A1/A2 Milk Testing & RT-PCR Verification

What A1 and A2 mean

β-casein is one of the principal casein proteins in bovine milk. It occurs in several genetic variants; A1 and A2 are the two most relevant commercially. The variants differ by a single amino acid in the β-casein chain — histidine in A1, proline in A2.

Because the difference is genetic, the variants an animal produces are fixed for that animal. Milk pooled from many animals reflects the A1/A2 make-up of that pool.

In-house RT-PCR capability

We operate a real-time PCR facility and use RT-PCR to check A1/A2 in the animals in our sourcing pools. Each animal's A1/A2 status is determined and recorded against its identification, so the composition of a sourcing pool is documented rather than assumed.

RT-PCR A1/A2 verification vs milk protein composition testing

This distinction is the most commonly misused point in A2 marketing, so we state it plainly:

• RT-PCR A1/A2 checking (DNA-based): establishes which β-casein variant an animal carries. Aggregated across a herd, it establishes the A1/A2 composition of a sourcing pool.
• Milk protein composition testing: characterises the β-casein variants actually present in a milk sample, using protein-level analytical methods. This is a different question requiring different instrumentation.

RT-PCR does not, on its own, quantify the β-casein variant ratio of a tanker of milk. Where a buyer requires lot-level protein characterisation, it is contracted as a separate specification parameter with its own stated method.

Sampling and documentation

Animal samples are collected against tag or registration numbers with a chain-of-custody record. RT-PCR results are stored against those identifiers and reconciled against the collection centres feeding each supply programme. Batch documentation issued with a despatch references the verification status of the sourcing pool alongside the compositional and hygiene results for that lot.