It is difficult to differentiate between poisoning due to these sources and to treat separately as nitrates can be converted into nitrites; both forms are toxic.
Animals most affected
Cattle, sheep, goats, horses, pigs, (all animals).
Nitrates: the salts are irritant to mucous membranes. Nitrites: cause methaemoglobinaemia and have a direct-acting toxic effect on the nervous system and blood vessels.
Note: nitrates are converted to nitrites in the gastrointestinal tract; nitrites to nitrates in the blood.
Toxic doses are difficult to quantify precisely, varying according to the diet or with the food supply. Fasting or food deprivation increases the overall toxicity: concentrated or cereal-based foods reduce it (this affords
the optimum degradation of nitrates into nitrites, then to ammonia).
Oral doses in mg/kg:
Neurological and circulatory effects
Death is possible during the acute phase following the onset of convulsions, or if the animal becomes comatose. (This is common when the level of methaemoglobinaemia reaches 70-80%.) A subacute form of poisoning may develop, although rare, with death occurring in 14 hours without any clinical signs presenting.