Too much of a good thing may be plaguing U.S. dairy cows. A recent conversation on The Dairy Podcast Show visited the topic of copper toxicity in lactating dairy cattle. Host Barry Bradford, CE Meadows Endowed Chair in Dairy Management and Nutrition at Michigan State University, expressed concern about the condition to guest Jose Santos, DVM and professor in the Department of Animal Sciences, University of Florida.
Bradford said he believes a high fraction of dairy cows in the developing world are probably on the borderline of copper toxicity.
“There is a valid concern about copper, because there has been overfeeding of it,” said Santos. In a recent survey among feed labs, he found only about 10% of dairy feed samples were being analyzed for minerals. “That tells me that most nutritionists don’t bother to analyze for minerals, and even less for trace minerals.”
Santos explained that if the trace mineral values in the baseline diet are ignored, and more supplemental trace minerals are added to the ration, an overdosing situation occurs.
Impaired Liver Function
When cows accumulate too much copper, it piles up in the liver. The result can be liver damage at the cellular level, liver necrosis, and impaired liver function. Theo Wieggers, a dairy veterinarian in New Zealand, noted that copper imbalance happens regularly there, because New Zealand’s soils have extremely low levels of copper, so it must be “manually” managed in the ration.
Copper recommendations for dairy cows were closely examined in the drafting of the 8th revised edition of the Nutrient Requirement of Dairy Cattle (NASEM 2021). Recommended dietary levels remained fairly steady for average lactating cows (11 mg/kg DM). However, requirements increased for dry cows by 40% (17 mg/kg DM) and decreased 45% (9 mg/kg DM) for high-producing cows.
These recommendations also can be affected by other, antagonistic minerals in the diet. Sulfur, molybdenum, and iron are important dietary components that can negatively impact copper absorption. Excess copper can be detected via blood tests and liver biopsies of either live or harvested animals.
Affected cows may also show jaundice of the mucous membrane around the eyes. Bradford hypothesized that one source of additional copper in feedstuffs may be the result of the best of intentions in dairy management: the humble footbath. “We’ve been using copper sulfate for footbaths for two decades, yet maybe we haven’t analyzed trace minerals for homegrown crops for 10 years,” he observed.
Santos advised regular evaluation of feedstuffs for trace minerals, especially in forages that are harvested close to the soil. In addition to more accurately assessing total copper content of rations, “it could produce some cost savings. To me it’s logical. We don’t ignore other nutrients.”
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