The effectiveness of copper fertiliser in maintaining the copper status of deer at moderate to high pasture molybdenum contents

Copper (Cu) deficiencies are an important concern of the New Zealand livestock industry, particularly for deer. Cu fertiliser application to pastures has been proven to be effective, providing the particle size is suitable and the pasture has low molybdenum (Mo) concentrations (< 1 ppm). Afield study was set up to determine the effect of Cu fertiliser application on deer grazing pastures of moderate to high Mo concentrations (2-8 ppm). Mobs of deer (red x elk and red x wapiti weaners) grazed both Cu fertilised and non-fertilised paddocks on farms near Rotorua (pasture Mo 6-8 ppm) and in Southland (pasture Mo 1-2 ppm) over the winter of 2003. An initial application of solidCuSO(4) (12-15 kg ha(-1)) applied in April 2003 failed to elevate pasture Cu above an effective level of 11 ppm due to large particle size (97.8% > 2.0 mm) and slow dissolution. Liquid CuSO4 at 5-6.7 kg ha(-1) was sprayed on pasture in June/July, and grazed by the trial animals. This application resulted in a significant increase in serum Cu (P < 0.05) when compared to untreated controls (16.8 versus 9.1 mu mol litre(-1) after 14 days at Rotorua and 11.6 versus 7.8 pmol litre(-1) after 1 day in Southland). At the Rotorua site, deer serum Cu levels in the mobs grazing Cu fertilised pasture were maintained in excess of 15 gmol litre(-1) up to the trial completion in October 2003. In contrast at the Southland site, deer serum levels in the Cu fertilised treatment started to decrease by October 2003. The animal liver Cu levels at both sites were increased by grazing the Cu fertiliser amended pasture for both the August (656 versus 158 pmol kg(-1) fresh tissue, P < 0.001) and October (362 versus 83 mu mol kg-' fresh tissue, P < 0.01) samplings. The Cu spray application increased pasture Cu concentration for more than 3 months at Rotorua but only 2 months in Southland. Despite the extremely high initial pasture Cu concentrations achieved (> 1000 ppm), there were no visible signs of animal health problems with the animals grazing at the time of spraying. However, further research is required to determine the effect of such high pasture Cu concentrations on deer before a suitable level of Cu application to pasture and animal withholding period can be recommended. The results of this study showed that even at herbage Mo levels ranging from 1-3 ppm in Southland and 2-8 ppm near Rotorua, copper sulphate (5-6.7 kg CuSO4 ha(-1)) sprayed onto pastures in mid winter resulted in the herbage Cu concentration being increased to in excess of 100 ppm for 90 days. With this increase in herbage Cu, the animal Cu intake from grazing these pastures was sufficient to lift or maintain both serum and liver Cu levels in deer for up to 4 months.