While concern for a healthy diet is stressing many consumers, some scientific studies suggest negative impact on human health for a variant of a dairy protein. Beta-casein accounts for 30% of protein contained in milk and shows two genetic variants: A1 and A2.
Several epidemiologic papers are linking beta-casein A1 variant absorption to diverse chronic diseases. Direct impact of the A1 variant on human health hasn’t been measured yet and conclusions on the subject do not reach consensus in the scientific community.
Genetic selection to generate dairy bovine that produce only the beta-casein A2 variant has already started. While Beta-casein gene has two alleles, dairy bovine can show 3 genotypes: A1A1 (exclusive production of beta-casein A1), A1A2 (production of beta-casein A1 and A2) and A2A2 (exclusive production of beta-casein A2). Homozygous sire for beta-casein gene will transmit only one allele to the progeny (A1 for the A1A1 sire and A2 for the A2A2 sire), while heterozygous sire (A1A2) will transmit each allele 50% of the time.
Breeders who want to start beta-casein selection would ideally run genomics on their females and ask for this specific gene to be tested. Homozygous A2 females would then be prioritized in the breeding strategy to their A1 homozygous and A1A2 heterozygous counterparts. Females identified as dams for the next generation would need to be bred to homozygous A2 sires. *Please note that while decreasing significantly the number of sires and females to include in the genetic strategy in regards to only one gene, genetic gain can be decreased for other important genetic traits.
Here is a list of a some bulls currently available through the STgenetics network that have been confirmed homozygous for the beta-casein A2 variant according to their genotype:
click here to view listing