Beta-Casein A2A2

Since 2003, after a New Zealand study about the effect of consumption milk with Beta-casein A2A2 on human health, in some countries has been increasing the interest on this topic. In Australia and in England there are already available in the shop milk “A2A2”, but in some other European countries this argument is still unknown.

Milk protein variants

Milk proteins can be divided in two main fractions: about 25% are whey proteins and not protein nitrogen compounds like urea; while 75 % are casein proteins, the most important since are one of the main compound involved in cheese production. The casein proteins are divided in 5 classes, one of which is Beta-Casein, that is about 36% of total casein.

Beta caseina

In general the proteins are single-chain of Amino acid (229 in the case of Beta-Casein) and the sequence of them are regulated by DNA. In the nature is possible to find several variants of the same protein, that can differ for a substitution of only 1 or 2 amino acids. In the case of Beta-casein are known 13 variants, but only A1 and A2 variants are frequent in the main dairy cattle breeds used for intensive milk production.
The original variant seems to be A2 but with a mutation occurred about 5000 years ago, start to be present in the dairy cattle population the variant A1. Due to the selection this last became the most frequent in Holstein Friesian population. However, the prevalence of the A2 and A1 beta-casein allele varies between cow herds and also between countries.

Genetic management for produce milk A2A2

The production of Beta-casein is controlled by only one gene, like other proteins in the milk example k-casein. Depend on the genotype, the cow will produce milk with only beta-casein A1 or A2 or a mixture of A1 and A2, if the animal has a genotype "A1A1"or "A2A2" o "A1A2", respectively.
A possible strategy could be to fixing the gene A2 in the population, removing step by step the A2 gene using bulls A2A2 or A1A2 checking with DNA test the daughters.
Intermizoo started a selective program for increase A2 gene frequency in the population. Here we provide a list of bulls with A2 gene.

 
 
List of Genomic and Proven Hostein, A2A2, available at our center
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