Metal Toxicity (Lead, Arsenic, Mercury and Selenium)
Lead, Arsenic, Mercury and Selenium are common metals that cause toxicosis in livestocks / animals. Source, clinical signs and treatment options discussed in this post.
Lead
Source
Ingestion of lead-based paints, discarded crankcase oil, solid lead, asphalt, golf balls, bullets and other lead products may cause toxicity in animals.
Contamination of herbage by metal processing industries and automobile exhausts is also the common source of lead toxicity in poultry, livestock and other domestic animals.
Clinical Signs
- Acute toxicity: Nervous signs include excitement, bellowing, staggering, muscular spasm or tetany, convulsions and blindness.
- Subacute toxicity: Digestive disorders: Such as anorexia, constipation or diarhoea, colic, ruminal atony and vornition are observed.
- Chronic toxicity or plumbism: Plumbism is manifested by locomotor disturbances, rigidity of joints, swaying movements, drop in milk yield, abortions, and blue-black discoloration of gums, roaring and anemia.
Treatment
Calcium disodium EDTA should be given in large animal as slow i.v injection of 6.6% solution @ 70 mg/kg/day divided in 2-3 doses for 3-5 days along with symptomatic treatment.
Arsenic
Source
Consumption of arsenicals (Sodium arsanite, potassium arsenite etc.) contamination of herbage and water by arsenate sprays, arsenical dips, weedicides, rodenticides and effluents from metal smelting works.
Licking of wood preserved with arsenical and dipping of unshorn sheep in arsenical dips.
Arsenicals inhibit a variety of enzymes and uncouple oxidative phosphorylation Arsenic has special affinity for intestines, liver and kidney as they are rich in oxidative enzymes.
Clinical Signs
Hemorrhagic gastroenteritis and preserved carcass is the characteristic feature of arsenic toxicity.
Treatment
Antidote: British anti lewisite (BAL)
- Large animals: 2-3 mg/kg Lm. As a 5% solution in 10% benzylbenzoate solution in peanut oil. Repeat the injections at 4-6 hr intervals on first 2 or 3 days and twice a day there after until recovery.
- Small animals: 2-5 mg/kg i.m. as 1 0% solution in oil. Sodium thiosulfate and other symptomatic measures should also be given
Mercury
Source
Accidental ingestion of seed and herbage treated with mercurial fungicides or mercurial affluents from the metallurgy and inadvertent use of mercurial ointments for skin lesions are the common source of poisoning in animals.
Clinical Signs
Acute toxicity
Nervous signs in dogs are manifested by excitement, tremors, convulsions and depression. GI disturbances in cattle, sheep and pigs include severe gastroenteritis, bloody diarrhoea, vomition with blood and dehydration.
Chronic toxicity
Inco-ordination, altered gait, stumbling, head pressing, muscle spasms, pale mucosae, epistaxis, dyspnoea and fever- are commonly noted following chronic toxicity of mercury in animal.
Treatment
No effective antidote. Treatment is mainly symptomatic.
Selenium
Source
Toxicity occurs mainly by ingestion of forage (Astragaus, Gonopsis, Stanleya, Xylorrhiza, Aster and Astriplex spp.) rich in selenium content or grown on selenium rich soil and inadvertent use of selenium containing feed additive and shampoo.
Clinical Signs
- Acute: Anorexia, colic, bloat, watery diarrhoea, pale mucosa, dyspnoea with fluid sounds from lungs are observed in acute toxicity in animals.
- Sub acute: In this condition animal stumble on fixed objects or obstacle due to blindness caused by clouded cornea etc.
- Chronic: Including all signs animal also shows lameness due to erosion of articular surface of long bones and separation of ‘loof wall below the coronary band. Hair defects are also seen.
Treatment
No effective antidote. The treatment must be aimed to expel out the unabsorbed selenium from GIT. The affected animal should be shifted to protein rich diets.
