Effects of the duration and timing of dietary methyl parathion exposure on bobwhite reproduction

Abstract

Two northern bobwhite (Colinus virginianus) reproduction tests were conducted concurrently to evaluate how the duration and time of initiation of methyl parathion exposure affected dose-response relationships of reproductive parameters. In the long-term exposure test, pairs of adult bobwhite were fed methyl parathion-amended diets (0, 7, 10, 14, 20 or 28 ppm) for 25 weeks: 10 weeks prior to the onset of laying, 6 weeks as they came into laying condition and 9 weeks during egg laying. In the short-term exposure test, quail received amended diets (0, 10, 14, 20, 28 or 40 ppm) for only three weeks during the egg laying period, followed by a three-week posttreatment period. Fourteen birds died in the long-term test, compared to two in the short-term test. Significant dose-related reductions in daily food consumption, egg production and the number of 14-d-old chicks were observed in both tests during the treatment periods. No dose-related effects on fertility, hatch-ability or chick weights were detected. In the long-term test, there were dose-related decreases in adult body weight, brain and serum cholinesterase activity and female serum calcium concentrations. Cholinesterase and calcium were not measured in the short-term test. Eggshell weights were significantly decreased in both tests, but a dose-related decrease in eggshell strength and thickness was detected only in the short-term test. During the posttreatment period of the short-term test, no dose-related effects on reproductive parameters were observed, except that egg production did not recover until the third week after treatment. Except for the number of adult mortalities, all dose-related effects observed in the long-term exposure test also were observed in the short-term test. The short-term test design had two advantages that reduced variability unrelated to the chemical treatments: infertile and incompatible pairs could be removed from the experiment and pretreatment values could be obtained to serve as controls for each pair.