The polymorphism in the β4‐defensin gene and its association with production and somatic cell count in Holstein‐Friesian cows

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Summary: The aim of this study was to find a polymorphism of the bovine β4‐defensin gene and search for its association with milk yield and composition and with the somatic cell count in milk. The data were from the years 1999 to 2004 on 212 Holstein‐Friesian (HF) dairy cows, descended from 70 sires. Based on the sequence of the bovine β4‐defensin gene (GenBank no. AF008307) the primers were designed for the amplification of the 924‐bp or 393‐bp long fragments. The 924‐bp long fragment was sequenced and the sequence was compared with that available in the GenBank. Ten putative nucleotide sequence polymorphisms were found in the intron of the bovine β4‐defensin gene. One of them, a C→T transition at position 2239, that creates a new NlaIII (Hin1II) restriction site, was genotyped with polymerase chain reaction‐restriction fragment length polymorphism (PCR‐RFLP) in a cohort of 212 HF cows. The CC genotype was the most common (72%). The heterozygous CT genotype was found in 26% of the genotyped cows and four cows (2%) were TT homozygotes. In order to determine the relationship between the polymorphism of the β4‐defensin gene and milk production traits a multi‐trait repeatability test‐day animal model was used. The Derivative‐free Multivariate analysis program was used for computation. The differences between estimates for genotypes were checked using Student's t‐test. The model included the animal genotype, year‐season of calving and parity as fixed effects and the animal additive genetic effect and permanent environmental effect of individual cows as well as dates of the tests as random effects. Significant associations were found between the RFLP‐NlaIII and milk fat, protein and lactose contents. Also, a significant effect was shown of the defensin genotype on the somatic cell count in the milk.

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