Effects of Intraoral, Intracrop, and Intragastric Administration of Copper Sulfate on Vomiting, Retching Behavior, and Nausea-Like Responses in Chicks.

Nausea and vomiting are induced by environmental distress and pain; understanding their etiology can improve animal welfare in modern farm operations. Oral administration of CuSO4 induces nausea and vomiting in some mammalian species and in pigeons. Although oral administration of CuSO4 induces retching in chicks, whether it causes true vomiting or nausea-like responses remains unknown. This study examined whether intraoral, intracrop, and intragastric administrations of CuSO4 induced vomiting, retching, and nausea-like responses in chicks (Gallus gallus domesticus). Food intake, crop emptying rate, and voluntary activity were used as indices of nausea-like responses. CuSO4 limited food intake, irrespective of the administration route, and markedly reduced the crop-emptying rate. Voluntary activity remained unaffected by intraoral administration, but decreased following intracrop and intragastric administrations. Four of the six chicks exhibited retching after intraoral administration of CuSO4; whereas intracrop and intragastric administrations failed to elicit this behavior. Similarly, CuSO4 failed to cause any vomiting. These findings indicate that CuSO4 does not act as an emetic agent in chicks; rather it induces nausea-like responses. Route-dependent effects further suggest that exposure within the oral cavity is required for the excretion of CuSO4, possibly serving as a protective behavioral mechanism to reject irritant compounds before they enter the lower gastrointestinal tract.