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Effects of milk protein variants on the protein composition of bovine milk

J. M. L. Heck^*,1,2, A. Schennink^,2, H. J. F. van Valenberg^*, H. Bovenhuis, M. H. P. W. Visker, J. A. M. van Arendonk and A. C. M. van Hooijdonk^*

^* Dairy Science and Technology Group, Wageningen University, PO Box 8129, 6700 EV Wageningen, the Netherlands
Animal Breeding and Genomics Centre, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands

¹ Corresponding author: jeroen.heck{at}wur.nl

The effects of β-lactoglobulin (β-LG), β-casein (β-CN), and -CN variants and β--CN haplotypes on the relative concentrations of the major milk proteins -lactalbumin (-LA), β-LG, _S1-CN, _S2-CN, β-CN, and -CN and milk production traits were estimated in the milk of 1,912 Dutch Holstein-Friesian cows. We show that in the Dutch Holstein-Friesian population, the allele frequencies have changed in the past 16 years. In addition, genetic variants and casein haplotypes have a major impact on the protein composition of milk and explain a considerable part of the genetic variation in milk protein composition. The β-LG genotype was associated with the relative concentrations of β-LG (A » B) and of -LA, _S1-CN, _S2-CN, β-CN, and -CN (B > A) but not with any milk production trait. The β-CN genotype was associated with the relative concentrations of β-CN and _S2-CN (A² > A¹) and of _S1-CN and -CN (A¹ > A²) and with protein yield (A² > A¹). The -CN genotype was associated with the relative concentrations of -CN (B > E > A), _S2-CN (B > A), -LA, and _S1-CN (A > B) and with protein percentage (B > A). Comparing the effects of casein haplotypes with the effects of single casein variants can provide better insight into what really underlies the effect of a variant on protein composition. We conclude that selection for both the β-LG genotype B and the β--CN haplotype A²B will result in cows that produce milk that is more suitable for cheese production.

Key Words: milk protein composition • protein variant • casein haplotype • dairy cow

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				A. M. Caroli, S. Chessa, and G. J. Erhardt Invited review: Milk protein polymorphisms in cattle: Effect on animal breeding and human nutrition J Dairy Sci, November 1, 2009; 92(11): 5335 - 5352. [Abstract] [Full Text] [PDF]

				G. C. B. Schopen, J. M. L. Heck, H. Bovenhuis, M. H. P. W. Visker, H. J. F. van Valenberg, and J. A. M. van Arendonk Genetic parameters for major milk proteins in Dutch Holstein-Friesians J Dairy Sci, March 1, 2009; 92(3): 1182 - 1191. [Abstract] [Full Text] [PDF]