Zinc toxicity occurs when chickens ingest zinc-containing metal objects. Once these objects are in the stomach or gizzard, they begin to corrode and the zinc is readily absorbed into the bloodstream. Zinc causes damage to the red blood cells, causing them to rupture. This results renal failure secondary to hemoglobinuria.
What are the symptoms of zinc toxicity?
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
Potential sources of zinc exposure
Besides its use as a dietary mineral, zinc in it's metallic form is used as a protective coating for metals, such as steel and iron (known as galvanizing). Pretty much any metal intended for use outdoors is likely galvanized. This is why it's really important that when erecting poultry enclosures, to pay attention to any bits of metal cut from hardware wire so that they don't scatter across the ground for the birds to eventually ingest. The same goes for any small bits of hardware---such as nails, washers, nuts, and bolts. Also, any US pennies mited after 1982 contain 97% zinc and 2.5% copper. Other less common zinc toxicity sources include: any products containing zinc oxide (aka Desitin and generic diaper rash ointments, sunscreen, deodorant, and anti-dandruff shampoos), zippers, monopoly game pieces, and other metallic toys or cheap jewelry. 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.
How zinc toxicity is diagnosed
Diagnosis of zinc toxicity is based on history of exposure to zinc-containing objects, clinical signs, radiography, pathologic findings, lab tests. 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. Radiographs might be helpful for identifying the presence of metallic foreign objects in the bird's gizzard or stomach, but do not confirm or deny whether the bird has zinc toxicity.
What is the treatment for zinc toxicity?
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.