How to Test Bulls and Cows for the Beta Casein Gene Variants

Dr. A. SamadAlthough there is weak scientific evidence about the benefits or ill effects of A1-casein milk but due to aggressive marketing world over consumers are shifting to A2 milk. The consumers should understand some basic facts about the issue. As the name indicates the expression of A2 or A1 type casein in milk will depend on two gene variations or alleles A1 and A2. Hence in cow and bull population you will encounter three types of genes, A1A1, A1A2 and A2A2 for casein protein. Normally the alleles are either recessive or dominant. The dominant allele will express itself even in the presence of recessive allele whereas a recessive allele can express only if both alleles in a gene are recessive. In case of A1/A2 however it is different. When present both can be co-expressed. For example, if a cow is of A1A1 type then it will produce only A1 milk, whereas a cow with A1A2 genotype will yield milk containing both A1 and A2 beta casein (probably in equal proportion). Likewise, cow with A2A2 genotype will yield milk with only A2 variety of casein. An A2 milk can be classified only when the genotype of cow is A2A2.

What test is done?

It is a simple genetic test called polymerase chain reaction or PCR. The test is done in a lab wherein DNA of the animal to be tested is mixed with specific primers that make multiple copies of the gene which can be then separated on gel and compared with standards.

What material is required? Any tissue such as blood, milk or hair can be sent to the lab.  Since hair can be stored for long period a bunch of hair with follicles is enough.

Which laboratories do these tests: For details visit our website www.indiancattle.com and search for diagnostic laboratories or insert key word ‘PCR’ test.

Action to be taken on results? In case of female you can select either A1A2 or A2A2 genotype but for bulls you must select only A2A2 genotype.

Is there a rapid test to differentiate A1/A2 milk at the milk collection centres? No, there is no such test available in the market as yet. PCR test which takes at least half a day is the only test available.