Guinea pigs very commonly develop ovarian cysts as they age and it is thought that the incidence approaches 100% among sows over 5-6 years old. These cysts can be unilateral or bilateral and vary in size from a few millimetres to a few centimetres. Ovarian cysts are asymptomatic if they remain small and are non-secreting. Large cysts may compress abdominal organs and secretory cysts cause hair loss through an endocrine mechanism; this hair loss is manifested as bilateral, symmetrical, non-pruritic alopecia that starts on the flanks and extends progressively to the hind quarters (Fig. 1).
Gentle palpation of the abdomen may reveal the presence of bulky formations. The cystic nature of the formations can be confirmed by ultrasound examination.
The definitive treatment consists of ovariohysterectomy. An alternative is ultrasound-guided aspiration of the cysts and administration of leuprorelin (100 mg/kg s.c. every 3 weeks). Another possibility is gonadotropin releasing hormone (25 mg/animal repeated once after 2 weeks) or human chorionic gonadotropin (1000 U i.m. repeated once after 7-10 days.