This report describes transient ulcerative dermatitis, severe thrombocytopenia, and mild neutropenia in 6 foals from 4 mares from geographically diverse regions of the United States. The foals presented at Ͻ4 days of age with oral and lingual ulcers, and crusting and erythema around the eyes, muzzle, and perineal, inguinal, axillary, trunk, and neck regions. There was a severe thrombocytopenia (0-30,000 platelets/L), leukopenia (1,200 white blood cells/L), and mild neutropenia (500-1,800 neutrophils/ L). Four of the 6 foals had petechiae and ecchymotic hemorrhages and 3 had bleeding tendencies. Results of examination of a bone marrow biopsy from 1 foal were normal and results of a platelet surface immunoglobulin test in another were negative. Histopathology of the skin in all foals showed subepidermal clefting with subjacent vascular dilation, dermal hemorrhage, and superficial papillary necrosis. The foals were treated supportively with broad-spectrum antibiotics (5/6), corticosteroids (3/6), gastric ulcer prophylaxis (6/6), whole-blood transfusion (4/6), and platelet-rich plasma (1/6). The skin lesions and thrombocytopenia (Ͼ50,000 platelets/L) improved in 2 weeks (4/6). Two foals had a decline in their platelet counts when the steroids were decreased and needed protracted treatment. All foals survived and were healthy as yearlings. Two mares that had 2 affected foals each, upon subsequent pregnancies to different stallions, had healthy foals when an alternate source of colostrum was given. The findings in the cases in this report suggest a possible relationship between colostral antibodies or some other factor in the colostrum and the thrombocytopenia and skin lesions, although further investigation is warranted to confirm or refute this hypothesis.Key words: Dermatopathy; Horse; Neutrophil; Platelet; Skin.T he purpose of this paper is to describe a syndrome of transient ulcerative dermatitis, severe thrombocytopenia with bleeding tendencies, and neutropenia in neonatal foals. The physical examination, clinicopathologic, clinical progress, and histopathology of skin biopsy findings of 6 neonatal foals from geographically diverse regions of the United States will be presented. Materials and MethodsThe medical records of 6 neonatal foals examined between 1998 and 2002 with a transient ulcerative dermatitis and severe thrombocytopenia were summarized. The foals were seen at 3 referral hospitals throughout the United States, including Cornell University Hospital for Animals, Ithaca, NY (n ϭ 2), Washington State University Veterinary Teaching Hospital, Pullman, WA (n ϭ 2), and Peterson and Smith Equine Hospital, Ocala, FL (n ϭ 2). A CBC and skin biopsy were performed on all foals. The skin biopsies were fixed in formalin and the slides were evaluated by 1 dermatologist (WHM) retrospectively for the purposes of publication. Data collected from the record included the signalment and parity of the mare and events (medications, illness, and vaccinations) that occurred during pregnancy and parturition, the health of t...