Reproductive cycle and pregnancy monitoring in the common hippopotamus (Hippopotamus amphibius) through salivary steroid analyses and trans-abdominal ultrasonography.

The use of an enzyme immunoassay (EIA) was validated to monitor progestogens in common hippopotamus Hippopotamus amphibius saliva and transabdominal ultrasonography was used to diagnose and monitor pregnancy in this species. Both faecal and saliva extracts contained elevated progestogens indicative of luteal phases and gestation. Faecal and saliva progestogen concentrations of six adult female hippos revealed a strong positive correlation between the two sample types (r=0.60–0.85). Salivary and faecal progestogen analysis revealed a cycle length of 31.8±6.9 days and 33.4±2.9 days and average non-pregnant luteal phase duration of 17.3±1.5 days and 14.0±1.5 days, respectively. Progestogen concentrations (faecal and saliva samples collected ~days 0 to 90) from a full-term pregnancy (saliva: 1,167.1±1,269.4 pg/ml; faecal: 2,812.4±1,657.5 ng/g) were higher on average than luteal phase concentrations (saliva: 335.0±358.1 pg/ml; faecal: 1,399.5±613.0 ng/g). Comparatively, progestogen concentrations (saliva samples collected days 0 to 181; faecal samples collected ~days 120 to 181) of a pre-term (premature live birth ~181 days) pregnancy (saliva: 244.3±155.2 pg/ml; faecal: 501.7±492.2 ng/g) were on average lower than concentrations observed during the full-term pregnancy and/or luteal phase. The nulliparous female that gave birth pre-maturely was trained for voluntary transabdominal ultrasound exams conducted weekly. Intrauterine fluid and foetal tissue were observed 79 days following last confirmed mating. Foetal spine, rib cage, beating heart and internal organs were visible at 156 days. In summary, salivary progestogen monitoring and transabdominal ultrasonography appear suitable for tracking reproductive activity and diagnosing and monitoring pregnancy in the common hippo.