MAPPING ECONOMIC TRAIT LOCI FOR SOMATIC-CELL SCORE IN HOLSTEIN CATTLEUSING MICROSATELLITE MARKERS AND SELECTIVE GENOTYPING

Marker-assisted selection (MAS) uses genetic marker genotypes to predi ct an animal's production potential and will provide additional select ion information for progeny testing. With the discovery of highly poly morphic microsatellite markers, the tools now exist to begin the searc h for economic trait loci (ETL), which is the first step toward MAS. T he objective of this study was to identify ETL for somatic cell score in an existing Holstein population. Using the granddaughter design, so ns from seven grandsire families were genotyped with 20 autosomal micr osatellites from five chromosomes (4, 8, 13, 17, 23), with an emphasis on chromosome 23, which is the location of the bovine major histocomp atibility complex (BoLA). Selective genotyping was used to reduce the number of genotypes required, in which the 10 highest and 10 lowest so ns from the phenotypic distribution curve were tested (140 sons in sev en families). One marker (513), located near BoLA, showed evidence of an ETL in three of five polymorphic families. Additional sons were gen otyped from the five families to estimate the effect and to compare se lective and 'complete' genotyping. Both methods detected an ETL at mar ker 513, but in different families. This study provides evidence of th e usefulness of microsatellite markers and the granddaughter design in the detection of ETL; however, additional markers need to be evaluate d to determine the usefulness of selective genotyping. Based on the re sults from the 20 studied markers, the most likely position of a somat ic cell score ETL lies near marker 513, located on chromosome 23.