Genomic Approaches to Left-Sided Abomasal Displacement in Italian Holstein Cattle: Results from a Comprehensive Research Project

A sample of 64 Italian Holstein cows was analysed to investigate the genetic architecture of left-sided abomasal displacement (LDA). LDA is one of the most common disorders of the digestive system in dairy breeds, causing economic losses due to treatment costs, premature culling, and reduction of milk yield. Among predisposing factors, LDA is induced by impaired abomasal motility that causes an accumulation of gas. Moreover, previous studies have shown the existence of a genetic component, with heritabilities estimated between 0.2 and 0.5. A total of 17 cases and 47 controls were available from 5 commercial herds. All cows were genotyped with the Illumina 50k bovine SNP chip. Two methods of analysis were used: a genome-wide association study (GWAS) of cases and controls and the analysis of runs of homozygosity (autozygosity-by-difference). In total, 39 SNPs located on 19 bovine (Bos taurus) chromosomes (BTA) showed associations with LDA (−log10 P-values >3.0). Two of these SNP, located on BTA13 and BTA12, showed genome-wide significant associations with LDA at −log10 P-values > 4. SNP on BTA12 is located in the region of SLITRK5 gene, a member of the SLITRK family. SLITRK genes are expressed predominantly in neural tissues with a neurite-modulating activity. On chromosome 14, a common stretch of homozygosity in cases and controls was detected, in the region close to the DGAT1 mutation.