Quantification of nitrogen metabolism parameters in fasting sheep

Abstract

Three whole male sheep of the early Merino breed, with an initial average weight of 50.8 kg, were subjected to eight days of fasting, observing the live weight and the excretion of feces and urine on a daily basis. Samples were analyzed to determine the concentrations of fecal dry matter and fecal and urinary nitrogen. By regression, the real weight loss (PPR, excluding fecal weight) was estimated at 66.6 g per day. The mobilized nitrogen (NM) was calculated by multiplying the PPR by the presumed value of 16% crude protein in the lost tissue. By the intercepts of the regressions of urinary nitrogen and fecal nitrogen excretions vs. Time, endogenous urinary nitrogen (NEU) and fecal metabolic nitrogen (NMF) were estimated at 317 and 59 mg per unit of metabolic weight (W0.75), respectively. By analogous methodology, the basal net nitrogen (NNB), taken as the sum NEU + NMF, was estimated at 364 mm / W0.75, and the recycled nitrogen (NR, taken as the difference NM - ENU, at 16.76 g per day The maintenance protein requirement was estimated in two ways at 5.4 g / W0.75, as (NNB × 6.25) divided by an efficiency factor of 45.64%.