Association of udder traits with single nucleotide polymorphisms in crossbred Bos indicus-Bos taurus cows

The size, support, and health of udders limit the productive life of beef cows, especially those with Bos indicus background, because, in general, such cows have a reputation for problems with udders. Genomic association studies of bovine udder traits have been conducted in dairy cattle and recently in Continental European beef breeds but not in cows with B. indicus background. The objective of this study was to determine associations of SNP and udder support scores, teat length, and teat diameter in half B. indicus (Nellore), half Bos taurus (Angus) cows. Udders of cows (n = 295) born from 2003 to 2007 were evaluated for udder support and teat length and diameter (n = 1,746 records) from 2005 through 2014. These included a subjective score representing udder support (values of 1 indicated poorly supported, pendulous udders and values of 9 indicated very well-supported udders) and lengths and diameters of individual teats in the 4 udder quarters as well as the average. Cows were in full-sibling or half-sibling families. Residuals for each trait were produced from repeated records models with cow age category nested within birth year of cows. Those residuals were averaged to become the dependent variables for genomewide association analyses. Regression analyses of those dependent variables included genotypic values as explanatory variables for 34,980 SNP from a commercially available array and included the genomic relationship matrix. Fifteen SNP loci on BTA 5 were associated (false discovery rate controlled at 0.05) with udder support score. One of those was also detected as associated with average teat diameter. Three of those 15 SNP were located within genes, including one each in vitamin D (1,25-dihydroxyvitamin D-3) receptor (VDR), protein tyrosine phosphatase, receptor type, R (PTPRR), and interleukin 22 (IL22). These are notable for their functional role in some aspect of mammary gland formation or health. Other candidate genes for these traits in the vicinity of the SNP loci include signal peptidase complex subunit 3 homolog (SPCS3) and dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 2 (DYRK2). Because these were detected in Nellore-Angus crossbred cows, which typically have very well-formed udders with excellent support across their productive lives, similar efforts in other B. indicus breeds should be completed, because that may facilitate further refinement of genomic regions responsible for variation in udder traits important in multiple breeds.