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Overview of Veterinary Toxicology


Steve M. Ensley

, BS, DVM, MS, PhD, Kansas State University

Last full review/revision Apr 2021 | Content last modified Jul 2021

For a discussion of common poisonings in poultry, see Poisonings Poisonings read more .

Veterinary toxicology involves the evaluation of toxicoses, identification and characterization of toxins and determination of their fate in the body, and treatment of toxicosis. The recent worldwide melamine contamination in pet and swine feed, pet jerky treats causing illness and death, and concerns with use of beta-agonists in food animals demonstrates the relevancy of veterinary toxicology to current animal health and food safety. Veterinary toxicology can be challenging because of the low frequency of cases observed in a practice setting. When a toxicosis occurs, it often involves a large number of animals and may also involve litigation. A current veterinary toxicology reference book is helpful to ensure the correct samples are obtained and submitted for diagnosis.

A toxic agent is referred to as a toxicant or poison. The term toxin refers to a poison produced by a biologic source (eg, venoms, plant toxins); the redundant term biotoxin is occasionally used. A toxicant is generally considered a toxic substance that is either the main product or a byproduct of human activity (eg, pesticides manufactured for commercial use, dioxins produced as a byproduct of industrial processes). Toxicosis, poisoning, and intoxication are synonymous terms for the disease produced by a toxic agent. Toxicity (sometimes incorrectly used instead of poisoning) refers to the amount of a toxic agent necessary to produce a detrimental effect.

Acute toxicosis refers to effects during the first 24-hour period. Effects produced by prolonged exposure (≥3 months) are referred to as chronic toxicosis. Terms such as subacute and subchronic are used to cover the large gap between acute and chronic.

All toxic effects are dose dependent. A dose may cause undetectable, therapeutic, toxic, or lethal effects. A dose is expressed as the amount of compound per unit of body weight, and toxicant concentration as part per million or part per billion. These quantitative expressions are also used for feedstuffs, water, and air, as well as for tissue levels.

LD50 is the dose that is lethal to 50% of the subjects in a test sample. It is an estimator of lethality and the most common expression used to rate the potency of toxicants. Other terms used for prediction of illness or lethality include no observed effect level (NOEL), maximum nontoxic dose (MNTD), and maximum tolerated dose or minimum toxic dose (MTD).

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Food Hazards
Consumption of the fruit, seed, stem, or leaves of avocados can cause toxicity in animals. Ingestion of sufficient quantities of avocado fruit is most likely to cause myocardial necrosis in which of the following species?
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