Aspects of nitrogen metabolism in sheep-fed mixed diets containing tree and shrub foliages

摘要

Data on N utilisation by sheep-fed diets containing foliages were analysed to develop prediction equations for N excretion in faeces (FN) and urinen(UN), and to determine endogenous N excretion. Overall, 218 dietary treatments from forty-four publications were compiled in the database. Thisndatabase was split into three subsets: without foliage in the diets (FL-0); foliage levels (FL) in between 0 and 310 g/kg (FL-L); FL in between 310nand 800 g/kg diets (FL-H) to study the effects of foliages on metabolic faecal N (MFN) and endogenous urinary N (EUN). Nitrogen intake (NI)nas single independent factor was the best predictor of FN (R 2 0·75), UN (R 2 0·81) and total N excretion (R 2 0·86). Addition of dietary Nnconcentration and FL for FN (R 2 0·82), dietary N concentration and foliage NI for UN (R 2 0·85), and FL and foliage NI for total N excretionn(R 2 0·92) as supporting predictors to this relationship slightly increased R 2 values. The monomolecular and exponential models slightly improvednthe prediction of N excretion with NI as a predictor compared with the linear model. The excretion of MFN was greater for FL-H compared withnFL-0, but was similar between FL-0 and FL-L, and FL-L and FL-H. However, EUN decreased in FL-H compared with FL-0 and FL-L, but wasnsimilar between FL-0 and FL-L. In conclusion, using NI as the primary predictor produced an accurate prediction of N excretion. Inclusion ofnfoliages in the diets may shift N excretion from urine to faeces and increase the excretion of MFN and EUN.