COULD TRACE MINERAL DEFICIENCIES BE AFFECTING YOUR COWS’ PREGNANCY RATES?

The disease investigation unit at the Western College of Veterinary Medicine (WCVM) in Saskatoon is contacted every fall by veterinarians concerned about poor conception rates in a client’s herd. Once recognized risk factors for poor fertility like infectious disease, poor body condition, insufficient time between calving and breeding, and problems with bull power have been ruled out, concerns about trace mineral deficiencies are often raised.

One of the trace minerals commonly implicated as a cause of open cows in the fall is copper. There are two types of copper deficiency: primary, resulting from a deficiency of copper in the diet; and secondary, resulting from the reduction in copper absorption or utilization due to the antagonistic effects of molybdenum, sulphur, and iron. Copper deficiency is common in cattle worldwide and reported clinical signs have included unthriftiness, changes in hair coat colour, diarrhea (occurs in secondary copper deficiency due to the high molybdenum), lameness, and unsteady gait.

Nutritional deficiencies are most often a herd problem. In the case of copper, clinical signs of deficiency generally appear first in calves, rather than cows. Milk is a poor source of copper but, under normal conditions, a calf is able to store large amounts of copper in its liver during the last trimester of its pregnancy. However, this doesn’t occur if a cow is copper deficient during this time. Without adequate liver stores, the calf will be copper deficient until it is old enough to eat and digest forage containing copper. However, immature forages are naturally low in copper which can further increase the occurrence of copper deficiency in the spring and summer for young cattle on pasture. Unfortunately, many cows do not show visible clinical signs like changes in hair coat colour until the animal is severely depleted of copper. This means that identifying deficient cows is very difficult without lab testing.

A recent study of 40 Saskatchewan beef herds conducted by WCVM researchers found 46 per cent of the cows at the start of breeding season had blood copper levels considered marginally deficient (< 0.5 ppm), even though 80 per cent of the producers supplemented with trace mineral supplementation prior to calving and 55 per cent of them supplied trace mineral after calving. Interestingly, the copper levels in thin cows were very similar to the cows in good body condition. That’s an important point for producers to remember — you cannot tell what the mineral status of a cow is simply by looking at the body condition. Cows that are copper deficient are not more likely to be thin than cows that are in good body condition.

A critical question for producers is, “Will moderate or severe copper deficiency cause my herd’s reproductive efficiency to decline?” Some studies have found no relationship between blood copper status and fertility parameters, whereas others have found varying levels of fertility. Complicating the issue further is the many interactions between various trace minerals. Poor conception rates and delayed puberty have been documented when secondary copper deficiency was induced by supplements of molybdenum, but not when it was due to a low dietary copper or supplements of iron. Many studies examining trace minerals and reproductive health have used only small numbers of animals, frequently dairy cattle, under research conditions. Previous research has also examined trace mineral supplementation or deficiency as a single determinant of reproduction.

A recently completed field study in Saskatchewan found that the pre-breeding copper status of cows was related to their pregnancy outcome. The more copper deficient a cow was, the more likely she was to be open — even when copper levels were considered in combination with body condition score, calving to breeding interval and age. Only 17 per cent of these cows had high blood molybdenum levels (> 0.1 ppm) and these cows were not more likely to have low copper levels, nor were they more likely to be open. A great discussion of molybdenum in forages can be found in the May 2009 issue of Canadian Cattlemen (“Is molybdenum lurking in your forages?”).

Part of the discrepancies in the literature is a result of the various testing methods used to assess copper status. Liver copper content remains the gold standard for measuring body copper reserves. Blood copper levels are more commonly used in field investigations because blood samples are easier to collect, but this method does have some limitations. When a cow is deficient for copper in her blood, she most likely has depleted liver stores and requires supplementation. However, normal blood copper levels do not guarantee that the cow is receiving enough copper. A cow with normal blood levels may or may not be deficient. Given the cost, convenience and risk to animal well-being, blood samples are the most practical for trace mineral evaluation in the field.

The mineral status of your animals is directly influenced by the minerals present in your soil and water, the types of forages harvested or grazed, and your mineral supplementation. Including trace mineral analysis with your forage and water testing can provide some insight as to the common deficiencies or toxicities in your area. High sulphate is not uncommon in many livestock water sources throughout Western Canada, especially surface run-off dugouts or sloughs in drought years. These sulphates can interfere with the absorption of copper from the intestine and result in a secondary copper deficiency. So even if the copper in your forages or supplement appear adequate, your cows may become deficient because the copper is being bound and made unusable to the cow.

Differences in copper requirements between continental and British breeds of cattle have been identified. Copper is mainly lost from the body through bile from the liver. Continental breeds lose copper in their bile at twice the rate of British breeds on the same diet.

Correction of a primary or secondary copper deficiency is commonly achieved by feeding a mineral supplement. Injecting cattle with copper is a possibility, but it is only a short-term fix. Maintaining a copper-to-molybdenum ratio of greater than 5:1 in your ration is ideal and toxicity will soon follow if the copper-to-molybdenum ratio drops to less than 2:1.

It is critical to keep in mind that too much copper can cause toxicity, so just because a little is good, doesn’t mean that a lot is better!

Beyond copper, many beef producers continue to be concerned about the selenium and vitamin E status of their cattle. The supplementation of these two micronutrients has been related to a reduced occurrence of retained placentas, metritis, cystic ovaries, services per conception, and interval from calving to conception in dairy cattle. However, the relative contribution of selenium and vitamin E does vary between reports.

Many factors influence the success of your cows’ reproduction, and developing a solid nutritional program, with appropriate trace mineral supplementation, will ensure that your cows are in the best shape possible for timely rebreeding, maintaining healthy pregnancies and passing adequate levels of nutrients to their calves.

The authors are veterinary researchers at the Western College of Veterinary Medicine in Saskatoon.

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