β-casein is one of the major proteins in cow’s milk and occurs mainly in two well-known forms: A1 and A2. The review shows that intensive selection for high milk production has contributed to a higher frequency of the A1 variant in modern dairy breeds, while many indigenous and locally adapted cattle breeds remain enriched in the A2 variant. Human studies most consistently suggest that A2-only milk may improve short-term gastrointestinal tolerance in some milk-sensitive consumers, although broader health claims require further evidence. The article places the A1/A2 question in a One Health framework, linking animal genetics, dairy production, consumer responses and the conservation of locally adapted cattle genetic resources.
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https://doi.org/10.3390/vetsci13050473
