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Abstract
Mastitis is a complex inflammatory disease of the mammary gland that is caused by the invasion of pathogens. This leads to reduced synthetic capacity, compositional changes and increased somatic cell counts (SCC) in milk. Toll-like receptor 4 (TLR4) is a cell surface receptor that recognizes lipopolysaccharides (LPS) of gram-negative bacteria. Its role in pathogen recognition and the subsequent immune response and differential expression of the gene during mastitis have prompted the investigation of TLR4 gene as a candidate to improve mastitis resistance in dairy cattle. The aim of this study was to analyse the possible association of a single nucleotide polymorphism (SNP) in putative co-receptor-binding region 2 (T4CRBR2) of the TLR4 gene with somatic cell score (SCS) and milk-related traits in 408 Iranian Holstein cows. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was performed for genotyping. The effect of the genotype on the traits of interest was analysed using the general linear model (GLM) procedure of SAS software. The B allele frequency was 0.634 and the distribution of genotypes was not in Hardy-Weinberg equilibrium in the overall population. The B allele of the SNP was associated with higher 305-day milk yield and breeding value for milk yield, and lower fat percentage and lower SCS, as compared with allele A. The association between TLR4 polymorphism with SCS and milk production traits reported in this study suggests that this SNP has the potential to be used as a marker for selection, based on molecular information.Keywords: TLR4 gene, mastitis, candidate gene, milk-related traits, single nucleotide polymorphism, SNP
Highlights
Mastitis is a complex disease, which can be defined as inflammation of the mammary gland
The result of the test for Hardy-Weinberg equilibrium for this locus indicated that the genotypes in herds three, four and five did not show any significant deviation from Hardy-Weinberg equilibrium, while herds one, two and the overall population were not distributed according to Hardy-Weinberg equilibrium (Table 1)
Toll-like receptor 4 (TLR4) has been mapped to the distal end of bovine chromosome 8 (White et al, 2003) and Quantitative Trail Loci (QTL) affecting somatic cell score (SCS), and clinical mastitis have been found on this chromosome
Summary
Mastitis is a complex disease, which can be defined as inflammation of the mammary gland. This disease is caused by the invasion and multiplication of pathogenic microorganisms in the mammary gland, leading to reduced synthetic capacity and compositional changes (Harmon et al, 1994). This is followed by an influx of leucocytes into the milk and as a result an increase of the milk somatic cell counts (SCC) (Auldist & Hubble, 1998).
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