Heavy Metal Plasma Concentration: Daily Fluctuations (of Zinc) and Clinical Implications
Presenting Author: Karen Rosenthal, DVM, MS, Dipl ABVP (Avian),
Department of Clinical Studies, University of Penn, Philadelphia, PA
Interpretive Review and comments by Dr. Nemetz:
Over the last two decades, zinc toxicity in birds has become a common and controversial subject. The diagnosis of zinc toxicity in a bird is not always straight forward since clinical signs can be nonspecific, including depression, lethargy, anorexia, and weight loss. Since zinc blood levels in other species follow diurnal patterns, this paper was an attempt to see if this occurred in birds as well.
It was found that zinc DOES fluctuate throughout the day following a diurnal pattern like other species researched. The study showed that zinc levels were highest in the morning then decreased throughout the day with levels fluctuating as much as 25-33%. Mean zinc values seen was 1.74 - 2.1ppm. Other heavy metals were evaluated and copper was also found to fluctuate with the lowest level found at midday. Mean value of copper was 0.135ppm.
Dr. Rosenthal presented an intriguing paper, but we still do not have the answer to "what is" zinc poisoning and what is not. The paper does state that when evaluating a patient for chronic zinc toxicosis both a morning and evening blood level should be evaluated. If only one sample is taken, it should be an evening sample.
Zinc toxicosis is commonly seen at The BIRD Clinic. Acute toxicosis (blood levels often > 7ppm) usually present with regurgitation, marked lethargy, anorexia, and depression. The highest level recorded of a surviving patient was 22.8ppm (2009). Chronic toxicosis is more difficult to diagnose since the birds are receiving smaller quantities over time from sources such as galvanized cages, bolts, washers, and other zinc coated products and symptoms overlap with many other disease processes.
Dr. Nemetz recommends, to minimize the risk of zinc toxicosis, owners change all metal hardware in their bird's cage from galvanized to stainless steel products.