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

1. A primary growth crop of perennial ryegrass (Lolium perenne L., cv. S23) was partially wilted and ensiled after the application of either formic acid-water (1:3, w/v; 7.11 l/t fresh herbage; control diet C) or formic acid-formaldehyde (1:1, w/w; 8.8 l/t fresh herbage; formaldehyde treated diet F) which supplied 50 g HCHO/kg crude protein (nitrogen (N) x 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 (diet FU). 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 x 3 Latin Square experiments, and measurements were made of the digestion of energy, carbohydrate and N. 3. The formaldehyde-treated silage had a lower content of fermentation acids and ammonia-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 less than 0.05, P less than 0.05 and P less than 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 less than 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 acids of dietary origin at the duodenum increased (P less than 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 less than 0.001) in cattle fed formic acid-formaldehyde silage diets compared with the control silage due to the reduction in degradation of protein at ensiling and in the rumen.