The effect of formaldehyde treatment of the forage portion of the diet, the addition of branched-chain volatile fatty acids and/or sulphur on the utilization of nitrogen and carbohydrate by sheep

Formaldehyde treatment of dietary protein to reduce its degradation in the rumen has been reported to be beneficial in some instances. Four levels of formaldehyde (0.0%, 0.8%, 1.0% and 1.2% on an air dry basis) were applied to a dehydrated and hammermilled grass-clover forage. In vitro nitrogen digestibility and ammonia-nitrogen production at *the microbial stage of incubation were reduced significantly (p < 0.05) as the level of formaldehyde was increased. Nitrogen digestibility for the combined microbial and acid-pepsin stages of incubation was significantly (p < 0.05) reduced only at the 1.2% level of formaldehyde application compared to the untreated forage. Ram lambs ranging in body weights of 29kg to 36kg were then used in studies of nitrogen and carbohydrate metabolism. One percent formaldehyde was applied to the grass-clover forage. Each of the five diets (14% C.P. on D.M. basis) contained 50% grass-clover forage, 38% cassava, 11% barley and 1% sheep mineral premix on a dry matter basis. Diet one contained the untreated forage while the others contained the formaldehyde treated forage. Diets three and five were supplemented with isovaleric acid (3.0g/Kg diet) and isobutyric acid (2.3g/Kg diet). Diets four and five were supplemented with sulphur in the form of sodium sulphate. The apparent digestibility coefficients of acid-detergent fibre and cellulose were increased significantly (p 0.05). Ruminal fluid levels of isovaleric and isobutyric acids were significantly (p < 0.05) higher for animals fed diet three than for animals fed diets two and four. Formaldehyde treatment of the forage resulted in significantly (p < 0.05) higher levels of valeric acid and lower levels of ammonia in ruminal fluid. Ruminal fluid levels of total volatile fatty acids, acetic, propionic and butyric acids and rumen pH were not affected significantly (p < 0.05) by formaldehyde treatment of the forage. The ratio of microbial protein-nitrogen (estimated from RNA-N) to total abomasal digesta nitrogen was significantly (p < 0.05) decreased by formaldehyde treatment of the forage except for the diet supplemented with VFAS (diet three). The concentration of non-protein-nitrogen in abomasal digesta was significantly (p < 0.05) reduced by formaldehyde treatment of the forage. Abomasal digesta pH, concentration of total nitrogen, RNA-N, microbial protein-nitrogen, acid-detergent fibre, and cellulose were not affected. The reduction in the ratio of microbial protein-nitrogen to total abomasal digesta nitrogen and non-protein-nitrogen by formaldehyde treatment of the forage suggests that the treatment reduced microbial degradation of dietary protein except perhaps for the diet supplemented with VFAS (diet three). Nitrogen balance was significantly (p < 0.05) improved by formaldehyde treatment of the forage except for the sulphur supplemented diets. Sulphur supplementation tended to offset the beneficial effects of formaldehyde protection of the forage protein. Supplementation with VFAS did not further enhance nitrogen utilization. Formaldehyde treatment of the forage significantly (p < 0.05) improved sulphur balance except for the diet supplemented with both sulphur and VFAS (diet five). Daily feed intake and urine output per unit metabolic body size and growth rate over a seventeen-day period were not significantly (p < 0.05) affected by formaldehyde treatment of the forage. The flow of total digesta, organic matter, dry matter, acid-detergent fibre, cellulose and total nitrogen through the duodenum for a 24-hour period was markedly higher for the diets containing the formaldehyde treated forage. The flow of microbial protein-nitrogen and non-protein-nitrogen however was markedly depressed by formaldehyde treatment of the forage. A sheep fitted with a duodenal re-entrant cannula was used for this study.Land and Food Systems, Faculty ofGraduat