| ||Trace elements of most concern in Alberta | Trace element deficiencies - a broad perspective | Trace mineral supplementation | Mineral supplements | Special conditions
Most of the forage grown in Alberta is deficient in several trace minerals. These minerals are so named because they are required in minute or trace amounts. Table I shows the average trace mineral content in some common Alberta grown feedstuffs. The majority of the forages we grow do not contain enough copper, zinc, selenium or manganese to meet the requirements of beef cattle.
Trace Elements of Most Concern in Alberta
Essential trace elements are necessary for the well being of the animal. These are needed in sufficient quantities to promote health and to optimize production and reproduction. All trace elements are toxic when fed in excessive quantities. Table 2 is a summary of suggested minimum target levels for dietary trace minerals. The levels are approximations, as requirements are affected by many factors.
More than 90 percent of the feed produced in Alberta is low in copper. Cases of copper deficiency are common. Symptoms of deficiency include anaemia, impaired reproduction in cows, bleaching of the hair coat, scours, unthriftiness, stunted growth and sudden death. A greater incidence of internal and external parasites has been noted in copper deficient animals. There is also an increased tendency for bones to fracture in calves and an increased incidence of lameness. The suggested minimum requirement for copper in cattle rations is 10 mg/kg.
Table 1. Average Trace Mineral Content of Selected Alberta Grown Feedstuffs
Table 2. Suggested Minimum Target Levels for Trace Mineral in the Diets of Beef Cows in Alberta
Concentration in the diet
mg of element per kg
of dry feed
More than 90 percent of the feed grown in Alberta is considerably lower in zinc than the 50 ppm suggested minimum; in fact, most feeds contain only half of the amount suggested for cattle. Symptoms of deficiencies include reduced growth rate, an increased incidence of footrot and other foot infections, and reduced fertility in bulls. Zinc deficiency inhibits utilization of vitamin A. Reports of clinical cases of zinc deficiency are rare in Alberta, as diagnosis is difficult. Routine supplementation is recommended.
The majority of the feed grown in Alberta is inadequate in manganese. The suggested allowance is 60 ppm. Impaired reproductive performance in the cow may be among the first symptoms of a deficiency and may be the only recognizable symptom observed in many cases. Calves from manganese deficient dams have been observed with contracted and twisted fetlocks at birth.
The selenium content of feeds grown in Alberta is quite variable and ranges from levels as low as one-tenth of that required by cattle to levels that are many times what animals require. There can be a marked difference in selenium content of forage from year to year. Alfalfa and mixed hay containing alfalfa contain higher levels of selenium than do grass, clover and cereal forages. Grains are lower in selenium than are forages. Approximately 45 percent of alfalfa and alfalfa grass forages are below the recommended 0.2 mg/kg level of this element, while 65 to 70 percent of cereals and grasses are deficient in selenium. Approximately 90 percent of barley grain samples contain less than the recommended allowance.
Any feed grown in Alberta can be low in selenium. However, the likelihood of experiencing selenium deficiency is greater in the areas west of Highway 2 and north of Highway 16.
Selenium deficiency is a significant problem in Alberta. Deficiency symptoms include white muscle disease, reduced resistance to diseases, birth of dead or weak calves, increased incidence of retained after-births, and lowered cow fertility. The minimum suggested allowance for selenium in the diet is 0.2 mg/kg. Higher levels than this may be required in some instances.
The addition of selenium to commercially manufactured supplements for cattle is regulated by Agriculture Canada. Under current regulations, feed manufacturers can add the levels of selenium shown in Table 3.
The role of vitamin E is similar to that of selenium and a deficiency can produce similar effects. Vitamin E should also be given when selenium supplementation is warranted.
The level of iodine in forages in Alberta is low and supplementation is necessary. Symptoms such as goiter, decreased milk yield, impaired fertility and increased incidence of retained placenta have been reported.
Organic iodine (i.e., ethylene diamine dihydroiodide, mere commonly known as EDDI) is of special concern to nutritionists.
This compound has been used at high levels (100 to 400 mg/head/day) as an aid in the prevention of footrot in cattle. Recent research indicates that 30 to 50 mg/head/ day may be just as effective. The efficacy of treatment levels for the prevention of footrot is being debated. Prolonged use of these high levels may pose significant risks of toxicity in cattle. Signs of toxicity in cattle include elevated temperatures, dry coughing, and runny noses and eyes. Often, young calves allowed to consume salt or mineral mixes high in iodine are the first to show signs of toxicity. High dietary levels of iodine result in elevated levels in milk and muscle of treated cattle and is of concern in human health.
Clinical cases of iodine toxicity have been seen in cattle in Alberta. Incorrect use of EDDI salt and mineral mixes appears to be the likely cause. Agriculture Canada has recently restricted EDDI use to nutritional levels (0.1 to 10 mg/kg to total dry feed).
Cobalt deficiencies have not been reported in Alberta. Since the cobalt status of our feeds and livestock has not been widely studied, it would be prudent to continue to supplement this element.
The usual source of supplemental cobalt and iodine is cobalt-iodized salt (blue) and trace mineralized salt. Most calcium-phosphorus mineral supplements also contain these elements.
Trace Element Deficiencies - a Broad Perspective
Many symptoms of deficiency have been listed with each of the trace elements discussed. These lists are by no means complete as cattle may exhibit a wide range of symptoms depending on the severity of the deficiency and the length of time the animals have been deficient. Diagnosis of trace mineral deficiencies can be very difficult, even for professionals. Most of the work has been done with individual elements and the effects of multiple trace element deficiencies have received little attention. It is likely that most of the trace mineral deficiency problems experienced by cattle in Alberta are of a sub-clinical nature. Several "Farming for the Future" projects in Alberta have demonstrated 20 to 36 lb. increases in weight gain in yearlings on pasture through trace mineral supplementation. In other projects where cow/calf pairs were provided with trace mineral supplements, improvement in weaning weights of 14 to 26 lb. have been seen. It is interesting to note that reduced growth rates were not seen as a problem in these herds.
Improvements in reproductive performance of cows and heifers have also been observed with adequate trace element supplementation. More cows conceiving earlier in the breeding season resulting in increased weaning weights and fewer open cows have been common observations.
Recent research has demonstrated that copper, zinc, manganese and selenium are required for optimum functioning of the immune system in cattle. This suggests that adequate supplementation of these trace elements would be beneficial in helping the cow and her calf cope with disease-causing organisms that they would normally be in contact with. How much of these trace minerals is required to optimize immune function is not known. Some evidence suggests that more selenium is required to optimize immune function than is required to prevent white muscle disease, retained after-birth and other problems commonly associated with deficiency of this element.
Table 3. Summary of Levels of Supplemental Selenium Permitted in Cattle Feeds
Source: Agriculture Canada Trade Memorandum T-3-112, December 1. 1990
Allowable Supplemental Selenium Levels
|Limit Fed Feeds||Selenium can be added at a level not to exceed an intake of 3 mg of selenium/head/day.|
|Complete Feeds||Selenium can be added at a level not to exceed 0.3 mg of selenium per kilogram of diet.|
|Trace Mineralized Salt||When fed free-choice selenium can be added at a level not to exceed 120 rng of selenium per kilogram of TM salt.|
|Minerals||When fed free-choice selenium can be added at a level not to exceed 30 mg of selenium per kilogram of mineral.|
Trace Mineral Supplementation
Producers who have upgraded the trace mineral status of their herds through provision of the appropriate supplement have observed improvements in the general health of the animals and in growth and reproductive performance; This is not surprising when you consider that herds not receiving mineral supplements are deficient in at least two trace elements, and can be deficient in as many as five. The benefits of trace mineral supplementation outweigh the relatively small cost. The most common and convenient way to overcome these problems is by feeding a mineral supplement that contains adequate levels of these elements. Feed testing is the easiest way to determine which minerals are low in the feed and what levels are required in a supplement to overcome these shortages, Many cattle minerals sold in Alberta are not high enough in several of the trace elements to overcome the shortages we experience; therefore, take care in choosing a mineral supplement.
Trace element nutrition of livestock is extremely complicated. Many interactions occur between the trace elements and between trace elements and other nutrients. These interactions can be very complex and many are not well understood. In addition, the quantities of trace elements needed is very small. All trace elements are toxic if fed in excessive quantities. For these reasons, trace element nutrition is best left to knowledgeable professionals.
Calcium/phosphorus mineral mixes
Mineral mixes containing calcium and/or phosphorus would be good sources of supplementary trace elements if the levels of trace elements in the mix fell in the middle to upper end of the range shown in Table 4. Such minerals could be fed with red or blue salt. To promote consumption of mineral which is often unpalatable, mix the salt and mineral and feed this combination as the only source of
If the mineral you choose contains trace elements at or below the lower end of the range shown in the table, mix it with a trace mineralized salt that contains trace elements recommended in Table 4.
Table 4. Guides to Selecting Minerals of Suitable Trace Element Content for Alberta Conditions
2,000 - 3,000
10,000 - 12,000
8,000 - 10,000
70 - 200
40 - 60
30 - 80
Minerals, other than trace-mineralized salt, intended for free-choice feeding, under current federal regulations can contain no more than 30 mg of selenium/kg of mineral. If higher levels are required, a mineral may be manufactured as a "customer formula feed' or under the prescription of a veterinarian.
Trace mineralized salt (TM Salt)
Several different trace mineralized salt formulations are available in Alberta. Some of these products do not contain adequate levels of several of the trace elements to overcome the deficiencies we experience.
When calcium/phosphorus minerals are not fed, or where the trace element content of the mineral is low as outlined in the following section, an appropriate trace mineralized salt should be fed.
Table 4 should help in deciding if a salt is a good source of supplementary trace elements. Compare your salt mix to this table and if your salt falls within the range shown, chances are it will meet the needs of the cattle when eaten at 42 g/head/day, the expected free choice intake of loose salt. It is best, of course, not to guess. Feed testing is a quick and inexpensive way to determine what your situation is. Private feed labs and Alberta Agriculture offer analysis for most of these trace elements.
Special circumstances do exist in Alberta where the recommended allowances for some trace elements as shown in Table 2 may not be adequate. Table 4 was formulated to address this problem. The upper end of the range shown allows for extra supplementary levels of most elements. However, copper is a special problem that may require even higher levels than shown in Table 4. High sulphate water and/or high molybdenum in the feed may increase the need for copper above the levels recommended. Only a few feeds containing elevated levels of molybdenum have been seen in Alberta. Special mineral mixes will have to be formulated to handle these problems. This is best accomplished by working with a nutritionist or livestock specialist and veterinarian experienced in dealing with these problems.
Adapted from Alberta Agriculture Beef Herd Management Reference Binder and Study Guide - 302