Ultrasonographical and endocrinological characterization of the unique ovarian activity during the estrus cycle and the pregnancy in Asian elephants (Elephas maximus)

AuszugFor different Orders of mammals, various established estrus cycle models exist, describing strategies for ovarian activity and reproductive hormone secretion profiles. Related species typically follow similar reproductive strategies. The elephant however, deviates from these well described reproductive scenarios. Their isolated taxon position hinders direct transfer of established cycle mechanisms from large ungulates resulting in many interesting and unexplained features in their estrus cycle and pregnancy - the longest described for any mammal known today - including: why they possess multiple corpora lutea (CL) despite being uniparous; why they express two LH peaks during the follicular phase of the estrus cycle timed 19-21 days apart; how they maintain their extraordinarily long pregnancy and what happens meanwhile on the ovaries. Another intriguing fact is the unexplained duration of both the estrus cycle and the pregnancy. The present study combined both ultrasound and endocrine techniques on more than 30 Asian and two pregnant African elephants, in order to find consensus on some of these unexplained observations during the cycle and the pregnancy. Ultrasonography and endocrinology performed separately are proven, non-invasive tools which characterize the in situ reproductive events in the female. However, only the combination of these two techniques gives a detailed image of the ongoing ovarian activity and the corresponding reproductive organs. While ultrasonography enables direct observation, the hormone measurements provide additional functional analysis.