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Copper
Written by John Turner Consultancy for Agifert
Copper is an essential trace element required for both plant growth and animal nutrition. The minimum requirement for animalslis slightly higher than the minimum requiement for plant growth so symptoms of copper deficiency are observed in grazing animals before it is clinical in pasture plants.
Syptoms of deficiency:
A wide variety of symptoms may arise from copper deficiency. In young animals, deformed leg bones, fractures of leg bones and high mortality rate due to anaemia and heart failure common symptoms. In older animals, reduced growth rate, reduced production, scouring, light or faded hair/coat colour and general unthriftiness are common symptoms. Copper deficiency may be associated with increased incidence of metabolic disorder, particularly in dairy cows around calving time.
Different classes of stock have different requirements for copper:
Sheep have a lower requirement for copper than cattle or deer and are more likely to suffer from copper toxicity due to a relatively low ability to excrete excessive dietary copper. Copper is required for the normal growth of bone, hair and skin so animals that are growing rapidly and female animals in late pregnancy are most likely to show copper dificiency.
Factors that affect the copper content of pastures:
There is some correlation between soil copper level and the copper content of plants however use of a soil test alone is not good enough to base a copper treatment recommendation on. Soils with low copper status in general are sandy Soils and peat soils. Application of high rates of lime will reduce copper availability to plants and alkaline soil(pH greater than 7) is also associated with low copper levels in plants. Low soil trmperature will reduce the copper levels up to 3 times that of grass growing under the same conditions.
Factors that affect copper absorption by animals:
Molybdenum is well known as a trace element that reduces the absorption of copper by animals and the factors that increase the molybdenum content of pastures are similar to those that decrease the copper content. These are high pH and wet soils including peat. The molybdenum level in pastures grown in late winter may be up to 3 times the level grown on the same site during hot dry summer conditions.
There is some debate about what is the desired level of molybdenum in pastures. Levels of between 1 and 2 ppm are not considered to have a severe effect on copper absorption by cattle however where the level is close to deficient for clover growth (0.15 ppm in summer), copper absorption may be slightly enhanced and 'mask' a simple deficiency in copper. The logic of running low Mo levels which may compromise clover growth and pasture production as an alternative to supplementing copper to livestock is questionable. Sheep may actually suffer from 'molybdenosis' due to lack of molybdenum leading to copper toxicity (Symptoms are black liver and liver failure) despite the diet having a normal copper level.
Dietary sulphur and iron at high levels (due to soil or mud ingestion) also affect the absorption of copper from forage. Forage brassicas generally have high levels of dietary sulphur.
Level of Copper required in pasture or feed:
Sheep have adquate copper at levels between 6 and 10 ppm which is a typical ryegrass based pasture level.
Cattle require about 10 ppm however in controlled feeding situations, levels of up to 20 ppm are recommended for cows during late pregnancy and for rapidly growing yearlings. Deer have at least as high a requirement for copper as cattle, the porduction of antlers/velvet from stags is likely to mean that they have a similar copper requirement to hinds.
To raise the copper level of pasture by 5 ppm, 5 grams of copper is required per 1000 kg of dry feed.
Testing for copper status:
Soil test data is of limited value in determining copper status of pastures and stock however where pasture herbage levels are low and the soil test level also appears low,soil application of copper as a solid fertiliser may be an option.
Blood test of animals or liver biopsy is used to determine the copper status of animals. Copper is stored in the liver and this reserve is used to maintain blood copper levels. The problem with the blood test is that it will not indicate low until the liver reserves are very low,but it is a convenient test to conduct. The liver biopsy is the best test but it is very invasive.
Options for Copper application:
Copper may be included in soil applied fertiliser as either copper sulphate (water soluble) or copper hydroxide (low solubility-slow acting) however raising the copper level in ryegrass to about 10 ppm for cattle or deer is not easily achieved.Application of more than 5 kg copper sulphate/ha may reduce pasture growth. Environmental factors affect the efficiency of uptake of soil copper by plants, particularly in winter/spring for dairy cows.
Mineralised salt blocks and drenches may contain copper but the amount is generally not sufficient to overcome copper dificiency. Copper addition to drinking water may be beneficial however this may not be effective for dairy cows during winter/early spring when pasture water content is high.
Injection of stock to treat copper deficiency is effective but this is a shock dose and ideally the copper supply to animals should be maintained at an adequate level. Bolus treatments provide a steady supply of copper but this may not be sufficient during peak demand periods such as late pregnancy in dairy cows. Foliar application to pasture or feed is a good option. Application timing for dairy cows after zinc treatment for FE is completed and 1 to 2 months prior to calving. For deer hinds in late pregnancy, stags at the start of horn growth and young stock after weaning. Be very careful about recommending copper for sheep, they have a low requirement and there is a risk of toxicity.