The objective of the present study was to determine the microbial nitrogen entering Baloochi lamb duodenums when fed with diets differing in protein sources (alfalfa, cottonseed meal, soybean meal or molasses + urea) with similar amounts of ERDP using a developed HPLC isolation method of urinary purine derivatives. In addition, ruminal pH and N- NH3 (mgL-1) were determined at before, 1, 2, 3, 4 and 6 hours after feeding. Data related to the microbial protein entering the duodenum (ranged from 6.3 to 9.8 g/ lamb/ d), ruminal pH and N – NH3 in lambs receiving the experimental diets indicated that the effect of protein sources, when diets provided similar amounts of ERDP, is not significant (except for N – NH3 at 1 and 2 hours after feeding (40.39 and 33.06 mg/dl, respectively) where the N – NH3 concentration in the rumen of lambs fed with diet containing urea + molasses was significantly higher (P<0.05) than that in the others).
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