UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory
Beta Casein – A2 Genotyping
Introduction

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.

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The new test offered by the VGL 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
A1/A1
A1/A1
A1/B
A1/A1
B/B
A1/A1
A1/A2
A1/A2
A1/I
A1/A2
B/I
A1/A2
A2/A2
A2/A2
A2/B
A1/A2
I/I
A2/A2

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.
Breeds
# of animals
Beta casein variants
A1
A2
B
C
F
I
Brown Swiss
8
93.8
6.3
Devon
6
50.0
25.0
25.0
Dexter
78
32.7
60.3
6.4
0.6
Guernsey
6
8.3
75.0
16.7
Holstein
17
8.8
70.6
2.9
2.9
14.7
Jersey
40
6.3
65.0
17.5
11.3
Jersey Cross
15
16.7
56.7
26.7
Mini Jersey
14
21.4
50.0
25.0
3.6
Shorthorn
8
25.0
75.0

For more information about A2 Corporation and A2 Milk®, visit the A2 Milk Company Website

As a licensed laboratory, VGL is required to disclose the following:

VGL is an a2MC Accredited Tester. Beta Casein and A2/A2 Gene tests conform to the specification, and are validated to the standards, of The a2 Milk Company (a2MC). a2MC owns various intellectual property rights (including patent rights, trademarks, and technical and commercial know how) relating to the production and sale of milk with reduced beta casein A1, under the brand a2 MILK®.

It is possible that commercial use of test results may fall within the scope of such intellectual property rights and any person who intends to form a herd of animals used to produce and sell milk with reduced beta casein A1 should contact a2MC.

a2MC may access and use information from the VGL relating to the A2/A2 or Beta Casein Gene test carried out by the VGL for the purpose of, and limited to, milk supply.

References:

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. S Jianqin, X Leiming, S Lu, GW Yelland, J Ni and A Clarke. Nutrition Journal 2016:15-35.DOI: 10.1186/s12937-016-0147-z
https://nutritionj.biomedcentral.com/articles/10.1186/s12937-016-0147-z

A2 Milk, Farmer Decisions, and Risk Management. Woodford, Keith. 2007. Proceedings of the 16th International Farm Management Association Congress, Peer Reviewed Papers Vol2, pp 641-648. University College, Cork, July 2007. (Eds S. O’Reilly, M. Keane, P. Enright. ISBN:978-92-990038-3-1).
https://researcharchive.lincoln.ac.nz/handle/10182/417

Health implications of milk containing beta-casein with the A2 genetic variant. Bell SJ, Grochoski GT, Clarke AJ. Crit Rev Food Sci Nutr. 2006;46(1):93-100.
http://www.ncbi.nlm.nih.gov/pubmed/16403684

Polymorphism of bovine beta-casein and its potential effect on human health. Kaminski S, Cieslinska A, Kostyra E J. Appl. Genet. 2007;48(3):189-98.
https://www.ncbi.nlm.nih.gov/pubmed/17666771

 
Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL