Nitrogen partitioning in sheep offered three perennial ryegrass cultivars at two allowances in spring and autumn

摘要

The objective of this study was to determine the nitrogen (N) partitioning in sheep fed freshly cut diploid high-sugar (water-soluble carbohydrate, WSC) ryegrass (HSG), tetraploid ryegrass (TRG) and conventional diploid ryegrass (CRG) offered at 1.1 and 1.8 times maintenance energy requirements (MEm) in spring and in early autumn. Overall, N intake was higher for sheep fed HSG compared with sheep fed CRG (P=0.03), with sheep fed TRG being intermediate. Faecal-N output was higher for HSG than for TRGand CRG (PO.001), urinary-N output was higher for TRG than for HSG, which were both higher than CRG (P<0.001) and N-retention in the body was higher for CRG compared with TRG (P<0.001), with HSG being intermediate. Relative to N intake, urinary-N outputwas higher (P<0.001) and faecal-N output (P<0.001) was lower in TRG compared to CRG and HSG with bigger differences among cultivars in spring than in autumn. Faecal-N output, urinary-N output and N-retention were higher at 1.8 x MEm than at 1.1 x MEm (P<0.001) and higher in autumn than in spring. Feeding CRG and HSG resulted in reduced urinary-N excretion relative to N intake compared with TRG in both spring and autumn and forage WSC intake was one of the main explanatory variables for differences in urinary-N as proportion of N intake.