Quantitative trait locus-by-environment interaction for milk yield traits on Bos taurus autosome 6

Abstract

Genotype-by-environment interactions for production traits in dairy cattle have often been observed, while QTL analyses have focused on detecting genes with general effects on production traits. In this study, a QTL search for genes with environmental interaction for the traits milk yield, protein yield, and fat yield were performed on Bos taurus autosome 6 (BTA6), also including information about the previously investigated candidate genes ABCG2 and OPN. The animals in the study were Norwegian Red. Eighteen grandsires and 716 sires were genotyped for 362 markers on BTA6. Every marker bracket was regarded as a putative QTL position. The effects of the candidate genes and the putative QTL were modeled as a regression on an environmental parameter (herd year), which is based on the predicted herd-year effect for the trait. Two QTL were found to have environmentally dependent effects on milk yield. These QTL were located 3.6 cM upstream and 9.1 cM downstream from ABCG2. No environmentally dependent QTL was found to significantly affect protein or fat yield.

Figure 1.—

Likelihood-ratio curves of milk yield with and without interaction with herd-year–milk-yield solution. In addition to a peak at ∼60 cM, which does not show interaction, six significant peaks (P < 0.0001) with significant interactions (P < 0.005) were found. Those are indicated with circles. Some common genes and markers are indicated as dots on the x-axis.

Figure 2.—

Likelihood-ratio curves for protein yield with and without interaction with herd year–protein yield. Three peaks were found close to the casein complex, but none of the peaks showed significant interaction. Some common genes and markers are indicated as dots on the x-axis.

Figure 3.—

Likelihood-ratio curves for fat yield, with and without interaction. Some common genes and markers are indicated as dots on the x-axis. No significant QTL for fat yield with interaction with herd-year–fat-yield solution was found.

Figure 4.—

The predicted solutions of the haplotypes of the two detected environmentally dependent QTL. Only haplotypes represented in the grandsires are presented. Each haplotype solution is presented as a linear function of the environmental descriptor herd year, to show how the haplotypes differ both in their general effect on milk yield and in their environmental sensitivity.