This resource has been partially reviewed and updatedA member of The Open Sanctuary Project’s staff has updated one or more sections within this resource. by a member of The Open Sanctuary Project’s staff as of October 28, 2021

It can be a challenge to ensure cow residents have healthy, happy lives after coming to a sanctuary, and there are many different aspects of care to consider each day. Unfortunately, toxic hazards are sometimes overlooked in the hustle and bustle of operating a sanctuary. While minor exposure to many of these toxins are unlikely to cause serious problems, large amounts can cause severe health issues and sadly, even death. There are also some toxins that are highly dangerous even in small amounts.

In order to help ensure you never run into this problem, we have compiled this resource of common plants and other potentially toxic things that been known to be a problem for cows.

Plants That Are Toxic To Cows

Please see The Open Sanctuary Project’s Global Toxic Plant Database and filter Species Afflicted by cowsWhile  "cows" can be defined to refer exclusively to female cattle, at The Open Sanctuary Project we refer to domesticated cattle of all ages and sexes as "cows." in order to see a list of plants across the world that are toxic to cows. Please note that, while comprehensive, this list may not contain every single plant toxic to cows!

Other Potential Cow Toxins

Blue-Green Algae

Blue-green algae are usually often found in stagnant, slow-moving water when temperatures are high. Consumption of this algae can result in poisoning in cows and other animals. Symptoms often occur quickly after ingestion. Symptoms of weakness, muscle tremors, paralysis, respiratory distress and staggering may be observed, as well as jaundice due to liver failure. In more severe cases, they may collapse and die. Photosensitization may be a delayed result of ingestion, causing reddening and irritation of the area around the mouth, the ear, udder, or other areas of the body.

Cantharidiasis (Blister Beetle Poisoning)

Blister beetles contain cantharidin, a chemical that works as a defense mechanism against predators. Cantharidin can injure or kill cows when ingested, though horses are more seriously affected. Contact is usually made when cows eat alfalfa hay that beetles were gathered up in and crushed during harvesting. First cutting hay is less likely to contain blister beetles as they tend to gather later in the season. Cows that ingest cantharidin may experience symptoms such as diarrhea, depression, abdominal pain, recumbency, increased heart and respiratory rate, dehydration, frequent urination, and in severe cases, death.

If you suspect Blister Beetle Poisoning, contact your veterinarian immediately. If early veterinary care is provided, afflicted cows may recover.

Copper

While cows are more resistant to copper poisoning than some other ruminants, it is still possible for them to ingest too much, causing toxicosis. It has been reported that Jersey cows may be more susceptible to poisoning than some other breeds of cows. Over supplementation in the diet with mineral blocks and food can cause toxicosis as can ingestion of plants, like clover, that absorb copper from soils rich in the mineral. Symptoms of copper poisoning are:

• Weakness,
• Lack of appetite
• Depression
• Dullness
• Poor light reflexes
• RecumbencyRecumbency is the state of leaning, resting, or reclining.
• Brown blood
• Foul-smelling diarrhea
• Blood in the urine
• Jaundice
• Death

Grain Overload (Acidosis, Grain Poisoning)

Grain overload occurs when cows eat large amounts of grain, which causes carbohydrates to rapidly ferment in their rumen, instead of being normal. When this happens, lactic acid is also produced causing the gut to slow down. It also causes dehydration and even death in severe cases!

Grain overload can happen when cows have access to unharvested grains but usually happens when they get into storage bins and gorge themselves. A fast change in diet to grains can also cause acidosis.

Signs of grain overload include:

• Dehydration
• Muscle weakness
• Recumbency
• Depression
• Bloating
• Staggering
• Diarrhea
• Lameness
• Shock
• Renal Failure
• Heart failure
• Death

If you suspect a cowWhile  "cow" can be defined to refer exclusively to female cattle, at The Open Sanctuary Project we refer to domesticated cattle of all ages and sexes as "cows." has grain overload, contact a veterinarian immediately. Treatment depends on the severity of the condition. Following grain overload, the rumen lining takes some time to repair, and some animals may develop secondary infections that will require veterinary treatment.

Lead Toxicity

Lead poisoning can be serious for afflicted cows. While lead was once used in paint (and even pesticides), it can also be found in the environments where old machinery or railroad ties, or leaded gas was once stored. Cows could ingest paint by chewing or licking surfaces that contained lead or even by ingesting certain plants that have absorbed lead from the polluted soil.

To be safe, you can have the soil tested. Local agricultural extension offices or environmental conservation services are good places to contact to learn more about testing your soil. The process should be fairly easy. In the meantime, be sure to prevent residents from accessing areas where you suspect they may come into contact with lead.

You may see the following symptoms:

• Salivation
• Muscle spasms
• Convulsions
• Eyelid twitching
• Blindness
• Grinding teeth
• Incoordination
• Lack of appetite
• Constipation
• Then diarrhea
• Headpressing

Consult a veterinarian immediately if you suspect a cow has ingested lead or is beginning to show symptoms of lead poisoning.

Molybdenum

Molybdenum poisoning can occur when there are abnormally high quantities of molybdenum in the soil or when the right balance of copper and molybdenum is off. Cows (and sheep) are particularly susceptible to this type of poisoning. Areas with shale or peat type soils or areas where minigin operations or metal production can prove a particular area of risk. is usually chronic and acute toxicity is rare. Symptoms of poisoning may include greenish diarrhea, stiffness, lameness, muscle weakness,poor coat health, and impaired growth. To counteract the effect of molybdenum, your vet may recommend certain dosages of copper supplementation. Any treatment should be discussed with them first.

Mycotoxins

Mycotoxins are a toxin produced by molds (fungi) that are harmful to many animals. Mycotoxins can affect cows through contaminated food or bedding. Moist, warm environments encourage mold growth. While cows are more resistant to the effects of mycotoxin than horses or some other animals, they can still be seriously affected. The type and amount of mycotoxin a cow comes in contact with affects whether the health issues are acute or chronic. Pregnant cows may be more susceptible to some mycotoxins, causing additional reproductive health symptoms. Some signs of different mycotoxin poisoning include:

• Diarrhea
• Appetite loss
• Weight loss
• Respiratory issues
• Increased susceptibility to diseases
• Impaired growth
• Poor coat quality
• Stiffness
• “Knuckling”
• Recumbency
• Lethargy
• Jaundice

Prevention is key in preventing serious health issues related to mycotoxin toxicosis. Luckily, there are a number of steps you can take to help protect resident cows:

• Store any grains, hay, or other foods in cool, dry, and clean areas.
• Keep grains and concentrates in secure food storage bins.
• Try to keep food storage areas protected from mice and rats and other wildlife.
• Use the oldest food first and try to use up open bags within a few weeks, fewer even during the summer.
• Clean storage cans and bins thoroughly.
• Check with the manufacturer or supplier of the product to see if they regularly test for the presence of mycotoxins in grains before mixing food. If they don’t, try to find another supplier.
• If you are concerned about the possibility of mycotoxin contamination, have your food stores tested. This could be especially important if you have cows that show initial signs of mycotoxin exposure.

Pesticides, Herbicides, And Rodenticides

It may not come as a surprise that pesticides, some herbicides, and rodenticides can cause toxicosis in cows if ingested. If cows ingest plants that have been sprayed with certain herbicides, they can become ill or even die. Many herbicides have been developed to be safer for animals but ingestion of large amounts can cause poisoning. Many pesticides can also cause toxicosis.

Rodenticides can as well and we encourage sanctuaries to seek out alternatives. While rats and mice can pose challenges for sanctuaries, it is important to respect them and use compassionate mitigation practices. Many rodenticides are anticoagulants (They prevent the blood from clotting) though there are other rodenticides that can cause serious issues and fatality if ingested. It is imperative that they do not come into contact with these poisons. There are many new and innovative ways to address rodent populations that are more effective and compassionate.

Early treatment is critical. If you suspect a cow may have ingested any of the poisons above, contact your veterinarian immediately. Blood tests may confirm poisoning.

Selenium

Selenium is a highly toxic element when taken in quantities larger than the necessary dietary amount. While selenium poisoning can be an issue for many animals, cows and other animals that graze are generally at a higher risk. Plants can contain varying amount of selenium depending on the presence and environmental factors in the soil. Poisoining can be acute or chronic. Acute symptoms of poisoning may include: weak and/or rapid pulse, dilate pupils, bloating, abdominal pain, labored breathing, watery diarrhea, pale blue mucous membranes, elevated temperature, and abnormal movement. Chronic poisoning may present as either a condition called “blind staggers”, caused by the ingestion of plants with water soluble selnium, or as alkalai poisoning, caused by the ingestion of plants or grains with insoluble selenium. However, it is now thought that blind staggers may actually be the result of consuming excess sulfur through water or food.

Symptoms of blind staggers may include loss of appetite, staggering, tripping or running into things due to visual imparment, loss of the use of front legs, paralysis of tongue and swallowing muscles, salivation, blindness, rapid, labored breathing, and death. This process may take a matter of weeks. Alkalai poisoning generally occurs after years of exposure, resulting in symptoms such as anemiaAnemia is a condition in which you don't have enough healthy red blood cells to carry adequate oxygen to the body's tissues., joint stiffness, dullness, emaciation, lameness, coat dullness or loss, hoof sloughing, hoof deformities, and severe pain.

Selenium deficiency can also be an issue in various regions and cause health issues. Talk with your vet about proper dietary considerations for cow residents and how to avoid selenium poisoning or deficiency in your area.

Snakebites

Venomous snakebites are not common, but when they occur, should be treated seriously and immediately. A snake can bite several times, so if you notice a snakebite, look for others. Snake venom varies by species, and the severity of a bite can also be influenced by the size, age, and the number of bites. Most venoms can impair blood clotting and damage the heart, while some others contain neurotoxins. Signs of snakebite may include:

• Swelling at site
• Pain
• Bleeding
• Salivation
• Rapid heart rate
• Lameness
• Depression
• NecrosisNecrosis is the death of most or all of the cells in an organ or tissue due to disease, injury, or failure of the blood supply. of surrounding tissue
• Black spots on skin
• Staggering
• Death

Seek veterinary care immediately if a cow is bitten by a venomous snake. Do NOT try to suck the venom out or place a tourniquet. Keep the cow calm while seeking immediate veterinary care. Depending on the severity of the bit, treatments may include antivenin, pain medications, fluid therapy, wound treatment, tetanus vaccination, and antibiotics. Check out our Compassionate Wildlife Practices At Your Animal Sanctuary for some tips on how to dissuade snakes from your property.

Wood Stains And Paints

Some wood stains and paints can be toxic to cows. Cows may try to chew on painted surfaces and can become ill if the stain or paint is toxic. Try and purchase paints and stains that are specially made for barns and fencing and listed as animal or “livestockAnother term for farmed animals; different regions of the world specify different species of farmed animals as “livestock”.” friendly.

Potentially Toxic And Questionable Foods

Consider These Variables
You may see food on this list that you have fed to your residents without any apparent issue. That may be because some foods are toxic in higher amounts while others are toxic in small amounts or whether they are being consistently offered the food over some time. It can also depend on the individual. We all have sensitivities to different things. Just as there are dogs who have eaten chocolate and don’t show clinical or subclinical signs of poisoning, there are many dogs that weren’t so lucky. The amount that may cause one resident to become ill (or even die) may be different for another resident. Different breeds or species can also affect their sensitivity to a toxin. In addition to these considerations, certain plants, fruits, vegetables, and other foods listed below may contain varying amounts of the toxin. The toxicity in some fruits and vegetables may even depend on their ripeness, the amount of sun exposure, the temperature, and more! Lastly, in an exploitive agricultural context, some studies or practices may encourage or include the feeding of certain foods with the intent being on production rather than individual long-term health. Below we have put together a list of foods that are known to contain some toxin that is potentially harmful to cows. We hope that providing this information will help you provide the best care possible to your residents. When possible, we have researched scientific papers to provide solid sources and tried to give more details. However, it is not an exhaustive list and is not meant to replace veterinary advice.

If You Have The Slightest Doubt…
Just because something might not be listed here as a toxic food or substance for cows, please do not take that to mean it’s safe to give them! Even normally non-toxic produce can cause health issues if given in large amounts. Check our Daily Diet, Supplement, & Treats For Cows resource and see if it’s listed as safe for cow residents. If you aren’t positive that it will be safe for cows, it’s best to avoid feeding it to them to be as safe as possible!

In addition to the above, we cover some foods that can be toxic to cows and foods that are often questioned in terms of toxicity but may be fairly benign:

• Anything With Pesticides Or Herbicides: Most vegetables and fruits are sprayed with these chemicals, which are certainly a source of concern when feeding your residents treats. Organic produce is safe from these chemicals, but for those foods that have been sprayed, it is important to peel or scrub with a produce wash to remove any chance of ingestion to avoid poisoning. You should never allow residents access to areas that have been sprayed to avoid poisoning.^1,2,3

• Avocado: The chemical, persin, that is present in avocado trees (bark, leaves, skin, and pit) is very toxic to many species, including cows.^4,5,6 Cows are in danger of ingesting persin through avocado leaves if they have access to trees. Lactating cows that have eaten the leaves of avocado trees develop non-infectious mastitis.^5,6  Cows that have ingested persin could also present with symptoms such as lethargy, swollen skin, difficultly breathing, coughing, a lack of oxygen in the blood, causing skin discoloration (blue), and possibly death in extreme cases, though there isn’t any data specifically referring to death in cows.⁵ Different varieties may contain more persin than other varieties. Guatemalan varieties are more commonly associated with poisonings and have higher amounts of persin than some other varieties though other varieties can still be toxic.^4,5 
• Bitter Almond: Ruminants are more susceptible to cyanide poisoning than animals with a simple stomach.^7,8 The leaves and seeds of bitter almond trees can cause cyanide poisoning in large enough amounts.^7,8 Do not feed leaves or seeds of bitter almond trees. While sweet almonds may contain a small amount of cyanide, bitter almonds contain significantly more.⁷ The nuts you find at the store are generally sweet almonds that have been processed. However, for those living in areas where almond trees abound, be sure you keep residents far away. Symptoms of acute cyanide poisoning can include hyperventilation, low blood pressure, salivation, weakness, excitement, convulsions, staggering, coma, shock, respiratory failure, and death within a few minutes to hours.^7,8,9 Both fresh and wilted leaves can be a source of poisoning, though wilted leaves, especially those after a frost, are considered especially dangerous.⁹ Living spaces should be free of cherry trees and leaves or pits shouldn’t be directly fed. 
• While many cows nibbling on brassicas such as broccoli, cauliflower, cabbage, turnips, brussel sprouts, mustards, radishes, and rape will be just fine, brassicas do have the potential to cause health issues in cows.^{10,11,12,13,14,15,16}  It is often tolerated in certain amounts in cows. It is a common agricultural practice to use certain brassica crops as fodder which increases the likelihood of someone experiencing a toxicosis-related issue. Research indicates that some brassica-related cropA crop is a pouched enlargement of the esophagus of many birds that serves as a receptacle for food and for its preliminary maceration. toxicoses are related to a number of factors such as whether the plants were poor quality, stressed from drought, or were sprayed with certain pesticides, the specific variety of plant, the maturity of the plant, the part of the plant, and how much the cows consumed over a period of time and whether they were slowly introduced to the crop or not.^11,12,13,14 There have been documented reports and studies of different kinds of brassicas causing various issues.
  • Cabbage causes poor body condition, dull coats, and anemia in a herd of cows.¹⁰
  • Grazing in rutabaga fields causes lethargy, jaundice, lack of appetite, photosensitizationPhotosensitization is the accumulation of photosensitive compounds beneath the skin., liver disease,  and death in a herd of cows used for dairy production.¹⁶
  • Kale, rape, turnips can cause hemolytic anemia in cows if that is the basis of their diet. Symptoms include weakness, brown or red urine, collapsing, and death.^11,14
  • Brassicas may absorb enough amounts of nitrites that can result in nitrate poisoning in large enough amounts. Symptoms include respiratory distress, tremors weakness, high heart rate, and dark brown or blue mucous membranes in severe cases.^11,12,14,16
  • Bloat, rumen acidosis, pulmonary emphysema can be caused by the ingestion of a large amount of brassicas^11,14,16 
  • Forage turnips and intake of large amounts of other brassicas can cause polioencephalomalacia (PEM), a neurological disease with clinical symptoms of head pressing, convulsions, blindness, circling, loss of coordination, recumbency, involuntary eye movement.^12,14,15 

Toxicosis can be chronic, developing over a period of time while being fed brassicas or acute, developing quickly after unmanaged access or excessive amounts being consumed.^11,16 Use caution when offering brassicas to cow residents. Avoid roots or seeds. Treats are unlikely to cause issues and larger amounts may be okay for some but not others. Play it safe and dole out brassica with care. 

• Cassava: Cassava has the potential to cause cyanide poisoning. Ruminants are more susceptible to cyanide poisoning than monogastric animals^.17 In many regions, cassava is an important part of the diet for humans and, in an agricultural context, animals.¹⁸ Different species of animals exploited in agriculture are sometimes given a diet that consists, in part, of cassava (tuber, leaves, peels) that has been processed but sometimes fed fresh.¹⁹ There are a number of ways to process cassava that affects the amount of HCN including heating, drying, fermenting, chopping, grating, peeling, soaking, boiling, grinding, and ensiling).^18,19 When correctly processed and/or supplemented with sulfur, the feeding of a percentage of certain cassava products and by-products has been done without toxicity issues as noted in multiple studies.^18,19,20 According to some studies, fresh peels appear to contain the highest levels of toxin.¹⁹ Some symptoms of acute cyanide poisoning can include hyperventilation, low blood pressure, salivation, weakness, excitement, convulsions, staggering, coma, shock, respiratory failure, and death within a few minutes to hours.^7,8,9,21,22 In cases of chronic cyanide poisoning,  calves may have stiff joints, developmental issues, and muscle weakness.²¹ In some cases, afflicted cows may become incontinent, causing urine scald, and there may be a softening of the spinal cord.^17,22 Other symptoms include a lack of coordination, head shaking, and pawing at their back end.^17,21,22 Take extreme care when considering feeding cassava products to cow residents, especially if you are not fully familiar with the risks and the proper ways to process cassava. Always speak to your veterinarian first.
• Cashew Apples: The fruit of the cashew tree has been known to cause intoxication in cows when fed fresh.^23,24 The symptoms include staggering, lethargy, and laying down.^23,24 If you live in an area with cashew trees, be mindful that cow residents do not have access to uncontrolled amounts of the cashew apple. 
• Cherry Leaves: The leaves, as well as the pits, of cherry trees, can cause cyanide/prussic acid poisoning.^7,8,9,21,22 Ruminants are especially susceptible to cyanide poisoning through the ingestion of plants as the toxin is released during fermentation in the rumen and quickly absorbed into the bloodstream.^{8,9, 22}Both fresh and wilted leaves can be a source of poisoning, though wilted leaves, especially those after a frost, are considered especially dangerous.⁹ Living spaces should be free of cherry trees and leaves or pits shouldn’t be directly fed. If feeding cherries as treats, remove all pits first. Symptoms of poisoning include bright cherry red mucous membranes, staggering, salivation, excitability, muscle tremors, difficulty breathing, vomiting, weakness, lying down, and coma, and death in extreme cases.^7,8,21,22

• Chocolate contains theobromine (and caffeine) that can be toxic in certain amounts in cows.^25,26,27While concentrations of the toxin theobromine and caffeine are fairly lower in many chocolate products, the darker the chocolate, the more theobromine it contains.^25,27 Cocoa bean shells and other chocolate byproducts are sometimes used as supplementation to diets for a number of farmed animalA species or specific breed of animal that is raised by humans for the use of their bodies or what comes from their bodies. species.^25,26,28 Depending on the amount of theobromine (and caffeine) contained in the waste/byproduct, the type of cocoa/chocolate product (husks, meal, confectionary waste), the percentage of waste/byproduct is included in the overall diet, and even the age of the cow, the diet may prove to be “acceptable” in an agricultural context or it may cause inhibited growth or decrease the amount of milk a cow exploited for milk can produce.^25,26,28 In one instance, calves being fed chocolate byproducts experienced excitability, high heart and respiratory rates, and seizures. One calf died.²⁵ In a case study. Cows exploited for their milk experienced muscle tremors and convulsions after eating chocolate chips that had been added to their diet. Multiple cows died^.27 Avoiding chocolate altogether is the safest bet. 
• Citrus: Citrus has the potential to be toxic in certain amounts and in certain forms as it contains chemicals like saponins and limonene, as well as furocoumarins which can cause toxicity issues in a number of species.^29,30,31,32 While offering unpeeled orange sections as treats shouldn’t be much of an issue for cow residents, care should be taken to ensure citrus isn’t a large part of their diet and that they aren’t provided whole, unpeeled fruits. One study revealed that cows fed tangerine “waste” and whole lemons suffered from esophageal obstruction from the whole lemons.²⁹ Citrus culled fruits and, more often, citrus byproducts are sometimes used as supplementation to diets for a number of farmed animal species without apparent ill effect in certain conditions.³³ It is important to avoid feeding moldy or old oranges as they can contain mycotoxin, citrine, which can cause serious health issues.³⁰ In another study, multiple cows exploited for their milk were fed citrus pulp as part of their diet over 6 weeks and died.³¹ Two of the cows had enlarged lymph nodes under their jaw and elevated heart rate before they died.³¹ Another two individuals also had a high heart rate, accompanied by weight loss, high levels of urea, and creatine in their blood (which can cause the kidneys to shut down), and high levels of sugar in their blood (hyperglycemic), and weight loss.³¹ The post-mortem examinations of 10 affected cows revealed hemorrhages to the intestinal tissues and the tissue on the outside of the heart, and pneumonia.³¹ In a different study, researchers found that replacing cornmeal with a higher percentage of dried citrus pulp was causing damage to rumen tissue.³² Care should be taken not to offer too much citrus and observe residents for any individual changes in stool or signs of discomfort.
• Corn Stalks contain nitrates (like many plants) but are more likely to be the cause of nitrate poisoning than many other plants though certain plants like sorghum and sudangrass are particularly high risk.³⁴ (Nitrates turn to nitrite through a physiological process, hence nitr-ite poisoning is caused by cornstalks high in nitr-ates.). Stalks of corn contain the highest levels of nitrates in the plant, though the leaves also contain nitrates, as well as the grain itself, just in lower amounts.³⁴ It is a good idea to find out if plants in your region have a high risk of accumulating unhealthy levels of nitrates. Talking to your local extension office can be helpful. Nitrite poisoning is a higher risk if a resident has ingested cornstalks or leaves after they have wilted, which can happen after a bout of cold weather.³⁴ Younger plants generally also have higher concentrations.³⁴ Calves, pregnant cows, and cows that are dealing with health issues may be at a higher risk^.34,35,36 Symptoms of nitrate poisoning include vomiting, diarrhea, staggering, dizziness, respiratory distress, increased heart rate, muscle tremors, weakness, a bluish tinge to the skin, and death.^35,36,37 Chronic poisoning can cause weight loss, difficulty gaining weight, loss of fetus, watery eyes and a dull, coarse coat, and interfere with thyroid function.³⁵ Cornstalks can also contain mycotoxins. Many different types of mycotoxins can affect cows. Different mycotoxins may present with different signs of poisoning, both acute and chronic, and end in death, in severe cases.

• Fruit Pits: Fruits with pits/stones (such as peaches, apricots, cherries, and plums) are often fine to offer to your cow residents as treats, so long as the pits have been removed. In addition to the risk of larger whole fruits and pits becoming lodged in the digestive tract (which has happened with whole citrus fruits in cows), the pits contain cyanide, a toxin.^7,8,9,17,22 Additionally, while cherry leaves are infamous for causing cyanide poisoning, the ingestion of the leaves of other stone fruits should be avoided as well until there is more information about their potential toxicity risks, especially after a cold shock in the weather or drought.^7,9 Ingestion of these, especially cracked and broken bits of seeds and pits that release cyanide, can cause symptoms of poisoning including staggering, salivation, excitability, muscle tremors, difficulty breathing, weakness, lying down, heart issues, GI distress, seizures, and could even result in coma and death in extreme cases.^7,9,22
• Green Potatoes: Green potatoes (and potato vines), particularly the skins and sprouts “eyes”, contain solanine, which can be poisonous to cows.^38,39 If fed raw and whole, there is also a risk of choking.³⁸ Overingestion can also potentially cause bloat issues if a large amount of raw potatoes is consumed quickly.³⁸ Solanine is part of a natural defense against insects and fungus. It can cause serious illness and even death in high enough amounts. Symptoms may include dilated pupils, weakness, depression, recumbency, eczema on feet and legs, sores on and in the mouth, staggering, gastric distress, respiratory distress, coma, and suffocation.^38,39,40 The most solanine is found just under the skin, so potato peels are best avoided entirely.^39,41 Potatoes that have been in the sun will have increased solanine.^38,39 Potatoes also contain chaconine, another chemical that can be toxic to cows.³⁹ Solanine is heat stable, meaning just boiling won’t necessarily reduce the solanine, though it has been posited that the toxin leaches into the water from the potato (which should be disposed of), which would reduce the amount in the actual potato as would peeling before boiling.⁴¹ Frying is said to do a better job of breaking down solanine in potatoes but fried potatoes aren’t very healthy for cow residents.^40,41 The level of toxic compounds can vary depending on environmental factors like climate and the type of soil it is grown in.⁴⁰ If you decide to offer a bit of potato as a treat, to be safe be sure they are free from green colorations and sprouts “eyes” and are peeled, boiled, the water drained and they are rinsed before offering. Never feed potato vines.
• Green Tomatoes: Eating a few ripe tomatoes isn’t likely to cause any issues but green tomatoes, as well the rest of the plant, contain a solanine-like glycoalkaloid, tomatine, as well as other chemicals that have potential toxic effects.^43,44,45,46 Feeding tomato pomace has been shown to possibly inhibit fermentation in the rumen, resulting in weight loss in cows.⁴⁷ There have been anecdotal reports of possible poisoning of cows from eating large amounts of tomato vines though nothing deadly. Generally, studies seem to indicate ripe tomato byproducts are safe for cows in certain amounts but most of these studies use dry tomato peels, seeds, or tomato pomace, not whole fresh tomatoes (though these were mentioned) and not green tomatoes.⁴⁷ Perhaps, more importantly, these studies are production-focused rather than individual-focused for longevity and well-being so what is considered acceptable here may not be considered acceptable from a nonexploitive standpoint. Still, there was nothing to indicate that eating a few ripe tomatoes will cause toxicity issues. Individuals are different though and should always be observed for any adverse reactions to new food or treats. The amount of tomatine reduces drastically as the fruit matures so it is safest to avoid green tomatoes and flowers, leaves, and vines and only offer ripe tomatoes in limited amounts to avoid possible gastric upset.⁴⁵
• Onions: Onions are toxic to cows. Onions can and have caused serious illness and even death in cows when a large number of onions were consumed.^48,49,50,51 Symptoms of onion poisoning may include sluggishness, lack of appetite, staggering, high heart rate, high respiratory rate, collapse, aborted fetus, decrease in rumen motility, Haemolytic anemia, dark colored feces, dark red urine, and, in some cases, death^.48,49,50,51 While large amounts of onion consumption produced the above effects, the amount that will affect individuals can vary and may not be known. Avoid feeding onions to cow residents or allowing residents to access areas where onions are growing.
• Processed Human Food: Processed foods, especially those that are super greasy, salty, or sweet, while not necessarily toxic, are not healthy for cows and should be avoided or strictly limited as an occasional treat.
• Rhubarb Leaves: Rhubarb contains high amounts of oxalic acid (in the leaves) which could be toxic to cows if ingested in large enough amounts.^52,53,54 The stalks contain significantly less oxalic acid than the leaves.⁵⁵ Although cows are less likely to experience clinical disease than sheep, the possible symptoms of poisoning may include stones in the urinary tract or bladder, hypocalcemia (low calcium levels in the blood) which can cause lethargy, lack of appetite, difficulty moving, and recumbency. Some other symptoms may include kidney issues and possible failure, and digestive distress and bloat^52,53,54 Possible poisoning depends on a number of factors including whether the individual has gradually been eating rhubarb or other plants containing high amounts of oxalic acid, how quickly they have consumed them, and the overall amount they have consumed.⁵³ 

• Salt: Salt poisoning can have serious consequences and even be fatal in cows.^56,57,58 Prevention is key. can result in cows from a normal amount of in the diet but a lack of access to adequate water or excessive amounts of salt in the diet.^56,58 (If you suspect salt poisoning, call your veterinarian immediately as soon as possible. Offering unrestricted amounts of water after deprivation can actually cause serious issues so smaller amounts over a period of time are safer. Ask your vet what the appropriate amount and intervals are in case of salt poisoning.)^56,58 Cows poisoned by salt may experience symptoms such as increased thirst, salivation, dark urine, depression, vomiting, diarrhea, abdominal pain, lack of coordination, circling, head pressing, seizures, muscle twitching, involuntary eye movements, blindness, collapse, coma, and death, in severe cases.^56,57,58
• Sweet Potato (Old, bruised, moldy): While any moldy food should be avoided to prevent potential poisonings, old, bruised, and moldy sweet potatoes have been associated with interstitial pneumonia in cows.^59,60,61,62 Discarded sweet potatoes considered unfit for human consumptions are used as food for cows in some agricultural contexts. Older or bruised sweet potatoes may have mold that can have fatal symptoms for cows who consume them. Symptoms of poisoning from molds on sweet potatoes include increased respiratory rate, shortness of breath or labored breathing, drooling, extended tongue, extended/elevated necks, and heads, grunting, open-mouthed breathing, frothing at the mouth, blue discoloration of the skin, and death in severe cases.^{59,69,61,62,63}  Be sure any sweet potatoes you offer are free from bruising and mold. Chopping them up into smaller chunks can help prevent choking.
• Visibly Moldy Or Rotten Foods: In addition to sweet potatoes, other rotten or moldy foods can contain mycotoxins that can cause serious health issues for cows.^30,64,65 Different mycotoxin poisoning can result in different symptoms, ranging in severity. Some of these symptoms can include itching, respiratory distress, aborted fetuses, a suppressed immune system, liver damage, neurological issues, and death.^30,64,65,66

SOURCES: POTENTIALLY TOXIC FOODS

1. Herbicide Poisoning In Animals | Merck Veterinary Manual (Non-Compassionate Source)
2. Chapter 44 – Toxicity of Herbicides | Veterinary Toxicology (Non-Compassionate Source)
3. Suspected Poisoning Of Domestic Animals By Pesticides | Science Of The Total Environment
4. Guide To Poisonous Plants | Colorado State University (Non-Compassionate Source)
5. Avocado Toxicosis In Animals | The Merck Veterinary Manual
6. Histopathological Changes Caused By Accidental Avocado Leaves Toxicity In RabbitsUnless explicitly mentioned, we are referring to domesticated rabbit breeds, not wild rabbits, who may have unique needs not covered by this resource. | International Journal Of Pharmaceutical Science And Research (Non-Compassionate Source)
7. Review On Cyanide Poisoning In Ruminants | Journal Of Biology, Agriculture, And Healthcare (Non-Compassionate Source)
8. Prussic Acid Poisoning In Livestock | Washington State University Extension (Non-Compassionate Source)
9. Prussic Acid Poisoning Potential In Frosted Forages | Iowa State University (Non-Compassionate Source) 
10. Cabbage Poisoning In Ruminants | Journal Of South African Veterinary Association (Non-Compassionate Source)
11. PhotosensitivityPhotosensitivity: Oversensitivity of skin to light. In Cattle Grazing Brassica Crops | Institute Of Veterinary, Animal, And Biomedical Sciences, Massey University (Non-Compassionate Source)
12. Hepatogenous Photosensitisation In Cows Grazing Turnips (Brassica Rapa) In South Africa |  Journal Of South African Veterinary Association (Non-Compassionate Source)
13. Disease signs reported in south-eastern Australian dairy cattle while grazing Brassica species | Australian Veterinary Journal (Non-Compassionate Source)
14. Forage-Related Cattle Disorders  Brassicas: Be Aware Of The Animal Health Risks | University Of Kentucky College Of Agriculture, Food And Environment Cooperative Extension Service (Non-Compassionate Source)
15. Polioencephalomalacia In Ruminants | The Merck Veterinary Manual
16. Investigating The Cause Of Brassica-Associated Liver Disease (BALD) In Cattle: Progoitrin-Derived Nitrile Toxicosis In Rats | Toxicon: X (Non-Compassionate Source)
17. Review On Cyanide Poisoning In Ruminants | Journal Of Biology, Agriculture And Healthcare (Non-Compassionate Source)
18. Effects of feeding fresh cassava root with high-sulfur feed block on feed utilization, rumen fermentation, and blood metabolites in Thai native cattle | Tropical Animal Health And Production (Non-Compassionate Source)
19. Detoxification Of Cassava Products And Effects Of Residual Toxins On Consuming Animals | The Food And Agriculture Organization (FAO) (Non-Compassionate Source)
20. Feed Intake, Digestibility And Energy Partitioning In Beef Cattle Fed Diets With Cassava Pulp Instead Of Rice Straw | Asian Australasian Journal Of Animal Sciences (Non-Compassionate Source)
21. Cyanide Poisoning In Ruminants | University Of Kentucky, College Of Agriculture, Food, And Environment, Cooperative Extension Service (Non-Compassionate Source)
22. Cyanide Poisoning in Cattle | Journal Of Dairy And Veterinary Sciences (Non-Compassionate Source)
23. Poisoning By Cashew Apple (Anacardium Occidentale L.) In Cattle | Acta Scientiae Veterinariae (Non-Compassionate Source)
24. 24. Use Of Cashew Apple Fruit Silage In The Cattle Fattening Diet | Livestock Research For Rural Development (Non-Compassionate Source)
25. The Effects of Chocolate and Chocolate by-product Consumption on Wild and Domestic Animals | Chocolate In Health And Nutrition (Non-Compassionate Source)
26. Nutritive Value Of Palm Kernel Cake And Cocoa Pod Husks For Growing Cattle | Journal Of Tropical Agriculture And Food Science (Non-Compassionate Source)
27. Case Of Suspected Theobromine Poisoning In Dairy Cattle | Journal Of Animal Physiology And Animal Nutrition (Non-Compassionate Source)
28. The digestive and physiological visceral organs of male Bali cattle were fed with cocoa bean shell | IOP Conference Series: Earth And Environmental Science (Non-Compassionate Source)
29. Bloat In Cattle Secondary To Esophageal Obstruction By Citrus Limon (Sicilian Lemon) | Pesquisa Veterinaria Brasileira (Non-Compassionate Source)
30. Citrinin As A Possible Cause Of The Pruritus, Pyrexia, Haemorrhagic Syndrome In Cattle | Veterinary Record (Non-Compassionate Source)
31. Suspected Citrus Pulp Toxicosis in Dairy Cattle  | Journal Of Veterinary Diagnostic Investigation (Non-Compassionate Source)
32. Replacement Value Of Dried Citrus Meal For Cornmeal In Beef Cattle Diets | Institute Of Food And Agricultural Science, University Of Florida (Non-Compassionate Source)  

33. Citrus Byproducts As Ruminant Feed: A Review | Animal Feed Science And Technology (Non-Compassionate Source)
34. Nitrate Toxicity In Livestock | Oklahoma State University Extension (Non-Compassionate Source)
35. Nitrate Toxicity in Beef Cattle | Oregan State University, Beef Cattle Sciences (Non-Compassionate Source)
36. Nitrates, Nitrites, And Health | University Of Illinois: Colleges Of Agriculture And Veterinary Medicine (Non-Compassionate Source)
37. Forage-Related Cattle Disorders Nitrate Poisoning | University Of Kentucky , College Of Agriculture, Food, And Environment (Non-Compassionate Source)
38. Cautions | University Of Nebraska-Lincoln, Institute Of Agriculture And Natural Resources (Non-Compassionate Source)
39. Steroid Alkaloids | Cornell College Of Agriculture And Life Sciences (Non-Compassionate Source)
40. Toxicants That Affect The Autonomic Nervous System (And, In Some Cases, Voluntary Nerves As Well) | Veterinarian Toxicology (Non-Compassionate Source)
41. Natural Toxicants | The Food And Environment Research Agency
42. Common Poisonous Plants | Cornell University Library (Non-Compassionate Source)
43. Poisonous Plants Of Veterinary And Human Importance In Southern Africa | Journal Of Ethnopharmacology (Non-Compassionate Source)
44. Feeding Tomatoes to Livestock : Ohio State University, College Of Food, Agricultural, And Environmental Sciences (Non-Compassionate Source)
45. Waste to worth: vegetable wastes as animal feed | CAB Reviews
46. Plants May Be A Source Of Toxicity To Cattle During Drought | The University Of Tennessee Agricultural Extension Office (Non-Compassionate Source)
47. Tomato Seeds As A Novel By-Product Feed For Lactating Dairy Cows | Journal Of Dairy Science (Non-Compassionate Source)
48. Onion Poisoning Of Young Cattle | The Veterinary Record (Non-Compassionate Source)
49. An Incidence Of Onion (Allium Cepa) Toxicity In Cattle And Buffaloes | Toxicology International (Non-Compassionate Source)
50. Onion Poisoning In A Herd Of Dairy Cattle | The Veterinary Record (Non-Compassionate Source)
51. Therapeutic Management Of Onion (Allium Cepa) Poisoning In A Bullock: A Case Report |  The Pharma Innovation Journal (Non-Compassionate Source)
52. Chapter 4 Urinary System | Jubb, Kennedy & Palmer’s Pathology of Domestic Animals: Volume 2 (Sixth Edition)
53. Alcohols And Acids | Plants
54. Investigation Of Clinical Hypocalcaemia In Cattle And Goats At The Selected Veterinary Hospitals In Bangladesh And India | Journal of Dairy, Veterinary & Animal Research (Non-Compassionate Source)
55. Natural Toxicants: Naturally Occurring Toxins of Plant Origin | Encyclopedia Of Food Safety
56. Overview Of Salt Toxicity | Merck Veterinary Manual (Non-Compassionate Source)
57. Salt Poisoning In Beef Cattle | Veterinary And Human Toxicology (Non-Compassionate Source)
58. Salt Poisoning | Veterinary Handbook Disease Finder (Non-Compassionate Source)
59. Suspected Sweet Potato Poisoning In Cattle In The UK | The Veterinary Record (Non-Compassionate Source)
60. Atypical Interstitial Pneumonia Associated With Sweet Potato (Ipomea Batatas) Poisoning In Adult Beef Cows In The UK | Cattle Practice (Non-Compassionate Source)
61. Effects Of 4-Ipomeanol, A Product From Mold-Damaged Sw et Potatoes, On The Bovine Lung | Veterinary Pathology (Non-Compassionate Source)
62. A Review Of Interstitial Pneumonia In Cattle | Veterinary And Human Toxicology (Non-Compassionate Source)
63. Fog Fever | UC Davis Veterinary Medicine (Non-Compassionate Source)
64. Occurrence Of Mycotoxins In Cassava (Manihot Esculenta Crantz) And Its Products | International Food Journal Of Safety, Nutrition And Public Health (Non-Compassionate Source)  

65. Bovine Abortion And Death Associated With Consumption Of Aflatoxin-Contaminated Peanuts | Journal Of American Veterinarian Medical Association (Non-Compassionate Source)
66. Occurrence And Significance Of Mycotoxins In Forage Crops And Silage: A Review | Journal Of The Science Of Food And Agriculture (Non-Compassionate Source)  

While this list isn’t exhaustive, it can certainly help you keep resident cows safe, healthy, and happy!

ADDITIONAL TOXICITY SOURCES:

Poisoning of Livestock by Plants | Ontario Ministry Of Agriculture, Food And Rural Affairs (Non-Compassionate Source)

Algal Poisoning Of Animals | The Merck Veterinary Manual

Blue-Green Algae And Livestock | South Dakota State University Extension(Non-Compassionate Source)  

Blister Beetles | North Carolina State University Extension Service (Non-Compassionate Source)  

Case Report: Blister Beetle Poisoning (Cantharidiasis) Of Dairy And Beef Cattle | The Bovine Practitioner (Non-Compassionate Source)  

Copper poisoning in a dairy herd fed a mineral supplement | The Canadian Veterinary Journal (Non-Compassionate Source)

Chronic Copper Toxicity | NADIS Animal Health Skills (Non-Compassionate Source)  

Grain Overload in Ruminants | The Merck Veterinary Manual (Non-Compassionate)

Grain Overload, Acidosis, Or Grain Poisoning In Stock | Department Of Primary Industries And Regional Development’s Agriculture And Food (Non-Compassionate Source)

Lead Poisoning In Animals | The Merck Veterinary Manual (Non-Compassionate Source)

Acute Lead Poisoning In Western Canadian Cattle — A 16-Year Retrospective Study Of Diagnostic Case Records | The Canadian Veterinary Journal (Non-Compassionate Source)

Feed Supplements: Microminerals | Encyclopedia Of Dairy Science (Non-Compassionate Source)

Molybdenum Toxicity In Animals | The Merck Veterinary Manual

Occurrence And Significance Of Mycotoxins In Forage Crops And Silage: A Review | Journal Of The Science Of Food And Agriculture (Non-Compassionate Source)  

Bovine Abortion And Death Associated With Consumption Of Aflatoxin-Contaminated Peanuts | Journal Of American Veterinarian Medical Association (Non-Compassionate Source)

Mold And Mycotoxin Issues In Dairy Cattle: Effects, Prevention And Treatment | Dairexnet (Non-Compassionate Source)

Effects Of Mycotoxins In Cattle | Vet Folio (Non-Compassionate Source)

Toxin Topic: Snakebites And Horses | The Horse (Non-Compassionate Source)

Organophosphates (Toxicity) | The Merck Veterinary Manual

Overview of Rodenticide Poisoning | The Merck Veterinary Manual

Common Weeds Poisonous to Grazing Livestock | Ontario Ministry Of Agriculture, Food And Rural Affairs (Non-Compassionate Source)

Herbicide Poisoning In Animals | The Merck Veterinary Manual

Overview Of Selenium Toxicosis | The Merck Veterinary Manual

Chronic Selenium Toxicosis | The Merck Veterinary Manual

Snakebite In Domestic Animals: First Global Scoping Review | Preventative Veterinary Medicine (Non-Compassionate Source)

Plants Poisonous to Livestock | Cornell University, Department Of Animal Science (Non-Compassionate Source)

Animal-Friendly Barn And Fence Paint For Horse Stalls | Stuff For Petz