Characterisation of peptides in silages made from perennial ryegrass with different silage additives

The effects of applying either formic acid (5.4 g kg^-1 ), a mixture of formic acid (2.7 g kg^-1 ) and formaldehyde (1.5 g kg^-1 , 81 g kg^-1 herbage crude protein) or two concentrations of a cysteine peptidase inhibitor, cystamine (5 or 50 g kg^-1 ), to perennial ryegrass (Lolium perenne) on the nitrogen (N) distribution of the resulting silages were investigated, with emphasis on changes in concentration, composition and molecular weight of silage peptides. Herbage (156 g dry matter kg^-1 and 141 g water-soluble carbohydrate kg^-1 dry matter) was ensiled in triplicate in laboratory silos for 100 days. Formic acid and the formic acid/formaldehyde mixture reduced soluble non-protein N and ammonia N concentrations (P < 0.01); in addition, formic acid increased peptide N concentrations (P < 0.05). Cystamine at 50 g kg^-1 reduced ammonia N concentrations (P < 0.01) and increased peptide N concentrations (P < 0.05), but when applied at 5 g kg^-1 had little effect. Gel filtration of silage extracts on Sephadex G-25 suggested that a small proportion (0.06-0.11 g kg^-1 peptide N) of silage peptides had a chain length of 7-9 amino acids, but remaining peptides were smaller with chain lengths of 2-6 amino acid residues. Amino acid analysis of silage peptides indicated that additive treatment had little effect on peptide amino acid composition but that peptides with a chain length of 7-9 amino acids contained lower proportions of isoleucine and arginine. © 2000 Society of Chemical Industry.