Allergy to milk is the only auto-allergic disease in cattle. It is characterized by the retention and absorption of milk itself, making milk proteins, especially alpha casein, have access to the bloodstream, resulting in a type I hypersensitivity. The purpose of this report is to describe a case of auto-allergic disease in cattle. Here we report the case of a four-year-old Jersey female bovine, which was pregnant and weighing 400Kg. The animal was being treated at (hidden for revision) and had a history of an acute allergic reaction. Its owner reported sudden onset of skin lesions, salivation, and difficulty breathing. As the animal was participating in an agricultural exhibition, it was not being milked to generate mammary gland engorgement (milk retention). In physical examination findings wherein there is presence of multifocal urticarial papules and plaques, mainly on the sides and right and left flanks, besides the absence of pruritus, edema in mucocutaneous regions of the upper and lower eyelids of the right and left eyes, submandibular edema, excessive salivation, inspiratory dyspnea with half-open mouth breathing, respiratory distress, apathy, cough, tachycardia tachypnea, ruminal hypomotility and increased volume of the mammary gland, characterizing milk retention. Clinical suspicion was milk allergy with anaphylactic reaction (type I hypersensitivity). Treatment was based on promethazine administration (1mg/kg; IV) and immediate full milking of the mammary gland. After 12 h of treatment, clinical respiratory signs resolved, and after 24 h, skin changes resolved completely. Based on clinical signs and treatment success, the clinical suspicion of milk allergy causing anaphylactic reaction (type I hypersensitivity) was confirmed.