|Murray, Gemma G.r.|
|Woolhouse, Mark Ej|
|Conradie Van Wyk, Ilana|
|Bronsvoort, Barend M De Cro|
Submitted to: Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2013
Publication Date: 11/9/2013
Citation: Murray, G., Woolhouse, M., Tapio, M., Mbole-Kariuki, M.N., Sonstegard, T.S., Thumbi, S., Jennings, A., Conradie Van Wyk, I., Kiara, H., Toye, P., Coetzer, K., Bronsvoort, B.S., Hanotte, O. 2013. Genetic susceptibility to infectious disease in East African Shorthorn Zebu: a genome-wide analysis of the effect of heterozygosity and exotic introgression. Heredity. 13:246. Interpretive Summary: Determining the genetic composition of indigenous cattle breeds in developing countries is a first step towards genetic improvement to meet global food security challenges. This study is a report on the correlation between genetic composition of East African Zebu cattle of Kenya with incidence of disease. Data collected from a full year of veterinary records were analyzed against 50,000 single nucleotide polymorphisms (SNPs) information across the genome. Of importance, indigenous cattle inheriting a portion of genome derived from European taurine were more likely to contract illness related to livestock disease. Inbreeding of indigenous cattle was also found to be a contributing factor affecting incidence of illness. Together, these results provide a basis to further investigate genes that confer animal survival and production capacity in the harsh extensive environments of Kenya. This information will be vital to developing DNA tools for accelerating genetic improvement in unimproved, indigenous cattle.
Technical Abstract: Positive multi-locus heterozygosity-fitness correlations have been observed in a number of natural populations. They have been explained by the correlation between heterozygosity and inbreeding, and the negative effect of inbreeding on fitness. Exotic introgression in a locally adapted population has also been found to reduce fitness (outbreeding depression) through the breaking-up of co-adapted genes, or the introduction of non-locally adapted gene variants. In this study we examined the relationships between genome-wide heterozygosity and introgression, and death and/or illness as a result of infectious disease, in a sample of calves from an indigenous population of East African Shorthorn Zebu (Bos primigenius) in western Kenya. These calves were studied from birth to one year of age, as part of the Infectious Disease in East African Livestock (IDEAL) project. Some of the calves were found to be genetic hybrids, resulting from the recent introgression of European cattle breed(s) into the indigenous population. European cattle are known to be less well adapted to the infectious diseases present in East Africa. Therefore, if death and illness as a result of infectious disease has a genetic basis within the population, we would expect both a negative association between introgression and fitness, and a positive association between heterozygosity and fitness. In this indigenous livestock population we observed a negative association between heterozygosity and death and/or illness as a result of infectious disease and a positive association between European taurine introgression and death and/or illness as a result of infectious disease. We observe the effect of both inbreeding and outbreeding depression in the East African Shorthorn Zebu, and therefore find evidence of a genetic component to vulnerability to infectious disease. These results indicate that the significant burden of infectious disease in this population could, in principle, be reduced by better breeding practices.