Abstract #129

# 129
A2 variant of β-casein: Friend or foe?
Lydia R. Harrison*1, David R. Winston1, Kristy M. Daniels1, 1Virginia Tech, Blacksburg, VA.

Two predominant alleles for β-casein exist in dairy cattle: A1 and A2. Cows that are homozygous for the A1 allele produce a variant of β-casein that differs by 1 amino acid from cows that are homozygous for the A2 allele. With the increasing prevalence of niche markets for dairy products, A2 milk has moved into the spotlight, bringing with it conflicting views about possible benefits. Three studies were evaluated to determine the impact of A2 milk on the dairy industry, from producers to consumers. Bugeac et al. (2015) found that Holstein-Friesian cows homozygous for the A2 allele produced 2,564 kg more milk over the lactation period compared with homozygous A1 cows. However, although A2 cows exhibited an increase in yield, Poulsen et al. (2017) examined the relationship between β-casein variants and milk coagulation properties and identified a possible negative impact for processors. Milk with the A2 variant was associated with longer rennet coagulation times and lower curd firming rates, making it a poor choice for cheese production. Finally, Jianqin et al. (2016) explored possible effects of A1/A2 versus purely A2 milk on the gastrointestinal physiology of consumers who had reported an intolerance to “traditional” (commercially available A1/A2) milk. Switching from A1/A2 to purely A2 milk was reported to reduce stomach inflammation in 36.4% of those who suffered from it, compared with only 11.1% who improved when switched from A2 milk to the A1/A2 combination. In addition, A2 milk was associated with fewer gastrointestinal symptoms and shorter transit times. Although there is great potential for additional research, these studies have indicated that while the A2 allele may reduce the efficiency of cheese production, it can provide milk yield benefits to farmers and possibly positive health effects to consumers.

Key Words: A2 variant, β-casein, protein structure