1. Three experiments were conducted on the ability of cats to utilize dietary carbohydrates. In two experiments, the digestibilities of carbohydrates were measured by the chromic oxide-marker technique using a balanced Latin-Square allocation of treatments: in the third experiment, the effect of age and diet on the activity of intestinal β-galactosidase (lactase) (EC 184.108.40.206) and β-fructofuranosidase (sucrase) (EC 220.127.116.11) of kittens was measured.
2. In Expt 1 the digestibilities of six individual carbohydrates, glucose, sucrose, lactose, dextrin, raw maize starch and wood cellulose added to a meat-based basal diet were measured.
3. In Expt 2, a similar meat-based basal diet was used and the effect of three processing methods (fine and coarse grinding, and cooking) on the apparent digestibility of the starch in maize and wheat grain was measured.
4. In Expt 3 the effects of the inclusion of either 200 g lactose or 200 g sucrose/kg in an all-meat diet and of age on the β-galactosidase and β-fructofuranosidase activities of the small intestine of weanling kittens were measured.
5. Adult cats efficiently (> 0.94) digested all six individual carbohydrates added to the diet with the exception of cellulose, which was indigestible. The digestibility coefficients of glucose, sucrose and lactose were significantly (P < 0.01) greater than that of starch. The inclusion of lactose caused diarrhoea in some cats and significantly (P < 0.01) reduced apparent digestibility of crude protein (nitrogen × 6.25) in the total ration.
6. Fine grinding significantly enhanced the digestion of starch in wheat and maize grain, but the effect was greatest for maize grain. Cooking had a similar effect to fine grinding for wheat grain, but an effect intermediate between coarse and fine grinding for maize grain.
7. Intestinal β-galactosidase activity decreased with age in kittens (71-106 d). Neither β-fructofuranosidase nor β-galactosidase activities were significantly affected by the addition of sucrose and lactose to the all-meat diet.