African cattle represent a complex mosaic of Bos taurus (taurine) and Bos indicus (zebu) with most breeds containing varying levels of taurine-zebu admixture. The two types of cattle diverged at least 500,000 years ago and significant genomic differences have accumulated since that time. One important evolutionary adaptation in certain African taurine populations is a genetically determined tolerance to infection by trypanosome parasites (Trypanosoma spp.), which are transmitted by infected tsetse flies (Glossina spp.) and cause African animal trypanosomiasis (AAT) disease.
The annual financial burden of AAT is approximately $4.5 billion and AAT is one of the largest constraints to livestock rearing in the areas of sub-Saharan Africa with significant tsetse densities. The West African B. taurus N’Dama breed is trypanotolerant; they have the ability to control parasite loads and to limit disease pathology compared to trypanosusceptible zebu breeds. However, B. indicus or hybrid animals are generally larger, produce higher milk yields and are therefore favoured by many farmers. Using local ancestry analysis of genome-wide high-density SNP data, we have examined hybrid West African cattle populations to study subchromosomal admixture. These results are also integrated with gene expression data from bovine trypanosome infection studies to further explore the functional biology of differentially introgressed genomic regions.