Little is known on how blood biochemistry differs among avian chicks, especially in sexually monomorphic species. In this study we sampled blood chemistry of 342 white stork Ciconia ciconia chicks from nests in western Poland during four years (2005-2008). Special attention was paid to the effect of chick age and sex on blood biochemistry. Since white stork is a monomorphic species, the sex of chicks was established by a molecular technique. Nine blood biochemical parameters were studied: total protein concentration, urea, uric acid, triglycerides, total cholesterol, high density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), aspartate aminotransferase (AST) and alanine aminotransferase (ALT). There were sexual differences in total protein, uric acid, cholesterol, HDL and AST. However, total protein and uric acid only differed significantly between sexes if an age effect was included as a covariate in the analysis. Triglycerides decreased significantly, and AST, increased significantly with chick age. We confirm that blood biochemistry varies with chick age, but we also found significant differences between the sexes. Therefore, to understand changes in blood parameters, and to establish reference ranges useful in captive rearing of this endangered species, establishing gender may be important, even in very young individuals.
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