Abstract:

【Objective】 The objectives of the present study were to elucidate the relationship between Toll-like receptor 1 (TLR1) gene and mastitis resistance of Holstein cows and to provide a scientific basis for marker-assisted selection for mastitis resistance of dairy cattle. 【Method】 Polymorphisms of all exons of TLR1 gene were detected in 208 Holstein cows by PCR-SSCP and PCR-RFLP. The relationship between polymorphisms of TLR1 gene and somatic cell score (SCS) in Holstein cows was analyzed by least squares linear model. 【Result】 Four polymorphic sites, G1409A, A1475C, G1550A and G1596A, were found, and G1596A mutation resulted in an amino acid change of isoleucine→valine. For G1409A polymorphic site, two genotypes (AA and AB) were found in 208 Holstein cows by digesting the PCR products with restriction endonuclease BsiYⅠ, and the frequency of AA and AB genotypes was 0.375 and 0.625, respectively. Chi-square test showed that Holstein cows were not in Hardy-Weinberg equilibrium. Least squares mean of SCS for AA was not significantly lower than that for AB (P＞0.05). For A1475C polymorphic site, two genotypes (CC and CD) were found in 208 Holstein cows by digesting the PCR products with restriction endonuclease BstXⅠ, and the frequency of CC and CD genotypes was 0.178 and 0.822, respectively. Holstein cows were not in Hardy-Weinberg equilibrium. Least squares mean of SCS for CC was not significantly lower than that for CD (P＞0.05). For G1550A polymorphic site, three genotypes (EE, EF and FF) were found in 208 Holstein cows by digesting the PCR products with restriction endonuclease BsiYⅠ, and the frequency of EE, EF and FF genotypes was 0.236, 0.370 and 0.394, respectively. Holstein cows were not in Hardy-Weinberg equilibrium. The difference of the least squares means for SCS between EE, EF and FF was insignificant (P＞0.05). For G1596A polymorphic site, three genotypes (GG, GH and HH) were found in 208 Holstein cows by digesting the PCR products with restriction endonuclease BclⅠ, and the frequency of GG, GH and HH genotypes was 0.260, 0.567 and 0.173, respectively. Holstein cows were in Hardy-Weinberg equilibrium. Least squares mean of SCS for HH was significantly lower than that for GH (P＜0.01) or GG (P＜0.0001), least squares mean of SCS for GH was significantly lower than that for GG (P＜0.01). 【Conclusion】 HH was the most favorable genotype, GG was the most unfavorable genotype for mastitis resistance. The results preliminarily indicated that allele H of G1596A polymorphic site of TLR1 gene is a potential DNA marker for improving mastitis resistance in dairy cattle.

Key words: holstein cows, TLR1 gene, mastitis, somatic cell score, PCR-RFLP