The effect of dietary crude protein level, cereal type and exogenous enzyme supplementation on nutrient digestibility, nitrogen excretion, faecal volatile fatty acid concentration and ammonia emissions from pigs

Abstract

A 2 × 2 × 2 factorial was used to investigate the interaction between dietary crude protein level (CP) (220 g/kg versus 160 g/kg), cereal type (wheat versus barley) and exogenous enzyme supplementation (with or without enzyme) on nutrient digestibility, nitrogen balance and manure ammonia (NH 3) emission and faecal volatile fatty acid (VFA) content. The enzyme supplement used contained endo-1,3-(4)-β-glucanase (EC 3.2.1.6) and endo-1,4-β-xylanase (EC 3.2.1.8). Diets were formulated to contain similar concentrations of net energy (9.8 MJ/kg) and lysine (10.0 g/kg). Following a 14-day dietary adaptation period, 32 boars, 4 boars per treatment (80.0 kg, S.D. = 3.6 kg), were transferred to metabolism crates where urine and faeces were collected separately over 7 days. NH 3 emissions were measured over 240 h using a laboratory scale procedure. There was a significant interaction between cereal type and enzyme supplementation in the apparent digestibility of gross energy (P<0.05) and total faecal volatile fatty acid concentration (P<0.05). Pigs offered the barley-based diets containing an enzyme supplement had a significantly higher gross energy digestibility and a significantly lower concentration of total volatile fatty acids in the faeces than unsupplemented barley diets. However, there was no effect of enzyme supplementation in wheat-based diets. Pigs offered diets containing 220 g CP/kg excreted significantly more N (P<0.01), urinary N (P<0.05) and faecal N (P<0.01) and had a lower than those offered diets containing 160 g CP/kg. Pigs offered barley-based diets excreted significantly less urinary nitrogen (P<0.05) and more faecal nitrogen (P<0.001) and had a lower apparent N digestibility (P<0.001) than pigs offered wheat-based diets. There was a significant three-way interaction in manure NH 3 emissions from 0 to 240 h (P<0.05). Enzyme supplementation significantly increased NH 3 emissions in the barley-based diet at the 220 g CP/kg concentration while it had no effect on the wheat-based diet. However, at the 160 g CP/kg concentration, enzyme supplementation had no effect on NH 3 emissions. In conclusion, the excretion of pollutants, viz. nitrogen, ammonia and volatile fatty acids could be reduced by lowering dietary CP level and by increasing the level of barley in the diet. Enzyme supplementation increased NH 3 emissions with barley-based diets.