Effect of formic acid and a bacterial inoculant on the amino acid composition of grass silage and on animal performance

An Italian ryegrass and hybrid ryegrass sward was harvested on 11 May 1994. The mean dry-matter (DM) content of the herbage was 197 g kg(-1) fresh mat ter (FM), and mean nitrogen and water-soluble carbohydrate contents were 20 and 272 g kg(-1) DM respectively. Approximately 72% of total nitrogen (TN) was in the form of protein-nitrogen. The herbage was treated with either n o additive, formic acid (3.3 1 t(-1)) (Add-F, BP) or inoculant (2.3 1 t(-1) ) (Live-system, Genus) and ensiled in 100 t silos. Changes in effluent comp osition with time showed that silage fermentation and protein breakdown wer e delayed by treatment with formic acid. Formic acid and inoculant treatmen ts also inhibited amino acid catabolism during ensilage. All silages were w ell fermented at opening with pH values < 4.0 and ammonia-N concentrations of <less than or equal to> 50 g kg(-1) TN after 120 d ensilage. Treatment h ad an effect on protein breakdown as measured by free amino acid concentrat ion, with values of 21.5, 18.2 and 13.2 mol kg(-1) N at opening (191 d) for untreated, formic acid-treated and inoculated silages respectively. Amino acid catabolism occurred to the greatest extent in untreated silages with s ignificant decreases in glutamic acid, lysine and arginine, and increases i n gamma amino butyric acid and ornithine. The silages were offered ad libit um without concentrate supplementation to thirty-six Charolais beef steers for a period of 69 d (mean live weight 401 kg). Silage dry-matter intakes a nd liveweight gains were significantly (P < 0.05) higher on the treated sil ages. Silage dry-matter intakes were 7.42, 8.41 and 8.23 kg d(-1) (s.e.d. 0 .27) with liveweight gains of 0.66, 0.94 and 0.89 kg d(-1) (s.e.d. 0.058) f or untreated, formic acid-treated and inoculated silage-fed cattle respecti vely. In conclusion, additives increased the intake of silage and liveweigh t gain by the beef steers, and it is suggested that this may be caused in p art by the amino acid balance in these silages.