A1/A2 Genetic Background of Cows, But Not Their Horn Status, Influences Milk Protein Digestion

The influence of horn status and the genetic variant of the (A1/A2) β-Casein milk protein on milk quality and digestion is the subject of much debate. This study shows that the milk of cows with a genetic difference in β-Casein is digested slightly differently in the human stomach, but that horn status has no effect in this regard.

The effects of the horn status (horned or disbudded) of cows and of their β-casein genotype (see text box) on the composition and quality of their milk is the subject of much debate. To give one example, it is frequently claimed – particularly by proponents of biodynamics –that the milk of horned cows is more digestible and healthier than that of hornless cows, despite there being no scientific basis for this assertion.

This study* investigated whether the milk of horned and disbudded cows differs in terms of its composition, and whether it is digested differently. The investigation was based on previous, albeit methodologically limited, studies that suggested an influence of disbudding on milk components. Probably one of the most debated factors potentially influencing milk digestion is the genetic variant of the milk protein β-casein. To rule out as well as investigate this influence, genetic variants of β-casein were also taken into account. The study analysed 128 milk samples from 64 horned and 64 disbudded Brown Swiss and Original Braunvieh cows carrying one of three genetic variants of β-casein (A1A1, A1A2 and A2A2). The influences of horn status and the genetic β-casein variant on detailed milk composition and milk-protein digestion were tested separately in in vitro experiments simulating human digestion.

From gross milk composition to the individual amino acid

The main and subsidiary components of the milk were quantified in all milk samples. The samples were then digested in vitro and analysed at various levels, from the large proteins to their component parts, the smallest peptides and amino acids.

No differences were found in the main components of the milk, the fatty acid profile, the main milk proteins and free amino acids, either between horned and disbudded cows or between those with different variants of β-casein. The β-casein variant did, however, influence the digestion pattern (peptide pattern) of β-casein in the stomach. The variations appeared precisely at those points on the amino acid chain where the A1 and A2 variants of β-casein differ (see text box). These differences disappeared after passage through the small intestine, however. Further investigations are needed to determine whether the differences affect human digestion and wellbeing. Horn status did not influence the digestibility of milk in this study. This was found to be the case despite the use of extremely sensitive methods capable of unambiguously highlighting the difference between milk from cows with genetic differences in β-casein based on a single amino acid, i.e. on a tiny detail in overall milk composition.

*The study was funded by the Fondation Sur-la-Croix.