Association of toll-like receptors 2 and 6 polymorphism with clinical mastitis and production traits in Holstein cattle.

Mastitis is a costly disease of dairy cattle as it causes a loss in milk yield and milk quality in affected cows. Toll-like receptor (TLR) genes play a role in the host response to a variety of organisms including those inducing mastitis. In the present study, we investigated the polymorphism of TLR2, 4, 6 and 9 genes in Holstein cattle and their possible association with clinical mastitis (CM), milk somatic cell scores (SCS) and milk production traits. From a large commercial Holstein herd, thirty-eight blood samples were collected; 19 from cows without a previous lifetime history of mastitis (non-susceptible), and 19 from Holstein cows with at least three previous episodes of mastitis (susceptible). Genotyping of the four TLRs was done using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLPs) with Rsa1, MSP1, Hha1, HaeIII, and Taq1 enzymes guided with DNA sequencing. Seven novel non-synonymous single-nucleotide polymorphisms (SNPs) were identified among TLR2, 4, and 6 in susceptible animals. Association was found in Taq1-TLR2 gene polymorphism with CM, fat percentage and peak yield (PY). The association of Taq1-TLR6 and PY and lactation persistency was also shown. Mutations in TLRs that were repeatedly reported in susceptible cows provide potential genetic marker assisted selection (MAS) for mastitis resistance in dairy cattle.