Unravelling and Exploiting Genetic Variation in Milk Quality Traits

Genetic variation within a population provides the basis for genetic improvement of the population. Little is known about the extent of or the basis of genetic variation in milk-quality traits. The release of the first draft of the dairy cattle genome opens new opportunities to uncover more information about individual genes and their effect on important traits in cattle. The outline is presented of the Dutch Milk Genomics Initiative to identify genes that contribute to natural genetic variation in milk-quality traits, in particular in milk-fat and milk-protein composition. The objective of the research is to provide tools for improved breeding programs to exploit natural genetic variation in milk-quality traits and to provide knowledge needed for innovative dairy products.

The collection and analysis of milk and DNA samples on 2000 individual cows of the Dutch Holstein-Friesian population was started in January 2005. Quantitative genetic methods have been used to estimate the amount of genetic variation in traits. This analysis also provides insights in genetic correlations between traits. This information can be used to predict consequences of breeding strategies. Molecular markers can be used to detect chromosomal regions (QTL) that contribute to the genetic variation in a trait. The principles of this approach will be presented. The advantages and disadvantages of using different types of markers (microsatellites or SNPs) in a whole genome scan have been compared. The program builds on the combined expertise that has been developed and successfully applied to identify QTL affecting production and functional traits in dairy cattle and other farm animals. Opportunities to exploit the genetic information in breeding schemes are discussed. The program aims to create knowledge on the genetic variation in milk composition with knowledge of the relevance of milk composition for processing and human health.