Genes involved in bovine milk-fat composition
2009
Schennink, A.
The aim of the research described in this thesis was to identify genes that underlie the genetic variation in bovine milk-fat composition. The fat composition of milk samples from approximately 2,000 Dutch Holstein Friesian cows in their first lactation was measured by gas chromatography. Quantitative genetic analysis showed substantial genetic variation in milk-fat composition: heritabilities were high for short and medium chain fatty acids and moderate for long chain fatty acids. We demonstrated that polymorphisms in the DGAT1 and SCD1 genes had clear influence on milk-fat composition and explained large part of the genetic variation in milk-fat composition. Sequencing of the coding regions of SCD1 in a number of animals representing 6 dairy cattle breeds, buffalo, goat and sheep identified new polymorphisms within and between species. In addition to these 2 major genes, polymorphisms in 5 other genes were shown to affect bovine milk-fat composition. To identify chromosomal regions linked to variation in milk-fat composition, without any prior knowledge on genes or functions, a genome-wide scan was performed. Quantitative trait loci (QTL) were detected for short and medium chain fatty acids on 4 chromosomes, and QTL were detected for long chain fatty acids on 3 chromosomes. Furthermore, effects of DGAT1 and SCD1 genotypes on conformation traits in the Dutch Holstein Friesian cattle population were analyzed and suggested an association between DGAT1 genotype and conformation traits related to body size. We conclude that selective breeding could make a significant contribution to change the fat composition of cow’s milk, and that selective breeding can capitalize on genotypic information.
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