SOURCES AND CAUSES OF POISONING

SOURCES OF POISONING

Poisoning and the intensity of harmful effects depend on the form of exposure to toxic substances. Poisoning in human beings may be accidental, intentional, malicious or as an occupational hazard.  Poisoning in animals is generally either accidental or malicious. Intoxication of animals may occur from various sources. However, intentional toxicity in humans may be through abuse (narcotics) or by way of therapy through inadvertent use of drugs (adverse effects of drugs) or for committing suicides.

Sources of poisoning are diverse. These may enter the body by way of contact, inhalation, ingestion etc. may be accidentally, unintentionally or intentionally. Depending on the sources, these are categorized as:

l. Natural sources: Most of the intoxicants of natural origin enter the body through food chain (food or water). Some of the rocks and soils are very rich in some of the toxic minerals e.g. fluorine, arsenic, selenium, lead, etc. Thus, the plants, crops or grasses grown in these areas are rich sources of these intoxicants e.g. high quantity of nitrates in well water, copper in non-graminous plants, nitrate in spinach and selenium in seleniferous plants, etc.

Toxic plants: Certain areas are rich in poisonous plants depending on the agroclimatic conditions, geographical locations, etc. Despite the existence of literally hundreds of toxic plants, plant intoxication is less important except as a local prob­lem. Toxic plants are often refused by animals (as many times they have repulsive smell or contain highly irritant juices) and are eaten only when other herbage is scarce during the peak summer or winter months, e.g. Lantana, Datura, Quercus incana, Acacia leucophloea, Sudan grass, oleander, etc. Some of the fodder crops are very rich in toxic principles such as cyanogenetic glycosides, nitrates, nitrites, oxalates, selenium, etc.

Mycotoxins are another common natural source of poisoning in both, human beings and animals as stored feed stuffs, particularly the concentrates rich in maize, groundnut, rice bran, oil cakes, etc. are very rich in mycotoxins. Several reports of mycotoxicosis in humans, animals and birds are there.

Other natural sources of toxins are: bacterial toxins, venoms and other zootoxins e.g. scorpion toxin, tick toxins, bufotoxin, etc.

Toxic animals: Accidental biting or stinging by poisonous reptiles, insects, etc. often leads to poisoning in animals, e.g. snakes, spiders, scorpions, and bees.

Toxic minerals: Minerals are usually dangerous when they con­taminate water or when accumulate in plants from mineral rich soil. Poisoning may occur in animals after continuous ingestion of forages, feed, feed supplements, or water high in mineral contents, e.g. arsenic, selenium, fluoride, molybdenum, and copper.

II. Man-made sources: Humans are one of the biggest, most common and threatening sources of poisoning. Humans induced poisoning may be accidental, malicious or occupational. These toxicants are common sources of poisoning in animals and human beings as they are readily available and some are potentially toxic.

I.                    Accidental Poisoning: Accidental poisoning may occur when animal takes some toxicant accidentally or is added unintentionally in its feed, fodder or drinking water. Such toxicants come either from natural sources or from manmade sources.

II.                  Malicious Poisoning: Numerous cases of malicious poisoning in animals are recorded every year. In such cases, the toxicant employed is almost a readily available compound, e.g. insecticides, datura, strych­nine and warfarin.

(i) Accidental poisoning: Poisoning through the contamination of food and water with toxicants, industrial effluents, improper and injudicious use of drugs and chemicals including food additives, food preservatives or colouring agents, rodenticides, pesticides, herbicides, fumigants, accidents in chemical processing units like Bhopal gas tragedy (Dec. 3-4, 1984), chemical and biological warfares, radiation hazards or accidents in atomic energy generating units (Chernobyl episode). Similarly, animals are also poisoned due to dumping of industrial wastes and pasture treatments. Careless handling and use of agrochemicals, disposal of containers of chemicals or agrochemicals and domestic materials add to manmade sources of poisoning. Industrial and petrochemical emissions and other environmental pollutants have over the years been recognized as one of the greatest threat not only to human and animal health but also the entire ecosystem. Environmental problems have assumed dimensions of global magnitude.

Industrial toxicants: Contamination of water and herbage by in­dustrial effluents often leads to outbreak of poisonings among animals. Besides this, industrial gases, vapours, and dusts also produce adverse effects on the health of animals, e.g. chromium, nickel, lead, sulphur dioxide, nitrogen dioxide and chlorine.

Agrochemicals: Agrochemicals constitute the biggest source of accidental poisoning in all species. Careless use of pesticides is responsible for innumerable cases of fatal poisoning in animals. Rat baits (rodenticides) are the worst offenders in small animals and birds. Other important agrochemicals causing intoxication in animals are phosphorus, insecticides, fertilizers and fungicides.

Domestic materials: Various commonly used household chemicals and substances may cause intoxication in domestic animals especially pets, e.g. lead paint, disinfectants (mainly phenol), solvents, paraffin, and spot removers.

Therapeutic agents: Drugs when used in high dosage or by improper route may give rise to toxic effects. Toxic reactions occasionally seen following the correct dosage are due to idiosyncrasy or impurities in drugs. Indiscriminate use of drugs may also lead to toxic and undesirable effects in animals.

Food/Feed and water: Almost any food/feed given in excess cause harmful effects. Food becomes toxic, if not stored properly or if get contaminated with harmful substances. Contamination of drinking water is a frequent cause of poisoning, e.g. aflatoxins, rubratoxins, botulinum toxin and castor cake.

Environmental pollution: Many of the adverse effects seen in the animals are due to increasing environmental pollutants, e.g. carbon monoxide and pesticides.

Improper management practices: Improper management conditions often accelerate the toxic effects of toxicants, e.g. poor ventilation, overcrowding, and diet deficient in essential nutrients.

(ii) Malicious or intentional poisoning: It is the unlawful or criminal killing of human beings or animals by administering certain toxic/poisonous agents. Incidence of such poisonings is more prevalent in human beings and less in animals. Yet some of the reports are there where Abrus, strychnine, rodenticides, arsenic trioxide or agrochemicals are mixed in food or drinking water or administered through some other route to kill the animals.

Pet Poisons

1. Foods – specifically chocolate, xylitol, and grapes/raisins.

Animals have different metabolisms than people. Some foods and beverages that are perfectly safe for people can be dangerous, and sometimes fatal, for dogs.

Chocolate Raisins Mushrooms Xylitol (sweetener) Grapes Vitamins Gum

Bones Chicken Macadamia Nuts Sugar Bread Cake Coffee

Corn Cobs Dough Meat Rawhide Salmon Avocado

·         Chocolate. Though not harmful to people, chocolate products contain substances called methylxanthines that can cause vomiting in small doses, and death if ingested in larger quantities. Darker chocolate contains more of these dangerous substances than do white or milk chocolate. The amount of chocolate that could result in death depends on the type of chocolate and the size of the dog. For smaller breeds, just half an ounce of baking chocolate can be fatal, while a larger dog might survive eating 4 ounces to 8 ounces. Coffee and caffeine have similarly dangerous chemicals.

Certain types of chocolate are very toxic to dogs. The chemical causing toxicity in chocolate is theobromine (a relative of caffeine). The darker, more bitter, and more concentrated the chocolate is, the more dangerous it is.

• Many sugarless gums and candies contain xylitol, a sweetener that is dangerous to dogs. When ingested, even in small amounts, it can result in a life-threatening drop in blood sugar or even liver failure. It causes a rapid drop in blood sugar, resulting in weakness and seizures.
• Raisins and grapes are often overlooked as one of the most toxic foods to dogs, and can result in kidney failure.
• Alcohol. Symptoms of alcohol poisoning in animals are similar to those in people, and may include vomiting, breathing problems, coma and, in severe cases, death.
• Avocado. You might think of them as healthy, but avocadoes have a substance called persin that can act as a dog poison, causing vomiting and diarrhea.

• Macadamia nuts. Dogs may suffer from a series of symptoms, including weakness, overheating, and vomiting, after consumption of macadamia nuts. Macadamia nuts are toxic for dogs and cause weakness, depression, vomiting, loss of coordination, tremors and hyperthermia.
• Mushrooms are a special problem because unless you're a mushroom expert, it's hard to tell the difference between toxic and non-toxic varieties. For this reason, if you suspect your pet has eaten a mushroom, especially outdoors, it's best to presume it's poisonous.
• Vitamin poisoning in pets often involves vitamin D. Some pet owners give their dog or cat a vitamin D supplement, mistakenly assuming dogs and cats are as deficient as many people are in this important nutrient. However, most commercial pet foods have high levels of vitamin D added, so additional supplementation can create toxicity.
• Rawhide chews, especially those manufactured outside the U.S., which are often advertised as 'all natural,' are usually anything but. And they can pose a number of health problems for dogs, including choking, vomiting, diarrhea, exposure to chemical residues, salmonella poisoning and stomach torsion.
• You may be wondering how meat can be toxic for pets. Actually, it's spoiled, rancid meat that is most often the culprit. If you feed your pet real meat, whether from the local butcher or contained in a commercial raw pet food, you should know the rules for handling it. For example, fresh raw meat should be frozen for at least three days before serving it to your pet. This will kill any bacteria or parasites that may be present.
• If you prepare a homemade raw diet for your dog or cat, don't include guts. Do not feed the stomach and small and large intestines. Those are the parts of the prey we get rid of, because those are the parts that harbor parasites. You also can't allow frozen meat in any form to thaw and then re-freeze it. Once it's thawed, it must be eaten immediately or thrown away.

·         Cooked leftover meat that sits around too long can also turn rancid and potentially toxic, so practicing proper food waste disposal is the key to keeping your pets from being poisoned by spoiled food.

• Avocados contain a substance called persin which in large quantities may be toxic to dogs and cats. However, there is much debate on this subject and no definitive answer. A definite problem with avocados is that dogs are known to swallow the pits and develop dangerous blockages in the GI tract.
• Salmon can cause poisoning in two ways. Old or leftover rancid fish can be found by your pet in a dumpster or garbage can, or the raw meat can cause "salmon poisoning."

Raw salmon (and other fish that swim upstream to spawn) can harbor a parasite called Nanophyetus salmincola. The parasite can harbor a rickettsial organism, Neorickettsia helminthoeca, which causes "salmon poisoning." Freezing fish meat can inactivate both, but depends on several factors including temperature, the length of time needed to freeze the fish tissue, length of time the fish is held frozen, and the fat content of the fish.

Freezing and storing at -4°F (-20°C) or below for 7 days, freezing and storing at -31°F (-35°C) for 15 hours, or freezing at -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours is sufficient to kill the parasites. In a nutshell, if you feed raw salmon, freeze it for at least a week to be sure your pet won't suffer from "salmon poisoning."

2. Insecticides – including sprays, bait stations, and spot on flea/tick treatments.

        Ingestion of insecticides and pesticides, especially those that contain organophosphates (e.g., disulfoton, often found in rose-care products), can be life-threatening to dogs, even when ingested in small amounts. While spot-on flea and tick treatments work well for dogs, they can be very toxic to cats when not applied appropriately. Cat owners should read labels carefully, as those that contain pyrethrins or pyrethroids (a derivative of the Chrysanthemum flower), are severely toxic if directly applied or ingested.

3. Mouse and rat poison – rodenticides.

        There are many types of chemicals in mouse and rat poisons, all with different active ingredients and types of action, making all of them potentially poisonous to dogs. Depending on what type was ingested, poisoning can result in internal bleeding, brain swelling, kidney failure, or even severe vomiting and bloat. Mouse and rat poisons also pose the potential for relay toxicity, meaning pets – and even wildlife – can be poisoned by eating dead rodents poisoned by rodenticides.

4. Prescription medications for people. Drugs that might be beneficial or even lifesaving for people can have the opposite effect in pets. And it doesn’t always take a large dose to do major damage.

Some of the most common and harmful medications that poison dogs include:

·         Prescription anti-inflammatory and pain medications can cause stomach and intestinal ulcers or kidney failure. NSAIDS human drugs – such as ibuprofen, naproxen. Common drugs including NSAIDs (e.g. Advil®, Aleve® and Motrin) can cause serious harm to dogs when ingested, causes stomach and intestinal ulcers as well as potential kidney failure. The use of human NSAIDs in dogs is dangerous and should never be given without consulting Pet Poison Helpline or a veterinarian.

• Antidepressants can cause vomiting and, in more serious instances, serotonin syndrome -- a dangerous condition that raises temperature, heart rate, and blood pressure, and may cause seizures. Antidepressant human drugs – such as Prozac, Paxil, Celexa and Effexor. Of all prescription medications, antidepressants account for the highest number of calls to Pet Poison Helpline. When ingested, they can cause neurological problems in dogs like sedation, incoordination, agitation, tremors and seizures.
• Blood pressure medications.

 5. Household cleaners – sprays, detergents, polishes.

        Strong acidic or alkaline cleaners pose the highest risk due to their corrosive nature, and include common household products like toilet bowel cleaners, lye, drain cleaners, rust removers, and calcium/lime removers. Remember that “natural” does not necessarily mean safe, as some natural products can cause severe reactions. While general cleaners like glass products, spot removers and most surface cleaners have a wide margin of safety, it is still wise to keep them out of reach.

Household products, from cleaners to fire logs. Just as cleaners like bleach can poison people, they are also a leading cause of pet poisoning, resulting in stomach and respiratory tract problems. Not surprisingly, chemicals contained in antifreeze, paint thinner, and chemicals for pools also can act as dog poison. The pet poisoning symptoms they may produce include stomach upset, depression, and chemical burns. 

6. Fertilizers – including bone meal, blood meal and iron-based products.

        While some fertilizers are fairly safe, certain organic products that contain blood meal, bone meal, feather meal and iron may be especially tasty – and dangerous – to dogs. Large ingestions can cause severe pancreatitis or even form a concretion in the stomach, obstructing the gastrointestinal tract.

7. Over-the-counter medications. This group contains acetaminophen, ibuprofen and naproxen, as well as herbal and nutraceutical products (fish oil, joint supplements).

Sizeable ingestions of acetaminophen can lead to severe liver failure and even dry eye in dogs. However, it should be noted that it is a more significant threat to cats, as a single Tylenol tablet can be fatal.  

8. Amphetamine human drugs – ADD/ADHD medications like Adderall and Concerta.

        Medications used to treat ADD (Attention Deficit Disorder) and ADHD (Attention Deficit Hyperactivity Disorder) contain potent stimulants, such as amphetamines and methylphenidate. Even minimal ingestions by dogs can cause life-threatening tremors, seizures, elevated body temperatures and heart problems.

9. Veterinary pain relievers – specifically COX-2 inhibitors like Rimadyl, Dermaxx and Previcox.

        Carprofen, more commonly known by its trade name Rimadyl, is a veterinary-specific, non-steroidal anti-inflammatory drug. While it is commonly used for osteoarthritis, inflammation, and pain control in dogs, if over-ingested in large amounts, it can result in severe gastric ulceration and acute kidney failure in dogs. 

10. Pet medications. Just as we can be sickened or killed by medications intended to help us, cases of pet poisoning by veterinary drugs are not uncommon. Some of the more commonly reported problem medications include painkillers and de-wormers.

11. Plants. They may be pretty, but plants aren’t necessarily pet friendly. Some of the more toxic plants to dogs include:

• Azaleas and rhododendrons. These pretty flowering plants contain toxins that may cause vomiting, diarrhea, coma, and potentially even death.
• Tulips and daffodils. The bulbs of these plants may cause serious stomach problems, convulsions, and increased heart rate.
• Sago palms. Eating just a few seeds may be enough to cause vomiting, seizures, and liver failure.

12. Lawn and garden products. Products for your lawn and garden may be poisonous to pets that ingest them.

Causes of poisoning in Livestock

If your livestock or pets are acting sick or strange, they may have been poisoned by a common toxin. This chart details the most common sources and symptoms of animal poisoning.

1. Water Contamination

Algae

• Occurs when dense bloom of blue-green algae produces potent neurotoxin.
• Causes convulsions and sudden death in livestock, wildlife and birds.
• Algae sampling and testing required to confirm poisoning.

Salt

• Occurs when animal ingests high concentrations of salt or is deprived of water, especially in hot weather or in cold weather when water freezes.
• Poultry, feeder pigs and ruminants are susceptible.
• Blindness, deafness or paralysis may result.

2. Soil Imbalances

Selenium

• Occurs when livestock consume high selenium content in forage on alkali soil found on Great Plains of U.S., western Canada and Mexico.
• In its most severe form, causes blindness and staggering. Can also cause cracked hooves and lameness.
• Soil testing recommended for diagnosis.

Molybdenum

• Caused by imbalance in copper/molybdenum ratios in soil, most common in western U.S.
• Ruminants, especially young cattle, are most susceptible.
• Causes severe scours and emaciation.

3. Feed Contamination

Gossypol

• Excess pigment found in cottonseed products causes cumulative toxicity.
• Immature ruminants and pigs are most susceptible.
• Prolonged exposure causes weight loss, weakness and loss of appetite.

Ammonia 

• Caused by abrupt addition of feed-grade urea or ammonium salts to the ruminant diet.
• Mature ruminants are most susceptible, as they convert nonprotein nitrogen to ammonia, which is toxic.
• Causes muscle tremors, weakness, difficulty breathing and death.

Mycotoxins 

• Worldwide problem caused by ingestion of moldy feed, corn, or certain varieties of mold-infected pasture grass and forage (e.g., fescue grass, rye, sweet clover).
• All species of livestock, horses and poultry are susceptible.
• Wide variety of signs are possible, including lameness, paralysis, listlessness, jaundice and internal bleeding.
• Feed analysis required to confirm toxicosis.

Fluoride 

• Found in feed-grade phosphates, well water with high levels of fluorine or airborne factory waste.
• Usually requires long-term exposure and results in abnormalities of the skeleton and teeth.
• Signs may include mottling and staining of the teeth or softening of bones.

Copper 

• Usually the result of improperly formulated mineral mixes or certain plants causing mineral imbalances.
• Primarily affects sheep.
• Signs are related to liver damage and include diarrhea, pain, dehydration, jaundice and blood in the urine.

Canthardin 

• Caused by blister beetles, primarily in the southwestern U.S.
• Beetles swarm in alfalfa hay during harvesting and are ingested by horses, sheep or cattle.
• Signs include salivation due to oral ulcers, abdominal pain, shock and blood in the urine.

4. Farm Supplies

Lead

• Very common culprit in farm animal poisonings.
• Found in paint, batteries, grease and used motor oil.
• Most common in cattle and dogs, but all animals may be affected.
• Symptoms include dullness, lack of coordination, blindness or convulsions.

Coal Tar 

• Found in tar paper, creosote-treated wood, clay pigeons and tarbased flooring.
• Pigs often affected after chewing treated wooden farrowing crates; cats are very sensitive as well.
• Neurological signs, weakness, collapse and sudden death are often seen.
• May also cause decreased growth rate in young pigs.

5. Household Poisons

Chocolate 

• The obromin in unsweetened baker's chocolate can cause severe illness; cases usually involve dogs.
• Five ounces of baker's chocolate can be fatal to a 20-pound canine.
• Typical signs are nervousness, vomiting, diarrhea, seizures and occasionally coma.

Houseplants 

• Most often involves holiday poisonings of kittens and puppies chewing on poinsettias, Easter lilies, mistletoe, philodendrons, spider plants and others.
• Signs vary widely, but often include vomiting and neurological symptoms
• Toxicity varies greatly among individual plants.

Cleaning Supplies and Medications 

• Bored, young or inquisitive dogs may chew through plastic bottles and pill containers.
• Most household cleaners will cause severe vomiting and diarrhea.
• Tylenol, Advil, Aleve and other over-the-counter medications may be toxic and potentially fatal to cats and dogs.

Causes of Poisoning - Plants

Introduction

There are many plants which contain chemicals or which accumulate chemicals that are poisonous to livestock. The results of poisoning can range from minor irritations and slightly lowered animal performance to severe cases where the animal is in a great deal of distress and may die. This Factsheet is an introduction to the ways and means that plants can poison livestock. It also describes plants which mechanically injure animals or may cause irritation of skin on contact.

It would simplify matters if plants could be classified into two groups, poisonous and non-poisonous. Unfortunately, this cannot be done for many factors are responsible for the toxic principles in plants. What may be a harmless plant species in one circumstance could be deadly in another.

There are many plant factors that contribute to the toxic principles in plants. Individual plant species and varieties may differ in their poisonous content from early growth to maturity. With some plants, there is an increase in their ability to poison with advanced stages of growth, whereas with others the danger lessens. The state of the plant when eaten may also be important. In some cases, damage to the plant or wilting may produce poisonous chemicals in the plant which were not present in the fresh material. In other cases, such as with buttercups, the poison is contained in the fresh plants but not dried ones. Certain parts of a plant may be poisonous and other parts not. Rhubarb is a good example. The leaf stalk is eatable while the leaves are very poisonous.

Animal factors also influence the ability of plants to poison. Different animal species are susceptible to different plants and poisons. The age of the animal is also important. Young animals are often more susceptible than older ones, but it isn't always the case. Animals may build up resistance to certain poisons by being exposed to small quantities at first. Then, if a large quantity is consumed, they are resistant because their metabolism has already adjusted to handle the poison. An animal that is hungry or has certain dietary deficiencies is more likely to eat toxic quantities of a poisonous plant than a well fed animal.

Classification of Poisons

There is a large variety of toxic substances that have been associated with plant poisonings. Unfortunately for many plant species, the nature of the toxic substance has not yet been identified. However, most of the important poisonous plants in Ontario contain toxic agents from one or more of the following groups.

Alkaloids

Alkaloids are organic basic substances with a bitter taste, examples of which are morphine, atropine, nicotine, quinine and strychnine. The alkaloids generally are irritating to the gastrointestinal tract producing nausea, colic and diarrhea and also act on the central nervous system to produce blindness, muscular weakness, convulsions and death. Toxic alkaloids are found in the following plants; swamp and death camas, lupines, buttercups, marshmarigolds, larkspur, the nightshades, squirrel corn and Dutchman's breeches.

Glycosides

Glycosides are natural plant products that contain the sugar glucose. They can be subdivided into three main groups.

 

Cyanogenic glycosides

Cyanogenic glycosides are not themselves poisonous but in the presence of certain enzymes are hydrolyzed and produce hydrocyanic acid (HCN) which is highly toxic. HCN interferes with the oxygen exchange from the lungs to the body tissues so that various tissues including the brain are starved for oxygen and are consequently injured. The symptoms are muscle tremors, difficult, rapid respiration and convulsions. Often these are not seen because death occurs within minutes.

There are many factors that influence the amount of cyanogenic glycosides in plants. Some plant species normally have high levels, the highest levels occurring in early growth stages and decreasing as the plants mature. Climatic conditions, soil factors, shade and other factors that slow plant growth and development increase cyanogenic glycoside content. Low soil moisture, high nitrogen and low phosphorus all favor HCN production. Wilting, frost and other forms of physical damage to plants may induce a rapid increase in HCN content.

Cyanogenic glycosides occur in sorghums, sudan grass, marsh-arrow grass and wild cherries.

Saponin glycosides

Saponin glycosides produce a violent gastroenteritis with vomiting, diarrhea and colic. If the saponin glycosides are absorbed into the bloodstream, they cause a breakdown of red blood cells and injury to the central nervous system producing convulsions and paralysis. This form of glycoside is found in purple cockle, cow cockle, bouncingbet and pokeweed.

Mustard oil glucosides

Mustard oil glucosides found in plants belonging to the Mustard family cause severe gastroenteritis. Symptoms are severe colic and purging.

Nitrate

Nitrate poisoning of animals is actually nitrite poisoning occurring when nitrate is reduced to nitrite in the gastrointestinal tract. The nitrite is absorbed into the bloodstream where it reacts with hemoglobin to form methemoglobin. This compound, which is brown in color, is incapable of releasing oxygen. In acute cases of poisoning in cattle, 60 to 80% of the total hemoglobin is comprised of methemoglobin. Sheep generally do not develop as much methemoglobin and are therefore more resistant to this form of poisoning.

The symptoms of acute poisoning are trembling, staggering, rapid breathing, and death. Chronic poisoning may result in poor growth, poor milk production and abortions. In cattle, there is evidence that vitamin A storage is affected.

Some plant species are naturally good accumulators of nitrates. Common plant species that are associated with nitrate poisoning are shown in Table. The legume and grass species that are used for pastures or hay crops are not considered good nitrate accumulators, but given the right conditions can accumulate concentrations of nitrate that are potentially hazardous.

There is a direct response in plant nitrate concentration to increasing levels of nitrogen fertilization. Nitrate accumulation is greater when nitrate fertilizers are used than when either urea or ammonium sulfate is the nitrogen source.

A number of environmental conditions can influence the accumulation of nitrates in plants by altering mineral metabolism in the plant. Drought, uneven distribution of rainfall, and low light intensity have each been identified as climatic factors that bring about an accumulation of nitrates and nitrites in the stems and leaves of plants.

Table. Common plant species associated with nitrate poisoning.

Weeds	Crops
prostrate pigweed	oats
tumbling pigweed	rye
rough pigweed	wheat
lamb's quarters	barley
Canada thistle	corn
Russian thistle	sorghum
milk thistle	sudan grass
annual sow thistle	sugar beets
perennial sow thistle	mangels
poison hemlock	turnip
wild morning glory	rutabaga
spotted spurge	rape
prickly lettuce	kale
witch grass	broccoli, cucumbers, squash, celery

Molybdenum

Molybdenum poisoning can occur when there are abnormally high quantities of molybdenum in the soil. Animals pasturing on areas that meet this condition are often subject to acute scouring. The animals become emaciated, produce less milk, and their coats become rough and often faded. Legumes, particularly red and alsike clovers, are usually associated with molybdenum poisoning. To counteract the effect of molybdenum, it is necessary to add copper to the diet of the animals. A veterinarian should be consulted first before feeding copper.

Copper

Copper may also accumulate in plants in amounts great enough to cause toxic effects if soils are rich in copper or deficient in molybdenum. Clovers are good accumulators of copper and are generally associated with copper poisoning.

Selenium

Selenium is a highly toxic element when taken in quantities larger than what is needed for normal metabolism. In most plants, the level of selenium is related to levels in the soil. The symptoms of selenium poisoning are: dullness, stiffness of joints, lameness, loss of hair from mane or tail and hoof deformities. The acute form of poisoning is often called "blind staggers".

Ergot

Ergot is a fungus that infests grasses and if eaten in sufficient quantities is poisonous due to the production of a mycotoxin. Ergot's presence is observed by hard, dark-colored masses in flowering grass heads. These purplish or dark brown masses are usually two to five times larger than the grass seed and are called ergot bodies.

The active toxin, ergotoxine, stimulates the nerve centers that cause contraction of the small blood vessels supplying the different parts of the body. The result of ergot poisoning depends largely upon the amount of the fungus consumed. When only small quantities have been taken in, recovery without any serious symptoms may take place. Where large quantities have been consumed, dry gangrene in the extremities, possible abortion in pregnant animals and death may result.

General symptoms such as lack of appetite, dullness, abdominal pain, and subnormal temperature are common. Two distinct types of symptoms may develop in severe cases:

Nervous form

Dullness and depression are evident. There may be muscular trembling, convulsions, contractions of legs, and delirium. The animal suffers from gastrointestinal catarrh, refuses food, and gradually develops a wasting condition. A very rapid type in which the animal may die in spasms or convulsions is sometimes seen.

Gangrenous or general form

The stoppage of blood due to the contraction of the small blood vessels causes necrosis (death) of the extremities, particularly the feet, the tail, or tips of the ears. The affected part is cool, and dries up; a small furrow or line of separation appears and completely surrounds the limb, dividing the living tissue from the dead. There is little or no loss of blood, and seldom any pus present. Death may also occur due to the invasion of bacterial organisms, "secondary invaders", as well as from gangrene. Cases that do recover may be crippled for life.

The following are some of the crop, pasture and wild grasses on which ergot has been known to develop: oats, barley, wheat, rye, red top, bent grasses, meadow foxtail, brome grasses, orchard grass, reed canary, timothy fescues, blue grasses, quack grass, poverty oat grass, and foxtails.

Mycotoxins

Other mycotoxins are produced by some fungi that infect corn and cereals. The mycotoxins are produced only if the right environmental conditions are met and these conditions vary depending on the fungus. It is possible for mycotoxin production to take place while the crop is still standing in the field or after it is harvested and in storage.

In Ontario, the two most common forms of mycotoxins are vomitoxin and zearalenone. Vomitoxin causes the animal which eats the contaminated feed to vomit. Usually, however, animals refuse to eat the feed.

Zearalenone is a female estrogen. Symptoms in swine, the class of livestock that is usually affected, are as follows: females show signs of irregular heat, immature gilts develop a marked swelling and inflammation of the external genital organs, reduced litter sizes, and males may lose libido.

Coumarin

Coumarin, a chemical found in sweet clover, is responsible for the reduced palatability of this legume and is associated with a reduced blood clotting ability in the animals who eat sweetclover. Coumarin itself, however, does not cause this latter problem. Dicoumarol, a chemical derived from coumarin, during heating or spoilage of sweet clover hay or silage is the chemical that is responsible. If the clotting ability of the blood is lowered, it is possible that animals may bleed to death from slight wounds, dehorning, castrating or from internal hemorrhages.

Other Types of Poisoning or Injury to Animals

Photosensitization

Certain plants contain toxic agents which, when eaten, render the animal sensitive to strong sunlight. The damage that results can range from sunburning and swelling of the sensitive areas to the formation of ulcers and gangrene. Animals may also become blind.

Photosensitization cases are divided into two groups, primary and hepatogenic. Primary phototoxic plants have toxins that directly photosensitize the skin either through contact or by ingestation. When eaten, the toxins are absorbed and circulated in the blood to the skin where they are activated by the rays of the sun. The unpigmented (white) skin is affected.

The second group, the hepatogenic phototoxic plants, do not directly cause photosensitization. These plants have toxins that damage the liver. The liver damage prevents a breakdown product of chlorophyll (phylloerythrin) from being removed in the bile fluid. The phylloerythrin is circulated to the capillaries of the skin where it is activated by the sun and produces symptoms similar to those with primary photosensitization. It is important with hepatogenic cases to treat the damaged liver.

Saint John's-wort, spring parsley and buckwheat cause primary photosensitization. Blue-green algae causes hepatogenic cases.

Plants affecting milk and its production

Certain plants are known to decrease milk production. They may also make the milk or milk products unpalatable and unsuitable for human consumption. The following lists some of these plants:

• curled dock
• broad-leaved dock
• wild onion
• wild garlic
• buttercup
• marsh marigold
• lupines
• Saint John's-wort
• wild carrot
• burdock
• false flax
• flixweed
• wild mustard
• hedge mustard
• turnips
• rape
• spurges
• buckthorn
• yarrow
• garlic mustard
• stinking mayweed
• ox-eye daisy
• ragweed
• tansy
• absinth
• wormwood
• white snakeroot
• chicory
• stinkweed
• jimson weed

Algae in Water

Water may contain blue-green algae which can poison livestock. This type of algae is usually found in stagnant or slow-moving water during July and August. Long periods of warm weather and a high content of organic matter in the water favor its growth.

As a general rule, symptoms develop very rapidly and resemble an allergic reaction. Animals may be found dead at the water's edge or after having walked a few metres. Convulsions may occur, but more frequently the animal sinks to the ground, and dies without struggling. Smaller amounts of poison cause weakness and staggering, followed by recovery.

In some instances, apparent recovery from an attack is followed in a few days or weeks by evidence of photosensitization. There may be inflammation of the muzzle, the skin of the ear, the udder, or other parts of the body. Jaundice is often seen, and constipation is a common symptom. Such cases usually recover under good care.

Plants Causing Mechanical Injury

Some plants cause physical or mechanical injury to animals, and this injury may be external or internal. When this occurs, there is also the danger of infection of these injuries which may prove to be even more serious. This is sometimes the case with Canada thistle.

The barbs or awns of foxtail barley, downy brome, and wild rye are often troublesome in the mouths and throats of animals that have fed on these plants. The small, backward-pointing spines cause the awns to stick in the mouth or throat, and they are difficult to dislodge.

The spines of the fruit of the sandbur are quite stiff, and an animal grazing may injure its muzzle while cropping, or if burs get into its mouth they may cause a painful injury.

The burs of cocklebur and burdock, are also a source of annoyance. When the burs are eaten, they form an indigestible ball in the stomach. The spines injure the wall of the digestive tract and may thus open the way for secondary infection.

The sap from some plants, such as the spurges and buttercups, is a source of irritation to the skin of animals. After contact with the plant juices, the skin becomes inflamed and painful blisters may form. This type of damage to the mouth reduces the animal's desire or ability to eat.