A recent study by Wojtusik et. al., at the Cincinnati Zoo measured hippopotamus salivary progesterone levels to determine the pregnancy status and likely due dates.

Careful reproductive management is essential to maintain sustainable populations of hippos outside their native ecosystems. Hormone monitoring allows for characterization of the reproductive cycle and gestation, but non-invasive sample collection for hormone analysis can be complicated. Fecal hormone measurement in hippos is difficult because of their semi-aquatic lifestyle, and salivary progesterone measurement would be ideal. In the current study, progesterone levels were measured using our Progesterone ISWE Mini-Kit (ISWE003) to determine if saliva offers a comparable alternative to fecal hormone monitoring. Fecal and saliva progestogen concentrations revealed a strong correlation between the two sample types suggesting saliva offers a comparable alternative. Salivary progestogen monitoring and trans-abdominal ultrasonography appear suitable for tracking  reproductive activity and monitoring pregnancy in the common hippo.

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