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Hohmann, Lisa G.; Yin, Tong; Schweizer, Helen; Giambra, Isabella J.; König, Sven and Scholz, Armin M. (2021): Comparative Effects of Milk Containing A1 versus A2 beta-Casein on Health, Growth and beta-Casomorphin-7 Level in Plasma of Neonatal Dairy Calves. In: Animals, Vol. 11, No. 1, 55

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Bovine milk generally contains two types of the milk protein beta-casein, A1 and A2. Enzymatic digestion of the A1 type yields the opioid peptide beta-casomorphin-7, which is suggested to adversely affect human and animal health. This study aimed to compare the effects of milk containing either homozygote A1 or A2 beta-casein on health and growth parameters in 47 dairy calves during the first three weeks of life. Additionally, we studied, for the first time, the levels of intact beta-casomorphin-7 in plasma of calves fed milk of alternative beta-casein genotypes. Milk feeding of A2-milk led to a lower milk intake and a looser fecal consistency (higher prevalence of diarrhea) compared to A1-milk. Nevertheless, weight gains and end weights of calves of both feeding groups were similar, which might be caused by the associated higher protein content of milk containing the A2 variant. Intact beta-casomorphin-7 was detected in plasma after A1- and A2-milk consumption, but was almost 5 times higher for A1-calves. In summary, A2-milk minimized the cleavage of the opioid peptide beta-casomorphin-7 and might have advantages in the development of pre-weaned dairy calves. Research has shown that digestion of A1 beta-casein (beta-CN) affects gastrointestinal motility and opioid activity through the release of the peptide beta-casomorphin-7 (beta-CM7). In the case of the A2 variant, the cleavage of beta-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 beta-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 x 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 beta-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 beta-CM7 in plasma of calves fed milk of either A1 or A2 beta-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 beta-CM7 in calves.

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