Copper, according to internationally renowned dairy scientist Jesse P. Goff, is “the trace mineral where deficiency is common and toxicity is also common.” That observation, combined with the wide array of bodily functions in the dairy cow that involve copper, makes it a good idea to keep an eye on this trace mineral in dairy cattle rations.
According to Dr. Goff, director of research and new product development for West Central in Ralston, Iowa:
•Growing tissues have a copper content of 1.5 milligram per kilogram of weight gained
•Copper is found in colostrum at about 0.6 milligrams per kilogram, and at about 0.2 milligrams per kilogram in milk
•About 0.5 milligram copper is incorporated into fetal, placental and uterine tissue growth daily in early gestation, increasing to between 1.5 and 2.0 milligrams per day during the last month of gestation.
Copper is involved in production of melanin pigment, development of strong bone and connective tissues, the transport of iron for hemoglobin synthesis and most importantly, in immune function. “Copper is a component of superoxide dismutase,” Goff reported, “which protects cells from the toxic effects of oxygen metabolites, which is particularly important to phagocytic cell function.”
Deficiency and toxicity
The current National Research Council recommendations for dairy cattle, regardless of breed, is 15 parts per million (ppm), or about 157 milligrams per day, in the total daily ration. The maximum tolerable level is 100 ppm.
Symptoms of copper deficiency are many, including scours, anemia, fragile bones, poor growth and poor reproduction. The classic sign is faded pigmentation of the hair around the eyes. What is not easily observed, according to Roger Hemken, professor emeritus at the University of Kentucky and chair of the 1989 NRC Nutrient Requirements of Dairy Cattle, is loss of immune function.
More dramatic is toxicity. Copper toxicity occurs when the liver can no longer absorb any more copper. The liver dumps the copper into the bloodstream and the blood copper level shoots up, causing a hemolytic crisis. In hemolytic crisis, the blood loses its normal oxygen-carrying capability, ending in death.
“Talking with producers who have had a problem,” Hemken said, “what happens is that a high-producing cow suddenly gets sick, goes off feed within a week to 10 days, drops milk production, then dies.”
The only sure way to tell if it is copper toxicity is to have a tissue biopsy.
“In most of the cases of copper toxicity that I have worked with, all were feeding less than 50 ppm,” Hemken noted. “It’s not something that you are going to walk into your barn one day and 50 percent of the herd is dead. And for that reason it is hard to diagnose.”
Jersey vs. Holstein: A difference?
Awareness of copper toxicity dates back to the mid-1990s, when it was determined as the cause of cattle deaths in several high-producing Jersey herds located in different regions of the U.S.
Subsequent research at the University of Kentucky suggested Jerseys may have a lower tolerance of dietary copper compared to Holsteins.
According to Dr. Patrick French, who worked with Hemken, “The studies show that for Jerseys, copper accumulates in the liver quicker than for Holsteins.”
The Kentucky team found Jerseys stored more copper in the liver than did Holsteins. At a higher copper supplemental level, Jersey cattle increased their liver copper concentration more rapidly than Holsteins.
French, manager of ruminant nutrition and research for Southern States Cooperative Inc., in Richmond, Virginia, has also completed studies in the mixed-breed herds at Virginia Tech and Oregon State University.
In trials at Virginia Tech, cattle were fed a ration supplemented at NRC requirements. Liver copper levels for Jerseys were 40 percent higher than for Holsteins. At Oregon State, the total diet included from 20 to 25 ppm of copper, with 8 ppm coming from forage and grain and the balance supplemental. At Oregon State, copper was twice as high in Jerseys as Holsteins.
The take-home message? It is not unusual to find Jerseys 50 percent to 100 percent higher than Holsteins.
The reasons are unclear. “Either Jerseys absorb it more efficiently,” French said, “or they don’t excrete it as much. No one has ever nailed that down for Jerseys compared to Holsteins.”
Implications for mixed-breed herds
No matter what the explanation may ultimately be, owners and nutritionists working with mixed-breed herds should be aware of this difference. “Bob James of Virginia Tech once talked to me about a herd he was consulting that was a mixed herd of Jerseys and Holsteins,” Hemken said. “The same amount of copper was fed to both. The owner lost some Jerseys but didn’t lose any Holsteins.”
Similarly, Hemken noted talking to a Jersey breeder in Georgia who purchased his feed from a Holstein producer. The Jersey breeder lost cows, but the Holstein producer never did.
“If you follow NRC recommendations, you should have no problems,” French said. “There is no reason to have more than 20 to 23 ppm in your ration. Oversupplementation or supplementation above requirement will not improve productivity.”
There are two schools of thought on how to manage the level of dietary copper in the ration, French explained. “Either you take into account copper in the grain and forage portion of the ration and adjust accordingly, or you ignore it and supplement at 10 ppm.”
With that said, “you need to take into account the amount of copper that you’re supplementing that is complexed to an amino acid or peptide. These products are absorbed with greater efficiency and supply more mineral because bioavailability is greater.”
The Kentucky researchers also found higher levels of whole cottonseed and cottonseed meal increased the amount of copper absorbed. “We believe it is the gossypol in the cottonseed that helps the absorption,” Hemken said.
The point? “If Jerseys are more efficient at absorbing copper, then an additive effect would be expected,” French advised. “You need to keep an eye on this and reformulate, if necessary.”
On the opposite side, there are interfering factors. One is iron. In another study, Hemken and colleagues fed copper at levels higher than 40 ppm to Jersey and Holstein steers in order to create toxicity. By the end of the study, no steers had died and it was determined they were fed rations with iron levels as high as 500 ppm. The high levels of iron had interfered with the copper absorption, preventing toxicity.
In French’s view, the maximum tolerance for copper, 100 ppm, stated in the NRC requirements can confuse the question of how much copper to supplement in the ration. “One can look at levels of 40 or 50 ppm, and say, it’s half of that, so it should be okay.”
The problem, French said, is that “maximum tolerable level is defined as the dietary level, when fed for a limited time, that will not impair animal performance. ‘Limited time’ is key since time is not defined. It could mean a week, month or several months.”
But how long for copper, no one knows. “There are no long-term studies.”
Based on the research and his experience, French observed, “Jerseys could tolerate that once or twice, but they couldn’t tolerate it for very long.”
•If you are working with Jersey cows in any situation, you need to be aware of this potential problem.
•An occasional unexplained death in a herd, or an increased death rate could be due to copper toxicity. Look at the level of copper being supplemented. Higher levels need to be investigated further.
•If you have had a problem, don’t cut back too much on the amount of copper being supplemented. Copper deficiency has been found to depress the immune response system, making the animal less resistant to disease, and lower reproductive efficiency. Studies have also shown cows that are copper deficient are more susceptible to mastitis. PD
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—Submitted by the American Jersey Cattle Association