| Four experiments were conducted to study the urea toxicity dose on rabbit, the variation of non-protein nitrogen in blood and gastrointestinal tract of rabbit after administered urea and nitrogen metabolism supplemented with urease inhibitor.In the first experiment, 15 young and healthy New Zealand rabbits (three months of age and two kg in body weight) were randomly distributed into three groups, I , II and III. The rabbits in I , II and III groups were given 3%, 6% and 9% urea of daily feed intake (daily feed intake is about 150 g per rabbit), respectively, by tube. The rabbits in groups I and II did not have noxious symptoms, and the rabbits in group III had markedly noxious symptoms and two rabbits died. By analysis of blood biochemical indices, after administering urea we found that serum ammonia nitrogen and urea nitrogen concentrations increased, and about 1 hour to a peak, then gradually decreased. The concentrations of ammonia nitrogen and urea nitrogen of dying rabbits were 21.4 mg/L and 1082.21 mg/L, respectively. After administering urea, the activity of serum GOT and GPT increased, and the values of dying rabbits were 28.18 and 70.05 units, respectively.In the second experiment, 20 young and healthy New Zealand rabbits (2.5 months and 1.9 kg) were divided randomly into four groups, one control group and three experimental groups. Basal diet was fed to the rabbits in the control group and low protein ration (10.12% CP) was fed to the rabbits in experimental groups I , IK III with addition 1 %, 2% and 3% urea, respectively. Results were showed as follows: No significant difference (P>0.05) was determined statistically between control group and experimental groups, however, there was an increasing trend in average daily weight gain with the increase of the urea level in the ration and the group III grew best (26.0 ± 4.6 g). By analysis of blood biochemical indices, after feeding we found that the ammonia and urea concentration increased, and then tended to be stable. The value of blood average ammonia of control group and groups I, II and III was 7.22 ± 0.43 mg/L, 5.65 ± 0.47 mg/L, 7.30 ± 0.34 mg/L, 9.36 ±0.39 mg/L, and the value of average urea was 165.54 ±2.49 mg/L, 203.54 ± 3.09 mg/L, 189.04±5.81 mg/L, 207.38±8.80 mg/L respectively. The activity of bloodaverage GOT and GPT in experimental groups was higher than that of the control group, but they did not exceed the normal range.In the third experiment, 20 young and healthy New Zealand rabbits (2 months of age and about 1.3 kg in body weight) were divided randomly into four groups. Basal diet was fed to the rabbits in group I , and low protein(10.12% CP)diet supplemented with 3% urea was fed to the rabbits in groups II ,111 and IV, in addition, groups III, IV with the addition of 10 mg/kg and 20 mg/kg urease inhibitor(AHA), respectively. Results were showed as follows: No significant difference (P>0.05) was determined statistically between all groups, and the average daily weight gains of rabbits in groups III, IV were higher than those of group II, and lower than those of group I . By analysis of blood biochemical indices, we found urease inhibitor had no effects on ammonia nitrogen and urea nitrogen. The values of blood ammonia nitrogen of groups I ,11, III and IV were 11.47 ±0.47 mg/L, 12.07± 0.61 mg/L, 12.69 ± 0.61 mg/L, 10.87 ±0.70 mg/L, respectively, and there was no significant difference between all groups(P>0.05); the values of urea nitrogen were 151.37 ±1.95 mg/L, 213.65±9.55 mg/L, 228.09±9.45 mg/L, 218.46±6.10 mg/L, respectively, and the values of groups II, III and IV were significantly higher than those in group I . The urease inhibitor had effect on the activity of GPT, and the value of GPT in group IV was the lowest; GOT level was not significantly affected by urease inhibitor addition.In the fourth experiment, six New Zealand rabbits with chronic cecal fistulas were used to study the effects of diets contained urea and urease inhibitor on physiological environment in the cecum. Experiment consiste...
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