Plants Poisonous to Animals

Pets often chew on or ingest household plants, which can result in poisoning ( see Table: Poisonous Houseplants and Ornamentals). Houseplants vary in their degree of toxicity. Inquisitive puppies and kittens tend to mouth or chew almost everything. Many pets become bored or restless if left alone or confined for long periods, and chewing on objects for relief is common. Pets of all ages explore changes in their environment. For example, pets commonly chew the leaves or ripe berries of plants that are placed in the home during holidays.

Poisonous range plants can affect animals in many ways, including longterm illness and debilitation, decreased weight gain, reproductive problems, and death ( see Table: Poisonous Range Plants of Temperate North America). Poisonous plants are an important cause of economic loss to the livestock industry. Due to their diet and grazing habits, horses are much more likely to be poisoned by ingesting range plants than other companion animals.

Most poisonous range plants fall into two general categories: those that are indigenous to a range and increase with heavy grazing and those that invade after overgrazing or disturbance of the land. Poisonous plants are present in most range plant communities, so proper range management is important. Often, animals are poisoned by plants because hunger or other conditions cause them to graze plants that would not be eaten under normal circumstances. Overgrazing, trucking, trailing, corralling, or introducing animals onto a new range tend to induce hunger or change behavior, and poisoning may occur.

Not all poisonous plants taste bad, and they are not found only on overgrazed ranges and pastures. In addition, poisonous plants do not always harm animals when eaten. For example, plants such as lupine and greasewood may be part of an animal’s diet, and the animal is poisoned only when it consumes too much of the plant too fast.

Making a definitive diagnosis of plant poisoning is difficult. It is important to be familiar with the poisonous plants growing in the specific area and the conditions under which animals may be poisoned. A tentative diagnosis is possible if the following information is available: 1) local soil conditions, including deficiencies or excesses of various minerals, 2) the syndromes associated with each of the poisonous plants in the area, 3) the time of year when each plant is most likely to cause problems, 4) the history of the animal(s) over the last 6 to 8 months, and 5) any change of management or environmental condition that may have caused the animal to change its diet or grazing habits.

• Also see professional health content regarding plants poisonous to animals such as houseplants and ornamentals, range plants of temperate North America, and poisonous plants of Australia.