The relevance of milk protein polymorphisms for dairy cattle breeding
1992
Bovenhuis, H.
An isoelectric focusing method is described that is suitable for phenotyping a large number of milk samples due to its short separation time and its high capacity. To estimate milk protein gene frequencies for breeds represented in the crossbred population and to estimate the fraction of animals misclassified a maximum likelihood model was developed. The estimates revealed that Dutch Friesians and Holstein Friesians differ for β-casein and β-lactoglobulin gene frequencies. Associations between milk protein genotypes and milk production traits were estimated using an animal model. Results from the present study and from literature indicate that the <em>K</em> -casein gene or a very closely linked gene affects protein percentage, and the β-lactoglobulin gene or a very closely linked gene affects fat percentage. A maximum likelihood model was constructed to estimate effects of both a marker gene and linked quantitative trait locus (QTL) on quantitative traits in segregating populations. Significant effects of QTLs linked to βB-casein, <em>K</em> -casein and β-lactoglobulin on fat percent were found. The effects of selection for <em>K</em> -casein and β-lactoglobulin genotypes were studied by using stochastic simulation of a closed adult MOET nucleus breeding scheme. Results showed that selection for <em>K</em> -casein and β-lactoglobulin genotypes has the potential to increase selection response.
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