Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 1997
Publication Date: N/A
Interpretive Summary: Genetic gain in dairy cattle has been based on progeny testing of potential sires, but progeny testing requires five years to complete and is not very effective for health and reproductive traits. Using DNA markers associated with genes affecting economically important traits, breeders may be able to naturally increase disease resistance without affecting gains in milk production. Using data from DNA markers, called marker-assisted selection, provides information for the selection of the best bulls. The main objective of this study was to identify DNA markers that would predict a low incidence of somatic cells (an indicator of disease) in milk. Fifteen DNA markers were studied in seven large U.S. Holstein families. Variations with some of these DNA markers were associated with significant effects for seven economically important traits--somatic cell score, milk yield, protein yield, protein percentage, fat yield, fat percentage and productive herdlife. Three DNA markers were associated with significant effects for several traits and may be useful in marker-assisted selection to reduce disease and increase milk and protein yields in some families.
Quantitative trait loci (QTL) affecting health and milk production traits were studied in seven large half-sib U.S. Holstein families using the granddaughter design. Selective genotyping was used as an initial screening of seventy-six microsatellite markers located throughout the genome, searching for potential QTL for somatic cell score. Following the initial search, markers segregating with significant effects were further studied by genotyping all available sons from the seven families. Genotyping for fifteen markers was completed and allele substitution effects across and within families were analyzed. Potential QTL for somatic cell score, fat yield, fat percentage, protein yield and protein percentage were identified. Three markers (BM203, BM4505 and BM2078) were associated with significant allele substitution effects for different traits and may be useful in marker-assisted selection in specific cfamilies. Comparisons between these data and previously identified QTL support the location of a QTL for milk yield and protein yield on chromosome 21.