Abstract:

Over the last half century, new artificial insemination technology, methods for genetic evaluation, and breeding material from other countries have been introduced in Swedish cattle breeding. In this study, we aimed at investigating changes in homozygosity and genomic inbreeding over time in commercial dairy breeds. Genotype data from 50K and 150K SNP arrays for in total 5,636 Swedish Red and 3,115 Swedish Holstein bulls born 1956-2015 were analysed. The highest levels of both average homozygosity and inbreeding coefficient based on runs of homozygosity were seen in the earliest period of the data, although rapidly decreasing until the 1980s. After a period of more stable estimates, the inbreeding coefficients increased in both breeds after the introduction of genomic selection around 2010. Principal component analysis of relatedness showed a gradual transition over time for both breeds, but most pronouncedly for Swedish Holstein that was much influenced by foreign Holstein bulls.