The digestion by cattle of grass silage made with formic acid and formic acid–formaldehyde

1. A primary growth crop of perennial ryegrass (Lolium perenneL., cv. S23) was partially wilted and ensiled after the application of eitherformic acid–water (1:3, w/v; 7.1 1/t fresh herbage; control diet C) or formic acid–formaldehyde (1:1, w/w; 8·81/t fresh herbage; formaldehyde treated diet F) which supplied 50gHCHO/kg crude protein (nitrogen (N) × 6·25). The two silages were fed separately and a third diet comprising formaldehyde-treated silage, supplemented with urea (20 g/kg dry matter dm) at the time of feeding was also examined (dietFU). 2. The three diets were fed at a level of 16 g dm/kg live weight to six 3- to six-month-old cattle fitted with rumen and re-entrant duodenal cannulas in two 3 × 3 LatinSquare experiments, and measurements were made of the digestion of energy, carbohydrateand N. 3. The formaldehyde-treated silage had a lower content of fermentation acids and ammoma-N and a higher content of water-soluble carbohydrate and total amino acids. The apparent digestibility of organic matter, energy and N were depressed (P < 0·05, P < 0·05 and P < 0·01 respectively) by treatment with formaldehyde, but cellulose and neutral-detergent fibre digestibility were unaffected. 4. Within the rumen the digestion of organic matter, cellulose and neutral-detergent fibre were unaffected by formaldehyde treatment or supplementation with urea. Microbial protein synthesis in the rumen was similar for the three diets (average 131 g/kg apparently digested organic matter in the rumen). 5. The application of formic acid-formaldehyde increased (P < 0·05) the amount of food protein escaping degradation in the rumen (4·76 diet C, 6·89 diet F; 7·07 diet FU g/kg protein intake). The contribution of amino acidsof dietary origin al the duodenum increased (P < 0·05) from 50 (diet C) to 80 (diet F) and 82 (diet FU) g/kg DM intake, and the flow of total amino acids at the duodenum was 33% higher (P < 0·001) in cattle fed formic acid–form aldehyde silage diets compared withthe control silage due to the reduction in degradation of protein at ensiling and in therumen.