Quercus species: Oak

Family

Fagaceae

Common Name

Oak

Plant Description

A genus of some 600 species of long-lived shrubs to large trees from temperate and tropical areas, oaks are perennials and mostly deciduous, although oaks of tropical and sub-tropical areas are evergreen, or "live-oaks". Leaves are usually glossy green, and vary considerably in shape from characteristic lobed leaves to some species that have entire or serrate edged leaves. Staminate (male) flowers are produced as yellowish catkins, while the female or pistillate flowers are greenish and inconspicuous The fruits are nuts (acorns) with a characteristic scaly, basal, cup-like carp. As a general rule white oaks, those with rounded leaf lobes have edible acorns, while red oaks with pointed leaf lobes tend to be bitter and inedible (Fig. 332 and Fig. 333).

Figure 332. Quercus gambelii.

Figure 333. Quercus rubra -

Toxic Principle and Mechanism of Action

The leaves in particular contain polyphenolic compounds such as tannic acid, and gallic acid that are astringents, or compounds capable of precipitating protein [1]. When absorbed in large quantity the tannic acid reacts with the protein of cells, denaturing it, and in the process destroys the cells. The primary sites of tannic acid damage are in the intestines, liver, and kidneys. There is great variability amongst animal species as to their susceptibility to oak poisoning. Goats and deer can thrive while browsing on oak, and even cattle can eat oak provided it does not become a predominant component of their diet.

Risk Assessment

Oak leaves pose the greatest risk to livestock that eat them when there are no other forages available. All animals are susceptible to oak poisoning depending on the quantity eaten [2,3]. Large quantities of acorns that have fallen to the ground may be a problem to horses that eat them in quantity. Occasionally avian species may be poisoned if they eat quantities of the leaves or acorns [4]. No reports incriminate oaks a cause of toxicity in dogs or cats. Consumption of acorns by dogs however has the potential for causing poisoning as occurs in other animals.

Clinical Signs

Initially anorexia and constipation followed by diarrhea and colic can be expected. This is followed by dehydration and renal failure with proteinuria, glucosuria hematuria, and marked elevations of blood urea nitrogen and creatinine levels.5 The prognosis is poor once renal failure has developed as renal tubular degeneration is severe.

Treatment

Intravenous fluid and electrolyte therapy is indicated to help maintain kidney function. However, the animal should be carefully monitored as vascular damage may result in the leakage of fluids into body compartments compromising organ function. Intestinal protectants may be helpful in reducing the gastrointestinal consequences of oak poisoning.