An enzymatic synthesis and composition of .alpha.-hydroxy carboxylic acid and .alpha.-amino acid or peptide co-oligomers is disclosed wherein a residue of the .alpha.-hydroxy carboxylic acid is linked to a residue of the .alpha.-amino acid or peptide by an amide linkage. Proteolytic enzyme papain catalyzes co-oligomerization of the .alpha.-hydroxy carboxylic acid and .alpha.-amino acid. The degree and distribution of oligomerization varies upon the type and concentrations of different reaction mixtures utilized and upon the length of allowed reaction time. The resultant oligomers may be provided to ruminants as bioavailable amino acid supplements that are resistant to degradation in the rumen.