9. RHUBARB, PIE PLANT

Rheum rhaponticum

(dock family)

TOXICITY RATING: Low, unless animals are fed the leaves intentionally.

ANIMALS AFFECTED: All animals may be affected, those being fed garden trimmings are particularly at risk (cattle, swine, sheep and goats).

CLASS OF SIGNS: Staggering, trembling, breathing difficulties, weakness, diarrhea, increased drinking and urinating, death.

PLANT DESCRIPTION: This herbaceous garden perennial (fig. 9) develops from a heavy rootstock. Its leaves grow from the base of the plant on stout, shiny, red stalks. Heart-shaped and 1 to 2 feet long by 1/2 to 11/2 feet wide, the leaf blades have a smooth and shiny surface, darker above, with five main veins and wavy margins. The hollow stems end in greenish-white flower clusters in late spring.

SIGNS: The leaves contain oxalic acid, soluble oxalates,and citric acid, although the stems are edible. Some oxalates are insoluble and cause local irritation but the oxalates in rhubarb (and other species, such as sorrel or dock, Rumex) are soluble, and cause systemic problems, especially in the kidneys, or they can affect the electrolytes in the body, such as the balance of calcium and magnesium. Poisoning can be acute, when large amounts of oxalates are consumed quickly, or may be chronic, where smaller amounts are eaten over a longer period of time. Low blood levels of calcium and kidney failure are commonly reported findings in soluble oxalate toxicity.

Affected animals will appear depressed, and may stagger and tremble and be weak. Often, they will drink and urinate more as kidney function declines. Diarrhea may be noted, and affected animals may die if the electrolyte balance is extremely deranged or if the kidneys fail.

FIRST AID: There is no specific antidote for oxalate toxicity. If an animal is observed eating a large quantity of rhubarb or other oxalate plant, call a veterinarian immediately. If the plants were ingested a day or more previously, only supportive care can be given. A veterinarian will be able to provide assistance, although death may result from electrolyte imbalance or from kidney failure.

SAFETY IN PREPARED FEEDS: Rhubarb is not safe in hay, nor is any other oxalate-containing plant.

PREVENTION: Ruminants have some ability to adapt to oxalate plants if they are introduced to them gradually, since the rumen bacteria will detoxify the oxalates to a certain degree, although feeding these plants is never recommended. Do not allow animals to ingest large amounts of oxalate plants quickly, and it is best to not allow the feeding of oxalate plants at all. Do not incorporate weeds or rhubarb leaves into feed for animals, especially ruminants and swine, since these animals are not finicky eaters. Always make sure that animals have sufficient water, since oxalate toxicity is worsened if animals go thirsty.