Genetic variants of beta-casein, a protein of cow's milk, can be classified into two groups, A1 and A2, based on the specific amino acid in position 67 of the protein. This A1/A2 group designation may be of interest to breeders developing herds for human health benefits.
$33 one test per animal
$73 DNA/A2/Diagnostic Package (includes DNA + A2 + 1 Diagnostic Test); $10 each additional test on same animal
The solids found in cow’s milk are composed of fat, protein, lactose and minerals. Beta-casein is one of six milk proteins and is produced by the CSN2 gene. Fifteen genetic variants of CSN2 are known which cause changes of certain amino acids in the beta-casein protein and alter its properties. Based on the amino acid in position 67 these variants can be classified into 2 groups - A1 and A2. Variants that belong to the A1 group (His67) are A1, B, C, F and G. Variants that belong to the A2 group (Pro67) are A2, A3, H1, H2, I, J, K and L. The levels of bioactive peptide beta-casomorphin 7 (BCM7) produced from the metabolism of beta casein is several-fold higher for variants in the A1 group than in the A2 group. Higher levels of BCM7 have been associated with negative health effects in humans.
This test identifies variants within the A1 and A2 groups thus providing a more detailed resolution of the beta casein gene in cattle. Breeders interested in developing herds for human health benefits should focus in selecting against variants of the A1 group (A1-free). Relative to levels of BCM7 production, variants within each group behave similarly but may differ in other properties.
The A2 genotyping test as specified by the A2 Milk Company classifies beta casein only according to the A1 and A2 group designation. The correspondence between the new VGL results and the group designation for common variants detected in cattle are provided below as an example. The same principle applies to other less frequent variants.
Table 1. Correspondence of genotypes between the new VGL test (variant-based) and A2 Milk Company nomenclature (group-based)
Variant based result
Group based equivalent
Table 2 below summarizes raw percentage frequency of variants observed among samples tested with the new VGL test. Breed classification is as provided with samples and may include crossbred animals if this information was not disclosed. Although the numbers may not represent actual frequency in breeds, the table provides information about which variants are observed and how common they may be in the different breeds.
Table 2. Percent frequency of beta casein variants among samples tested by the VGL. Frequencies may be biased as they are not based on random sampling of each breed.
Bell, S.J., Grochoski, G.T., & Clarke, A.J. (2006). Health implications of milk containing beta-casein with the A2 genetic variant. Critical Reviews in Food Science and Nutrition, 46(1), 93-100. doi: 10.1080/10408390591001144
Woodford K. (2007). A2 milk, farmer decisions, and risk management. In S. O’Reilly, M. Keane, & P. Enright (Eds.), Proceedings of the 16th International Farm Management Association Congress, Peer Reviewed Papers Vol2(pp. 641–648). Cork, Ireland: Cork University College. https://hdl.handle.net/10182/417
Kamiński, S., Cieślińska, A., & Kostyra, E. (2007). Polymorphism of bovine beta-casein and its potential effect on human health. Journal of Applied Genetics, 48(3), 189-198. doi: 10.1007/BF03195213
Jianqin, S., Leiming, X., Lu, X., Yelland, G.W., Ni, J., & Clarke, A.J. (2016). Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk. Nutrition Journal, 15:35. doi: 10.1186/s12937-016-0147-z