Management of Problem Feeds

Both forages and grains can contain substances that are harmful to livestock. So it's important that producers are aware of these and their possible effects. Animal health problems can be reduced, or avoided altogether, if these potential "problem" feeds are managed and fed properly.

The problems of greatest concern to Manitoba farmers are mouldy feeds, nitrates, ergot, sweet clover poisoning and prussic acid.


Older varieties of reed canary grass can contain alkaloids which have negative implications for livestock performance when forage from these varieties is fed. Most newer reed canary grass varieties have been bred to be alkaloid free. If seeding reed canary grass, ensure that the variety chosen is a low alkaloid or no alkaloid variety.


Bloat can occur when ruminant animals are pastured on lush alfalfa or other legumes, such as red clover. It may also occur when animals are fed chopped alfalfa forage in a confinement situation.

Bloat is a distension of the rumen caused by an abnormal collection of gases. During normal digestive processes, large amounts of methane and carbon dioxide gases are produced in the rumen and are "belched up." In cases of bloat, however, the gases are trapped in the digesting food and pressure builds in the rumen, causing the left side of the abdomen to become distended. If relief is not available, the pressure continues to increase until the animal dies, usually by suffocation.

For information on the control and prevention of bloat, refer to the Manitoba Agriculture and Food fact sheet Bloat in Cattle and Sheep, Agdex number 400-20.

Coumarin Poisoning

Coumarin poisoning can cause livestock death. These fatalities are unnecessary and can be prevented by proper management. A substance called dicoumarol present in poorly preserved sweet clover hay, prevents blood from clotting. Livestock may bleed to death from the slightest injury, either internally or externally.

The first sign of coumorin poisoning may be the death of one or more animals. Warning signs include stiffness, lameness, dull attitude and swellings beneath the skin over all parts of the body but primarily at the hips, legs, brisket or neck. Blood may be present in the feces, urine or milk and may be apparent in the nostrils.

A satisfactory laboratory analysis for dicoumarol has not been developed for conditions in Manitoba. Producers feeding sweet clover should observe the following management practices:

  1. Sweet clover should be fed for seven to ten days and then completely replaced with alfalfa for seven to ten days. It is important that the animals be taken off sweet clover completely for the seven-to-ten-day period. This allows the animal time to clear the dicoumarol from its system.
  2. Sweet clover should not be fed for at least two weeks and preferably four weeks before the start of parturition and during the calving or lambing period.
  3. Surgery (dehorning, castration, etc.) should be avoided on animals consuming sweet clover.
  4. Make sure animals have proper mineral supplements.
  5. If a problem does develop or is suspected, contact your veterinarian immediately.


Some turf type varieties of tall fescue and perennial ryegrass can contain endophytes. Endophytes are a fungus that live within the grass plant that can produce toxins that have negative implications for livestock health. If growing a turf type perennial ryegrass or tall fescue for seed, straw residues from this seed production should be tested for level of endophyte toxin present in the straw prior to feeding the straw to livestock. If seeding perennial ryegrass or tall fescue for pasture or hay production, ensure that you are selecting a forage type perennial ryegrass or tall fescue.


Ergot bodies have the same general shape as a seed but are larger, purple to black in color, and hard. They are caused by a fungus which replaces individual seeds or kernels on the head of the plant. Although ergot is most common in rye, it may also infect triticale, wheat, barley, oats and grasses such as wheat grass, quack grass, smooth brome, wild rye and blue grasses. Ergot is most common during wet seasons and may be present in greater concentrations near the edge of a field than in the center.

Seed containing ergot may cause serious problems for animals when consumed in either forage or grain.

Ergot causes two types of poisoning. One type causes convulsions, staggering, muscle spasms of the hind legs and sometimes temporary paralysis. This type is usually found in sheep, horses, and carnivores but seldom in cattle.

The second type of ergot poisoning causes lameness that may be followed by the loss of the end of the tail, ears and perhaps hooves. Loss of these parts is due to a dry form of gangrene caused by impaired circulation and reduced blood supply to the body's extremities. This form of ergotism occurs in cattle and pigs. It may take two weeks to three months for symptoms to develop. In the meantime, rate of gain, milk production, and reproduction suffer. Sows fed ergot generally have their litter but no milk.

Generally speaking, if grain contains more than 0.1 percent ergot (10 ergot bodies per litre of grain) it should not be fed to livestock. If more ergot is present, contaminated grain can be mixed with clean grain to reduce the concentration. Grain infected with any amount of ergot should never be fed to pregnant or lactating animals.

Although poultry can tolerate higher levels of ergot than other livestock, feeding poultry rations with high levels of ergot for an extended time can result in loss of appetite, increased thirst, diarrhea, vomiting and weakness. Convulsions, paralysis and death may follow. Gangrene of the comb, wattles, or toes may follow short-term feeding of ergoty rations. Growing or laying rations have shown no ill effects up to 0.3 per cent of the ration.

Mouldy Feeds

Moulds can affect animal production in several ways. Certain moulds produce compounds which are toxic to animals. Mouldy feeds also have less feed value. If adequate supplements aren't provided, weight loss and reduced overall performance result. Some moulds are unpalatable and will cause a drop in feed intake and, therefore, performance.

Inhalation of spores produced by moulds can cause both human and animal respiratory problems. "Farmer's Lung" is a common ailment when producers routinely handle dusty and mouldy feed.

For moulds to grow, certain environmental conditions are required. These are:

  1. Greater than 15 per cent moisture.
  2. A readily available energy source such as carbohydrates.
  3. Oxygen.
  4. Heat - Heat requirements differ greatly depending on the type of mould.

Prevention and Reduction of Mould Growth

Some management practices can reduce mould growth. Damaged kernels mould easily. Therefore, reducing insect damage, using proper settings on the combine, and harvesting as soon as the grain is mature will help to reduce mould growth. Quick drying and ensuring moisture content is less than 15 per cent in stored grains also inhibit mould growth.

There are several commercially prepared preservatives that help to prevent mould. Ammonia can also be used to preserve high moisture.  


Of the 200,000 known species of mould, about 100 have been shown to produce toxic compounds. These moulds produce chemical compounds (mycotoxins) which are poisonous when eaten. They can be present in both grains and forages. The mycotoxins of greatest concern in Manitoba include those produced by the moulds Aspergillus, Penicillium and Fusarium.

The effects of mycotoxins on cattle and sheep are not as well documented as in pigs and other monogastric (single stomach) animals. Cattle and sheep are less susceptible to mycotoxin-related problems because their digestive systems detoxify the problem compounds.

In severe cases of poisoning, feed refusal, infertility and abortions can occur. Low level poisoning occurs more frequently but may go unrecognized because the symptoms are not specific. Reduced weight gain and feed intake as well as lowered productivity may result. Affected animals may also have less resistance to infection and the effectiveness of vaccines could be reduced.

Zearalenone, produced by Fusarium moulds, can cause severe reproductive problems in swine. Swollen, reddish vulvas, enlarged uteri, rectal or vaginal prolapses, infertility, small litters, weak piglets and an increased frequency of mummified pigs can occur.

Diarrhea, vomiting, internal hemorrhaging, weight loss and feed refusal can also occur as a result of other Fusarium moulds.

Feeding Mouldy Forages and Grains

  1. Avoid feeding mouldy feed to young, pregnant or lactating animals.
  2. Feed the questionable feed to a small group of animals for several weeks. Note their feed intake and weight gain as well as any health problems.
  3. Reduce the mould concentration by mixing the mouldy feed with clean feed.
  4. Introduce mouldy feeds into a ration gradually since they are often unpalatable.
  5. Balance the ration. Slight nutrient deficiencies can make animals more susceptible to mycotoxin poisoning.
  6. Provide supplemental vitamin E.
  7. Analyze feed for mould type.

Analyses of Mouldy Feeds

The types of moulds present in a feed can be identified in a laboratory. The testing procedure takes 7 to 10 days.

However, the testing does not determine the presence of mycotoxins. Mycotoxin-producing moulds, such as Fusarium, can exist without actually containing mycotoxins. Mould identification does, however, warn producers of a possible problem.

The detection of mycotoxins is extremely difficult. This service can be arranged in response to an existing animal health problem, and after the moulds present in a feed have been identified.

Producers interested in having a mould analysis done on their feeds should send a sample to a feed testing laboratory.  

Feed Quality

Moulds also affect feed quality. Losses in dry matter, energy and vitamins occur whenever moulds are present.

A few inches of mould on the outside of bales can greatly lower the amount of dry matter produced. Table 1 shows the losses in dry matter which occur when different amounts of spoilage are present in large round bales.

Moulds reduce the value of a feed regardless of whether mycotoxins are present. Noticeable mould growth is estimated to reduce feeding value by a minimum of 10 per cent. As mould growth increases, greater loss of nutrients occurs. If a kernel of grain is completely covered with mould, less than five per cent of its original energy is present.

Thiamin and vitamin E can also be destroyed by moulds.

Table 1: Trimming Bale Losses

Spoilage (cm)

Spoilage (kgs)

% of Bale Spoiled
















Source: Watson, Missouri, 1985


Nitrate accumulation in forage can be the result of several factors including:

  1. Level of fertilization. High levels of nitrogen fertilizer and/or manure application may contribute to high nitrate levels in the forage.
  2. Forage type. Weeds and cereal crops are likely to contain higher nitrate levels than legumes and grasses. Seeds do not accumulate nitrates.
  3. Forage maturity. Early stages of cereals may contain higher nitrate levels.
  4. Light intensity and temperature. Poor light intensity increases nitrate accumulation. Increasing temperatures also increase the nitrate content.
  5. Drought and frost. Toxic levels of nitrates in forages are a possibility whenever normal growth of plants is disrupted by hail, drought, spray drift or frost.

If conditions improve and the plant starts actively growing, some of the accumulated nitrates may be used up in a few days. This usually occurs only in the top leaves which are exposed to sunlight. The bottom leaves, which are shaded, may still contain high levels of nitrates.

Nitrates in feed are converted to nitrites during digestion. This reduces the oxygen-carrying capacity of the blood and the animal can die by suffocation.

Symptoms of severe nitrate poisoning include labored breathing, frothing at the mouth, rapid pulse, weakness, diarrhea, frequent urination, incoordination and convulsions. Death may occur in three to four hours. Non-fatal doses may result in loss of appetite, lowered milk production, slow growth and abortions in cows that recover.

Nitrates in forages can be detected only by chemical analysis. If you suspect a problem, take a sample of the feed to your local agricultural representative for a spot test. This will determine if nitrates are present. Analysis at a feed testing laboratory will determine the actual level of nitrates and recommend corrective action.

Any amount of nitrate nitrogen over 0.5 per cent of the total ration dry matter should be regarded as potentially serious. Consult a veterinarian promptly when suspected cases of nitrate poisoning are found.

Nitrate poisoning can be controlled by good management. High nitrate forages can be mixed with low nitrate level forages, thus reducing the overall toxicity of the ration. Feeding adequate levels of energy and vitamin A reduces the risk of nitrate toxicity. Ensiling forage tends to reduce nitrate levels by 40 to 60 per cent as fermentation reduces some of the nitrates to gas.

Prussic Acid

Dangerous levels of prussic acid (hydrogen cyanide) can be found in both native and tame forages. These levels are most common in the new growth which occurs after a period of slow growth caused by frost or drought.

Sorghum, sorghum sudan, flax and birdsfoot trefoil can contain high levels of prussic acid. Arrow grass and chokecherry leaves are two native plants which are also prone to high levels. Chokecherry leaves are not very palatable but cattle will eat them if feed is scarce.

Most of the prussic acid in plants exists as a bound, nonpoisonous chemical. When normal plant growth is disrupted as a result of frost, for example, prussic acid is released from the bound form and the poison accumulates in the plant. If new shoots emerge after the frost or a period of slow growth, the forage should not be grazed until the new growth reaches a height of at least two feet. The poisonous property is greatly reduced if the forage is thoroughly cured as hay or silage. Horses and pigs are less susceptible to poisoning than cattle are. Producers are advised to have the suspect hay or silage tested for prussic acid prior to feeding it to livestock, as death can occur after only a small quantity is eaten.

Symptoms of prussic acid poisoning include nervousness, abnormal breathing, trembling and staggering, respiratory paralysis and severe convulsions. The animal can die within 30 to 45 minutes. Prussic acid does not accumulate in the body, so animals which don't show signs of poisoning won't be affected after the problem feed is removed.