Effects of DGAT1 variants on milk production traits in German cattle breeds1

Abstract

Various QTL mapping experiments led to the detection of a QTL in the centromeric region of cattle chromosome 14 that had a major effect on the fat content of milk. Recently, the gene encoding diacylglycerol O-acyltransferase (DGAT1) was proposed to be a positional and functional candidate for this trait. This study investigated the effects of a nonconservative lysine to alanine (K232A) substitution in DGAT1, which very likely represents the causal mutation, on milk production traits. Existing granddaughter designs for Fleckvieh and German Holstein, the two major dairy/dual-purpose breeds in Germany, were used to estimate allele frequencies and gene substitution effects for milk, fat, and protein yield, as well as fat and protein content. A restriction fragment length polymorphism assay was applied to diagnose the K232A substitution in DGAT1. Estimates of the allele frequencies for the lysine-encoding variant were based on maternally inherited alleles in sons and amounted to 0.072 for Fleckvieh and 0.548 for German Holstein. Effects of DGAT1 variants on content traits were pronounced; estimates of the gene substitution effect for the lysine-encoding variant were 0.35 and 0.28% for fat content and 0.10 and 0.06% for protein content in Fleckvieh and German Holstein, respectively. Conversely, negative effects of the lysine variant of -242 to -180 kg for Fleckvieh and -260 to -320 kg for German Holstein were revealed for milk yield from first to third lactation, resulting in enhanced fat yield of 7.5 to 14.8 kg in Fleckvieh and 7.6 to 10.7 kg in German Holstein. For protein yield, however, mainly negative effects of -3.6 to 0.2 kg in Fleckvieh and -4.8 to -5.2 kg in German Holstein were observed. Pearson correlations between residuals of milk yield and content traits were decreased when omitting DGAT1 effects in the analysis, thereby indicating that DGAT1 contributes to negative correlations between these traits. Molecular tests allow for the direct selection among variants; however, the benefits of the alternative alleles depend on economic weights given to the different milk production traits in the breeding goal.

The Breeding Values of German Holstein Sires and the <i>DGAT1</i> Polymorphism

“…The intermediary heredity on the locus has been assumed. The present results are in accordance with those of THALLER et al (2003), , GRISART et al (2002), WINTER et al (2002), and WELLER et al (2003. Based on the paper and repeated results of other authors, the locus of DGAT1 is of great significance in breeding.…”

“…Afterwards, the frequency rose by selection, since from the 50s´ milk fat has been prefered. THALLER et al (2003) give the frequency of the allelic variant coding for Lysine in the German Holstein of 0.548; similarly PAREEK et al (2005) found in young sires of Polish Black and White cattle, traditionally upgraded with the American Holstein breed, a frequency of the allele DGAT1 K of 0.68, in sires in artificial insemination of 0.60, and in cows of 0.48; rather more than in our groups. By contrast, WELLER et al (2003) in Israeli Holstein cows give a frequency of 0.09, in sires of 0.16.…”

“…However, the breeding value for fat yield was almost the same in Lysine/Lysine homozygotes and Lysine/Alanine heterozygotes, and the protein yield was not significantly higher in the Discussion Because there was in both old and young sires a high breeding value for milk yield and a negative value for fat content in the homozygotes for the Alanine variant, the DGAT1 polymorphism may contribute to the negative correlations between the traits, similarly but more weakly for the protein content. THALLER et al (2003) also refer to this. It is also in accordance with SPELMAN et al (2002), where the polymorphism increased milk fat, and decreased milk protein yield and milk volume in the breeds analysed by them.…”

Genetic variability of milk fatty acids

“…Situated on BTA14, the DGAT1 gene encodes 489 amino acids and comprises 17 exons. By sequencing the bovine DGAT1 gene, a non-conservative lysine to alanine substitution was observed at position 232 (K232A) and seems to influence the major milk production traits, such as milk yield and milk composition (Grisart et al 2004;Thaller et al 2003;Winter et al 2002). Winter et al (2002) observed that the lysine variant is associated with greater milk fat content than the alanine variant.…”

Multiple Quantitative Trait Loci Mapping With Cofactors and Application of Alternative Variants of the False Discovery Rate in an Enlarged Granddaughter Design

“…The effect of this mutation was highly significant for all milk production traits in and then the all hypotheses i with i Յ î will be rejected. This procedure guarantees that FDR Յ (m 0 /m )q (Benjamini and German Holsteins (Thaller et al 2003), with a substan- between 0.36 and 0.9 genetic standard deviations. The estimated widths of the confidence intervals (Ta-…”