Effect of Different Ratios of α-Lactalbumin to β-Casein in Infant Formula on True Ileal Digestibility and Intestinal Morphology of Suckling Piglets

Breast milk (BM) is the optimal nutrition source for infants, providing highly digestible proteins. In contrast, the digestibility of proteins in infant formula (IF) varies, influenced by differences in proteins such as α-lactalbumin (α-La) and β-casein (β-CN). This study aimed to evaluate the true ileal digestibility (TID) of amino acids (AAs) in BM and IF with varying α-La and β-CN contents using neonatal piglets. Twenty-four 11-day-old piglets (4 groups; 6 replicates/group) received either a nitrogen-free diet, IF (high infant formula (HIF) with 1.74 g/100 α-La and 2.3 g/100 β-CN; low infant formula (LIF) with 1.07 g/100 α-La and 1.85 g/100 β-CN), or BM (1.82 g/100 α-La and 3.05 g/100 β-CN) for 7 days after 3 prefeed days. IF had higher concentrations of nitrogen, serine, threonine, and proline than BM. Glutamic acid was the most abundant AA in IF and BM, while methionine in BM and LIF or tryptophan in HIF was the least. BM showed the highest TID of AAs, with the LIF had the lowest. The HIF group's TID for AAs, especially tryptophan, was similar to BM and significantly better than LIF. These results suggest that adjusting the α-La and β-CN ratio in IF can improve AA digestibility, approaching BM levels.