An experiment (complete randomised design) was conducted to investigate the linear and quadratic effects of barley β-glucan inclusion level on total tract nutrient apparent digestibility, nitrogen excretion, intestinal microflora, volatile fatty acid (VFA) profile and manure ammonia emissions in pigs. Twenty-four boars (66 kg) were assigned to one of four treatments: (T1) 0 g/kg barley (control diet) (5.6 g/kg β-glucan), (T2) 222 g/kg barley (12.1 g/kg β-glucan), (T3) 444 g/kg barley (18.9 g/kg β-glucan) and (T4) 666 g/kg barley (25 g/kg β-glucan). Barley was substituted for wheat in the diet. The diets were formulated to contain similar concentrations of digestible energy and digestible lysine. There was a linear decrease (P < 0.001) in the total tract apparent digestibility of dry matter, organic matter, gross energy and neutral-detergent fibre with increasing β-glucan concentration. Faecal nitrogen excretion was affected by dietary β-glucan concentration (quadratic P < 0.05). There was a linear decrease in Enterobacteria concentrations (P < 0.05) with increasing dietary β-glucan concentration. Increasing dietary barley levels caused a linear decrease in colonic (P < 0.01) and caecal pH (P < 0.001). Total caecal VFA and propionic acid were affected by dietary β-glucan concentration (quadratic, P < 0.05). There was a linear decrease in the proportion of acetic acid (P < 0.001), isobutyric acid (P < 0.01) and isovaleric acid (P < 0.05) with increasing levels of dietary barley in both the caecum and colon. There was a linear increase in the proportion of propionic acid (P < 0.001) and butyric acid (P < 0.05) with increasing barley in the colon. In conclusion, high level of dietary β-glucan (25 g/kg) is required to reduce offensive odour forming branched-chain VFAs; however, diet digestibility is compromised at such levels.