Common Toxic Diseases

By Robert B. Hillman.

Poisonings occur in domestic animals from many sources and under a great variety of circumstances. Most poisonings result from accidental ingestion of the toxic substance, and any dietary deficiency that leads to an abnormal appetite will increase the likelihood of eating toxic materials. Some conditions that might lead to ingesting abnormal materials include: Lack of salt, low calcium or phosphorus in the diet, lack of roughage (fiber), starvation, and boredom.

Lead is one of the most common causes of poisoning in farm animals. Lead-based paint ingested by licking or chewing old painted woodwork is the most frequent source of the toxic material. Other common sources include painting materials (paint buckets, dropcloths), putty, old batteries, plumbing materials, gasoline, linoleum, and some fruit sprays.

Clinical signs include blindness, and nervous signs which vary from extreme excitement with bellowing, frothing of the mouth and attempts to climb the walls, to dullness and depression with head pressing, falloff of appetite, and failure to respond to any external stimulus.

In suspected cases of lead poisoning a veterinarian should be consulted immediately. Treatment can save some animals if applied soon enough and if an overwhelming dose of lead has not been ingested.

Arsenic is another common cause of poisoning in livestock due to its many uses in agriculture. It has been employed in insecticides, anthelmintics, weed killers, sheep and cattle dips, and wood preservatives. Poisoning occurs when these products are used improperly or if animals are allowed to ingest them.

Large doses of arsenic lead to death so rapidly that the animal is never seen to be ill. With smaller doses, signs include intense abdominal pain (colic), staggering gait, diarrhea, dehydration, and shock. While the outlook usually is unfavorable, rapid treatment with specific agents and fluid support will result in saving a few of the less severely poisoned animals.

Copper, Fluorine

Copper also has many uses in agriculture and can produce animal poisonings. Copper sulfate is used in orchard sprays, for treatment of pastures to control liver flukes, and for a foot soak to prevent foot rot. Improper use or allowing animals to graze too soon after use of copper sulfate can result in poisoning.

Copper poisoning is seen most frequently in sheep but does occur in cattle and usually results when animals have ingested forage containing small amounts of excess Copper for a considerable period of time.

At a time of stress (shipping, giving birth, etc.), the animal becomes acutely ill as the excess copper that has been slowly stored in the liver is suddenly released, resulting in destruction of the animal's red blood cells. The animal becomes weak, icteric (yellow), and has a dark brown urine. Supportive treatment with fluids and a change of diet may save some animals.

Fluorine poisoning usually follows contamination of forage with fine ash from manufacturing plants that process metals at high temperatures (aluminum, steel, etc.). Signs of fluorine poisoning include tooth lesions (discoloration and uneven wear), poor growth, weight loss and lameness. Treatment is aimed at removing the source of fluorine (change diet, reduce pasture contamination) and supportive care.

Urea is used as a feed additive in the diet of ruminants as a cheap substitute for more expensive protein sources.

Properly used, it is safe and effective. When improperly used (improper mixing, added at too high a level, spilled), it can cause poisoning.

Signs of urea toxicity occur shortly after ingestion and include bloating, increased salivation, incoordination, increased urination, and difficulty in breathing. Prompt veterinary treatment of the rumen by relieving the bloat and giving acidifying agents and cold water will result in saving most cattle with urea poisoning.

Organophosphate pesticides are used extensively in agriculture as animal sprays, systemic insecticides, and as treatments for seed grains and soil insecticides. If these products are improperly mixed and applied, or if they are ingested, poisoning results.

Signs of organophosphate poisoning include constricted pupils, increased salivation, diarrhea, muscle twitching, incoordination, and death.

Treatment is aimed at removing the toxic material by washing with lots of water if the poisoning is due to improper spraying, or giving absorbents and laxatives if the toxic material has been eaten. Specific veterinary treatment to counteract the drugs is also essential.

Dangerous Plants

Many plants can produce toxicity in cattle. Cows do not normally eat poisonous plants but if forced to by overgrazing or attracted to them by some change in the environment, poisoning can occur. Poisonings frequently follow dumping of green hedge clippings or garden refuse into a pasture. Cattle are attracted to the "new" material and investigate by tasting.

Clippings from Taxus or Japanese yew are a common cause of death in cattle due to the presence of an alkaloid that impairs functioning of the heart. Other plants (such as Cherry, Sudangrass) contain glycosides which release cyanide upon digestion. Cyanide prevents oxygen from leaving the blood to enter the cells and results in very rapid death of the animal.

Another group of dangerous plants accumulates toxic levels of nitrates when grown under certain conditions (high fertilization, stunted growth). Some common weeds (pig-weed, lambsquarter) and even some crops (oats, corn) will contain toxic levels of nitrate under these conditions. Nitrates are converted to nitrites in the rumen and they, in turn, combine with the blood making it incapable of carrying oxygen. If untreated, these animals can die from lack of oxygen.

Other toxic plants (St. Johnswort, buckwheat) can produce photosensitization, which results in the white portions of the body becoming sensitive to sunlight. If exposed to direct sunlight, these unpigmented areas will become reddened and swollen and, if not protected from the sun, these portions of skin will die and peel off. Other plants can produce excessive bleeding (Bracken fern, sweet clover) when eaten for a period of time.

Good management practices including providing ample palatable and nutritious forage, plus limiting exposure to toxic agents and plants will reduce the chances of poisoning.

Robert B. Hillman is Senior Clinician Section of Theriogenology, New York State College of Veterinary Medicine, Cornell University, Ithaca.