Global transcriptomic profiles of circulating leucocytes in early lactation cows with clinical or subclinical mastitis

Abstract BackgroundBovine mastitis, an inflammatory disease of the mammary gland, is classified as subclinical or clinical. Circulating neutrophils are recruited to the udder to combat infection. We compared the transcriptomic profiles in circulating leukocytes between healthy cows and those with naturally occurring subclinical or clinical mastitis.Methods and ResultsHolstein Friesian dairy cows from six farms in EU countries were recruited. Based on milk somatic cell count and clinical records, cows were classified as healthy (n = 144), subclinically (n = 48) or clinically mastitic (n = 22). Circulating leukocyte RNA was sequenced with Illumina NextSeq single end reads (30 M). Differentially expressed genes (DEGs) between the groups were identified using a DESeq2 package, followed by GO enrichment analysis. Both subclinical and clinical mastitis caused significant changes in the leukocyte transcriptome, with more intensive changes attributed to clinical mastitis. We detected 491 DEGs between clinical and healthy groups, 350 DEGs between subclinical and healthy groups and 170 DEGs between clinical and subclinical groups. Most DEGs were associated with cell killing and immune processes. Many upregulated DEGs in clinical mastitis encoded antimicrobial peptides (AZU1, CAMP, CATHL1, CATHL2, CATHL4, CATHL5, CATHL6, DEFB1, DEFB10, DEFB4A, DEFB7, LCN2, PGLYRP1, S100A9, TF and LTF) which were not upregulated in subclinical mastitis. This suggests that the leukocytes may have greater killing capacity in cows with clinical mastitis.ConclusionWe have, for the first time, described circulating leukocyte transcriptomic profiles in naturally occurring subclinical mastitis and assessed their differences from healthy cows and those with clinical mastitis.