Brief communication: Urinary nitrogen excretion and water balance of dairy heifers fed cut plantain or perennial-ryegrass pastures

The objective of our study was to quantify the effect of feeding plantain (PL) or perennial ryegrass (RG) to dairy heifers on urinary nitrogen (N) excretion and water balance. In an indoor cut-and-carry system, four Jersey × Friesian dairy heifers were grouped and randomly assigned to one of two dietary treatments of RG or PL for two weeks. Daily drinking water intake was lower (P=0.010; 2.8 vs 6.9 L), and forage (P=0.038; 53.7 vs 29.1 L) and total (P=0.046; 56.5 vs 36.0 L) water intake were greater for PL than for RG, respectively. Heifers fed PL excreted more (P=0.009) water in faeces and urine than did heifers fed RG (48.9 vs 21.9 L/day, respectively). Urine N% was lower (P=0.008; 0.23 vs 0.62%) and daily urine volume was greater (P=0.003; 35.8 vs 15.1 L/heifer) for PL than those of RG, respectively. Total urinary N excretion was similar between PL (91.1 g/day) and RG (96.7 g/day). These results indicate that, in comparison with RG, feeding PL to dairy heifers does not reduce urinary N output, but reduces urinary N concentration, due to a greater urine volume