New Zealand Journal of Agricultural Research abstracts
Effect of increasing pasture copper concentrations on the copper status of
grazing Romney sheep
N. D. GRACE
S. O. KNOWLES
J. R. ROUNCE
Dairy & Beef Division
AgResearch Grasslands Research Centre
Private Bag 11008
Palmerston North, New Zealand
D. M. WEST
Institute of Veterinary, Animal and Biomedical Sciences
Massey University
Private Bag 11222
Palmerston North, New Zealand
J. LEE
Dairy & Beef Division
AgResearch Grasslands Research Centre
Private Bag 11008
Palmerston North, New Zealand
Abstract Application of copper (Cu) fertiliser has previously
been shown to increase and maintain pasture Cu concentrations, but to date the
Cu status of grazing livestock has not been monitored. In this study, the
application of 0.4 to 4 kg Cu ha-1 to twelve experimental paddocks
on North Island, New Zealand hill country resulted in mean pasture Cu
concentrations of 12.9 to 140 mg Cu kg-1 DM. Herbage Cu levels were
maximal 65 days following application and had returned to pre-experimental
levels by 374 days. Romney lambs grazing treated pastures for 176 days had
liver Cu concentrations as high as 7750 umol (450 mg) Cu kg-1 liver
FW after 99 days, but showed no clinical signs of chronic Cu toxicity. Herbage
Cu concentration (and, by inference, Cu intake) was well correlated with liver
Cu accumulation (R2 = 0.84). An exponential function
described the mean pasture Cu concentration and liver Cu concentration
relationship. Bile and faecal Cu concentrations reflected Cu intakes, but
caeruloplasmin activity, and Cu content of plasma, kidney, and muscle were not
affected by treatments. An indirect method to assess animal Cu status,
erythrocyte Cu/Zn superoxide dismutase activity, was compared with liver Cu
concentration and found to be a predictor of liver Cu stores only in sheep
having low to moderate Cu intake. As a method to increase the Cu intake of
grazing sheep, Cu fertiliser applied at 1-2 kg Cu ha-1 per annum
results in pasture Cu concentrations of 10-20 mg kg-1 DM and has an
acceptable margin of animal health safety. In situations of Cu deficiency or
chronic Cu toxicity, the most reliable indicator of sheep Cu status is changes
in liver Cu concentration.
Keywords copper fertiliser; lambs; molybdenum; chronic
toxicity; liver; plasma; heritability
New Zealand Journal of Agricultural Research, 1998, Vol. 41: 377-386
0028-8233/98/4103-0377 $7.00/0 (c) The Royal Society of New Zealand
1998
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