According to Dr. Jeremy Schefers of the University of Minnesota Veterinary Diagnostic Laboratory, the rising levels of copper concentration in liver samples of dairy cattle received at the diagnostic lab remains a practical concern. The reason for the concern is the common usage of copper sulfate in footbaths on many dairy farms for the control of digital dermatitis.
As a result, manure with increasing copper concentrations is applied on cropland.
Ev Thomas of the Miner Institute in 2001 reported increased soil concentration of copper when copper sulfate is used in footbaths. In addition, the use of foliar application of micronutrients, including copper, are increasing. Therefore, managing copper usage in footbaths, cropland and dairy rations is essential for optimizing cow health and soil integrity.
Function and requirements
Copper is a key component for many vital enzymes necessary for strong bone and connective tissues. Ceruloplasmin and superoxide dismutase play a role in immune function, as both support antioxidant systems. Ceruloplasmin aids in the absorption and transportation of iron, which can bind to oxygen.
Superoxide dismutase protects cells from oxygen metabolites by forming hydrogen peroxide, thus allowing phagocytic cell function.
The amount of dietary copper required to supply what is needed for maintenance, growth and lactation will vary with the age of the animal. To meet the National Research Council (NRC) 2001 nutritional requirements for dry and lactating dairy cows, rations need to contain 13 to 15 parts per million (ppm) of copper.
When cattle consume excess copper, it begins to accumulate in the liver before toxicities become evident. During periods of stress, potentially large amounts of copper can be released from the liver into the bloodstream, causing destruction of red blood cells and eventually leading to death.
Historical copper levels
Copper in dairy rations can come from either supplemental sources or dietary feed ingredients. Because nutritionists have not traditionally tested for copper, they rely heavily on historical values. According to NRC 2001, average copper concentration in legume silages is 9 ppm and corn silage is 7 ppm. With the increasing use of copper sulfate and foliar applications, are these basal values increasing?
As part of a 2015 Vita Plus summer internship project, 50 dairy farms across Wisconsin were surveyed to compare copper levels in forages and TMRs to answer that question.
Copper levels on-farm
In the survey, producers were asked a series of questions to determine the amount of copper applied to cropable acres through manure and foliar application. Of the 50 farms surveyed, 44 used copper sulfate in footbaths. Of those 44 farms, four of them were also using a foliar application containing copper.
Producers contributed approximately 0.25 to 10.5 pounds of copper per acre per year, with the average producer adding 2.9 pounds of copper per acre per year.
The average corn crop yielding 150 bushels per acre only removes 0.11 pounds of copper per acre per year, according to L.G. Bundy in 1998. The additional copper begins to accumulate in the field. In addition to the low removal rate by crops, copper has a low solubility which can quickly lead to elevated soil copper levels.
Copper sulfate is a bactericide, hence its use in footbaths, which can also impact beneficial bacteria in lagoons and soil. Therefore, excess copper in soil can also harm crop production by binding up vital nutrients.
Copper levels in forages
Copper levels in legume forages averaged 9.8 ppm and ranged approximately from 5 to 30 ppm. Corn silage copper levels averaged 7.7 and ranged approximately from 3 to 21 ppm. Compared with historical values in the NRC 2001, these values are slightly greater.
While the averages are slightly higher, there is a great deal of variation from farm to farm. Dairies with especially high levels of copper in forages need to observe soil copper levels more closely.
Location in Wisconsin matters as well. Dairy farms in southeast Wisconsin had the highest concentration of copper in forages when compared to the other regions in Wisconsin (Figure 1).
Soil type, crop rotation and manure application may possibly contribute to the elevated copper concentrations. Based on individual farm and location, elevated copper levels in forage would warrant monitoring copper application and concentration in soil on cropland.
Copper levels in TMR
Variation in forage copper concentrations contributed to variation in copper concentration in the TMR being fed. Rations contained approximately 8 to 28 ppm of copper, with the average being approximately 18 ppm. Recommendations from NRC 2001 for lactating dairy cows is 15 ppm, while the maximum tolerable level for copper in dairy cattle is 100 ppm. Therefore, dietary copper levels did not excessively exceed guidelines.
There is also variation of absorption in dairy cattle between breeds. The American Jersey Cattle Association has documented that Jersey cattle accumulate copper in the liver quicker than Holsteins and should be managed accordingly.
Conclusion
In summary, the survey found that forage copper levels are slightly greater than the current NRC 2001 guidelines. In addition, forages in southeast Wisconsin – and potentially other regions – have greater concentrations of copper. This indicates a potential for copper to accumulate in soil through copper sulfate footbaths and needs to be monitored closely.
Most dairy farms find it difficult to eliminate copper sulfate completely, but proper use would prevent unnecessary amounts of copper in the environment. It is important to mix copper sulfate to the proper concentrations in footbaths. If copper concentrations are elevated on your farm, it may be time to investigate alternative footbath solutions.
Also, it is important to monitor manure application on cropland to ensure copper concentrations are evenly distributed across enough crop acres to maintain soil integrity. Monitoring copper levels in forages and soil is essential to establish baseline levels to evaluate copper concentrations in the future. PD
Zach Sawall is a dairy technical service specialist with Vita Plus.
