The current study aimed to compare acetylcholinesterase (AChE) activity in liver, kidney, and muscle tissues of ducklings (Anas platyrhynchos) following treatment with Cypermethrin (a pyrethroid) and Methamidophos (an organophosphate). Results showed a dose-dependent response (250 µg, 500 µg, and 1000 µg) in AChE activity at 30, 60, and 90 seconds. It was observed that cypermethrin displays a biphasic response, with initial inhibition of AChE followed by recovery or activation at higher doses (46.6-47.1 µg at 250 µg to 99-99.3 µg at 1000 µg). It may be related to enzyme induction, metabolic adaptation, or detoxification mechanisms in hepatic and muscular tissues. The pattern suggests moderate neurotoxicity, with potential for physiological compensation, as evidenced by the weight changes in the studied birds. Methamidophos exposure led to marked inhibition of AChE, consistent with organophosphate toxicity. Systemic enzyme suppression in liver (177–182%) and kidney tissues showed potent inhibition at 1000 µg (47%), whereas in muscle tissues, a striking hyperactivation(177–182%) was observed. The marked elevation of muscle AChE at the high dose may indicate neuromuscular hyperactivity or secondary enzymatic overexpression resulting from prolonged inhibition. The research concluded that it provided a more comprehensive insight into the neurotoxic actions and physiological responses of birds to pyrethroid and organophosphate compounds, which would help evaluate their potential ecological and environmental hazards.

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