MTT Agrifood Research Finland and the University of Liège, Belgium, have worked together successfully in locating a gene that regulates the total yield and protein and fat content of milk.
The scientists found a variation in the growth hormone receptor gene in the bovine chromosome 20. The variation in the receptor gene is associated with a major effect on milk yield and composition in Ayreshire, Holstein and Jersey cows.
Dr Johanna Vilkki of MTT said that developing associated markers for genes that affect milk traits is not highly prioritised in breeding since it is relatively easy to improve these traits by conventional selection.
The value of the finding is of great scientific interest and could also have significant impact on the dairy industry. This is the second time that a clear quantified association has been demonstrated between a single gene and bovine milk production. The MTT group is currently fine-mapping the genes that affect cows' susceptibility to mastitis. This is of interest to cattle breeders, since traits sensitive to environmental effects, such as disease resistance, are difficult to improve by conventional methods, and for economic and welfare reasons the eradication of mastitis is an important goal for dairy cattle breeders.
The present discovery will help breeders select bulls siring daughters with more economical milk production.
The 'water' version of the gene results in a 200 kg increase in annual production per cow, respectively decreasing the fat and protein content. The more cost-effective version of the gene will increase the average protein content in milk by 0.06 percentage units and the fat content by 0.15 percentage units, albeit at the expense of total milk yield. In 2002 the annual yield of the Finnish Ayrshire cow was 7,381 kg of milk with fat per cent of 4.36 and protein per cent of 3.36. According to Dr Vilkki, the vast majority of Finnish Ayrshire cattle are already carrying the more advantageous form of the gene.
The study, launched in 1999, was part of the EU biotechnology programme project EURIBDIS, in which altogether six European research groups cooperated. The sparse mapping of the entire genome of the Finnish Ayrshire, completed by MTT about two years ago, provided the basis for the present study.
MTT is a co-applicant in an international application for a patent for the use of the variation in the sequence of the growth hormone receptor gene in selection for milk-composition. There is only one comparable patent anywhere in the world, and that is also a result of work by the same international research group.
Simultaneously with the milk gene discovery, MTT's researchers have developed a method allowing diagnosis of the gene variants from a bovine embryo biopsy. This allows the results to be immediately applied in the ASMO breeding programme, where selection is enhanced by extensive use of embryo transfer.