Background: Dermanyssus gallinae, a blood-feeding ectoparasite of laying hens and wild birds, causes anemia, weakness, reduced egg production, and mortality in severe cases. It transmits pathogens including chicken pox virus, Newcastle virus, avian spirochaetosis, pullorum, and typhoid. Prolonged chemical acaricide use causes resistance, food residues, strict regulations, and increased demand for organic products. This study evaluated the in vivo acaricidal effect of Melia azedarach seed oil on D. gallinae under farm conditions. Methods: Melia azedarach fruits were shade-dried, ground, and extracted with hexane. In a commercial layer house in Mashhad, the first row was sprayed with 100 liters of solution containing 5 liters seed oil, 1 liter Tween80, and 94 liters water, repeated after 7 days. The fourth row (control) was sprayed with 1 liter Tween80 and 99 liters water. The second row was treated with 1% cypermethrin. Mite populations were monitored at days 2, 7, 9, 14, 21, and 28 post-treatment using semi-transparent plastic traps. Results: Mite counts were significantly lower in row one compared to the control at days 2, 9, 14, and 21 (P≤0.05). No significant difference was found between cypermethrin and control (P≥0.05). Melia azedarach seed oil efficacy on days 2, 7, 9, 14, 21, and 28 was 77.7%, 77.3%, 79.3%, 69.38%, 56.08%, and 38.67%, respectively. Cypermethrin showed 56.12% efficacy, primarily on day 2. Packed cell volume (PCV) significantly increased in the Melia azedarach group (P≤0.05), while control showed no significant change. Conclusion:considerable in vivo acaricidal effect against Dermanyssus gallinae under farm conditions. The efficacy of the seed oil was higher and more persistent than cypermethrin, suggesting that it can be considered as a promising botanical alternative to chemical acaricides. Moreover, the improvement in PCV in the treated group highlights its potential in reducing the adverse health impacts of poultry red mite infestations. Further studies on dosage optimization, formulation stability, and safety assessments are recommended to validate its practical application in poultry production.

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