Analysing the genetic basis of milk production traits.

Abstract

Abstract Genetic analyses of milk production traits have been based on a polygenic model that assumes that a trait is affected by an infinitesimal number of genes each with a very small effect. An updated review on the genetic parameters (heritabilities and genetic correlations) for milk components estimated using the polygenic model is provided in this review. There are many studies reporting estimates of genetic parameters for component yields of milk, fat and protein and concentrations of fat and protein. Few studies have considered lactose yield and percentage. A limited number of studies have reported estimates of genetic parameters for milk fat and protein composition. At the start of the new millennium, advances in DNA technology permitted the sequencing of bovine genome, the identification of large numbers of genetic markers across the genome in the form of single nucleotide polymorphisms (SNP) and the genotyping of thousands of these SNPs on individual animals at low costs. Based on these advances, genomic selection emerged as a new methodology to perform genetic analysis and estimate breeding values for milk production traits using genome-wide dense markers. Systems biology is becoming the new method to perform genetic analysis of milk production traits integrating results from genomics, transcriptomics, proteomics, metabolomics and bioinformatics studies. A conclusion from this review is that the genetic analysis of milk production traits has been changing dramatically during recent years from a polygenic infinitesimal model towards a systems biology approach.