|Rexroad Jr, Caird|
Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/1996
Publication Date: N/A
Interpretive Summary: Mastitis is an important dairy disease leading to decreased milk production and increased veterinary care, costing the industry approximately $2,000,000,000 a year. At the genetic level, there is an association between mastitis and milk production, arousing concern that continued selection for milk production may increase the incidence of mastitis. Using DNA markers, animal breeders may be able to naturally decrease mastitis indidence without affecting gains in milk production. Marker-assisted selection provides information for the selection of the best bulls. The objective of this study was to identify DNA markers that would predict a low incidence of somatic cells (an indicator of mastitis) in milk. Five chromosomes were studied in seven three-generation families. One DNA marker on chromosome 23 showed evidence of an association with somatic cell score in three of our seven families. Additional animals from these families were studied, supporting the conclusion of the association between the chromosome 23 DNA marker and somatic cell score. Based on the results from the five studied chromosomes, the most likely position of a DNA marker that may be useful in reducing mastitis incidence is on chromosome 23.
Technical Abstract: Marker-assisted selection (MAS) uses genetic marker genotypes to predict an animal's production potential and will provide additional information for progeny testing. With the discovery of highly polymorphic microsatellite markers (ms), the tools now exist to begin the search for economic trait loci (ETL), which is the first step toward MAS. The objective of this study was to identify ETL for somatic cell score (SCS) i an existing Holestin population. Using the granddaughter design, sons from seven grandsire families were genotyped with twenty ms from five chromosomes (chr. 4,8,13,17,23), with an emphasis on chr. 23, which is the location for the major histocompatibility complex (BoLA). Selective genotyping was used to reduce the number of genotypes needed, in which the ten highest and lowest sons from the phenotypic distribution curve were tested (140 sons). One marker (513), located near BoLA, showed evidence of an ETL across 3 of 5 polymorphic families. Additional sons available from the Dairy Bull DNA Repository semen bank were genotyped from the 5 families to estimate the effect and to compare selective and "complete" genotyping. Both methods detected an ETL at marker 513, but in different families. This study provides evidence of the usefulness of ms and the granddaughter design in the detection of ETL, however, additional markers need to be evaluated to determine the usefulness of selective genotyping. Based on the results from the twenty studied markers, the most likely position of the SCS ETL lies near marker 513, locatedon chr. 23.