Abstract:
Several Breeders within the Bonsmara cattle breeders’ association have been selecting for polledness otherwise known as the trait for the genetic absence of horns. There are less costs associated with polled animals, as they require less management input than horned animals. International stud breeders are willing to pay a premium for Bonsmara stud animals certified as homozygous polled, and Bonsmara breeders therefore requested a study for the identification of polled status, using DNA markers. Several microsatellite markers were tested in a linkage analysis on a number of Bonsmara families originating from three polled herds. All of the markers tested in the final Twopoint linkage analysis showed significant linkage with the polled trait. This indicates that the current model proposed for the gene action of polledness is applicable to the Bonsmara breed. Furthermore, by using the Transmission disequilibrium test (TDT), an allele of one of these microsatellites was found to be strongly associated with the polled trait. Due to an inherent lack of phase-known, three-generation families, tracing this allele through the test pedigrees to determine polled status was not possible. These results indicate that phase-known family data must be available so that microsatellite markers linked to the Polled trait can be traced visually to differentiate homozygote polled animals from heterozygote polled animals. Microsatellite markers are a tool that can add additional information in the conclusive determination of Polled status, but cannot as yet be used in isolation to test for polledness in the South African Bonsmara breed. Copyright
