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