Amino acid composition of the milk of some mammalian species changes with stage of lactation.

The research investigates how the concentration and composition of amino acids in milk varies between the initial colostrum phase and mature milk stage in six different mammal species.

Research Context and Objective

• The research is centered around the premise that the composition of milk, particularly in terms of amino acids, varies during the lactation period. The objective of the study is to compare the amino acid composition in colostrum (the first form of milk produced immediately following the delivery of a newborn) and mature milk across six different mammalian species.

Methodology and Results

• The researchers compared individual amino acid concentrations—how each amino acid measures up against the total amount of amino acids—in the colostrum and mature milk of humans, horses, pigs, cows, baboons, and rhesus monkeys.
• They found distinct changes in the amino acid patterns between the colostrum and mature milk in human, horse, pig, and cow. The levels of glutamate, proline, methionine, isoleucine, and lysine increased from colostrum to mature milk, while the levels of cystine, glycine, serine, threonine, and alanine decreased.
• Additionally, they found that the total concentration of amino acids in these four species dropped by about 75% from colostrum to mature milk.

Exceptions and Observations

• In baboons and rhesus monkeys, little transformation was observed in the composition of amino acids from colostrum to mature milk, and the total amount of amino acids saw an only about 25% reduction.
• The mature milk across the three primate species (humans, baboons, and rhesus monkeys) displayed more similarities in terms of both amino acid composition and total concentration. This was especially notable when compared to the colostrum.

Conclusions

• The main takeaway from the study is that, in those species where total amino acid concentrations fall significantly from colostrum to mature milk, the pattern of amino acids often changes as well.
• Interestingly, the research also suggests that these changes in amino acid patterns and total concentrations during lactation don’t necessarily correlate with the phylogenetic order, meaning they don’t appear to be linked to evolutionary relationships.