Lead poisoning is a common cause of toxicity in backyard chickens, game fowl, and free range chickens. Lead poisoning can present in chickens as acute or chronic form, depending on the extent of exposure or quantity of lead ingested. When chickens ingest high amounts of lead in a short period of time it is called acute lead toxicity. Exposure or ingestion to small amounts of lead over a long period of time is called chronic toxicity.
- Acute toxicity: Chickens that develop acute lead toxicity or poisoning will often present with sudden onset of muscle weakness, loss of appetite, marked weight loss, ataxia, drop in egg production and severe anemia.
- Chronic toxicity: Chronic lead toxicity may eventually result in degeneration of motor nerves in the chicken's spinal cord and axonal loss in the peripheral nerves. Muscle atrophy and myodegeneration are often also present.
When lead is ingested, due to its relatively insoluble nature, it will remain in gastrointestinal tract, in which small amounts will be slowly absorbed and released into the bloodsteam. Once in the bloodstream, lead causes damage to the red blood cells and limit their ability to carry oxygen to the organs and tissues that require it, resulting in anemia. Lead also interferes with the absorption of calcium, which is essential for bones, egg laying, muscle contraction, and proper nerve and blood vessel function. Highest concentrations of lead are usually found in the liver and kidney.
Sources of lead exposure
Lead sources are toxic to chickens whether it is ingested or inhaled. There are numerous possibilities for sources of lead in the environment.
The risk of lead contamination in a given environment varies depending on its history or prior use, geographic region, current use, age of structures, and how environmentally consciousness prior occupants of the land were.
Additional threat to humans
- Contaminated soil: There are many ways that soil can become contaminated with lead. Soil located on the side of the road of busy streets is frequently contaminated with lead, since lead was an ingredient in gasoline until the late 1970s. Soil that surrounds older painted structures, as lead-based paint may still be in the soil adjacent the building. The land could also contain lead contaminated waste (batteries, asphalt products, leaded gasoline, lead shot, putty, and spent oil) which may be above or buried within the soil. Any vegetation that grows on the soil will be contaminated with lead, making the vegetation hazardous to chickens who frequently seek out forage to eat when free ranging in grass. Lead concentrations up to 300 ppm are considered "safe", however natural non-toxic levels are between 10-50 ppm. Lead contamination is a problem in Australian backyards. A recent study by Professor Taylor found 40 percent of the 200 Sydney backyards he measured had lead levels in the soil above the Australian health guidelines.
- Contaminated water: Water can become contaminated with lead if it flows through old lead pipes or faucets--which was common during pre-1978 days.
- Contaminated food: Food that is stored in glazed bowls or imported from countries that use lead to seal canned food.
- Tiny lead objects: There are many common everyday products that contain lead. If any of these are discarded or stored in areas where chickens have access, they can ingest it (especially if it is a small shiny object). Lead-based objects include some toys, cheap jewelry, fishing equipment, hobby or sport objects (such as stained glass, paint, plaster, ink), and lead bullets for guns.
Lead poisoning also posses a threat to humans, especially young children, as the lead is also deposited into the hen's eggs. Consumption of lead can cause brain damage, high blood pressure, miscarriages, and behavioral problems in children.
Documented Lead Poisoning Cases in Poultry
|Affected||History||Clinical signs||Diagnostic Findings||Tests used||Ref|
|Adult backyard chicken||Unknown||Inability to stand, neck twisting, not eating or drinking, and death.||Brain and gizzard koilin lesions.||Necropsy; histopathology||CAHFS Connection, July 2013|
|Four 18-month-old chickens on a small farm in Auckland, New Zealand||Unknown||Loss of appetite and death||Gastrointestinal stasis; Lead levels in the blood in one of the chickens was 0.24 mg/L (abnormal exposure level is greater than 0.2)||Necropsy; Blood test||New Zealand Veterinary Journal, Quarterly review of diagnostic cases, April-June 2015|
|An adult chicken kept as part of a backyard flock||The owner of the flock was conducting renovations on the old structures on the property, which caused flakes of lead paint to scatter throughout the same yard that the chickens were grazing in.||Swelling of crop and loss of appetite, followed by death.||Blood lead levels were greater than 0.60 mg/L (normal is less than 0.4 mg/L)||Blood test||New Zealand Veterinary Journal, Quarterly review of diagnostic cases, January to March 2016|