At this time of the year, as we prepare for the winter feeding season, I receive several questions concerning feed toxins and other potential problems that might be a hazard to your cattle. Animal feeds are subject to contamination from different sources. More common during times of drought, these toxins have the potential to harm your cattle and could possibly cause death in extreme cases. The most common toxins we need to be aware of in our area include, but not limited to, mycotoxins, acorn toxicity, nitrates and prussic acid. Let’s look at each of these as a potential hazard and determine ways to prevent them from being a problem on your farm.
Mycotoxins is the general term that includes aflatoxins, vomotoxin, and fumonsion among others. These are types of fungi that have the capacity to impair an animal’s health and productivity. Mycotoxin contamination of forages and cereals frequently occurs in the field following infection of plants with particular fungi or entophytes. Contamination may also occur during processing and storage of harvested products and feed whenever environmental conditions are appropriate for spoilage fungi.
The mycotoxin we are most concerned with as a potential problem is aflatoxin. Aflatoxins usually are found under conditions of high moisture/humidity and temperature. Aflatoxin contamination of corn is a prevalent problem in warm humid regions where the toxin may infect the crop prior to harvest and remain viable during storage. Aflatoxin symptoms include reduced feed intake, reduced reproductive performance, poor feed efficiency and reduced susceptibility to stress. A test can be used to determine the aflatoxin level in your product. Once a level has been determined, you can decide the best way to feed the infected crop. If you do have a high aflatoxin product, this may mean you only have to blend the feed with other feeds to utilize it in animal feed.
Vomotoxin is another mycotoxin that we need to be aware of in animal feeds. Vomotoxin is very dangerous when fed at high levels. Horses are most vunerable to vomotoxin with signs being brain necrosis and death. Other clinical signs include abortions, uterine infections, nervous disorders, hemorrhaging and vomiting. Vomotoxins are less likely to occur than aflatoxins. These toxins can be found in grains and grain by-products. A test can determine the level of vomotoxin in your grains with even low levels causing concerns.
Fumonisin is another mycotoxin that we can see problems from. This toxin can be found in any of your grain products including oats, wheat, rye, barley and corn. The biggest concern with this toxin is from a depressed immune system. This will leave your animals more susceptible to disease and sickness. In horses, this is a cause of Equine Leukoencephalomalacia or deterioration of the brain.
While mycotoxins will always be a concern in grains from high moisture, humid regions of the country, we should also be concerned about the possibility of toxins found in acorns. During periods of decreased forage availability, cattle may seek out acorns as a food source. Ingestion of too many acorns can lead to poisoning. Acorns contain a substance called gallotannin. In the rumen, gallotannin is metabolized to gallic and tannic acid. Tannic acid is very toxic to renal tubules, and renal failure tends to be the hallmark of this disease. The toxins in acorns seem to concentrate in milk; therefore, fast growing calves on heavy milking cows will be the first to show signs. The most visible signs of a possible acorn problem is constipation followed by a decreased appetite. If cattle are removed from the acorns, most will recover in a couple of days. Continued exposure will lead to black, watery diarrhea; blood draining from the nose; severe depression; straining to urinate and defecate; and death. There is no specific antidote for this toxin. It is recommended to replace fluids and electrolytes to keep the kidney operating, use broad spectrum antibiotics to fight off infections, and use mineral oil as a laxative. The most common practiced preventative is to supplement with calcium hydroxide (hydrated lime) immediately before exposure has been effective in mitigating signs of acorn toxicity. The most obvious prevention would be to remove cattle from areas containing trees producing acorns.
Nitrate toxicity is caused by the consumption of feed or water containing high levels of nitrate nitrogen. Under most instances, forage plants will not contain levels of nitrates high enough to be toxic. When this does occur, it is a serious problem. The most common accumulation of nitrates occurs in crops such as corn, millet, Bermuda grass, fescue, sorghum-sudan and soybeans. Nitrates can also accumulate in weeds such as pigweed, goldenrod and ragweeds. Nitrates are most often found in crops that were heavily fertilized with nitrogen coinciding with the beginning of a drought period. It is impossible to examine a sample of hay or silage and determine the nitrate level. A laboratory analysis is required for this. I would highly recommend that any producer who even suspects that nitrates might be a problem to send off a sample for testing. The cost is inexpensive and could save you thousands of dollars this winter. Symptoms include labored breathing, muscle tremors and a staggering gait, after which the cow falls down and dies quickly with little struggle. The membranes of the eyes and mouth are bluish from a lack of oxygen. The blood will be brown in color and turn red when exposed to air. Nitrate toxicity usually results in death within a short period of time, but can be prevented if you are alert to the problem. Medication includes giving a 4 percent solution of Methylene Blue intravenously using 100 cc per 1,000 pounds of body weight.
Prussic acid is another potential toxin that producers should be aware of. Prussic acid is usually found in large stem crops such as sudans and millets. It is most often found in crops that are grazed right after a frost in the fall. Symptoms include nervousness, reduced feed intake, rapid body movements and death. The level of prussic acid will lower over a ten to fourteen day period after the frost. It is also safe to utilize hay that has been baled after a frost, as long enough time is given for the acid levels to be reduced.
Jimmy Hughes is AFC’s animal nutritionist.