The Breeding Values of German Holstein Sires and the DGAT1 Polymorphism

Abstract. The effect of the genotypes and alleles at nucleotide positions 10433 and 10434 of the DGAT1 gene on the breeding values for milk performance of German Holstein sires born in 1993 (n=66), and in 1998-2001 (n=200) was analyzed. The differences in breeding values had in both years the same trend.

In the younger sires, the breeding value for fat percentage was higher by 0.42 % in the Lysine homozygotes compared to the Alanine homozygotes (P<0.001). A higher milk breeding value in the Alanine homozygotes (811 kg) was found compared to the Lysine homozygotes (256 kg) (P<0.001), and the fat yield breeding value was higher in the Lysine sires (DGAT1^K/DGAT1^K 29.6, DGAT1^A/DGAT1^A 15.9). The breeding value for the protein percentage was higher in the sires carrying the Lysine variant (0.02) than in the Alanine homozygotes (- 0.03, P<0.05), and the protein yield was higher in the Alanine homozygotes (DGAT1^K/DGAT1^K 10.9, DGAT1^A/DGAT1^A 25.0, P<0.001). Because of the high emphasis of the index on the protein yield, the relative breeding value for milk was 110 among Alanine homozygotes, and 104 among Lysine. Comparing old and young sires, the genetic background against which the effect of DGAT1 is evaluated has changed. The selection on breeding value for protein yield increased the prevalence of DGAT1^A/DGAT1^A genotypes in protein and milk yield, and in relative breeding value for milk. In the old group, there was the highest protein yield in the heterozygous sires DGAT1^KA, it could be explained by another genetic background of the tested female population. Because the breeding value for fat percentage of heterozygous sires has lain within the values of homozygotes in both old and young sires, we assume the intermediary heredity on the locus. The differences of genotypic and allelic frequencies among old and young sires were not significant, however, there was certain tendency of increase of allele A (0.60 old sires, 0.64 young). On the results of this paper, the locus of DGAT1 offers information for evaluation of breed animals.