There are a variety of plants which contain or accumulate chemicals that are poisonous to cows. The results often include mild symptoms that can easily be managed such as irritations and slightly lowered animal productivity. In some cases, severe symptoms can be experienced whereby cows are in great distress leading to death. An important point to note is that even though cows are not readily provided with toxic plants, they can sometimes consume them while grazing. Agricultural research has, and is still playing a crucial role in enlightening farmers about various plants that cows should not feed on. In fact, animal poisoning is among the leading causes of low productivity and high mortality rates.  For this reason, it is of great importance for farmers to be aware of these poisonous plants so as to ensure that grazing fields are free from them. In addition, this will enable farmers to effectively manage animal health.

Brassica Plants

The brassica family is made up of crops such as turnips, cabbage, spinach and sukuma wiki which are highly palatable to cattle. However, in spite of their highly palatable nature, cows should not feed on plants belonging to the brassica family. Plants belonging to the brassica family are not recommended for cows as they have a potential of being poisonous. Brassica plants are well known for their toxicity in livestock that causes polioencephalomalacia. This is a brain disorder characterized by blind-ness, aimless wandering, lack of coordination, and twitching of ears, eyes, and skin. Other clinical signs may include circling, convulsions, and death. This illness often attacks cows after week of consuming brassicas like turnips. Note that although treatment is available, animals do not consistently respond to it.

Cows should not eat brassica as it is most likely to cause nitrate poisoning. Plants absorb a lot of nitrate which are converted to other nitrogenous compounds. These combine with haemoglobin in the blood to form methaemoglobin, which is incapable of transporting oxygen. Consequently, animals experience gasping and rapid respiration, rapid heart rate, muscle tremors and weakness. In severe cases, death can occur within a few days or even in hours of eating nitrate rich plants. In addition, acute respiratory distress syndrome may develop when cattle are given sudden access to brassicas (usually turnip fields) following relatively dry, high roughage diets. Affected animals stand with extended heads, dilated nostrils, and open mouths with protruding tongues. Death may occur within two days. Surviving animals have a slow recovery over several weeks.

Nightshade Plants

The nightshade family consist of numerous plants that are valuable as food, for example potatoes, tomatoes, eggplants. Although these make up a significant part of human food, cows should not eat plants belonging to the nightshade, or as formally called, solanaceae family. The fruit is now known to be safe but poisoning can occur from the ingestion of the leaves, vines, or unripe fruit. This is because the green part of plants in this genus produce many toxic alkaloids, including solanine, in their leaves, fruit and tubers. As such, cows should not eat any feed from the nightshade family. Toxic doses of solanine can cause significant mortality events in cows. Solanine toxicity often presents similarly to atropine toxicity as both can cause pupillary dilation, ataxia, muscular weakness, restless, thrashing, and changes in mentation. Additional symptoms include diarrhoea, haematochezia, anorexia, and hypersalivation. Solanine is mainly a gastrointestinal irritant hence these symptoms. Solanine symptoms often last for about 3 to 4 days. Note that cows can feed on nightshade leaves while grazing. It is therefore recommended for farmers to possess relevant knowledge in handling solanine poisoning. Acute ingestion can be managed by decontamination and activated charcoal and fluid therapy. A veterinarian can also be engaged.

Avocado Plants

Avocado plants are highly nutritious and so make up a significant part of the human diet. A popular assumption is that avocado leaves have similar benefits to animals hence can easily be transferred through consumption. This is however untrue. Avocado leaves contain a highly toxic compound known as persin. For this reason, cows should not feed on avocado leaves. This applies to stems and all parts of the avocado tree. In fact, a number of farmers across the globe have experienced the negative effects of persin on their livestock soon after the ingestion of avocado leaves; these include heavy financial losses due to decreased productivity. Although cattle rarely die from the consumption of avocado, they experience various illness. They tend to develop non-infectious mastitis.  They also experience gastrointestinal irritation, diarrhoea, respiratory distress, congestion, fluid accumulation around the tissues of the heart. Note that although death is rare, it can eventually occur if acute symptoms are not handled timeously. As previously mentioned, it is therefore highly recommended to make sure that grazing areas are free from avocado trees. A veterinary medical professional must be consulted when cows ingest avocado leaves.

Poisonous Plants

Most poisonous plants have an unpleasant taste and so animals avoid them. However, as earlier stated, animals may develop a taste for them in times of drought. In some cases, cows can unintentionally consume toxic plants while grazing. It is therefore important for farmers to have the ability to identify poisonous plants as cows should not feed on them. They should also be able to distinguish between symptoms of various types of plant poisoning. This help in guaranteeing animal safety. The following are some toxic plants that cows should not feed on:


  • Pig Weed – It is highly toxic in cows. Pig weed contain nephrotoxins that results in the accumulation of nitrates, soluble oxalates and even kidney failure. Poisoning is characterised by breathing problems, trembling, weakness, abortions, coma and death.
  • Hemlock – Cows should not feed on any part of hemlock plants. This is because they are highly poisonous and toxicity levels rise with every growing season. Cows affected experience nervousness, trembling, incoordination, depression, coma, death and birth defects. Signs are visible within 2 hours of consumption and respiratory failure can occur within 3 hours. Lethal dosages for cattle range between 450g to 900g.
  • Hairy Vetch – It is an excellent cover crop. None the less, cows should not feed on hairy vetch because of its toxicity. Cows that eat hairy vetch tend to experience kidney failure. The mortality rate for affected livestock is somewhere between 50 to 100%. Holsteins, Angus and Hereford cattle are most susceptible.