Urinary nitrogen concentration from dairy heifers grazing kale supplemented with either plantain or perennial ryegrass baleage in winter

The effect of feeding two different supplements (perennial ryegrass or plantain baleage) on urinary nitrogen (N) excretion from dairy heifers (8 months old, 180 kg liveweight (LW)) grazing kale was examined in two successive winters. Heifers (n=90 and 80 in Years 1 and 2, respectively) were offered 2.5 kg DM kale/100 kg LW/day and approximately 3 kg DM/heifer/day of either perennial ryegrass or plantain baleage. Urine samples were collected 2-4 times throughout winter, acidified and frozen before N analysis. Despite similar apparent N-intake, urinary N concentration from heifers supplemented with plantain baleage (0.36% N) was lower (P<0.05) than those supplemented with perennial ryegrass baleage (0.53% N). Creatinine concentrations in urine and observations of urination frequency suggest some of the decrease in urinary-N concentration may be due to increases in urine volume when heifers were fed plantain baleage. Liveweight gain (g/heifer/day) was similar (P>0.05) for heifers fed either supplement. The results indicate that feeding plantain baleage to dairy heifers grazing kale in winter may be a useful approach to decrease the N loading in urine patches with subsequent reductions in nitrate leaching.