Effects ofin ovo injection of carbamates on chick embryo hatchability, esterase enzyme activity and locomotion of chicks

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Abstract
Carbaryl and aldicarb, two carbamate pesticides used extensively throughout the United States, are known to act as acetylcholinesterase inhibitors. We have demonstrated previously that exposure to carbaryl and aldicarb in young chicks caused persistent locomotion alterations with no correlation to esterase inhibition. In this study, we investigated the effects of these carbamates when injected in ovo to chick embryos, at two time periods (days 5 and 15) during incubation. Carbaryl dosed at 45 mg kg−1 egg weight was extremely toxic to the embryos on day 5 of incubation. Hatchability was reduced to 0% as compared to 80% when carbaryl was injected on day 15 of incubation. Aldicarb at 1.5 mg kg−1 egg weight had no major effect on hatchability when injected either on day 5 or day 15 of incubation (hatchability = 90 and 100%, respectively). Plasma, liver and brain esterases were measured in the chick at different time points during incubation and after hatching. Brain acetylcholinesterase (AChE) and liver cholinesterase (ChE) were inhibited significantly during incubation in embryos dosed on day 15 with both carbaryl and aldicarb. Liver carboxylesterase was inhibited significantly during incubation with only the carbaryl treatment. All esterase enzyme activities returned to normal after hatching. Plasma ChE and carboxylesterase levels were not affected with either carbaryl or aldicarb treatment from 8 until 47 days after hatching. Neither carbamate had any effect on brain neuropathy target esterase (NTE) activity either during incubation or after hatching. The locomotion of chicks was affected in both treatment groups until 47 days after hatching. This study indicates that carbaryl and aldicarb may cause long-term delayed alterations in the chicks.