Zinc toxicity is a serious condition caused by ingestion of excessive amounts of zinc (Zn). Zinc is an important mineral needed in a chicken's diet, however high levels can be toxic. The dietary zinc requirement (based on young "broiler" chickens) is approximately 35 to 40 ppm (mg/kg). Anything greater than 2200 ppm (mg/kg) of zinc are considered to be toxic (pertaining to chicks). Chickens will absorb zinc in their proventriculus and small intestine. The rate of absorption depends on the amount and form of zinc ingested. Once absorbed, zinc is distributed throughout their bodies---specifically the liver, kidneys, bones, muscles, brain, intestinal mucosa, skin, pancreas, and retinas, where it damages these tissues.
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.
Clinical Signs of Zinc Poisoning
Clinical signs of zinc poisoning in chickens are nonspecific and varied. Most common signs observed in affected birds include:
- Reduced appetite
- Polyuria (production of abnormally large volumes of dilute urine)
- Polydipsia (excessive or excess drinking)
- Hematuria (the presence of red blood cells in the urine).
- Hematochezia (the passing of fresh blood per the anus, usually in or with feces).
- Dark or bright green diarrhea
- Foul-smelling feces
- Sudden death