Inbreeding depression is a reduction in performance or health due to the mating of closely related individuals. The overall aim of this study was to investigate the level of inbreeding in the Italian Holstein dairy cow breed and quantify its negative effect on productive performances. The level of inbreeding was estimated by pedigree (FPED) and genomic data by looking at stretches of homozygosity (FROH). Both methods revealed a reduction in milk yield, fat yield, and protein yield when inbreeding increased. Moreover, the study demonstrated that FROH was able to capture more inbreeding depression compared to FPED. In addition, the more recent inbreeding had a stronger negative impact on productive performances compared to ancestral ones. Then, since the amount of runs of homozygosity can vary across the chromosomes of an individual, the effect of each chromosomal homozygosity region on productive traits was also evaluated. The chromosome-level results might be included in breeding programs to limit the accumulation of homozygosity in particular regions that appear to have a more detrimental effect on productive traits. Overall, this study highlights the importance of avoiding inbreeding in animal breeding programs to keep productive animals in the long term.

Read the full article in the Journal of Animal Science.