Submitted to: Animal Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/7/2007
Publication Date: 10/1/2007
Citation: Gasparin, G., Miyata, L.L., Coutinho, L.L., Martinez, M.L., Teodoro, R.L., Furlong, J., Machado, M.A., Silva, M.V., Campos, A.L., Sonstegard, T.S., Regitano, L.C. 2007. Mapping of quantitative trait loci controlling parasite resistance in a F2 experimental bovine population. Animal Genetics. 38(5):453-459. Interpretive Summary: Mapping studies to identify quantitative trait loci (QTL) affecting health traits have been limited due to lack of phenotypic data. Characterizing these traits is critical to intensification of production in tropical environments. In this study, a crossbred experimental population optimized for mapping trait differences between tropically adapted dairy cattle and Holsteins was produced to identify regions of the genome conferring resistance or susceptibility to parasites (ticks and stomach worms) common to tropical production regions. Three novel QTL affecting tick resistance on chromosomes 5, 7, and 14 were identified. These QTL need further study to validate the findings. However, these results do provide the first evidence of tick resistance QTL, which will ultimately allow the introgression of disease resistance haplotypes into high production breeds of cattle. Moreover, these studies will provide new biological information on parasite resistance/susceptibility. Beyond affecting livestock health, understanding these traits also has potential impact on human health due to the potential reduced introduction of antibiotics and other drug residues into the food chain.
Technical Abstract: Since Bos taurus and Bos indicus cattle breeds have diverged at approximately 10.000 years ago, the differences in the process of domestication and subsequent selection for desired phenotypes is presumed to have contributed the phenotypic and genetic differences between these subspecies. Of particular interest is the phenotypic differences in resistance to disease. Generally, Bos taurus cattle are more susceptible to parasites than Bos indicus in tropical environments, and much of this difference is under genetic control. For these reasons we developed a B. taurus x B. indicus F2 experimental population to map quantitative trait loci for resistance to Boophilus microplus tick and to Haemonchus contortus and Cooperia spp. endoparasites. About 300 individuals have been measured for parasite load and analyzed for 23 microsatellite markers through interval mapping of chromosomes 5, 7 and 14. One suggestive chromosome-wide QTL (P< 0.05) in chromosome (Chr) 14 and two indicative regions (P < 0.10) in Chr 5 and 7 for resistance to tick were mapped. The additive effect of the QTL in Chr 14 corresponds to 3.18% of the total phenotypic variance observed. The results indicate that it is possible to conduct a QTL mapping approach to search for genome regions that control resistance to parasites on bovines. Validation of the results reported here in other populations will be necessary for future marker assisted selection.