Eight male lambs each aged approximately 11 months and having a body weight of 32.5 ± 2.5 kg were selected as experimental samples in the ongoing experiment. For the supplemented group, Monensin was fed at 22 mg/lamb per day. Relationships between dietary characteristics and fecal as well as urinary nitrogen losses were examined using data from the two treatments. Microbial N production was estimated using Non-linear Multiple regression in which the metabolizable energy and nitrogen intake variables formed part of the equation (r 2 = 0.94). The results revealed that Monensin supplement did not have any significant effect on DMI, ADG, FCR and blood parameters (P>0.05). But, protozoal population, rumen and urine pH, creatinine clearance and glomerular filtrate rate were significantly affected by the treatment (P<0.05). Metabolic Fecal Nitrogen (MPN) ranged from 124 to 181 mg/kg W0.75, and increased by increasing levels of Digestible Organic Matter (DOM) intake (r = 0.79). Endogenous Urinary Nitrogen (EUN) showed an opposite behavior, decreasing from 215 to 158 mg/kg W0.75, which could be attributable to urea recycling to the large intestine being enhanced by increasing hindgut fermentation with increasing DOM levels, as the composition of urinary nitrogen suggests. Total endogenous nitrogen was estimated at 339 mg/kg W0.75, which is very close to AFRC recommendations (350 mg/kg W0.75).