THE INFLUENCE OF DIGESTIBLE ORGANIC-MATTER AND NITROGEN INTAKE ON FECAL AND URINARY NITROGEN LOSSES IN SHEEP

Relationships between dietary characteristics and faecal and urinary n itro en losses were examined using data from 25 rations fed to Merino ewes. Metabolic faecal nitrogen (MFN) ranged from 153 to 280 mg/kg W-0 .75, increasing (P < 0.05) with increasing levels of digestible organi c matter (DOM) intake (r = 0.96). Endogenous urinary nitrogen (EUN) sh owed the opposite behaviour, decreasing from 181 to 76 mg/kg W-0.75, w hich could be attributable to urea recycling to the large intestine be ing enhanced by increasing hindgut fermentation with increasing DOM le vels, as the composition of urinary nitrogen suggests. Total endogenou s nitrogen (TEN) remained fairly constant, indicating that faeces and urine are complementary routes for the excretion of recyclable nitroge n compounds. The TEN overall mean value was very close to the value ad opted by AFRC (AFRC Technical Committee on Responses to Nutrients, 199 2. Report No. 9, Nutritive Requirements of Ruminant Animals: Protein. Nutr. Abstr. Rev. Ser. B 62, 787-835.) (333 vs 350 mg N/kg W-0.75). (C ) 1997 Elsevier Science B.V.