Copper is an essential trace element that is needed for many biological functions including growth, pigmentation, fertility, healthy nerve fibres and the immune system. In New Zealand (NZ), copper deficiency is a common occurrence and a major problem unless managed effectively.
There are two main causes of copper deficiency in cattle. Primary copper deficiency occurs when there is low copper availability in pasture due to naturally copper-deficient soils/lack of copper in fertilizer. Secondary deficiency or an induced deficiency is caused by ingestion of feed with excessive levels of molybdenum or sulphur which act as “antagonists” to copper uptake and absorption. Both examples exist in NZ, often simultaneously, and it is therefore vital to monitor and supplement copper in livestock.
Monitoring and maintaining adequate copper focuses on both sampling and supplementing the cattle themselves and the pasture they consume.
The liver is the primary store for copper in the body and the best way to assess copper status in cattle is to measure copper levels in their liver. This is typically done on liver samples from slaughtered animals, or by live-animal biopsy. Liver Copper (Cu) <45µmol/kg indicates copper deficiency. Blood can also be tested for copper levels, but it is a less accurate indicator in that it does not reflect long-term copper intake and storage.
Pasture analyses for copper and molybdenum concentrations provide only a rough guide to the copper status of cattle grazing them. Dietary copper is poorly absorbed and the complex interaction of copper with molybdenum, sulphur, iron, and zinc in the diet can further lower absorption. This makes it difficult to establish the copper levels in pasturage that are adequate for animal health because true absorption varies significantly.
The following is an outline for sampling techniques, in order of effectiveness:
- Liver biopsy (5-10 animals required)
o WHEN: Late autumn (not after seven months pregnant) or pre-mating.
- Blood samples (minimum 10 animals required)
o WHEN: Late autumn/winter.
- Pasture testing
o WHEN: Quickly grown grass in late autumn.
- Soil testing
o Of little value because there is a poor relationship between soil copper levels and plant copper levels.
Supplementation and duration of treatment
Copper levels must be low for several months before signs of deficiency are evident, so the goal should be to maintain stores at adequate levels at all times to prevent production losses. There are multiple methods of supplementation, all with varying costs, practicality, and efficacy. As previously stated, absorption of copper in ruminants varies greatly depending on the concentrations of the main copper antagonists molybdenum and sulphur, which must be taken into consideration when calculating the copper requirements. Additionally, care should be taken to not inadvertently cause copper toxicity with excess supplementation.
Copper can be given via slow-release intraruminal boluses, often combined with selenium and cobalt. These are often most suitable for youngstock where no water treatment dispenser is available and can last up to one year in cattle.
Copper compounds injected under the skin can correct a deficiency, but must be repeated every four to six months. This method is both less convenient and more expensive than supplying copper through fertilisers. Not recommended in pregnant cattle.
Multi-mineral supplements and PKE
Multi-mineral supplements are useful when individual animal treatment is impractical. However, some animals may fail to eat or lick the supplement which reduces its efficacy, or they may consume too much and risk toxicity. Subsequently, PKE is known for having high copper concentrations and it’s rare to need further copper supplementation if PKE is being fed.
Drenches and drinking water
Copper sulphate can be supplied through drinking water, but the dose rates cannot be controlled so they are not generally recommended. Drenches only have a brief effect and are not recommended for treating acute copper deficiencies.
Copper sulphate fertiliser can easily be incorporated into annual autumn or spring fertiliser and topdressing pasture with copper can increase the copper content rapidly. However, the effectiveness of topdressed pastures will be less in the presence of high molybdenum concentrations and molybdenum should therefore be applied conservatively. Where too much molybdenum has been applied, extra copper fertiliser may not be effective in correcting the induced copper deficiency. Only apply molybdenum fertiliser to correct deficiencies in plants and apply during the cropping phase. If molybdenum is applied to pasture, do not allow cattle to graze the area until after heavy rain.