Abstract:
BACKGROUND: In southern Africa, various options to manage elephant populations are being considered.
Immunocontraception is considered to be the most ethically acceptable and logistically feasible method for control
of smaller and confined populations. In this regard, the use of gonadotropin-releasing hormone (GnRH) vaccine has
not been investigated in female elephants, although it has been reported to be safe and effective in several
domestic and wildlife species. The aims of this study were to monitor the oestrous cycles of free-ranging African
elephant cows using faecal progestagen metabolites and to evaluate the efficacy of a GnRH vaccine to induce
anoestrus in treated cows.
METHODS: Between May 2009 - June 2010, luteal activity of 12 elephant cows was monitored non-invasively using
an enzyme immunoassay detecting faecal 5alpha-reduced pregnanes (faecal progestagen metabolites, FPM) on a
private game reserve in South Africa. No bulls of breeding age were present on the reserve prior to and for the
duration of the study. After a 3-month control period, 8 randomly-selected females were treated twice with 600
micrograms of GnRH vaccine (ImprovacW, Pfizer Animal Health, Sandton, South Africa) 5-7 weeks apart. Four of
these females had been treated previously with the porcine zona pellucida (pZP) vaccine for four years (2004-2007).
RESULTS: All 12 monitored females (8 treated and 4 controls) showed signs of luteal activity as evidenced by FPM
concentrations exceeding individual baseline values more than once. A total of 16 oestrous cycles could be
identified in 8 cows with four of these within the 13 to 17 weeks range previously reported for captive African
elephants. According to the FPM concentrations the GnRH vaccine was unable to induce anoestrus in the treated
cows. Overall FPM levels in samples collected during the wet season (mean 4.03 micrograms/gram dry faeces) were
significantly higher (P<0.002) than the dry season (mean 2.59 micrograms/gram dry faeces).
CONCLUSIONS: The GnRH vaccination protocol failed to induce anoestrus in the treated female elephants. These
results indicate that irregular oestrous cycles occur amongst free-ranging elephants and are not restricted to
elephants in captivity. The relationship between ecological conditions and endocrine activity were confirmed.
Free-ranging female elephants were observed to not cycle continuously throughout the year in the absence of
adult bulls.
