AbstractThe shell quality of eggs produced by northern bobwhite (Colinus virginianus) dosed with sulfanilamide was evaluated by a compression breaking strength test and by the shell thickness measurements that are used in the U.S. Environmental Protection Agency avian reproduction test to determine the effect of a chemical substance on eggshells. The relative sensitivities of the two methods in detecting shell quality changes in sulfanilamide‐treated quail were compared by relative response ratios, calculated as treatment period response divided by pretreatment values. The ratios demonstrated a clear shell weakening response and a less apparent shell thinning response. Significant differences in shell thickness of eggs from sulfanilamide‐treated hens and those from control hens were not demonstrated (α = 0.32 and 0.34), although highly significant differences in shell strength were demonstrated (α<0.0001). Scanning electron micrographs of weak shells of normal thickness revealed abnormal ultrastructure, usually poorly formed mammillae. Obtaining both shell thickness and shell strength information may provide better means to evaluate a chemical's effect on shell qu
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