Estrous Cycle Based on Blood Progesterone Profiles and Changes in Vulvar Appearance of Malayan Tapirs (Tapirus indicus)

Abstract

The progesterone (P₄) profiles and macroscopic vulvar changes of female Malayan tapirs were investigated in order to understand their fundamental reproductive physiology and to search for visual indicators of estrus. Blood was collected once or twice a week from seven female Malayan tapirs kept at four zoos. Serum or plasma P₄ concentrations were determined by radioimmunoassay. The P₄ concentrations changed cyclically throughout the years, and a total of 56 cycles was confirmed in the seven females. The length of the estrous cycle based on the P₄ profiles was 43.6 ± 2.0 days; however, this mean includes great variation in length, from 21 to 84 days. Mucous discharge from the vulva and vulvar swelling were seen when the P₄ concentrations were low before the beginning of a rise in most cases. In conclusion, captive female Malayan tapirs have variations of approximately 1 to 3 months in estrous cycle length, and visual changes in the vulva are helpful in estimating estrus in female Malayan tapirs.