Apparent component digestibility and manure ammonia emission in finishing pigs fed diets based on barley, maize or wheat prepared without or with exogenous non-starch polysaccharide enzymes

Abstract

A 3×2 factorial-design experiment was conducted with finishing pigs to examine the effect of cereal type (barley, maize or wheat) and a non-starch polysaccharide enzyme supplement (endo-1,3(4)-β-glucanase and endo-1,4-β-xylanase) on apparent nutrient digestibility, nitrogen (N) balance and manure ammonia (NH 3-N) emission. Diets were formulated to contain similar concentrations of digestible energy and lysine, sulphur amino acids, threonine and tryptophan. After a 14-day dietary adaptation period, urine and faeces were collected from 24 boars (four boars per treatment, 61 kg initial live weight), housed in metabolism crates. NH 3-N emission was measured over 10 days using a laboratory scale procedure. The procedure consisted of a sealed vessel containing 2 kg slurry, vacuum pump and three impingers in series per sample. The coefficient of total tract apparent digestibility (CTTAD) of dry matter (DM), gross energy (GE) and N digestibilities were higher in wheat-based diets than maize- or barley-based diets (P<0.01) while the CTTAD of NDF was lower in barley-based diets than maize and wheat-based diets (P<0.001). Enzyme inclusion had no effect on the CTTAD's of DM, GE, NDF or N. A lower proportion of N intake was excreted as faecal N in the wheat-based diets than the barley- or maize-based diets (P<0.001) and as ammoniacal N in barley-based diets than in maize- or wheat-based diets (P<0.01). There was a significant cereal×enzyme interaction (P<0.01) in the urine:faeces N excretion ratio. Enzyme supplementation increased the urine:faeces N excretion ratio in barley-based diets (P<0.05), but decreased the ratio in wheat-based diets (P<0.01) whilst the maize-based diet was unaffected. During manure storage (0–240 h), NH 3-N emission was affected by a cereal×enzyme interaction (P<0.01). Enzyme supplementation increased NH 3-N emission in the barley-based diet and decreased NH 3-N emission in the wheat-based diet. In conclusion, ammonia emission from the manure of finishing pigs is affected by the use of cereal types differing in the concentration of β-glucan and arabinoxylans and exogenous non-starch polysaccharide enzyme supplementation.