Copper (Cu)
The trace element where the right rate for one species can kill another — and the one most often locked up by something else in the pasture rather than absent from it.
Often searched as copper deficiency, copper toxicity.
What the pasture test should show
There is no single copper number — it is the one trace element where the requirement differs enough between species to matter, and where a rate that suits one can poison another. These are dietary concentrations; published pasture adequacy figures are different numbers, and both circulate.
| Species | Target, mg/kg DM | Deficient below | Toxicity watch |
|---|---|---|---|
| Sheep Sheep need little copper and are the most easily poisoned — keep well clear of cattle/goat/deer copper rates. | 5–8 | 5 | > 15 |
| Cattle Cattle need about twice the copper of sheep; high molybdenum or sulphur locks it up. | 8–11 | 7 | — |
| Deer Deer need ~2× the copper of sheep (≈ cattle) and tolerate more — copper is the number-one deer trace issue in NZ. | 10–12 | 8 | — |
| Goats Goats need roughly 2–3× the copper of sheep and store it poorly, so a low-copper "sheep" mineral under-supplies them. | 10–20 | 10 | — |
What it changes in the tools
- Copper by species — and which basis it is on
- Sheep 5–8, cattle 8–11, deer 10–12, goats 10–20 mg/kg DM, with a toxicity watch for sheep above 15. ⚠️ THE BASIS MATTERS AND THE LITERATURE MIXES IT. Published copper figures come as DIETARY concentrations (MSD: sheep 5–8; Grace & Knowles: cattle and deer need twice sheep, i.e. 10 vs 5) and as PASTURE concentrations, which are different numbers — B+LNZ put adequate pasture at 5–6 mg/kg DM for sheep provided molybdenum is under 1, and Morton (2024) gives pasture-adequate as sheep 5–6, cattle 9–11, deer above 11. Read our figures as dietary. Two of them are ours rather than published: cattle "deficient below 7" and the sheep toxicity watch at 15 are conservative lines we set, and goats at 10–20 sits below MSD's 15–25 — a growing goat needs more again.
- Source: Sheep 5–8 dietary: MSD Veterinary Manual (Nutritional Requirements of Goats, comparing the two species). Cattle and deer at twice sheep: Grace & Knowles (2012), Vet. Med. Int. 2012:639472. Pasture-adequate ranges: Morton (2024), J. NZ Grasslands 86:201–212 Table 1 (after Grace et al. 2010); B+LNZ Fact Sheet 95. Goats: MSD gives 15–25 and MSU Extension P3929 gives 10–80 (after Hart, Langston) — our 10–20 is narrower than either. ⚠️ The cattle <7 deficiency line, the >15 sheep toxicity watch and the deer 10–12 range are NOT published figures; NRC 2007 was cited here previously and could not be verified.
- Sheep grazing alongside
- A copper supplement or mineral mix dosed for goats, deer or cattle can cause fatal chronic copper poisoning in sheep. Never give the same high-copper product to sheep.
- Source: Merck/MSD Veterinary Manual; NRC 2007 Small Ruminants.
- Molybdenum lock-up
- Pasture molybdenum above 1 mg/kg DM antagonises copper; above 3 it also cuts the efficacy of oral copper supplements by 30–50%. Sulphur above 0.4% DM compounds it.
- Source: Grace & Knowles (2012).
Read it for your farm
Put your herbage test in and it reads the trace elements against these bands for your stock class.
These are published reference bands, not a diagnosis. Mineral deficiencies and toxicities are diagnosed from the animal — blood, liver or tissue — not from a pasture test alone, and the treatment rates are veterinary decisions. Talk to your vet before dosing stock.