Abstract
Ascorbic acid (AA) enhances innate immunity, alters gene expression and functions as a co-factor in specific enzyme reactions. Birds are unique in that they can synthesise ascorbic acid whereas humans and rodents lack this ability. Diagnostic tests that currently exist to measure ascorbic acid levels in birds are time-consuming and expensive. In the present study, a modified and improved reduction-based colorimetric assay was evaluated in turkeys, quail and chickens. The assay was rapid for quantifying ascorbic acid in plasma and tissue samples, and generated values consistent with those obtained using HPLC. Five breeds of heritage turkeys were studied, showing significant plasma AA differences among breeds and, within breeds, by sex. Quail displayed plasma AA levels similar to the corresponding values that were highest in turkeys, which again were significantly greater in males than females. Chicken plasma AA levels were comparable to the turkeys and quail. However, the spleens of chickens had AA levels more than 12-fold higher than plasma, which increased significantly with a 150 mg/kg AA feed supplement. These collective results show a broad utility for the modified AA assay, and demonstrate differences in birds by breed, sex and diet.
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