Comparative Effects of Milk Containing A1 versus A2 β-Casein on Health, Growth and β-Casomorphin-7 Level in Plasma of Neonatal Dairy Calves

Abstract

Research has shown that digestion of A1 β-casein (β-CN) affects gastrointestinal motility and opioid activity through the release of the peptide β-casomorphin-7 (β-CM7). In the case of the A2 variant, the cleavage of β-CM7 does not occur or occurs at a very low rate. Therefore, the aim of the study was to compare the effects of milk containing either homozygote A1 or A2 β-CN on health and growth parameters of dairy calves. Forty-seven neonatal calves (24 females, 23 males) of the breeds German Holstein (GH, n = 9), German Simmental (GS, n = 33) and their crossing (GH × GS, n = 5) were used in a 21-day feeding study. Fecal score (FS), respiratory frequency (RF), and rectal body temperature (BT) were recorded daily, whereas body weight was measured at birth and at day 21 to estimate the average daily weight gain (ADG). Additionally, blood was collected from calves three times during the experimental period and, for the first time, the respective plasma samples were analyzed for intact β-CM7. Consumption of A2-milk led to a lower daily milk intake (dMI) (p < 0.05). Furthermore, fecal consistency was softer for calves fed A2-milk (p < 0.05). Although 44% of A2-calves had diarrhea or revealed a tendency towards it (FS ≥ 3), A1-calves had a prevalence of 21%. Calves with a FS of 4 were offered an electrolyte solution and received a dietary food supplement for the stabilization of the fluid and electrolyte balance. Nevertheless, similar ADG and end weights (EW) of calves fed A1- or A2-milk (p > 0.05) indicate that A2-milk may compensate higher diarrhea rates and lower dMI due to the associated higher protein content. This is the first report of intact β-CM7 in plasma of calves fed milk of either A1 or A2 β-CN. Evidence from this study suggests that due to the change in the amino-acid sequence, A2-milk might be able to prevent or, at least, to minimize the cleavage of β-CM7 in calves.

Novel LNA probe-based assay for the A1 and A2 identification of β-casein gene in milk samples

“… De Noni (2008) evaluated the βCM -7 release during simulated gastro-intestinal digestion of bovine β -casein variants and milk-based infant formulas, and verified that this peptide was not released from variant A2 during whole experimental study. Hohmann et al, (2021) evaluated the serum levels of intact βCM -7 in calves fed with milk containing A1 or A2 β -casein, and verified that intact βCM -7 was 5 times higher detected in A1 -calves. According to these authors, calves supplemented with A2 -milk presented minimized cleaved opioid peptide βCM -7 levels and might have advantages in the development of pre-weaned dairy calves.…”

Immobilized Enzyme Microreactors for Efficient Analysis of Tryptic Peptides in β-Casein and β-Lactoglobulin

“…Finally, both β-casein and β-lactoglobulin exhibit polymorphism, but the different forms of these proteins have different properties. For instance, different forms of β-casein (A1, A2, B) vary in their calcium-binding ability [9], while different forms of β-lactoglobulin (A, B) differ in their thermal stability and allergenicity. In conclusion, β-casein and β-lactoglobulin, despite both being milk proteins, exhibit a wide range of differences in their structure, modi cations, and properties.…”