Priming with Oral Progestin Before Ovulation Induction Facilitates Ovarian Function in the Cat (Felis catus)

Abstract

Artificial insemination (AI) has been developed in multiple felid species as a tool for retaining gene diversity in threatened or endangered populations. Yet, pregnancy success remains low (< 5%) following AI in most felids, particularly in species that spontaneously ovulate. This failure has been attributed to variable ovarian status at the time of insemination and adverse residual effects caused by exogenous gonadotropins used to induce ovulation. Using the domestic cat as a research model, a new AI regimen that incorporated short-term ovarian suppression with oral progestin (altrenogest; ALT) before ovulation induction was investigated. The hypothesis was that oral progestin priming would prevent spontaneous ovulation, improve ovarian responsiveness to exogenous gonadotropins and mitigate adverse effects caused by persistent gonadotropin actions. Specific objectives were to: (1) increase fundamental understanding of the mechanisms controlling ovarian function; and (2) characterize how oral progestin priming prior to exogenous gonadotropin treatment influences ovarian responsiveness, fertilization, early embryonic development and luteal function in the cat. Fecal hormone monitoring was used to establish an ALT dosage that provides rapid, reversible ovarian suppression with no residual effects on estrous cyclicity. With this information, the influence of progestin priming on ovarian responsiveness to exogenous gonadotropin dosage was investigated. Priming increased ovarian sensitivity to gonadotropins, supporting the use of lower dosages for ovulation induction. Next, in vivo fertilization success and in vitro early embryonic development was characterized following laparoscopic, intrauterine AI in cats treated with ALT. Progestin-primed females demonstrated a good ovarian response to ovulation induction and more consistent embryonic development, compared to cats treated with gonadotropins alone. Furthermore, endocrine data revealed that normal luteal progesterone levels were maintained only in queens primed with the oral progestin. Finally, histology and quantitative RT-PCR were used to characterize the differential effects on luteal function observed. Aberrant CL progesterone production was not associated with changes in ovarian morphology, or the expression of six specific genes associated with luteal function and progesterone biosynthesis. Overall, these studies increased knowledge of domestic cat reproductive physiology and improved understanding of ovarian suppression for enhanced AI efficiency in felids.