Abstract:
Because of overpopulation of African elephants in South Africa and the consequent threat to biodiversity, the need for a
method of population control has become evident. In this regard, the potential use of the porcine zona pellucida (pZP) vaccine
as an effective means for population control is explored. While potential effects of pZP treatment on social behavior of African
elephants have been investigated, no examination of the influence of pZP vaccination on the endocrine correlates in treated
females has been undertaken. In this study, ovarian activity of free-ranging, pZP-treated African elephant females was monitored
noninvasively for 1 yr at Thornybush Private Nature Reserve, South Africa, by measuring fecal 5 -pregnan-3 -ol-20-on
concentrations via enzyme immunoassay. A total of 719 fecal samples from 19 individuals were collected over the study period,
averaging 38 samples collected per individual (minimum, maximum: 16, 52). Simultaneously, behavioral observations were made
to record the occurrence of estrous behavior for comparison. Each elephant under study showed 5 -pregnan-3 -ol-20-on
concentrations rising above baseline at some period during the study indicating luteal activity. Average 5 -pregnan-3 -ol-20-on
concentrations were 1.61 0.46 g/g (mean SD). Within sampled females, 42.9% exhibited estrous cycles within the range
reported for captive African elephants, 14.3% had irregular cycles, and 42.9% did not appear to be cycling. Average estrous cycle
duration was 14.72 0.85 wk. Estrous behavior coincided with the onset of the luteal phase and a subsequent rise in
5 -pregnan-3 -ol-20-on concentrations. Average 5 -pregnan-3 -ol-20-on levels positively correlated with rainfall. No association
between average individual 5 -pregnan-3 -ol-20-on concentrations or cyclicity status with age or parity were detected.
Earlier determination of efficacy was established via fecal hormone analysis with no pregnancies determined 22 mo post-treatment
and onward. Results indicate the presence of ovarian activity amongst pZP-treated female African elephants in 2 yr after initial
immunization. Further study should now be aimed toward investigating the long-term effects of pZP vaccination on the
reproductive function of female African elephants.
