Estimating myostatin gene effect on milk performance traits using estimated gene content for a large number of non-genotyped cows

The objective of this study was to estimate the myostatin (mh) gene's effect on milk, protein and fat yield in a large heterogeneous cow population, of which only a small portion was genotyped. For this purpose, a total of 13,992,889 test-day records derived from 799,778 cows were available. The mh gene effect was estimated via BLUP using a multi-lactation, multi-trait random regression test-day model with an additional fixed regression on mh gene content. Because only 1,416 animals were genotyped, more animals of additional breeds with assumed known genotype were added to estimate the genotype (gene content) of the remaining cows more reliably. This was carried out using the conventional pedigree information between genotyped animals and their non-genotyped relatives. Applying this rule, mean estimated gene content over all cows with test-day records was 0.104, showing that most cows were homozygous +/+. In contrast, when gene content estimation was only based on genotyped animals, mean estimated gene content over all cows with test-day records was with 1.349 overestimated. Therefore, the applied method for gene content estimation in large populations needs additional genotype assumptions about additional animals representing genetic diversity when the breed composition in the complete population is heterogeneous and only a few animals from predominantly one breed are genotyped. Concerning allele substitution effects for one copy of the mh' gene variant, significant decreases of -76.1 kg milk, -3.6 kg fat and -2.8 kg protein per lactation were obtaine genotype. Based on this result, knowledge of the mh milk performance traits in cattle d on average when gene content estimation was additionally based on animals with assumed known agenotypes and their effects has the potential to improve milk performance traits in cattle.