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Poisons - Toxic Agents

(41) Poisoning by a variety of agents is still not uncommon in pigs today although less so than when herds were small and less intensive. Many substances if taken at excessive levels become toxic and cause disease.

Poisoning can occur in an individual pig or in a group or even affect a whole herd. In the latter two cases a number of animals will be affected at the same time all showing similar clinical signs. A study of the history may indicate a common exposure to the poison by contact or ingestion.

If fed to excess many dietary components including minerals and vitamins, can cause diseases. Many medicines are highly toxic if used above their therapeutic levels.

It is a common fault with stock people when treating animals to assume that twice the dose will act twice as well. This is a fallacy. Overdosing may well have the opposite effect.

Examples of common substances that may cause poisoning

  • Antibacterial medicines - carbadox, furazolidone, monensin, sulphadimidine.
  • Trace elements e.g. iron, copper, zinc, iodine, selenium, arsenic, mercury, lead, fluorine.
  • Coal tars.
  • Gases - ammonia, carbon monoxide, hydrogen sulphide.
  • Insecticides - organophosphorus, carbamates, lindane, dieldrin.
  • Nutrients: essential minerals - copper, iodine, iron, manganese, selenium, zinc.
  • Rat poison - warfarin
  • Salt - if water is limited
  • Toxic plants.
Stress is a condition which occurs in all pigs when confronted with adverse management and environments. Better management of the environment has a beneficial effect on the health and the biological efficiency of the pig.

What does the pig do when stressed?

  • It increases the leucocytes in the blood.
  • It increases output of hormones (cortisol) from the adrenal gland and this depresses immunity.
  • It becomes more susceptible to disease.
  • It eats and drinks less.
  • The growth rate and feed efficiency get worse for a period.
  • It requires an increase in environmental temperature.
Major factors that may cause stress
  • Shortage of water supply.
  • Shortage of trough space.
  • Excessive stocking density.
  • Low, high or variable temperatures.
  • Draughts.
  • Movement, mixing, fighting.
  • Verbal or physical abuse.
  • Poor light.
  • Low levels of selenium or vitamin E may increase the susceptibility to stress.
  • High levels of vitamin A.
  • Inadequate or poor nutrition.
  • The act of farrowing or weaning.
  • Transport.
  • Changes in the environment e.g. changes in housing.
  • Exposure to disease

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