The value of increased heterozygosity in dairy cattle
Today mating decisions are mostly based on pedigree information. However, genomic information could be used to minimize inbreeding or increase heterozygosity in mating decisions, because it contributes with more information on the expected heterozygosity (He) than pedigree information. The underlying hypothesis is that the more heterozygous the offspring of a mating is, the larger the dominance effect and less inbreeding depression in purebred offspring. The purpose of this study was to estimate the size of He using SNP marker information and further the effect of increased heterozygosity on milk, fat and protein yield in Holstein (HOL), Red Dairy Cattle (RDC) and Jersey (JER) cows.
He was calculated SNP by SNP for all couples of genotyped parents. Genome-wide He was calculated as the mean heterozygosity over all the SNPs.
Data from 5,423 HOL, 2,245 RDC and 5,975 JER genotyped cows born between 2015 and 2017, which all had parents with GEBV were analyzed. The mean He levels were 0.328 for HOL, 0.336 for RDC and 0.308 for JER with standard deviations between 0.007 and 0.008.
Results showed a significant effect of He on milk, fat and protein for all breeds. For HOL, a 1%-point increase in He corresponds to an increase in 305 days yield of 122 kg milk, 3.7 kg fat and 3.7 kg protein. For RDC the effect was 99 kg milk, 2.9 kg fat and 2.9 kg protein per heterozygosity percentage point. For JER the effect was 42 kg milk, 3.2 kg fat and 1.8 kg protein per heterozygosity percentage point. This indicates that it could be beneficial to include He in the mating plan decisions.
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