Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 1997
Publication Date: N/A
Technical Abstract: Quantitative trait loci (QTL) affecting economically important traits are currently being identified in dairy cattle. Some of these QTL will be used to implement marker-assisted selection in which genetic marker genotypes will be used to predict an animal's potential prior to progeny testing. The objective of this study was to identify QTL for calving ease and the type traits in seven large Holstein families using the granddaughter design. Sixteen microsatellite markers located on ten chromosomes were used to genotype grandsires and their sons using the granddaughters' phenotypic values as the trait endpoints. Using results analyzed within family, each of two markers (BM203, chromosome 27; BM1443, chromosome 23) was associated with a significant effect (P < 0.01) on calving ease in one family. Due to the large number of evaluated type traits, composite indices were used to identify potential QTL for the type traits. Four markers (located on different chromosomes) were associated with significant within-family effects (P < 0.001) on the feet and legs, dairy and udder composite indices in different families. Since many of the type traits are correlated, MANOVA was used to identify potential QTL for four groups of traits. The groups were identical to those used to calculate the composite indices. Two markers were associated with significant effects pooled across families (P < 0.01) for the MANOVA udder and body groups. After verification of these QTL, producers may be able to manipulate these QTL to improve calving ease and body conformation in these large Holstein families.