The digestion by sheep of silages made with and without the addition of formaldehyde

Abstract

SUMMARYS.24 perennial ryegrass was conserved by ensiling directly (control) and after treatment with a solution of formaldehyde at the rate of 6 g HCHO/100 g crude protein. After storage for 90 days, part of the formaldehyde-treated silage was dried in a high-temperature drier.The quantitative digestion of the energy, carbohydrate and nitrogen moieties of the three diets and the production of volatile fatty acids and microbial protein within the rumen were measured using five sheep fitted with re-entrant cannulae at the proximal duodenum and terminal ileum.Treatment with formaldehyde depressed organic matter and energy digestion within the rumen compared with untreated silage (P< 0·001) and a further depression was observed on the dehydrated material. Both formaldehyde-treated silages showed enhanced flows of total amino acids into the small intestine compared with the control silage and net absorption from the small intestine was elevated by 13 and 21% respectively on these two diets. On the untreated silage over 71% of the protein entering the small intestine was microbial in origin whereas, due to depressed microbial growth and increased protection of feed protein from rumen fermentation, microbial protein comprised only 17% of duodenal protein on the two formaldehyde-treated silage diets. Fifteen and 81 % of the dietary protein passed undegraded through the stomachs to the duodenum on the control and the two formaldehyde-treated silage diets respectively.Total VFA production within the rumen was not significantly influenced by the treatments imposed, but on the untreated silage only 56% of the energy apparently digested in the rumen was converted to VTA energy whilst a mean value of 74% was recorded on the other two diets.Estimates of the total energy absorbed gave values of 10·6, 11·9 and 10·7 MJ/kg D.M. for the control, formaldehyde and dried, formaldehyde silage diets with absorbed protein energy representing 21, 22 and 26% of the total absorbed energy respectively.