The history and future of the cornual nerve block for calf disbudding.

Disbudding damages the germinal horn bud cells and prevents subsequent horn growth in young calves. Hot-iron cautery or caustic paste are the most common disbudding techniques and are unequivocally painful procedures. An important technique in controlling the acute pain experienced during disbudding is the cornual nerve block (CNB) that uses a local anesthetic agent and targets a branch of the trigeminal cranial nerve, the zygomaticotemporal nerve, as it travels along the temporal groove of the skull. Though CNB have been used since 1932, practitioners have reported variability in achieving full desensitization of the horn bud region since its inception. This failure may have led to the establishment of variations in the CNB technique, without consensus on a reliable and repeatable approach. Reasons for CNB failures may include technical errors by the practitioner, such as an injection into subcutaneous or deep muscle bodies; biologically important path variations in the zygomaticotemporal nerve and its cornual branches; and secondary innervation of the horn bud region, particularly the cornual branches of the infratrochlear nerve. Further investigation into documenting and understanding CNB failure and alternatives, such as regional perfusion, is warranted.