A new type of cow’s milk, called A2 milk, has appeared in the dairy aisles of supermarkets in recent years. Cows’ milk generally contains two major types of beta-casein as A1 and A2 types, although there are 13 genetic variants of β-casein: A1, A2, A3, A4, B, C, D, E, F, H1, H2, I and G. Studies have shown that A1 β-casein may be harmful, and A2 β-casein is a safer choice for human health especially in infant nutrition and health. The A2 cow milk is reportedly easier to digest and better absorb than A1 or other types of milk. The structure of A2 cow’s milk protein is more comparable to human breast milk, as well as milk from goats, sheep and buffalo. Digestion of A1 type milk produces a peptide called β-casomorphin-7 (BCM-7), which is implicated with adverse gastrointestinal effects on milk consumption. In addition, bovine milk contains predominantly αs1-casein and low levels or even absent in αs2-casein, whereby caprine milk has been recommended as an ideal substitute for patients suffering from allergies against cow milk protein or other food sources. Since goat milk contains relatively low levels of αs1-casein or negligible its content, and αs2-casein levels are high in the milk of most dairy goat breeds, it is logical to assume that children with a high milk sensitivity to αs1-casein should tolerate goat milk well. Cow milk protein allergy (CMPA) is considered a common milk digestive and metabolic disorder or allergic disease with various levels of prevalence from 2.5% in children during the first 3 years of life to 12–30% in infants less than 3 months old, and it can go up to even as high as 20% in some countries. CMPA is an IgE-mediated allergy where the body starts to produce IgE antibodies against certain protein (allergens) such as A1 milk and αs1-casein in bovine milk. Studies have shown that ingestion of β-casein A1 milk can cause ischemic heart disease, type-1 diabetes, arteriosclerosis, sudden infant death syndrome, autism, schizophrenia, etc. The knowledge of bovine A2 milk and caprine αs2-casein has been utilized to rescue CMPA patients and other potential disease problems. This knowledge has been genetically applied to milk production in cows or goats or even whole herds of the two species. This practice has happened in California and Ohio, as well as in New Zealand, where this A2 cow milk has been now advanced commercially. In the USA, there have been even promotions of bulls, whose daughters have been tested homozygous for the A2 β-casein protein.
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