A 3-year-old Quarter Horse mare presented with an approximate 1-month history of progressive weight loss, anorexia and lethargy that abruptly worsened 48 h before death. Post-mortem examination revealed free flocculent fluid and a large mass within the ventral abdomen that dorsally displaced the caecum and large intestine. An ovarian teratocarcinoma with metastasis to regional lymph nodes was diagnosed histologically. Although benign teratomas are the second most common ovarian neoplasm in equids, reports of malignant teratomas in horses are rare. This report documents an unusual presentation of a rarely reported malignant neoplasm of the reproductive tract in horses.

一头 3 岁的 Quarter Horse 母马表现出大约 1 个月的渐进性体重减轻、厌食和嗜睡病史，在死亡前 48 小时突然恶化。尸检显示游离的絮状液体和腹侧腹腔内的大肿块，背侧移位盲肠和大肠。组织学上诊断出卵巢畸胎癌转移至区域淋巴结。虽然良性畸胎瘤是马科动物中第二常见的卵巢肿瘤，但马匹恶性畸胎瘤的报道很少。这份报告记录了一种罕见的马生殖道恶性肿瘤的不寻常表现。