Fourth branchial arch defects (4-BAD) is a syndrome that consists of aplasia, or varying degrees of hypoplasia, of one or more of the cartilaginous or muscular structures derived from the fourth branchial arch, unilaterally or bilaterally. This case report describes the cases of 2 directly related siblings admitted with a complaint of abnormal respiratory noise at rest and complete exercise intolerance. Laryngeal palpation, resting upper airway (UA) endoscopy, lateral radiography of the larynx and cervical trachea, and laryngeal ultrasonography revealed multiple laryngeal and pharyngeal abnormalities. The clinical findings were compatible with the diagnosis of fourth branchial arch defects. A left partial arytenoidectomy and a unilateral ventriculocordectomy were performed in both cases. The follow-up endoscopies revealed a functional airway aperture. The surgery enabled the horses to be used for riding. Considering the direct family relationship between the horses, these cases would support a genetic component of 4-BAD.