Copper accumulation in dairy

In addition, it provides protection against oxidative damage via superoxide dismutase, immunity and hair pigmentation. However, copper is also toxic to ruminants, and the margin between deficiency and toxicity is quite narrow. Therefore, determining the right level of supplementation is quite challenging. In recent years, more and more reports have been published where copper toxicity was diagnosed as the cause of problems on farms or even death. So, how much should we feed?

Copper absorption is key

In general, copper absorption in ruminants is very low, typically varying between 1-5%. It is very well known that antagonists affect copper availability greatly. Well-known antagonists include high levels of iron (a ratio of Fe/Cu <50 is considered safe, with a maximum of 100) and zinc. Particularly sulfur and molybdenum (a ratio of Cu/Mo >3 is considered safe) are renowned antagonists. It's important to consider that iron and sulfur from drinking water should also be taken into account. The interaction of S-Mo-Cu, leading to the formation of the insoluble complex thiomolybdate, is particularly detrimental to copper availability; see figure 1.

How much copper to feed?

To know how much copper to feed, three factors are important:

1 Which animals are you going to feed: bodyweight, growth, production, gestation stage
 This will result in the calculation of the net requirement of copper per animal per day.

2 What is the current copper status of the herd
The analysis of copper levels in the liver (via a liver biopsy) is a reliable indicator of a potential copper excess. At least 3 cows should be sampled. Table 1 shows the relationship between liver copper level and the animals’ copper status (source: National Health Service for Animals, NL).

In international literature, a level of around 500 mg/kg DM in the liver is considered good, and over 1000 mg/kg is potentially toxic. When cows are under stress, such as during parturition or heat stress, lower levels of copper (ranging from 600 to 1000 mg/kg DM in the liver) can already become problematic. To assess the presence of a copper deficiency, copper analysis in tank milk can also be used. Levels lower than 20 μg/L indicate a deficiency. Blood analyses of copper can also indicate a deficiency: below 10 µmol/L or below 0.6 mg/L are an indication of too low copper status.

3 What is the level of antagonists in the diet

In table 2 an example is calculated for a cow of 600kg bodyweight, 35kg milk production, 22.8 kg DM intake of which 9 kg DM intake of compound feed with average levels of S and Mo in the diet.

Table 2. Overview of the effect of sulphur and molybdenum levels on the required copper supplementation of a dairy cow to meet her requirement.

Table 1 shows that the level of antagonists has a huge impact on the required level of added copper in the compound feed. In certain areas in peat-rich soils, molybdenum levels in pastures and clover can reach even up to 100mg/kg DM. So the risk of an impaired absorption of copper is certainly a possibility in different regions.

Copper supplementation advice

It is clear that copper supplementation is not straightforward and the recommendations are hugely affected by the presence or absence of antagonists in the diet. The first advice is to analyze silages and other forages on copper, sulphur, molybdenum, and iron to be able to calculate the total copper requirement of the cows. Be aware, that copper cannot be added to the diet without limits. EU regulation prohibits levels of >30 mg total copper/kg of feed (at 88% DM). In case of high levels of antagonists or when your dairy farm customers farm in a wide range of soil types/circumstances, organic copper should be considered.

In case copper accumulation or even intoxication is suspected: take liver biopsies. In the case of high values (>600 mg Cu/kg DM liver), revise the copper supplementation and reduce it.

If you would like to discuss the copper supplementation in dairy in detail, please contact us.