Common Name
Oak, Gambel's oak, Shinnery oak
Botanic Name
Quercus gambelii Nutt.
Plant Family
Gamble's oak grows in dense stands in the dry foothills and mountain slopes up to an altitude of 9,000 feet. Shinnery oak is confined more to the lower elevations and sandy soils of the southern states.
Animals Affected
Cattle sheep, goats, horses and pigs are susceptible to poisoning
Toxic Principle
The tannins found in the leaves, bark, and acorns of most Quercus spp produce poisoning through their effect on the intestinal tract and kidney. Tannins are potent, precipitators (astringents) of cellular protein. Oaks at any stage of growth are poisonous, but are particularly toxic when the leaf and flower buds are just opening in the spring. As the leaves mature they become less toxic. Ripe acorns are less toxic than when green. Ruminants frequently browse on oak without apparent problems provided they have ample access to normal forages and oak represents less than 50% of their diet.
Gamble's oak is a shrub or small tree reaching heights of 15-20 feet. Shinnery oak (Q. havardii) is a shrub seldom attaining heights over 4 feet. Oaks have alternate, simple, toothed, or lobed dark green glossy leaves. The plants are monoecious with the staminate flowers occurring in long catkins and the pistallate flowers occurring singly or in small clusters. The fruit, an acorn, is a nut partially enveloped by an involucre of scales (acorn cup). Other oaks have similar characteristics.
Initially animals stop eating, become depressed, and develop intestinal stasis. The feces are hard and dark but a black tarry diarrhea often occurs later in the course of poisoning. Abdominal pain is evidenced by teeth grinding and a hunched back.
Once clinical signs are evident, renal damage is severe warranting a poor prognosis. Aggressive fluid therapy may help to rehydrate the animal and maintain kidney function. Supplementing cattle with 10% calcium hydroxide is useful in reducing oak toxicity in areas where oak brush is likely to be consumed in quantity.
Renal System
red colored urine. Marked elevation in serum creatinine and urea nitrogen.
Hepatic System
Severe liver damage is detectable by marked elevations in serum liver enzymes. Animals may live for 5-7 days after the onset of clinical signs.
A mucoid, hemorrhagic gastroenteritis is a common finding in oak poisoning. Hemorrhages on various organs and excessive amounts of fluid in the peritoneal and pleural spaces are often present. The kidneys are usually found to be pale swollen and covered with small hemorrhages. Histologically the kidneys show tubular necrosis. Liver necrosis may also be evident.
Special Notes
Oak poisoning often occurs in the early spring when a late snow will cover the ground and cattle then browse on the oak buds that are leafing-out. Other oak species that have been associated with oak brush poisoning include Q. undulata, Q. turbinella. Oak trees make excellent shade trees when mature, and ideally should be planted outside animal enclosures. I n years when there is a heavy acorn crop, fallen acorns should be raked up and removed from areas where horses and other livestock may eat them in quantity. 'Acorn calf' syndrome is a feed associated congenital anomaly of beef calves in which the calves are born with deformed heads, joint laxity and dwarfism.Although originally thought to be caused by the pregnant cows eating large quantities of acorns, there is no proof that acorns or the tannins present in oaks are responsible for the problem. It is generally agreed that the problem is feed associated but a specific toxin has yet to be determined. Ref: Ribble CS, Janzen ED, Proulx JD. Congenital joint laxity and dwarfism: A feed associated congenital anomaly of beef calves in Canada. Can Vet J 1989; 30: 331-333.