Liveweight gain and urinary nitrogen excretion of dairy heifers grazing perennial ryegrass-white clover pasture, canola, and wheat

This study was carried out to examine liveweight gain (LWG), urinary nitrogen (N) concentration, and urinary N excretion of dairy heifers grazing perennial ryegrass-white clover pasture, dual-purpose wheat and dual-purpose canola. A temporal replicate design with two replicates was used to conduct the study. A total of 24–30 Friesian × Jersey heifers, aged 9–11 months were allocated into three dietary treatment groups (pasture, canola, and wheat) according to their initial LW (184 ± 7.0 kg; mean ± s.d.) and breeding worth (NZ$142 ± 11.3; mean ± s.d.). Feed was allocated every 4 days with allowance calculated according to feed requirement for maintenance plus 0.8 kg LWG/day. The LWG over the 26–28-day experimental period was higher (P < 0.001) for heifers grazing wheat (0.66 kg/day) and canola (0.53 kg/day) than pasture (0.35 kg/day). After the experimental period, heifers were grazed together in one herd on pasture. The LWG over the 28–44-day carryover period was higher (P < 0.001) in canola (0.86 kg/day) than wheat (0.57 kg/day) and pasture (0.61 kg/day). The concentration of urinary N was lower (P = 0.017) in canola (0.21%) and wheat (0.24%) than pasture (0.35%). Estimated urinary N excretion was lower (P < 0.001) in canola (52.5 g/day) and wheat (59.1 g/day) than pasture (98.9 g/day). Data suggest that grazing canola and wheat compared with pasture may improve heifer LWG and potentially reduce N losses to the environment by reducing the N loading of urine patches.

Live weight gain, urinary nitrogen excretion and urination behaviour of dairy heifers grazing pasture, chicory and plantain

SUMMARYThe objective of the present study was to investigate live weight (LW) gain, urinary nitrogen (UN) excretion and urination behaviour of dairy heifers grazing pasture, chicory and plantain in autumn and spring. The study comprised a 35-day autumn trial (with a 7-day acclimation period) and a 28-days spring trial (with a 7-day acclimation period). For each trial, 56 Friesian × Jersey heifers were blocked into five dietary treatments balanced for their LW and breeding worth (i.e. genetic merit of a cow for production and reproduction): 1·00 perennial ryegrass–white clover pasture (PA); 1·00 chicory (CH); 1·00 plantain (PL); 0·50 pasture + 0·50 chicory (PA + CH); and 0·50 pasture + 0·50 plantain (PA + PL). A fresh allocation of the herbage was offered every 3 days with allowance calculated according to feed requirement for maintenance plus gain of 1·0 kg LW/day. In both trials, LW gain was lower on CH than other treatments. In the spring trial, UN concentration and UN excretion were lower in CH and PL than other treatments. In autumn, a higher urination frequency was observed over the first 6 h after forage allocation in CH and PA + CH than other treatments. Data from the present study indicate that feeding CH alone limited heifer LW gain. However, heifers grazing swards containing chicory (CH and PA + CH) and plantain (PL and PA + PL) had the potential to lower nitrous oxide emissions and nitrate leaching from soil compared with heifers grazing PA, by reducing N loading in urine patches.

Tolerance of newly sown cocksfoot-clover pastures to the herbicide imazethapyr

In New Zealand, subterranean clover is recommended as a companion legume in mixed swards, particularly in dryland cocksfoot-based pastures. However, establishment of cocksfoot is slower than perennial ryegrass and therefore weed ingress is more common. An experiment at Lincoln University, Canterbury showed imazethapyr applied when clover was at the 3-4 trifoliate leaf stage, and cocksfoot at the 2+ leaf stage, increased the subterranean clover content of the pastures by at least 1000 kg DM/ha, despite initial visual phytotoxicity responses. Balansa and white clover pasture yields were not different to their unsprayed unweeded controls. Imazethapyr application controlled broadleaf weeds from early in the season. The herbicide application reduced cocksfoot yields by 70% in early spring, but yields recovered and were not different to the unsprayed unweeded controls at 1350 ± 260 kg DM/ha after grazing. Imazethapyr application improved subterranean clover pastures through an increase in clover content by suppressing weeds and temporarily reducing the rate of cocksfoot growth. Keywords: subterranean clover, Spinnaker herbicide, seedling, white clover, balansa clover