Genetic estimates and genome-wide association studies of antibody response in Tanzanian dairy cattle

Abstract

Identifying the genetic determinants of host defence against infectious pathogens is central to enhancing disease resilience and therapeutic efficacy in livestock. Here we have taken a genome-wide association approach to identify genetic variants associated with the presence of serological markers for important infectious diseases affecting dairy cattle in smallholder farms. Assessing 668,911 single-nucleotide polymorphisms in 1977 crossbreed cattle sampled from six regions of Tanzania, we identified high levels of interregional admixture and European introgression which may increase infectious disease susceptibility relative to indigenous breeds. Heritability estimates ranged from 0.03 (SE {+/-} 0.06) to 0.44 (SE {+/-} 0.07) depending on the pathogen assayed. Preliminary genome scans revealed several loci associated with seropositivity to the viral diseases Rift Valley fever and bovine viral diarrhoea, the protozoan parasites Neospora caninum and Toxoplasma gondii, and the bacterial pathogens Brucella sp, Leptospira hardjo and Coxiella burnetti. The associated loci mapped to genes involved in immune defence, tumour suppression, neurological processes, and cell exocytosis. We discuss future work to clarify the cellular pathways contributing to general and taxon-specific infection responses and to advance selective breeding and therapeutic target designs.