Zinc toxicosis has emerged as a clinically significant factor in companion and aviary psittacines. Zinc can lead to primary illness or it can be one component of clinical disease. It is important for avian veterinarians and bird owners to have an understanding of the role that zinc plays in health and illness of birds.
Zinc poisoning has been described in many species of birds. In tests performed on cockatiels, they were fed a high or low dose of zinc from galvanized coating. All the cockatiels in the high dose group became severely ill and died or were euthanized within two weeks. Even the low dose group induced significant chronic disease.
The signs of zinc toxicosis are often non-specific and identification of the problem requires a thorough history and zinc testing. It is well known that galvanized after welding wire contains enough zinc to cause disease, so cages should be cleaned with a wire brush and vinegar before placing birds in them. Birds need not ingest flakes of metal to become ill, as zinc may leach from the cage into rainwater, which the birds can drink.
Birds are inclined to play with and chew on toys, pieces of cage and locks, and may become acutely toxic from zinc. With acute toxicosis, birds may vomit, but may stop eating. Voluminous, green stools are commonly reported. Sudden death may occur.
With chronic disease, gastro-intestinal upset may occur. Kidney damage may result in a bird developing increased urination and water drinking. Feather picking is commonly observed in cockatoos with zinc poisoning, but conures also show feather picking frequently, as well. In one study performed by an avian veterinarian in California, 43 cockatoos suspicious for zinc toxicosis were tested, and of those, 37 were indeed ill from zinc, and 34 were feather picking. Ninety seven percent of those birds ceased feather picking and barbering after treatment for zinc toxicosis and environmental correction. Feather picking cockatoos should be worked up for zinc toxicosis. It appears that birds are very sensitive to poisoning from zinc.
Sources of zinc are many. Any white rust found on cage wire should be removed prior to use, as it contains zinc. Food can leach zinc out of cage wire, so aviculturists must be careful to not feed directly on the wire. Although powder coated cages are now quite popular, the powder coating method was developed for lawn furniture and some of these formulas contain zinc. Most cages are safe and contain 0-50 ppm zinc, but some cages can have zinc levels over 5,000 ppm, although this is rare.
Padlocks and some toy hangers have high levels of zinc. It is safest to replace cage hardware with stainless steel components. Galvanized dishes should never be used. Many additives and some treat sticks contain large amounts of zinc. Some paints and varnishes contain zinc and many common adhesives do, as well. Duct tape, kitchen hardware, twist ties, remote controls, flooring and flooring adhesives all may contain zinc. There may be significant amounts of zinc in the adhesive found on paper towel and toilet paper rolls. Birds should never be given these toys to chew up, as they may ingest zinc. Pennies contain zinc, and birds should never be allowed to play with money. (This is one reason why coins should NEVER be thrown into cages with any animals at a zoo!)
Diagnosis of zinc toxicosis is based on the history, physical exam and lab tests. It is important to note that a bird need not have visible metal (from a radiograph) in the gizzard (ventriculus) to be suffering from zinc toxicosis. Time and time again, I have heard someone say that they ruled out heavy metal poisoning by radiographs (x-rays), because no metal was visible. The only way to diagnose or rule-out heavy metal toxicosis is by having the blood examined for the presence of lead or zinc.
There are several effective treatments available. DMSA appears to be an effective oral therapy for zinc and lead. Calcium Versonate is an injectable medication that works well. The GI tract should be flushed to remove any toxins from the system. Rarely, surgery may be required to remove a piece of metal from the GI tract. If the bird is very ill, support care may be required, including fluids, warmth, supplemental feedings and other medications, as indicated.
Zinc toxicosis may resemble many other diseases because the signs are usually so vague and non-specific. It should always be considered in cases of feather picking. It may mimic Proventricular Dilatation Disease (PDD). Recently, there have been advertisements for a holistic treatment for zinc toxicosis (which the pet owner said was misdiagnosed as PDD by her vet). As far as I know, only specific chelation therapy, which chemically removes the metal from the bloodstream of a sick bird, can be used to safely treat heavy metal intoxication.
Zinc is quite common in our environment and it is important that we, as stewards of our birds, take all necessary precautions to prevent them from ingesting toxic metals. Provide your birds with a safe, toxin-free environment and evaluate all cages, equipment, toys and dishes to ensure that they are safe for them.
This information is derived from a paper presented by Dr. Fern Van Sant at the Association of Avian Veterinarian's Annual Conference and Expo, held in St. Paul, Minn. in August of 1998.
Copyright © 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
All Rights Reserved
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