Veterinary Taxicology

ANIMAL RELATED FACTORS

Animal species

• Variation among the different animal species in response to a toxic agent is mainly influenced by whether the animal is a ruminant or non-ruminant.
• In ruminants the diluting effect of the relatively large bulk of the rumen contents and the ability of the rumen microflora to metabolize foreign compounds will have a protective effect.
• The relatively shorter digestive tract of the non-ruminants is more efficient in absorbing ingested materials and this makes these species more vulnerable to the toxicants after ingestion.
• The anticancer drug methotrexate, is toxic to human beings, mice, rats and dogs. But, guinea pigs and rabbits do not show toxicity to methotrexate.
• Rabbits are resistant to atropine poisoning. Rats exhibit toxicity to red squill, while dogs are resistant to it. Sheep are more prone for copper poisoning.
• The anti-oxidants, butylated hydoxytoluene (BHT) and butylated hydroxyanisole (BHA) are potent inducers of epoxide hydrolases in mice but not in rats. In general, rats have low epoxide hydrolase activity relative to mice and rabbits.
• Hydroxylation (at least of sulfonamides) occurs in human beings and dogs. Some hydroxy-metabolites are excreted by active renal tubular secretion, while others are conjugated with glucuronic acid before excretion.
• Cats are highly susceptible to aspirin toxicosis (related to low glucuronide conjugation).

• Swine have low sulfotransferase activity, and thus little ability to conjugate xenobiotics to sulfate.

Size of the animal

• The amount of the material ingested per unit body weight determines whether or not intoxication occurs.
• Individual variations in the contribution made to the total body weightby the digestive tract and its contents and the body fat will also result indifferences in response between animals of the same weight exposed to the samequantity of the toxic agent.
• Marked differences exist among species, strains and individuals with regard to the amount of body fat and its mobilization.
• Mobilization of fat can greatly reduce the availability of adipose tissues to serve as a depot for xenobiotics. For acute exposures, this can increase the amount of xenobiotic in non-adipose tissues including the brain, as well as, sites of metabolism and excretion. For animals chronically exposed to lipid soluble metabolically-resistant compounds, mobilization of body fat can elevate plasma concentrations of the xenobiotic increasing the likelihood of toxicosis in the animal (or in it's developing or nursing offspring).
• Barbiturates when adminstered at body weight basis in Large White Yorkshire pigs may induce toxic effects due to the presence of large body fat.
• Age
• Very young and very old animals are in general more vulnerable to thevtoxic agents.
• Very young animals are affected more because of their poorly developed detoxification systems and very old animals are affected more because of the poorer state of health and age related lesions resulting in lowered metabolic and excretory capacity.
• Sex
• There is very little difference between the males and females in susceptibility to toxic agents. However, the rat is an exception.
• The production of malformations in the offsprings in females exposed to some periods of gestation and the effects produced by oestrogenic agents are also exceptions to this rule.
• General health
• Presence of renal, hepatic or cutaneous lesions and gut stasis influence the susceptibility.
• Nutrition
• Inadequate quantity and quality of feed supplied and the presence of gut parasites and their consequential nutritional effects could have a marked influence upon an animal’s response to a toxic agent.