Submitted to: Preventive Veterinary Medicine
Publication Type: Review Article
Publication Acceptance Date: December 28, 2001
Publication Date: N/A
Interpretive Summary: Selection based on calculated genetic merit has tremendously improved production in dairy cattle. Genetic improvement especially for lowly heritable animal health traits could be accelerated by directly selecting upon the molecular genetic differences by marker-assisted selection (MAS). To implement MAS, the causative genetic variation for phenotypic differences in economically important traits must be located in the genome. Quantitative trait loci (QTL) have been detected in U.S. Holstein grandsire families using the granddaughter design and analysis of variance. Selection for QTL, like those identified for dairy form, could be beneficial to producers because of the genetic correlation with metabolic disease and dairy form. The validation and characterization of dairy form QTL will be used as a model for developing other QTL- marker selection schemes that will benefit the dairy industry in a reliable manner. As an aid to identifying the genes underlying dairy- related QTL, expressed genes are being characterized. Information obtained from these gene sequences will be used to increase gene marker density near QTL, identify genetic pathways important for animal production and udder health, and find positional candidate genes underlying QTL.
Technical Abstract: Production in dairy cattle has been improved tremendously through selection based on calculated genetic merit. Hypothetically, genetic improvement could be accelerated even further by directly selecting upon the molecular genetic differences underlying economically important traits, especially those involved in animal health and disease resistance where estimated breeding values lack accuracy or availability. The genomic locations of important quantitative trait loci (QTL) associated with production and linear type traits have been detected in U.S. Holstein grandsire families. Before this information can be used by the dairy industry for reliable and accurate selection, QTL containing intervals need to be better resolved and characterized in relevant populations to determine the economic value of potential marker-assisted selection schemes. Two methods that can be used to further investigate potential QTL include increasing DNA marker density near QTL and analyzing QTL in extended pedigrees. Increasing genotypic and phenotypic information overcomes QTL interval refinement limitations inherent in historic experimental populations of dairy cattle. Furthermore, QTL inheritance can be traced from historic families of interest to current generations relevant to the industry to better estimate allelic frequency and effect. To complement QTL mapping studies, genes expressed in cattle have been sequenced and mapped. This information can be used to increase gene marker density near QTL, elucidate genetic pathways important for animal production and health, and identify positional candidate genes that may contain the causative genetic variation underlying dairy-related QTL.