Effect of dietary carbadox or formic acid and fibre level on ileal and faecal nutrient digestibility and microbial metabolite concentrations in ilealdigesta of the pig

A digestibility trial was carried out on six castrates (39-83 kg body weigh t) in a 6 x 4 changeover design to investigate the effects of dietary carba dox (50 mg/kg feed) and formic acid (8 g/kg feed) supplementations on the a pparent ileal and faecal digestibility of nutrients and fermentation charac teristics in the ileal digesta of pigs fed medium- or high-fibre diets (neu tral detergent fibre 189 and 219 g/kg dry matter, respectively). The pigs w ere fitted with T-cannulas according to the steered ileocaecal valve techni que. The true ileal digestibility of lysine supplied by soyabean meal was d etermined by the homoarginine method. Both carbadox and formic acid improve d significantly the apparent Heal digestibility of several essential and no nessential amino acids in the high-fibre diet but not in the medium-fibre d iet. Neither carbadox nor formic acid influenced the true ileal digestibili ty of lysine supplied by soyabean meal (P = 0.78). The additives decreased the Heal flow of purines (P = 0.01) and tended to decrease that of bacteria l nitrogen (P = 0.07), which indicates that improved apparent ileal amino a cid digestibilities were probably due to reduced bacterial protein synthesi s in the ileal digesta. The additives increased the apparent Heal and faeca l digestibilities of ether extract (P = 0.01), formic acid more than carbad ox (P = 0.01). The apparent Heal digestibilities of crude protein and calci um were improved in the high-fibre diet (P = 0.01) but not in the medium-fi bre diet (P = 0.87 and 0.80, respectively). The additives decreased the lac tate (P = 0.02) and increased the acetate concentration (P = 0.01) in Heal digesta sampled 6 h postprandial. The change in lactate concentration was g reater for the formic acid than the carbadox supplemented diet (P = 0.01). Propionate, n-butyrate and ammonia concentrations were not influenced signi ficantly by dietary treatments. In conclusion, the positive effect of dieta ry carbadox or formic acid supplementation on the apparent ileal digestibil ity of protein and other nutrients depended on diet composition. The additi ves did not affect the true ileal lysine digestibility in soyabean meal. Th e improved apparent ileal amino acid digestibilities were probably partly d ue to the reduced flow of bacterial nitrogen in the ileum, but this require s further investigation. (C) 2001 Elsevier Science B.V All rights reserved.