Because of the discrepancy of ultrasonographic and endocrine results of the two individual Greater-one horned rhinoceros of Fig 4, feed items given to these individuals were tested for cross reactivity cross reactivity with the group-specific 20α-OH-pregnane immunoassay.

The inset figure shows dilutions of extracts of meadow hay in comparison to the 20α-OH-progesterone standard curve used in the immunoassay.