|Chase, Chadwick - Chad|
Submitted to: Florida Cattleman
Publication Type: Trade Journal
Publication Acceptance Date: 12/16/2006
Publication Date: 12/23/2006
Citation: Mariasegaram, H., Chase, C.C., Olson, T.A., Chaparro, J.X. 2006. Identification of a gene controlling hair coat and potentially heat tolerance in cattle. Florida Cattleman. December 2006; 71(3): 50,52,54.
Technical Abstract: Heat tolerance is an important trait in the subtropics and Senepol were shown to be as heat tolerant as Brahman and both were more heat tolerant than other temperate breeds (e.g., Hereford, Angus, Holstein). One characteristic that was evident was that the Senepol had a short, sleek hair coat. In fact a number of tropically adapted Criollo or native breeds such as the Romosinuano from Colombia and the Carora from Venezuela all seem to have a high frequency for this short, sleek hair coat trait. Additional observations from crossbreeding studies at STARS led us to conclude that the short, sleek hair coat trait appeared to be controlled by a single gene with a dominant mode of inheritance. We refer to this short, sleek hair coat trait as slick. In numerous studies it was shown that slick-haired animals had rectal temperatures 0.9 to 1.1 degrees F lower than contemporaries with normal hair coats in Florida during summer. In dairy production in the U.S., a generally more intensive industry, most efforts have been placed on modifying the environment rather than on introducing tropical adaptation per se. An alternative means of improving thermotolerance in these cattle is to introgress favorable genetics from other breeds, such as the Slick hair gene from Senepol into Holstein. Introgression of the slick gene was initially accomplished by the use of AI and embryo transfer. Currently we have 15/16 Holstein cows and bulls and 31/32 calves. Obviously an important unknown is whether slick haired cows will have greater productivity during hot summer months in Florida in terms of milk production and pregnancy rates as compared to their normal haired contemporaries. At STARS we were interested in utilizing molecular techniques to identify this Slick hair gene. One important reason is to employ marker-assisted selection to identify homozygous slick sires that will sire only Slick-haired progeny. Mapping a gene involves identifying the chromosome the gene is located on, and its position along that chromosome. Genetic markers are essentially DNA sequences that are variable between individuals that we can use to map a particular gene on a chromosome. We performed a scan of the bovine genome using the DNA pooling strategy and typed over 300 microsatellite markers. Results indicated that bovine chromosome 20 was the most likely candidate chromosome harboring the Slick hair gene. The Slick gene was more accurately positioned on chromosome 20 using additional individuals (from new families) and targeted microsatellite markers in order to identify those markers most tightly linked to the Slick gene. We found a strong association between at least two closely positioned markers on chromosome 20 and the slick haired phenotype. These results suggest a possible role in marker-assisted selection. Some Senepol bulls were tested using these markers and the results indicated excellent potential for identifying homozygous Slick bulls. The same gene also appears to be responsible for the slick hair coat in Romosinuano cattle.