Most copper poisonings of dairy cows are invisible when they happen and are far more common than many people think.
Most of us can envision that when dairy cows are poisoned with dietary copper, they immediately go off feed, are depressed, and exhibit a host of clear-cut signals such as jaundice, dark red urine and then die within 3 days of having these symptoms. Such acute copper poisonings can happen, but they are a rare occurrence.
The more common form of copper poisoning in dairy cattle is chronic in nature. It takes months of long-term ingestion of high copper levels in the feed, and the symptoms could be attributed to another nutritional problem or even a common disease. Fortunately, dairy producers can prevent a serious copper toxic challenge, just by knowing how much dietary copper that dairy cattle really need in order to remain healthy, achieve successful breeding and finally produce large volumes of high milk.
Dietary copper is designated an essential “trace mineral” required in very small amounts in the dairy cow’s body in order to conduct several key body functions and to achieve good dairy performance. It plays an integral part in many enzyme systems that are involved; in hemoglobin synthesis (the protein that carries oxygen in red blood cells), in connective tissue, bone and central nervous tissue development, as well as those serving roles in immune function.
The National Research Council (NRC) recommends that the copper requirement to support these functions in dairy cattle is 10 mg/kg of diet (re: dm basis), which given a dry matter intake of 25 kg (dm, basis) means we need to supply about 250 mg per head per day. This actual amount fed will vary with age, breed, stage of lactation, and health status of the individual dairy cow.
It is quite common for her average dairy diet to be artificially supplemented with copper that may exceed NRC requirements (adjusted for all production requirements) by 50 – 300 per cent. This excess is added by nutritionists, largely to avoid a primary copper deficiency due to an absolute lack of copper in the diet, or a secondary copper deficiency caused by other dietary antagonists (such as molybdenum or sulphur) which binds natural copper in the cows’ body and renders it biologically unavailable for metabolism. Such unsolicited over-formulation with copper tends to drive the potential for a deadly copper poisoning.
Ironically, the present conscience among dairy scientists is that dairy cattle receiving in excess of 800 mg/head/d of dietary copper (re: 32 mg/kg of the total diet, dm basis) are at risk of such chronic copper toxicity.
A case study performed at North Carolina State in 2001, fed a group of milking dairy cattle; experimental diets containing up to 40 mg/kg copper, and found out at the end of the 61-day trial, that the cows on the high copper diets had accumulated a toxic level of copper in their livers. Although, dry matter intakes, average, milk production, milk components, and somatic cell counts were similar among the treatments, the researchers felt it was only a matter of time before these “copper toxic” cows would start to show clinical poisoning symptoms.
As a group, most healthy mature Holstein cows with one or more lactations are relatively resistant to dietary copper poisoning compared to other dairy breeds, such as Jersey cattle, or other classes of livestock such as young calves and other cattle living under stressful conditions. The former cattle can excrete large amounts of excess dietary copper in their manure, but one should be aware that this large capacity is finite. It can be overwhelmed by exceeding high copper levels fed in the diet, largely because there is no control mechanism that restricts copper absorption by the intestine and subsequent accumulation in the liver, which is the main tissue reservoir for copper, and mirror of the copper status of the animal.
It seems that anytime too much dietary copper is fed, the potential for a serious copper toxicity problem becomes apparent.
There are clinical symptoms to a chronic copper toxicity that should make dairy producers suspicious that something is definitely wrong in their herd. Lactating dairy cattle can initially express subtle decreases in feed intakes followed by a heavy loss of milk production. The health status of the animals may be also compromised. Inside the cow’s body, the liver is slowly shutting down as it releases large amounts of poisonous copper into the bloodstream. Toward the end, the more serious affected dairy cattle become jaundice and death may follow, shortly.
With the assistance of a veterinarian, a few liver biopsies and blood samples should be taken and tested to confirm a chronic copper toxicity case. However, dairy producers can avoid a lot of time-consuming and expensive investigations, by simply beforehand, know more about their dairy ration that they are feeding.
The following suggestions are helpful in assuring that dairy cows are receiving enough dietary copper without consuming too much:
1. Calculate total dietary copper in your ration: Estimate or test the copper levels in your forages, grains, and know the copper level in all purchased feed products. With the dry matter intake of each feed ingredient going into the diet, a total copper level can be determined. If this number exceeds 25% of NRC requirements, the cows could be getting too much copper.
2. Know the dietary copper sources in your ration: This is particularly important when purchasing dairy supplements, basemixes, and premixes. Knowing the copper final concentration of your ration without knowing the source of supplemental copper is of little value. Copper comes in many forms such as copper oxide, copper sulphate, and chelated copper forms, which have relative biological availabilities of 5%, 100%, and 125 – 150% in dairy cattle.
3. Watch for out for copper hidden in your feed by-products: It is common for dietary nutrients to be concentrated in common dairy feed byproducts. For example, some samples of corn distillers’ grains have been tested to contain 75 mg/kg of copper. Fed at 2 kg per head per day could technically supply at least 50% of the cows’ copper requirement.
4. Do not supplement “extra” copper unless you need it: A common practice on many dairy farms is to feed a loose-form commercial mineral in addition to any mineral pack formulated into the total diet for lactating dairy cows. If a commercial range mineral contains 4000 mg/kg of copper, and is fed at 75 grams per head per day, these dairy cows are receiving 300 mg of dietary cow, which not only meets the NRC requirements, but could practically match what is provided by the main dairy diet!
5. Feed dietary copper wisely: Granted, marginal copper deficiencies affect many prairie dairy farms. One should realize that feeding a more bio-available form of copper such as chelated copper to overcome a deficiency problem should follow the same rules of formulation to prevent an explosive copper toxicity.
Excessive copper in our dairy diets may lead to a potential copper toxicity problem in our dairy herds. The key to prevent such fatalities from happening is to know how much copper is going into your current diet, implement the NRC dairy copper requirements as a guideline, and make any slight adjustments to supply just the right amount of dietary copper to keep the cows healthy and productive.
Proprietor and published by Bowes Publishers Limited at 4504 - 61 Avenue, Leduc, Alberta, Canada T9E3Z1
