Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2002
Publication Date: January 15, 2003
Citation: Olson, T.A., Lucena, C., Chase, C.C., Jr., Hammond, A.C. 2003. Evidence of a major gene influencing hair length and heat tolerance in Bos Taurus cattle. Journal of Animal Science. 81:80-90.
Interpretive Summary: The ability to maintain internal body temperature under heat stress is a valuable asset for cattle in subtropical and tropical regions of the world. While variation in heat tolerance among breeds and breed crosses has been studied for many years, relatively few efforts have been directed toward increasing our understanding of the mode of inheritance involved in heat tolerance. Previous studies have shown that Senepol cattle are equal in heat tolerance to Brahman cattle and that Senepol crosses with temperate breeds show heat tolerance comparable to Brahman crosses. Observations of hair coat types of progeny of Senepol crossbred cows mated to temperate breed bulls suggested that they were segregating into two categories, one group with very short, sleek hair coats like those of purebred Senepol and one group whose hair coats were typical of temperate cattle. Here we present data from Senepol crossbred cows and Carora cows (a milking cattle breed in Venezuela) that support the existence of a single, major, dominant gene that is segregating in their calves. Furthermore, rectal temperatures were lower in slick-haired Senepol crossbred calves and slick-haired Carora crossbred cows when compared to their normal-haired contemporaries. These data suggest that the incorporation of the slick gene into temperate breeds could have a major effect on productivity of cattle in warm climates, particularly fertility of dairy cows through increased embryo survival and greater milk production during periods of heat stress. Incorporation of slick hair into temperate breeds of beef cattle should allow them to be raised successfully under conditions with greater heat stress than was previously possible. This process of incorporation and use would be facilitated through knowledge of the location and molecular basis of the slick glue.
Evidence was found that supports the existence of a major gene (designated as the slick hair gene), dominant in mode of inheritance, that is responsible for producing a very short, sleek hair coat. Cattle with slick hair were observed to maintain lower rectal temperature (RT). The gene is found in Senepol cattle and also criollo (Spanish origin) breeds in Central and South America. This gene is also found in a Venezuelan composite breed, the Carora, formed from the Brown Swiss and a Venezuelan criollo breed. Two sets of backcross matings of normal-haired sire breeds to Senepol crossbred dams assumed to be heterozygous for the slick hair gene resulted in ratios of slick to normal-haired progeny that did not significantly differ from 1:1. Data from Carora x Holstein crossbred cows in Venezuela also support the concept of a major gene that is responsible for the slick hair coat of the Carora breed. Cows that were 75% Holstein:25% Carora in breed composition segregated with a ratio that did not differ from 1:1 as would be expected from a backcross mating involving a dominant gene. The effect of the slick hair gene on RT depended upon the degree of heat stress and appeared to be affected by age and/or lactation status. The decreased RT observed for slick-haired crossbred calves compared to normal-haired contemporaries ranged from 0.18 to 0.4 C. An even larger decrease in RT, 0.61 C (P < 0.01), was observed in lactating Carora x Holstein F1 crossbred cows even though it did not appear that these cows were under severe heat stress. The improved thermotolerance of crossbred calves due to their slick hair coats did not result in increased weaning weights, possibly because both the slick and normal-haired calves were being nursed by slick-haired dams. There were indications that the slick-haired calves grew faster immediately following weaning and that their growth during the cooler months of the year was not compromised significantly by their reduced quantity of hair. In the Carora x Holstein crossbred cows there was a positive effect of slick hair on milk yield under dry, tropical conditions.