Abstract
Progestins are one of the most frequently used contraceptives in captive wild felids,1 although hormonal contraception can induce endocrine dysfunction or uterine pathology, such as endometrial hyperplasia, uterine inflammation, and uterine or mammary gland cancer.2-5 While most of these diseases are identified postmortem, application of ultrasonography can be an effective and reliable tool to diagnose reproductive disorders in live animals.6
An 11-year-old nulliparous Siberian tiger (Panthera tigris altaica) was treated with subcutaneous melengestrol acetate (MGA) implants for several years. Due to a changed estimate of the genetic value of the animal, a new breeding permission was granted in 1997. Following implant removal, the tiger did not demonstrate signs of estrus. An ultrasonographic investigation was undertaken to evaluate the general health status of this animal, and for reproductive assessment. Ultrasound examinations were performed as previously described.7,8
On ultrasound, the vaginal vault contained a small amount of clear fluid. A vaginal cyst was identified next to the caudal cervix, and the cervix itself appeared highly echogenic with mucosal edema. Typically, the uterine horns range in size from 1.5–2.0 cm in diameter, depending on age and reproductive status of the female. In this case the uterine diameter was strongly enlarged (4.0–6.0 cm) and the uterine body contained hypoechoic fluid. The endometrium appeared thickened and irregular, and an endometrial cyst was identified within the uterine body. Both ovaries were normal in size (right ovary: 3.1×1.5 cm; left ovary: 2.6×1.4 cm) and contained numerous (5–15) follicular-like structures (maximum diameter 0.9 cm). Palpation and ultrasonographic examination of the mammary tissue revealed several firm, round structures, ranging in size from 0.5×0.5 cm to 10.0×10.0 cm.
The ultrasonographical findings suggested a severe pyometra despite the absence of overt, clinical signs. An ovariohysterectomy was performed, and surgical findings included a friable, distended uterus containing approximately 3.0 L of purulent material. This tiger recovered well following surgery despite the gross pathological changes observed at surgery.
The application of ultrasonography presents a potential and reliable tool for assessing reproductive health in zoo and wild animals. In particular, it may be used during hormonal contraception as a noninvasive technique to monitor changes in the reproductive tract.
Literature Cited
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