Tackling psoroptic mange susceptibility in Belgian Blue cattle by a genomic approach

Genomic tools, such as single nucleotide polymorphism (SNP) genotyping arrays, are nowadays commonly used in animal breeding and research. As they have become widely available and affordable, these SNP arrays allow the collection of genomic information from (breeding) animals to obtain better characterizations of our local livestock breeds. This PhD research covers three aspects of the use of SNP genotyping arrays in these local breeds: the proper use of genetic diversity metrics, the genetic diversity screening of a local sheep breed and two Belgian cattle breeds, and the use of SNP data for the examination of the genetic basis of a disease in Belgian Blue cattle: psoroptic mange.

First, it is important to define genetic diversity measures properly. One of the most common measures for genetic diversity assessment are runs of homozygosity (ROH). This PhD provides recommendations for ROH detection. Furthermore, ROH are commonly used to detect genomic regions with high levels of inbreeding, called ROH islands. In this PhD research, open access SNP genotypes of more than 440 different populations were collected to perform an ROH island analyses.

Second, SNP genotypes can be used to investigate the genetic diversity of local sheep and cattle populations. This PhD research studies and discusses the genetic diversity of the Belgian Milksheep and the Belgian Red and Belgian White Red cattle. As assessment of genetic diversity is vital for long-term breed survival, these results will aid their respective flock- and herdbooks to preserve genetic diversity

Third, SNP genotypes can also be used to screen the genetic basis of diseases or disorders in our local livestock breeds. This PhD research uses SNP genotypes to study the genetic architecture of psoroptic mange susceptibility in Belgian Blue cattle. This condition is widespread within the breed and results in a decrease in animal welfare and economic losses. As Belgian Blue cattle is more susceptible than other cattle breeds, it has long been suggested that there is a genetic basis for this (over)susceptibility. This PhD research has therefore shown that the nt821(del11) mutation in the myostatin gene (MSTN), that is responsible for double muscling, can be linked to an increased susceptibility to psoroptic mange. However, there may be other genetic factors that contribute to this predisposition. These are studied in this PhD research with a heritability analysis and a genome-wide association study.