The addition of an enzyme composite comprising of β-glucanase and β-xylanase reduced manure odour compared with
both the barley-based diet and the wheat-based diet containing purified β-glucans. Thismayreflect the substantial reduction (approx. 25%) in daily faecal Nitrogen from pigs offered enzyme-supplemented diets. Faecal Nitrogen is predominately microbial in origin (Kirchgessner et al., 1994), and upon further fermentation may generate noxious compounds (Zahn et al., 2001; Blachier et al., 2007). However the reduction in faecal Nitrogen was not reflected in substantial reductions in odorous volatile fatty acids, reflecting the complex and interactive properties of odorous compounds in influencing manure odour (Hobbs et al., 1997). It is likely the composition of faecal Nitrogen as well as the quantities is relevant in determining the emission of odorous volatile compounds and
the expression of manure odour. Future investigative studies may benefit from identification and quantification of a wider
range of bacterial metabolites to greater define the effect of dietary modification in addressing manure odour emissions.