Improved heat tolerance via a cooler hair coat is an emerging reality in the Holstein breed. The SLICK haplotype is a dominant trait that produces cattle with a short, sleek hair coat.
The trait is caused by a mutation in the prolactin receptor gene. The SLICK condition has origins in the Senepol breed in cattle located on St. Croix, US Virgin Islands. Tim Olson and his colleagues at the University of Florida used crossbreeding to introduce the gene into the U.S. Holstein breed.
The Florida team also has conducted research comparing Holsteins with the SLICK phenotype to wild-type cattle with normal hair coats. One study evaluated both thermoregulation ability during hot weather. All cows were housed in the same free stall barn with fans and sprinklers. They found vaginal temperatures to be significantly lower in SLICK cows compared to those with normal hair coats.
In a second study, all cows were moved to a dry lot in which the only heat-abatement measure was shade cloth. In that trial:
- Increases in rectal temperature and respiration rate caused by heat stress during the day were lower for SLICK animals compared to those with typical hair coats.
- Sweating rate also was higher for SLICK cows.
A third experiment looked at the effect of heat stress on milk yield. The Florida researchers concluded that heat stress in the summer had a detrimental effect on all animals, but the reduction in milk production was less severe in animals with the SLICK trait.Similar beneficial effects of the SLICK trait on milk yield during heat stress has been observed in Puerto Rico.
The University of Florida has been registering SLICK animals with the Holstein Association USA, and has initiated a breeding program to increase genetic merit of the SLICK population for economically important traits. The goal is to provide producers in hot climates, and those breeding for export markets, with semen from SLICK bulls to facilitate incorporation of the gene into their herds.
The first bull to be marketed in this program is Slick-Gator Blanco (551HO03574), whose semen is available from STGenetics. Blanco (NM$373) is heterozygous for the SLICK mutation, meaning only one of two copies of the prolactin receptor gene transmits the SLICK phenotype. Therefore, half of his offspring will be SLICK and half will have hair of normal length.
Semen now is available from a second SLICK-carrier bull, Slick-Gator Lone Ranger (HOUSA000144046164), marketed by A Legacy Genetics. This sire, with a NM$616, also is heterozygous for SLICK. The University of Florida is continuing to pursue the SLICK breeding program, developing sires that are homozygous for SLICK, so all of their offspring would have the short, sleek hair coat.
Among dairy cattle, SLICK genetics also have been incorporated into Holsteins in Puerto Rico, Holstein-Jersey-Senepol crosses in New Zealand, the Carora breed and the JR dual-purpose breed in Venezuela.
For more information about the SLICK program and Holstein bulls with the SLICK mutation, contact Pete Hansen at the University of Florida, firstname.lastname@example.org, 352/392-5590.