Two experiments were conducted to evaluate the TDN and fiber levels of rabbit diets on the basis of growth, digestibility and heat production. In Experiment 1, twelve Japanese white rabbits (6 males and 6 females) weighing 1.5-2.5 kg were used for evaluating TDN levels of 65,68and 71%. The BW gain increased with an increase in the TDN level, though not significant. Digestibility of CP was significantly higher in the TDN 65% group than in the other two groups. Conversely, digestibility of ether extract was lowest in the TDN 65% group. Heat production did not differ among the groups. These results suggest that an increase in the TDN level concomitant with a 15% CP content may result in the accumulation of body fat. In Experiment 2, twelve Japanese white female rabbits weighing 1.2-1.6 kg were used for evaluating crude fiber levels of 10,14and 18%. The BW gain in the crude fiber 10% group was significantly higher than in the other two groups. The effect of increase in the crude fiber level on the BW was apparent when BW was more than 2.5 kg. Feed intake was also significantly higher in the crude fiber 10% group. Digestibility and heat production did not differ among the groups. These results suggest that the ideal crude fiver level is 10% as-fed in rabbits weighing more than 2.5 kg.

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Two digestion trials were conducted to examine effects of CP and carbohydrate in dry foods on apparent digestibility in adult cats. Apparent digestibility was determined by both total feces collection method and chromium oxide (Cr₂O₃) indicator method. In trial 1,12 adult cats were divided into three groups of four cats each, and three diets with different CP contents were randomly allotted to the three groups. Apparent digestibility of DM, CP and AEE tended to decrease with increasing dietary CP contents independent of the measuring method. In trial 2,12 adult cats were divided into three groups of four cats each, and following three diets were randomly allotted to the three groups to evaluate effects of dietary carbohydrate. The control diet contained no carbohydrate sources, the starch diet contained corn as a starch source, and the fiber diet contained beet pulp, cellulose powder and wheat flour as a fiber source. Apparent digestibility of DM, CP and NFE was lower in the fiber diet group than in the other two groups, independent of the measuring method. In contrast apparent digestibility of NFE was higher in the starch group. There were no striking differences among the groups on the differences between apparent digestibility determined by both measuring methods. The present results suggest that dry food with lower CP content causes irregular flow of the intestinal digesta. In contrast, dietary carbohydrate (NFE plus crude fiber) seems to have minimal effects on the intestinal digesta flow in of adult cats.

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In order to augment lactate production and nitrite reduction simultaneously in the intestines of dogs and cats, a bacterium that has both lactate-producing and nitrite-reducing capacity was iso lated from cat feces. The isolate was identified as Streptococcus bovis. The isolated S. bovis wa found to belong to the biotype II that has no ill effect on the host. The specific activity (the amount of enzyme per cell mass) of nitrite reductase (NiR) increased when the isolate was grown in the presence of nitrite, suggesting that NiR synthesis is stimulated by nitrite. When mixed fecal bacteria from an old dog or cat were cultured in a growth medium containing resistant starch, addition of the isolate increased lactate production and lowered culture pH. When similar culture experiments were performed with a medium containing nitrite, addition of the isolate stimulated nitrite reduction. However, when nitrate was added to cultures, addition of the isolate increased nitrite accumulation. This result can be explained by the fact that the rate of nitrate reduction by the isolate is higher than that of nitrite reduction. Therefore, the isolate needs to be so improved that NiR synthesis is enhanced. Use of the improved strain as a probiotic would increase lactate production and decrease nitrite accumulation in the intestines.

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