Abstract

Progesterone has myriad effects on the female cat’s reproductive system, all ultimately geared toward supporting embryo and fetal development from conception to parturition. In this role, progesterone also acts via feedback loops on the hypothalamus and pituitary gland to suppress ovarian follicular growth and estrogen production. These actions of endogenous progesterone can be mimicked by synthetic progestins, either administered parenterally, as depot injections or implants (e.g., for long-term contraception), or orally intermixed with daily diets. The primary advantage of oral delivery is ease of administration and rapid reversal on withdrawal. Oral progestin treatment has proven valuable for improving reproductive management of felid species as shown by the three following examples. First, oral administration of the progestin altrenogest (Regu-Mate, Merck Animal Health, Madison, NJ, USA), is highly effective for suppressing ovarian activity in domestic cats prior to exogenous gonadotropin treatment for assisted reproduction.¹ Our extrapolation of this approach to wild felids for fixed time laparoscopic oviductal artificial insemination (LO-AI) has resulted in multiple pregnancies in four small cat species (fishing cat, Prionailurus viverrinus; ocelot, Leopardus pardalis; Pallas’ cat, Otocolobus manul; sand cat, Felis margarita).² In our most recent LO-AI procedures in ocelots, three ovulatory females were inseminated following altrenogest-induced suppression (0.044 mg/kg BW; 30 days), 7 days of progestin withdrawal and gonadotropin treatment. Based on fecal progesterone analyses, two females appeared to conceive following LO-AI with frozen semen and subsequently gave birth to three viable kittens after 82 days of gestation. The second example involves the use of oral progestin as therapy for a 12-yr-old ocelot with suspected ovarian cysts. This proven founder female demonstrated persistent estrual phases that failed to abate following repeated breeding by the male, and ultrasonography revealed multiple cystic follicles on her ovaries. Daily oral treatment with altrenogest (0.044 mg/kg BW, 30 days) was implemented to suppress follicular growth and attempt to reset normal ovarian function. Two weeks following altrenogest cessation, the female returned to estrus, bred with the male and conceived, producing a healthy male kitten after an 81-day gestation. The third example involves oral progestin treatment for possible recurrent pregnancy loss in a 12-yr-old Amur leopard (Panthera pardus orientalis). This female experienced fetal loss due to dystocia at the end of her first pregnancy and then, over the next 2 yr, bred repeatedly with the male during multiple estrus phases. Although this leopard exhibited periods of acyclicity and/or elevated fecal progesterone consistent with induced ovulation and possible pregnancy, no offspring were produced. Occasional blood spotting 1–2 mo post-breeding supported the possibility of early pregnancy loss. Following one period of observed breeding, abdominal ultrasonography conducted 45 days later confirmed the presence of a developing fetus. The female was fed altrenogest daily (0.176 mg/kg BW) from day 50 to day 90 of pregnancy and then gradually weaned from progestin over the next 3 days. At day 99, the female went into labor and gave birth to a healthy female kitten, her first viable offspring. Our results indicate that oral progestin treatment is an effective method of ovarian suppression to precisely synchronize ocelots and other wild felids for successful fixed time LO-AI procedures. Knowledge of physiologically relevant progestin dosages gained from AI studies was directly applicable to treating suspected ovarian cysts in a founder ocelot, and for providing hormonal support of pregnancy in an aging nulliparous Amur leopard. These latter case reports provide evidence that oral progestin treatment may have further value therapeutically for correcting reproductive abnormalities in wild felids for improved reproductive management.

Acknowledgments

The authors thank the Institute of Museum and Library Services for financial support of these reproductive studies. The assistance of animal care staff at participating institutions (Oklahoma City Zoological Park, Pittsburgh Zoo & PPG Aquarium, Arizona Sonora Desert Museum, Audubon Zoo, El Paso Zoo, San Antonio Zoological Gardens) is greatly appreciated.

Literature Cited

1.  Stewart RA, Pelican KM, Brown JL, Wildt DE, Ottinger MA, Howard JG. Oral progestin induces rapid, reversible suppression of ovarian activity in the cat. Gen Comp Endocrinol. 2010;166(2):409–416.

2.  Swanson WF. Practical application of laparoscopic oviductal artificial insemination for propagation of domestic cats and wild felids. Reprod Fertil Dev. 2019;31(1):27–39.