In order to investigate the nitrogen utilization of grass diet in sheep, the present experiment was carried out using wethers fed only the fresh grass or hay prepared from the same origin. The results obtained were as follows ;
1) The digestibilities of crude protein were almost the same in sheep after feedings of fresh grass and hay. The retained nitrogen per kg of metabolic body size was calculated as 0.30 and 0.25 g in feedings of fresh grass and hay, and these figures were corresponded to 29.1 and 27.0% of digested nitrogen.
2) The concentration of ruminal ammonia was higher, but not significantly, after fresh grass feeding than after hay feeding. Ruminal pH and the concentration of ruminal VFAs were significantly higher in feeding of fresh grass than in feeding of hay.
3) The concentrations of blood urea-nitrogen and plasma total protein were significantly higher in fresh grass feeding than in hay feeding. The concentration of total free amino acids in plasma was slightly lower in fresh grass feeding than in hay feeding.
From the results obtained in the present experiment, it is concluded that the dietary nitrogen is more efficiently utilized in fresh grass feeding than in hay feeding.