Altrenogest-supported term gestation complicated by dystocia in a species exhibiting obligate embryonic diapause, the red panda (Ailurus fulgens)

This case report documents the use of oral altrenogest (Regu-Mate®) to support pregnancy maintenance in a red panda ( Ailurus fulgens styani ) with a history of gestational loss. Red pandas exhibit embryonic diapause with variable gestation lengths, complicating pregnancy monitoring and intervention. The subject, a 10 y multiparous female, experienced a pregnancy loss associated with low fecal progesterone metabolite concentrations. A comprehensive reproductive examination including endometrial biopsy was performed to rule out pathology, and the female paired again for breeding the subsequent breeding season. Following pregnancy confirmation via ultrasonography, a daily oral regimen of altrenogest (0.088 mg/kg) was initiated and continued until one week before predicted parturition, based on ultrasonographic monitoring. The pregnancy progressed to term and the female exhibited behaviors consistent with impending parturition; however, she experienced a dystocia, and the deceased cub was manually extracted. The male cub was slightly heavier than reported stillbirth weights, but necropsy revealed no congenital abnormalities. This is the first documented use of exogenous progestin supplementation in a species with obligate embryonic diapause and variable gestation length. Although the outcome was not as hoped, this case underscores both the potential utility and the inherent risks of exogenous progestogen therapy in species with delayed implantation.