Candidate genes for mastitis resistance in dairy cattle: a data integration approach

Genes and pathways revealed by whole transcriptome analysis of milk derived bovine mammary epithelial cells after Escherichia coli challenge

Mastitis, inflammation of the mammary gland, is the costliest disease in dairy cattle and a major animal welfare concern. Mastitis is usually caused by bacteria, of which staphylococci, streptococci and Escherichia coli are most frequently isolated from bovine mastitis. Bacteria activate the mammary immune system in variable ways, thereby influencing the severity of the disease. Escherichia coli is a common cause of mastitis in cattle causing both subclinical and clinical mastitis. Understanding of the molecular mechanisms that activate and regulate the host response would be central to effective prevention of mastitis and breeding of cows more resistant to mastitis. We used primary bovine mammary epithelial cell cultures extracted noninvasively from bovine milk samples to monitor the cellular responses to Escherichia coli challenge. Differences in gene expression between control and challenged cells were studied by total RNA-sequencing at two time points post-challenge. In total, 150 and 440 (Padj < 0.05) differentially expressed genes were identified at 3 h and 24 h post-challenge, respectively. The differentially expressed genes were mostly upregulated at 3 h (141/150) and 24 h (424/440) post-challenge. Our results are in line with known effects of E. coli infection, with a strong early inflammatory response mediated by pathogen receptor families. Among the most significantly enriched early KEGG pathways were the TNF signalling pathway, the cytokine-cytokine receptor interaction, and the NF-kappa B signalling pathway. At 24 h post-challenge, most significantly enriched were the Influenza A, the NOD-like receptor signalling, and the IL-17 signaling pathway.

Genomic Characterization and Initial Insight into Mastitis-Associated SNP Profiles of Local Latvian Bos taurus Breeds

Latvia has two local Bos taurus breeds-Latvian Brown (LBG) and Latvian Blue (LZG)-characterized by a good adaptation to the local climate, longevity, and high fat and protein contents in milk. Since these are desired traits in the dairy industry, this study investigated the genetic background of the LBG and LZG breeds and identified the genetic factors associated with mastitis. Blood and semen samples were acquired, and whole genome sequencing was then performed to acquire a genomic sequence with at least 35× or 10× coverage. The heterozygosity, nucleotide diversity, and LD analysis indicated that LBG and LZG cows have similar levels of genetic diversity compared to those of other breeds. An analysis of the population structure revealed that each breed clustered together, but the overall differentiation between the breeds was small. The highest genetic variance was observed in the LZG breed compared with the LBG breed. Our results show that SNP rs721295390 is associated with mastitis in the LBG breed, and SNPs rs383806754, chr29:43998719CG>C, and rs462030680 are associated with mastitis in the LZG breed. This study shows that local Latvian LBG and LZG breeds have a pronounced genetic differentiation, with each one suggesting its own mastitis-associated SNP profile.