value, 1.2% of the difference in TDN between treatments 2 and 3 would account for the difference in feed intake. The differences in the digestibilities of NDF and ADF exceeded this range. There may be additional unknown factors for the relatively higher digestibility in treatment 2. There are several reports suggesting the difference in fiber digestion between cattle and sheep. Bird4 and Playne15 suggested that the difference in the utilization of nitrogen and sulfur affected the activities of rumen microorganisms, when low quality diet was given. Rees and Little18, Poppi et al.16 and Prigge et al.17 suggested that the difference in the flow rate in the digestive tract would be the main reason for the difference in fiber digestion. Terada et al.20 compared the digestibility of nutrients among cattle, sheep and goats given rice straw wafer and rolled barley with different kinds of protein sources, i.e. soybean meal and urea. They suggested that the difference in fiber digestion between cattle and sheep increased as the animals received lower protein diets. The present study confirmed this result. The change in fiber digestibility of Ruzi grass hay according to the amounts of soybean meal supplement given revealed accurately a specific difference between cattle and sheep. The CF, NDF and ADF digestibilities were improved by the soybean meal supplement until the CP content in the whole ration reached 10% in sheep. The difference in fiber fraction digestibilities of the hay between the sheep given only the hay and those given soybean meal supplement so as to increase CP content of the whole ration more than 10% was more than 10 units in each fiber fraction. Beyond this level there was no effect of the soybean meal supplement on fiber fraction digestibilities. In cattle, fiber fraction digestibilities were relatively high in the animals even if they were not given soybean meal supplement. The values were then improved by a small amount of supplement by which CP content in the whole ration increased to 6.8%. Beyond this level there was no effect of supplement. The digestibility of NFE was higher in cattle than in sheep in the present study. Terada et al.20 also reported that the digestibility of NFE was higher in cattle than in sheep when roughage-based diet was given to the animals, and there was no difference in the digestibility of NFE between the animals when large amounts of concentrate was given. The nitrogen excretion into feces did not correspond to the levels of soybean meal supplement in sheep and was relatively constant. While in cattle, it increased when higher supplements were given. These were related to the differences in metabolic fecal nitrogen excretion, which was relatively higher in sheep than in cattle. Sheep would