Zinc toxicity occurs when chickens ingest zinc-containing metal objects. Chickens use their beaks to explore objects. They are especially attracted to metallic, shiny objects, making them at higher risk of metal poisoning.
Once ingested, the metal object begins to corrode and the zinc is readily absorbed into their bloodstream. Zinc causes damage to the red blood cells, causing them to rupture, resulting in renal failure secondary to hemoglobinuria.
Common sources of zinc:
- Fasteners: Nuts, bolts, screws, nails, etc.
- Coins: US pennies minted after 1982 contain 97% zinc and 2.5% copper.
- Galvanized zinc: Galvanizing is the most prevalent use of zinc, as it is an anti-corrosion agent. Pretty much any metal intended for use outdoors is likely galvanized. This is why it's really important that when erecting poultry enclosures and predator proofing, to pay attention to any bits of metal cut from hardware cloth, so they don't scatter across the ground for the birds to eventually ingest.
- Cheap jewelry
- Many toys, including monopoly game pieces.
- Pipe fittings
Free ranging chickens may potentially pick up and ingest buried metal, coins, galvanized nails and other zinc produced products hidden in the soil, especially following a rainstorm.
Symptoms of zinc toxicity are non specific, and mimic clinical signs seen in several other diseases. The most common clinical signs observed include:
- Ataxia (staggering, loss of balance, difficulty walking, loss of coordination, falling, stumbling, unsteady, tumbling)
- Diarrhea (loose feces, watery droppings)
- Pallor (pale face, comb and wattles)
- Paresis or paralysis of the legs (walking stiffly, unable or inability to move, lower limb rigidity)
- Polyuria (production of abnormally large volumes of dilute urine)
- Polydipsia (excessive or excess drinking)
- Weakness (inability to stand, sitting/resting on hocks, limp/lame)
- Weight loss
Zinc toxicity is diagnosed based on history of exposure to zinc-containing objects, clinical signs, radiography, pathologic findings, and blood tests.
- Radiographs: May identify metallic objects in the GI tract. However, the results do not confirm or deny whether the bird has zinc toxicity.
- Blood Chemistry: Elevated serum or tissue (liver, pancreas or kidney) zinc concentrations may be helpful to confirm the diagnosis, but the results may take too long to come back in time to be helpful.
Treatment for zinc toxicity requires supportive care to help stabilize the bird with fluids and reduction of stress. If a metal object is identified via radiographs, it will need to be removed. Once removed, chelation therapy may be needed since this will result in rapid decrease in zinc levels in the blood. Parenteral CaEDTA is the chelator most recommended for birds with zinc toxicity. Blood transfusions may be needed in some cases.