The objective of this study was to determine the biological protein value and rate of fermentation of saccharides in the caecum of rats fed diets containing wheat, hulled barley, or naked oats (cv. Akt), supplemented with β-glucanase. Sixty rats of an initial body weight of 71.3 g were fed for 28 days with diets containing 91.8-94.7% wheat, barley or naked oats, with or without β-glucanase in the amount of 1000 CU/kg, in subgroups W, B, O and WG, BG, OG, respectively. All of the diets were supplemented with lysine to about 5.5 g/100 g crude protein, and the barley diets with casein (3%). The feed efficiency ratio (FER) and biological value of protein (BV) were determined. At the end of the experiment the rats were euthanized and the caecum isolated. The weight, glycolytic activity and short-chain fatty acid (SCFA) content of caecal digesta were determined. The FER (gain:feed) of the oat diet was higher than that of the barley-plus-casein or wheat diets and equalled, respectively, 0.202, 0.183, and 0.162 g/g (P<0.01). The BV of oats was higher than that of wheat (69.1 vs 61.7; P<0.01), but lower than that of barley plus casein (79.3). Less digesta and digesta dry matter was found in the caecum of rats fed naked oats than wheat and barley (1.34 vs 1.57 and 1.70 g/100 g BW and 286 vs 360 and 389 mg/100 g BW, respectively; P<0.01). Feeding the oat diet (with the highest fat content) led to a decrease in the activity of many glycolytic enzymes in the caecum. The SCFA concentration in 1 g of caecum digesta in the animals fed naked oats and wheat was similar and higher than in the animals fed barley, whereas the SCFA pool was lowest in the oat group. The addition of β-glucanase did not increase the body weight gains of the rats, FER, and BV of the cereals, but did increase the degradation of β-glucans in the caecum, as indicated by the rise in the caecal SCFA concentration, most distinct in the rats fed the oat diet containing the most β-glucans.