- Distinguishing features
- Shrubs or trees with alternate lobed leaves; fruit is an acorn. Source. Various species of Quercus can cause oak poisoning.
- Oaks range in size from shrubs to tall trees. They have simple, alternate leaves with irregularly rounded lobes. Flowers appear as pendulant racemes or catkins and the fruit (known as an acorn) is a smooth nut with a basal cap.
- Geographic range
- Oaks have a wide geographic distribution.
- Toxic principle
- Tannins are naturally occurring plant polyphenols. Their main characteristic is that they bind and precipitate proteins. They can have a significant influence on the nutritive value of foods eaten by humans and animals because they are able to bind carbohydrates and proteins. Tannins are widely distributed in the plant kingdom. Oaks contain hydrolyzable tannins which are esterified with phenolic groups like gallic acid to form gallotannins. Such tannins are hydrolyzed by microbes and under acid conditions to release phenolic acids (gallic acid, pyrogallol, resorcinol) which are then absorbed. Both leaves and acorns, especially sprouted acorns, contain the toxin and toxicity is not diminished by freezing or drying.
- Oak poisoning is most common in cattle and calves, much less so in sheep and horses.
- The absorbed phenolic acids react with tissue proteins.
- Clinical signs
- Early signs are anorexia, dullness, rumen atony and constipation.
- Feces may be dark, solid and covered with a film of mucus, but can become black with a tarry or fluid consistency as a result of hemorrhagic enteritis.
- Poisoned animals become weak and prostrate 3-7 days after exposure and mortality may be high.
- Icterus, hematuria, dehydration, polyuria, and hyposthenuria are often present in advanced stages of the disease.
- Pregnant animals may abort.
- Laboratory diagnosis
- Urine may contain blood and granular and hyaline casts. Some diagnostic laboratories can detected phenolics like pyrogallol; this helps confirm exposure.
- Gastroenteritis, ascites, and hydrothorax may be seen.
- Subserosal petechial or ecchymotic hemorrhages are distributed over the surface of the gastrointestinal tract.
- Acorns may be found in the rumen.
- Gelatinous, blood-tinged edema occurs around the kidneys. Kidneys are enlarged, pale, and hemorrhagic with coagulative necrosis of the proximal convoluted tubules and pink-staining casts of epithelial cells and protein.
- Animals should be removed from further access to oak and given activated charcoal, oils, or ruminatorics.
- Parenteral fluids to correct dehydration and acidosis are helpful.
- A ration of 10%-15% calcium hydroxide in grain has been fed to aid precipitation of oak tannins and reduce mortality in cattle unavoidably grazing with access to oak trees.
Tannins are responsible for the astringent taste of wine or unripe fruit and also cause colors seen in flowers and autumn leaves.
Read more in the Poisonous Plants of Pennsylvania Publication