| Abstract: | The substitution of lysine for alanine (K232A) in the acyl-CoA-diacylglycerol acyltransferase, which is encoded by the DGAT1 gene, was tested for the significance for breeding evaluation of stud bulls of the holsteinized Black-and-White breed. The breeding value (deviation of milk productivity in daughters compared with cows of the same age) was estimated by the DYDC (daughter yield deviation to contemporary) method with modification. The frequency of allele 232K in the bulls examined was 0.28, lower than in Holstein bulls (0.4-0.6). The greatest effect of the A232K substitution was observed for the percent fat content in milk (1.4 sigma) and milk yield (0.76 sigma), and a lower effect was established for the milk protein yield (0.47 sigma) and percent protein content in milk (0.44 sigma). In the case of milk fat yield, the effect was nonsignificant. A method was proposed for converting the data on fat yield in order to obtain significant results in this case as well. The effect of the A232K substitution was estimated at 154 kg for milk yield, 2.8 kg for protein yield, 0.079% for percent fat content, and 0.015% for percent protein content. The results are discussed in the context of multiple pleiotropic effects of the K232A substitution in the DGAT1 gene. It is proposed that the K232A substitution of the DGAT1 gene be used as a golden standard in comparisons of the effect on milk productivity for the total gene set. This approach will allow a meta-analysis of the gene effects in spite of the differences in dairy cattle breeds and methods used to analyze their breeding value. In view of more than 30-year experience of using sperm of Holstein stud bulls, including those bred in North America, it was noted that the effect of the A232K substitution on milk productivity traits agreed well with the data reported for the North American commercial population of Holstein cattle. |
