It may well be that on the Canadian Prairies it would be unusual to find any molybdenum-deficient cropland. That certainly would have been true, let’s say, 70 or so years ago, when cropland was tilled and nitrogen fertilizer levels were relatively low. Some 40-50 years ago, Prairie wheat yields were around 25 bushels per acre and canola around 20. Now, N fertilizer levels are more than double and wheat and canola yields are around 50 and 40 bushels annually respectively.

Molybdenum is needed to convert the nitrate taken up by all crop plants into protein via the Mo-enzyme (nitrite reductase). In addition, in legumes, another Mo-enzyme (nitrogenase) is needed by the root nodule bacteria for nitrogen (N) fixation. Only tiny quantities of molybdenum are needed — but there are cropland factors that can limit or prevent molybdenum uptake by crop plants. The result may be inhibited crop growth, reduced yields or delayed maturity.

Let’s have a look at factors which may limit molybdenum crop plant availability and depress crop yields.

Nature

Molybdenum may be naturally deficient in a given area. In the northern U.S. state of Idaho, it was found that large areas — up to a quarter of the land in that state — could be naturally deficient in molybdenum. In a few areas in the central part of the state, the molybdenum level was so high in forage and hay in pastureland that it interfered with copper levels in livestock and caused a disease called molybdenosis, resulting in severe copper deficiency in pasturing animals.

Acidity

In very acidic soils — that is, those below pH 5 or 5.5 — there will be areas where the pH may be as low as 4 or 4.5, levels at which molybdenum may be unavailable and seeded canola in particular will remain in a tight rosette stage and grow very slowly if at all. The pH on such land must be adjusted either with lime (limestone) or wood ash.

Non-disturbance

In minimum or zero till, the surface soil of your cropland may be undisturbed for 10-15 years or more. If the cropland soil is perhaps between a pH of 5-6, then over this time the surface soils — say, down to two to three inches — can become acidified. Acidification of this surface soil is due to the use of nitrogen fertilizers, which acidify soil, and to crop residue, which can become acidic. The result is that this surface soil, at one to three inches, could have a pH of 3.5-4.5. This acidity immobilizes the soil molybdenum. The seedlings may pick up the soil nitrates, but without the molybdenum, the nitrates cannot be converted to proteins, in the absence of the molybdenum-based nitrate reductase enzymes. When the seedling roots move deeper into the soil with the higher pH, they likely will pick up sufficient molybdenum. This seedling delay could make the growing season longer — and the seedlings have a longer exposure to crop-damaging flea beetles.

Higher-demand crops

Legumes have greater needs for molybdenum than non-legume crops, since Mo is essential for N fixation in the legume root nodules. It is possible that legumes such as dry beans grown under irrigation in neutral or even in high-pH soil may have a need for Mo fertilization, due to the fact that the Mo which is normally present at low levels in soil may be leached below the root zones. We did run across irrigated bean growers who felt they got improved yields when they added a few ounces of Mo to the planted bean crop in southern Alberta.

Sulphate a suspect

In a review of several textbooks on the role of molybdenum, and one text in particular — Soil Nutrient Bioavailability, second edition, by Stanley Barber — I came across some new information. It appears sulphate in the soil can depress molybdenum availability. They compete for the same absorption sites on the root. For example, adding gypsum (calcium sulphate) to alkaline soil significantly decreases the uptake of molybdenum from 2.33 parts per million (p.p.m.) to 1.26 p.p.m. in tomatoes.

This same sulphate depression of molybdenum uptake was echoed in Marschner’s text and single superphosphate was identified as the cause. Triple superphosphate did not contain sulphate and was not a problem. Since our Prairie canola crops are high users of sulphur, this information should be explored. We may be depressing potential Prairie crop yields due to high or frequent applications of sulphate nutrients — a good reason to perhaps add an ounce or two of molybdenum to each acre of cropland.

Marschner also states that molybdenum deficiency is widespread in legumes growing in acidic soils. Additionally in this text, it states that molybdenum deficiency in cropland has a stalling effect on pollen formation in corn (maize). It causes delayed tasseling and results in a large proportion of flowers that fail to open. Both the above problems are preventable with a couple of ounces of molybdenum an acre.

When I was on the faculty at the University of Guelph, little attention was paid to crop-essential micronutrients. The rutabaga growers in Ontario, growing around 15,000 acres, worth about $12 million annually, invariably added a few ounces of sodium molybdate fertilizer to the intended rutabaga cropland. They said it enhanced rutabaga growth and quality. I would also point out that cauliflower growers in Ontario, on more than a few occasions, would come across a problem called whiptail. Whiptail is a disorder in the cabbage family (canola included) whereby the leaf rib develops but the leaf does not fill out. Search up “whiptail of cauliflower” on the internet. It’s a sign of molybdenum deficiency.

Another temporary way to alleviate Mo deficiency on acidic no-till or minimum-till soil is to deep harrow or till thin surface soil layer, to bring up the higher-pH soil that exists below the one- to three-inch level.

Sulphate, in the form of gypsum or single superphosphate, can depress plant uptake of Mo. Soil tests are not the most reliable methods for detecting available soil levels of Mo. So, if your cropland is on the acidic side — below pH 5.5 — and you follow a zero-till or minimum-till strategy, you may consider appropriate levels of Mo seed treatment, Mo foliar applications or Mo added to your fertilizer inputs at only a couple of ounces per acre. It’s a very small cost indeed if you suspect a Mo deficiency problem on your cropland.

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Early on in the 1970s with Alberta Agriculture, my colleagues and I were very surprised with the answers to the soil testing questions we asked. A large random number of growers replied to our questions and only around 10 per cent actually had their cropland tested for soil nutrients. In those early days it seems nitrogen (N) was really considered, phosphate (P) was sometimes looked at, and both sulphur (S) and potash (K) were essentially considered plentiful and ignored. A couple of scientists in Alberta sounded the alarm on sulphur, pointing out soil deficiencies of this nutrient in both Alberta and Saskatchewan. 

In my canola crop surveys, especially on sandy or sandy loam soils, we found lots of sulphur-deficient canola crops. I was told by several soil scientists they had never recommended sulphur. They seemed to assume the sulphur pollution in Eastern Canada, Ontario in particular, applied to the west. The real answer was that in previous years in the 1960s on the Prairies, the usual nitrogen source was ammonium sulphate or ammonium phosphate, both with high S contents at 24 and 14 per cent respectively. In the early ’70s, these products were replaced by urea and ammonia as nitrogen sources, with no thought of the S requirements of all field crops, particularly canola. In Ontario in the ’70s, it was not unusual to have 30 to 50 lbs. of S fall per acre in the industrial south, whereas on the Prairies less than two pounds per acre could be expected from aerial pollution annually. Pretty soon sulphur became a key nutrient Prairie-wide. 

A similar situation occurred with potash, especially in hay production. It was pointed out to producers that a four-ton crop of alfalfa could remove 175 lbs. of K per acre. In addition, the sale of baled cereal straw would remove 60-70 lbs. of potash per acre. 

Soon it became obvious crop production on the originally fertile Prairies was removing major crop nutrients at an alarming rate. 

In recent years (2022), according to Fertilizer Canada’s use survey, over 40 per cent of Prairie farmers sampled each canola and wheat field. The Canola Council of Canada states 40 per cent of its survey respondents test each field each year. Just over 50 per cent of high-yield growers test for nitrogen every year. 

As crop yields were expected to go higher and higher, the need for crop nutrient replacement became critical. Soils 150 years ago, from Manitoba to the B.C. Peace region, were losing their nutrient-rich organic matter. Soils which, around 1900, were two, five or 10 per cent organic matter were now down to one, two or five per cent organic reserves. Remember: a one per cent soil organic matter per acre, in its top six inches (15 cm), contains 10,000 lbs. of carbon, 1,000 lbs. of nitrogen, 100 lbs. of phosphate, 100 lbs. of sulphur and one per cent or less of boron. Soil organic matter slowly releases its nutrients — that is, its “black matter,” not to be confused with crop residues. A 10 per cent soil organic matter would release 70 to 90 lbs. of nitrogen under normal Prairie growing conditions when cultivated annually, along with P, S and boron. A one per cent soil organic matter, on the other hand, would only release seven to 10 lbs. of nitrogen, along with very small amounts of P, S and boron. 

In other words, if you do not replace these nutrients with the recommended amounts of N, P, K and S after an appropriate soil test, you cannot set a target yield. One pound of N is one pound of N, whether it’s applied as urea or some expensive N product. 

All of the fertilizer chemicals we apply are usually in the form of concentrated plant nutrients. They are not “synthetic” — they are just concentrated from nature for convenience. Organic N, P, K and S are factually the same as “chemical” N, P, K and S. So, if your target yield for wheat is 60 bu./ac. and you need 100 lbs. of additional N following a soil test, it doesn’t matter whether the N is in chemical or an organic form (poultry manure), it has to have 100 lbs. of available N per acre. 

To clarify this, read the fact sheet “Minerals for plant, animals and man” to understand soil testing and crop nutrients needed for target yields from alfalfa to wheat. 

Micronutrients 

Now that I’ve dealt with those four macronutrients, N, P, K and S, let’s also include calcium (Ca) or magnesium (Mg) on that list, since they are rarely if ever a nutrient problem. The exceptions for Ca and Mg are when soils are very acidic — that is, pH below 5. I will deal with both at a later time, since alfalfa should not be grown on soils below pH 6, and wheat, to optimize yield, should be grown on soils above 5.5. 

Now take a long look at the plant and animal importance of micronutrients on the Alberta fact sheet I referred to earlier, which for a while was the most requested publication in Western Canada. 

Copper and zinc 

There seems to be an attitude, among more than a few agronomists, that talking about micronutrients is “unmacho” and those are unimportant in Prairie agriculture. How wrong can they be? You can have all of the N, P, K and S for a target yield, but if a micronutrient is missing or deficient, your expected yield could crash, resulting in low-yielding sample grain. This is well documented for copper (Cu) or zinc (Zn) deficiency, especially in wet growing seasons. Zinc deficiency may occur on beans but is much more common on corn. For example, a 100-bushel crop of corn will remove around 1 ½ ounces of zinc. A 60-bushel crop of wheat will remove almost half an ounce of copper. Every crop grown will remove both these micronutrients, so after 100 years of crop production, you will have removed perhaps 100 ounces of zinc (six pounds) and 50 ounces of copper (three pounds actual copper). The lighter sandy Prairie soils likely only had five to six pounds of zinc and maybe three to four pounds of copper in the top six inches of soil. Do the math. 

There may be more zinc and copper deeper down, but that may be unavailable in wet growing years due to shallow crop rooting. Heavier clay and clay loam soils may contain higher levels of both Zn and Cu, but still the amount left in the soil can become crop-limiting. 

Iron and manganese 

Iron (Fe) is seldom limiting due to its abundance in most soils, but at very high pH levels (pH around 8) it may become unavailable to crops such as soybeans or corn. 

Manganese (Mn) is very similar in behaviour to iron at high soil pH and especially under dry soil conditions. In southwestern Alberta in dry springs, it’s not uncommon to see manganese deficiency in both wheat and barley that may be corrected after a few inches of rainfall or a foliar application of manganese. 

Molybdenum 

Molybdenum (Mo) is only needed at a few grams an acre but is totally important for the nitrogen metabolism of all crop plants. This micronutrient becomes less available to unavailable at a pH below 5. 

The late Phil Thomas and I solved a canola growing problem for the University of Idaho many years ago. The canola crop refused to grow past the rosette stage in one of its research fields. After very many questions and discussions, we concluded the field with a pH of 7 was devoid of available molybdenum. We were correct: a couple of ounces per acre solved the problem. Researchers in Idaho were able to show up to 25 per cent of the state was low or totally deficient in molybdenum. This could be the case on the Canadian Prairies, but no one has done the work. Crops, especially legumes (peas, alfalfa), will grow very poorly when soil levels of molybdenum are low. 

In alkaline and saline soils, molybdenum levels in hay or forages grazed on such cropland may be high. Such feedstock for cattle can result in molybdenum-induced copper deficiency on molybdosis. Check with an animal nutritionist if you suspect a problem. 

For producers growing crops, especially canola on acidic soils around pH 5, it would be wise to apply a few ounces of molybdenum to the cropland along with the bulk fertilizer or add to the crop seed for very little extra cost, a practice followed by several successful Prairie crop consultants. 

Boron 

We now know very low levels of soil-available boron (B) at around 0.1 part per million (p.p.m.) can result in ergot infection in barley and wheat due to pollen tube failure and very reduced yields. Recommended levels of boron should be in the region of 0.5 to one p.p.m.; that’s one to two pounds of actual boron per acre. Under dry soil conditions, boron is not very mobile, and it is suspected that flowering canola crops may not pick up sufficient boron. As a result of boron deficiency, many canola flowers fail to pollinate properly due to pollen tube failure, resulting in depressed yield. 

Just think: when you harvest any crop, you are removing not only N, P, K and S but all the micronutrients, Mg, Zn, Cu, Fe, Mn and B, on an annual basis. You are depleting your soil reserves and any micronutrient that falls below recommended levels will lower your target yield moderately or severely, depending on any given crop and its nutrient needs.

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In past years, most farmers and soil scientists were just getting to grips with sulphur and phosphate requirements of crop plants, let alone nitrogen and potash. It seemed as long as you had nitrogen fertilizer everything else would fall into line. Micronutrients such as zinc, copper, boron and manganese would never be in short supply, let alone something as “insignificant” as molybdenum. Well, molybdenum (Mo) is the key to the nitrogen gate and is also involved in sulphur and phosphate metabolism.

Some time ago a knowledgeable canola expert in Alberta and I were asked by agronomists at the University of Idaho to look into a canola crop failure in Idaho. These agronomists supplied us with the field history, nutrients added, soil analysis, herbicide history, pH and weather conditions. Their canola would emerge satisfactorily but grew slowly into the initial rosette stage and just stalled. The crop would not develop. The canola expert and I came to the same conclusion: an absence of molybdenum. The answer came back from Idaho: they could not detect any molybdenum in the soil.

Molybdenum levels were checked across Idaho, and it was found that molybdenum deficiencies occur in the northern half of the state, the central part has very high levels and the lower part of the state is seldom deficient.

Agronomists in Idaho have found that sandy soils with pH values of less than six or soils very high in organic matter can be deficient in Mo. Molybdenum is a key nutrient in nitrogen fixation in legume nodules. No Mo means no fixed nitrogen. Such soils respond phenomenally when treated with a few ounces of sodium molybdate per acre. Crop yields can double or more. Seed treatment with as little as an ounce of Mo can be highly effective on deficient soils.

Without molybdenum, plants are unable to metabolize any form of nitrogen (i.e. nitrate to ammonium) and to a lesser extent sulphur and phosphate. The whole plant process comes to a halt.

Molybdenum in Canada

I suspect we may have Mo-deficient areas on the Canadian prairies. Several Saskatchewan farmers east of North Battleford report that peas produce well-below expected yields on their cropland. I encouraged them to use molybdenum to no avail.

In the Peace Region of Alberta and B.C., significant acres of cropland have a pH of around 5.5 or less. At this pH, Mo becomes restricted or unavailable to field crops. In-furrow applications of crushed limestone on these low-pH soils show significant yield results, often wrongly attributed to the addition of boron. Crushed limestone raises the soil pH and releases Mo. Molybdenum becomes progressively more soluble as the pH level increases. Liming or wood ash application to acidic crop soils has an important role in making Mo available for plant growth and nitrogen fixation in legumes.

I grew up on a farm in Wales where the soil pH was around four to five. We never seeded a legume crop without a prior lime application.

Some 15 years back a colleague and I were visiting dry bean growers near Lethbridge. They remarked that in recent years, beans grown under irrigation needed more nitrogen to reach their target yield. Dry beans fix a percentage of their nitrogen via rhizobia. It occurred to us that in this high pH soil, around 7.5 to 8.2 pH, perhaps over many years of irrigation, available Mo had leached to the subsoil. My colleague suggested they try a few ounces of Mo per acre. The following year both growers reached their target yields without additional nitrogen. There is a strong possibility that Mo can be leached out of or into the subsoil on high-pH soils under irrigation.

If your legumes or other crops are not performing up to expectations, try a few ounces of molybdenum on a few acres or invest in some very inexpensive seed treatment. It will be the most inexpensive fertilizer that you will ever buy.

In more than a few parts of the Canadian Prairies we have areas of Mo toxicity. This occurs in alkaline, poorly drained cropland areas where soluble Mo can accumulate in the soil and consequently reaches high levels, particularly in hay crops. Cattle feeding on high Mo hay can develop severe copper deficiency, resulting in death or poor performance of milkers. This is referred to as molybdenum-induced copper deficiency. Cases have been identified in Manitoba, around Vita, south of Winnipeg, and the Swan River area, and in the northern Peace Region. I suspect there are more of these areas on the Prairies.

In a visit to a field at Fort Vermillion in the northern Peace Region, I diagnosed a failed canola field as herbicide damage. Soil analysis showed that samples taken from the field had a pH of 3.5. Now, you figure out the crop failure. I lost a $10 bet on this field to an Alberta soil scientist.

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Molybdenum, also often referred to in the abbreviated term “moly,” is one of the 16 essential elements for plant growth. It is a micronutrient particularly important in helping plants in their uptake of nitrogen. They don’t need much moly, but if the soil is deficient in molybdenum it can really have an impact on yield.

“The fact of the matter is that we don’t know much about it,” says Mike Dolinski, an agronomy specialist with Agri-Trend Agrology. He’s been speaking about molybdenum at several farm meetings this past winter and early spring.

“A soil analysis for molybdenum really isn’t worth the powder to blow it up, and tissue testing is a bit better, but not many farmers tissue test their crops,” he says. “We really don’t know what’s out there. What we do know is if your soil and ultimately your crop is deficient in molybdenum it affects nitrogen uptake which in turn reduces yields.”

Molybdenum is an essential component in two enzymes that convert nitrate into nitrite and then into ammonia before it is used to synthesize amino acids within the plant. It also needed by nitrogen fixing bacteria in legumes to fix atmospheric nitrogen. Plants also use molybdenum to convert inorganic phosphorus into organic forms in the plant.

While there are many unanswered questions about molybdenum, the good news is farmers don’t need to apply very much, it is relatively inexpensive, and it can be easily applied at just about any stage of crop development.

Dolinski first became aware of concerns when dealing with farmers and in Idaho who were seeing a response to molybdenum.

“The only theory I have about what’s happening in Western Canada is that in the past few years farmers are beginning to push crops for higher yields,” says Dolinski. “We are starting to see much higher yields. And those higher yields are removing more molybdenum.” The only natural source of molybdenum is through mineralization in the soil.

“Crops yields are getting bigger, higher rates of nitrogen are being applied and at the same time soils are becoming more acid — soil pH is dropping. And in most cases when soil pH drops most nutrients become more available. The reverse is true with molybdenum. As soils become more acid, moly becomes less available.“ He says at one time the micronutrient was referred to as “the poor man’s lime.”

Canola, pulses and legume crops have the highest requirements for molybdenum, says Dolinksi. Canola for example, uses about five times more than cereal crops such as wheat.

Crop signs of a molybdenum deficiency aren’t always obvious. In canola a deficiency can show up as cupping of the leaf margins in younger leaves, interveinal chlorosis (yellowing) of leaves, and a condition Dolinski calls “whip tale,” a narrowing of lower leaves.

Have a look at soil PH

So what is the fix? First of all Dolinski says to have a look at soil pH levels. If levels are up in the eight to 8.5 pH range he wouldn’t worry about molybdenum. If they are getting down to six pH range, producers of canola and pulse crops should begin to have concern. And if they’re in the 4.5 to five range, he’d apply molybdenum to all cropped acres.

Idaho farmers are using a product called sodium molydbate to correct molybdenum levels. It is very water soluble and can be applied as part of any field spraying operation. And you don’t need much. Moly levels can be boosted at a recommended rate of 50 grams (less than two ounces) of sodium molydbate per acre.

“Some people apply it as a seed treatment,” he says. “It can also be applied with a fertilizer, herbicide or first fungicide treatment.” Several crop nutrient supplements also carry molybdenum.

“Have a look at your soil pH levels to start with,” says Dolinski. “And if pH levels are getting into that warning zone, at least set up a few acres for an on-farm trial. ”

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According to Tee Boon Goh, a specialist in soil chemistry and mineralogy at the University of Manitoba, and Rigas Karamanos, a senior agronomist with Koch Fertilizer Canada, ULC, copper is an essential element for wheat growth. Goh and Karamanos are the co-authors of a pamphlet entitled “Does addition of copper increase the macronutrient content of wheat?” recently presented to the Manitoba Agronomists’ Conference at the University of Manitoba in December 2014.

Goh and Karamanos identify copper as essential to wheat because it is involved in a number of plant functions, such as electron transfers, chlorophyll production, protein synthesis and respiration.

Copper deficiency can have severe impacts on wheat yields. “Copper deficiency in wheat produces characteristic symptoms of yellowing and curling of young leaves, pigtailing of leaf tips, limpness or wilting, delay in heading, aborted heads and spikelets, head and stem bending, as well as stem melanosis disease in certain wheat cultivars,” says Goh.

The researchers tested the hypothesis that copper can be applied in an effort to increase macronutrient uptake, and in particular nitrogen uptake, and subsequently high protein in the wheat seed. They took into account 47 experiments that had been conducted on a total of 2,648 separate plots, and examined the impact of copper on protein levels (where measured), or the macronutrient tissue content in each of these 47 previously conducted experiments.

Wheat is sensitive to copper

Goh and Karamanos chose copper as their focus because, while lack of any of the micronutrients will cause yield losses in wheat, the crop is particularly sensitive to copper and manganese, and there is a large volume of research conducted on copper. “It is estimated that there are close to five million acres of deficient or potentially copper deficiency soils in the Prairies,” says Karamanos.

The study, almost exclusively funded by Western Cooperative Fertilizers Ltd. (Westco), showed 18 significant yield responses and 21 non-significant yield responses to the addition of copper to the soil’s macronutrient content.

“Claims that application of copper (either foliar or soil applied) increase nutrient content and in particular protein content are unfounded,” Goh and Karamanos concluded in their report.

“Micronutrients are essential elements; however, unless there is a deficiency in any given micronutrient, they contribute little to improving nutrients that are required in higher quantities, such as nitrogen, phosphorus, potassium and sulphur,” says Karamanos. “As a matter of fact, when soils are deficient in copper, correction of the deficiency resulted in a decrease in macronutrient concentration and protein content, as a result of a simple dilution effect.”

This is not to say that the targeted application of copper is not important in deficient soils.

Goh says that a large body of research in Western Canada clearly shows that targeted application of micronutrients, including chloride, copper, zinc and manganese, based on valid soil test criteria, contributes to significant yield increases.

The key word is “targeted”: non-targeted applications of copper in wheat results in no benefit to the crop. Untargeted copper applications, says Goh, “are a waste of money on expensive material.”

Plant health

According to Goh and Karamanos, the claim that copper can be applied to increase protein content in wheat is based on crops achieving “better health.” But they say “plant health” is a contested notion with many definitions.

“Although there are numerous studies on the general health definitions and health criteria in human medicine, plant health is not a well-defined and often misused term,” says Goh.

For consumers, Goh says, plant health may refer to crops free of pesticides and other chemicals with high nutritional value, whereas for regulators, it means crops free of heavy metals and toxins, for example. “For the producer, ‘plant health’ means crops achieving their full genetic potential, but even this varies depending on the type of crops. Plant health measures a wide spectrum of perceptions about the ‘fitness’ of a plant for varying objectives of groups of people and the debate is still on,” he says.

“This work addressed the impact of copper on other macronutrients from a plant nutrition perspective and in particular its effect on the nitrogen content, which is the main component of protein for which farmers are compensated,” says Karamanos of the study. “Any extrapolation to a loosely defined ‘plant health’ would be non-scientific at this point and only lead to confusion.”

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It needs to be clear that sheep and goats and cattle absolutely do not have the same copper needs. Over the years I have personally known two sheep producers who faced copper toxicity in their flock and it was devastating both financially and emotionally. Both times it was due to feeding a product that was supposed to be for sheep but the feed mill had mixed it wrong. The sheep were fed the product for several months with no ill effects. Then there was a weather stress. Immediately the flocks started to experience death loss. The feed was tested and discontinued but the damage was done. There was little the university or veterinarians could do and it took several months and much financial/emotional hardship before this settled. Therefore our management recommendations reflect a healthy respect for this condition.

Basic requirements

Generally, sheep require about five ppm (parts per million or mg/kg) of copper in their total diet. Sheep absorb copper from their diet in proportion to the amount of copper offered, not according to their dietary needs. Excess copper is stored in the liver. The storage level in the liver can take months or even years to reach a toxic level (more than 1,000 ppm DM). Toxicity can occur at levels above 25 ppm. However, dietary molybdenum levels also affect copper requirements and there are areas of Manitoba where high or low molybdenum levels can be an issue. If in doubt it is best to contact the local agricultural extension office or the provincial sheep specialist in your province for this information.

If molybdenum is high in feed, a special mineral mix can be ordered with a nutritionist’s prescription. Molybdenum forms an insoluble complex with copper to prevent copper absorption. If molybdenum levels are low (less than 1 ppm), sheep are more susceptible to copper toxicity. If molybdenum intakes exceed 10 ppm, copper deficiency may occur on diets that would normally be adequate. Sulphur further complicates the copper: molybdenum relationship by binding with the molybdenum.

Copper toxicity in sheep usually results from the accumulation of excess copper in the liver over a period of a few weeks to more than a year with no clinical signs. This usually occurs when sheep are fed a product that is made for cattle or specifically for goats. Cattle need about 10 times more copper than a sheep. When a sheep is under any kind of stress the liver will allow a sudden release of copper stores to a rapid breakdown of red blood cells. Affected sheep are lethargic and anemic. They may grind their teeth incessantly and experience extreme thirst. Membranes are very pale and may appear yellow, as jaundice sets in. Urine is a bloody colour. Death usually occurs one to two days after the onset of clinical symptoms. At post-mortem, tissues are pale to dark yellow and the kidneys are a very dark colour.

Other copper sources

Copper can be added in places other than feed or mineral mixes. In recent years, copper oxide wire particles (copper boluses) have been recommended as an anthelmintic (agent causing parasite death) for sheep and goats. Researchers are also re-evaluating copper sulphate drenches as a deworming agent. Copper has anthelmintic activity and has been historically used as a deworming agent in sheep; however, its use was discontinued because of toxicity issues. This is the situation with many “natural dewormers.” They can control parasites, but in effective doses they can increase the risk toxicity to the animal.

Copper deficiency in sheep can occur, although it rarely happens. It bears mentioning only because of the fact that soils in some areas are very high in molybdenum. Fresh grasses are poor sources of copper in comparison to hay. Acid soils increase copper and lower molybdenum in forages. Liming can increase molybdenum in the forage and alter the copper: molybdenum ratio. Where two or more of these three elements exist together on a farm, in quite ‘normal’ concentrations, they will act synergistically to bind out copper from a diet.

Effects of deficiency

Copper deficiency in ewes during mid-pregnancy may lead to swayback in lambs. This is due to a lack of copper during the formation of the neural tube. In young lambs, a copper deficiency may result in a poor fleece without its natural “crimp” which has been described as “steely wool.” Poor growth, anaemia, and increased susceptibility to bacterial infections can also be seen. Caution should be used in diagnosing a copper deficiency in sheep due to delicate balance of this mineral. Soil testing is highly recommended if a deficiency is suspected. The local agriculture office can help with this. There is also an online resource for water and soil testing in Canada at: www.certifiedorganic.bc.ca/rcbtoa/services/soil-testing-services.html.

A common inquiry is if people can house their goats and sheep together. We do not recommend it. Keeping our sheep housing separate for the winter months works the best for us. Over the years we have seen a lowering of fertility in our bucks if housed with our rams. We have seen does with kids that presented copper deficiency symptoms when housed with ewes. We do graze them on the same pastures but they are kept in separate night pens so they have access to their own mineral mixes.

Every season brings with it a new bunch of things to learn. Our wish is that people don’t have to learn things the way others have — the hard way. Minimizing the financial and emotional impact of mass death loss is a goal.

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