Copy number variation (CNV) is defined as large-scale deletions or gains of DNA fragments. CNVs can have a large effect when they are present in gene or in regions of regulatory elements. In livestock, CNVs have been studied for their possible association with economically important traits such as milk production and fertility.
The study highlighted possible associations between effective population size and CNV distribution in cattle breeds. Additionally, the study also concluded that CNV might be playing an important role in exhibition of traits related to immunity, olfaction, and coat colour.
The study reported differences in abundance of CNV counts between European cattle breeds. Cattle from British Isles, Balkan and Italian regions, on average, displayed higher abundance of CNV counts than Dutch or Alpine cattle. Many CNVs were partially or completely shared between cattle from the different regions indicating low population differentiation. These results were attributed to differential effective population size and selection pressure that exists between European cattle breeds. It was, however, noted that this hypothesis needs further validation using a large sample size.
The enrichment of CNVs in the immunity related genes may partially explain the immune response variability between different breeds to certain diseases. Additionally, genomic re-arrangement involving duplication of genetic segment, which was first reported in Belgian blue cattle and associated with coat colour-sidedness, was identified in English longhorn (EL) cattle.