The influence of digestible organic matter and nitrogen intake on faecal and urinary nitrogen losses in sheep

Abstract

Relationships between dietary characteristics and faecal and urinary nitrogen losses were examined using data from 25 rations fed to Merino ewes. Metabolic faecal nitrogen (MPN) ranged from 153 to 280 mg/kg W(0.75), increasing (P < 0.05) with increasing levels of digestible organic matter (DOM) intake (r = 0.96). Endogenous urinary nitrogen (EUN) showed the opposite behaviour, decreasing from 181 to 76 mg/kg W(0.75), 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 (TEN) remained fairly constant, indicating that faeces and urine are complementary routes for the excretion of recyclable nitrogen compounds. The TEN overall mean value was very close to the value adopted by AFRC (AFRC Technical Committee on Responses to Nutrients, 1992. 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).