Student - June 21, 2007

Genes determine milk fat composition

The hereditary characteristics of cattle determine to a large extent the fat composition of cow’s milk. This has been shown in a large-scale research project involving two thousand cows on four hundred Dutch dairy farms. The results will be published in the Journal of Dairy Science and Animal Genetics.

‘If we talked about our research, most people’s first response was that fat composition was largely determined by feed composition,’ tells Jeroen Heck of the Product Design and Quality Management Group, who measured the fat composition of the milk. Marianne Stoop of the Animal Breeding and Genomics Centre took the fatty acid composition values found in the milk and looked at the pedigrees of the cows involved in the research project. It became clear that there was a genetic component in the composition: there were considerable differences in composition between the different families.

Her colleague Anke Schennink then examined the DGAT-1 gene in the cows’ DNA profile. It was already known that this gene is important for the percentage of fat in the milk. However the gene turned out not only to be involved in the fat content, but also in the composition of the fat.

The researchers looked at all the different fatty acids found in milk, of which unsaturated fatty acids are regarded as more healthy for humans. One of the research results is that cows with a higher fat percentage in their milk produce relatively more saturated fatty acids.

Professor Johan van Arendonk, who is leading the Milk Genomics research project, says that the knowledge that the fat composition of the milk is genetically determined can be used in breeding. An important advantage shown up by the research is that the DNA profile of the bull can be used to predict the fat composition of the daughters’ milk. That means that milk composition can be managed without having to carry out expensive analyses, as is the case at present. Analysis costs 25 euros per sample. The dairy industry in turn can produce milk with different fat compositions for specific groups.

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