and by dam characteristics. It is described by two different traits: maternal calving ease, which is the ability to generate dams with good physiological predisposition to calving, and direct calving ease, which is the ability to generate calves that are easily born. The aim of this study was to identify regions of cattle genome harboring genes possibly affecting direct calving ease in the Piedmontese cattle breed. A population of 323 bulls scored for direct calving ease (EBV) was analyzed by a medium-density SNP marker panel (54,001 SNPs) to perform a genome-wide scan. The strongest signal was detected on chromosome 6 between 37.8 and 38.7 Mb where 13 SNPs associated to direct calving ease were found. Three genes are located in this region: LAP3, encoding for a leucine aminopeptidase involved in the oxytocin hydrolysis; NCAPG, encoding for a non-SMC condensin I complex, which has been associated in cattle with fetal growth and carcass size; and LCORL, which has been associated to height in humans and cattle. To further confirm the results of the genome-wide scan we genotyped additional SNPs within these genes and analyzed their association with direct calving ease. The results of this additional analysis fully confirmed the findings of the GWAS and particularly indicated LAP3 as the most probable gene involved. Linkage Disequilibrium (LD) analysis showed high correlation between SNPs located within LAP3 and LCORL indicating a possible selection signature due either to increased fitness or breeders’ selection for the trait.
Highlights
Reproductive health in cattle is an economically important trait and calving is a key element to improve productivity and animal welfare
Genome-wide Scan Distribution of genomic kinship values is shown in Figure 1; most sires share a genomic kinship value in the range 60.025 and higher values are very uncommon in the sample; the chosen statistical approach coupled with genomic control should be able to correctly take into account the population structure while conserving enough statistical power
Among the 41333 polymorphisms of the Illumina BovineSNP50 retained after quality control, 2030 were associated to direct calving ease
Summary
Reproductive health in cattle is an economically important trait and calving is a key element to improve productivity and animal welfare. Calving is influenced by many environmental and genetic factors: in cattle it is affected by calf morphology [1] and by dam characteristics [1] and can be described by two traits: maternal calving ease and direct calving ease. Both refer to calving without human intervention, the first attributed to the mother and the second to the calf. In addition to birth weight, other important factors as calf shape, the size of cow pelvic area or the gestation length may contribute to calving ease [2]. The use of large-scale single nucleotide polymorphism (SNP) genotyping and genome-wide association (GWA) studies allow to identify genomic regions and hopefully mutations that underlie the desired performance
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