AMINO-ACID-COMPOSITION OF THE MILK OF SOME MAMMALIAN-SPECIES CHANGES WITH STAGE OF LACTATION

To determine whether the amino acid composition of milk changes during lactation, we compared the amino acid pattern (concentration of each individual amino acid relative to the total amino acid concentration) of colostrum with that of mature milk in six mammalian species. In the human, horse, pig and cow, the pattern of amino acids changed between colostrum and mature milk: glutamate, proline, methionine, isoleucine and lysine increased; cystine, glycine, serine, threonine and alanine decreased. In these four species, the total amino acid concentration also decreased 75% between colostrum and mature milli. In the baboon ( Papio cynocephalus anubis and Papio cynocephalus anubis/Papio cynoceph alus cynocephalus) and rhesus monkey (Macaca mulatta), however, there was little change in the pattern of amino acids between colostrum and mature milk, and total amino acid concentration decreased only about 2 5% between colostrum and mature milli. Mature milk rather than colostr um was the most similar among the three primates in both amino acid pa ttern and total amino acid concentration. We conclude, in those specie s in which total amino acid concentrations decline substantially betwe en colostrum and mature milk, amino acid patterns also change. The pre sence of a change in amino acid pattern and total amino acid concentra tion during lactation appears to be unrelated to phylogenetic order.