In this study two doses of 600 μg GnRH vaccine failed to induce anoestrus in female elephants as was anticipated. The apparently ineffective or incomplete action of the vaccine was possibly a consequence of under-dosing or the booster was administered too late to down-regulate the second cycle in some females that had already entered their luteal phase before treatment, as the stage of the oestrous cycle was unknown at the time of vaccination. An additional possibility might be incomplete delivery of the treatment due to the viscous nature of the solution. The long oestrous cycle of the African elephants [12, 13] and the effect of the variability of the ecological conditions on FPM concentrations [10, 11] made it difficult to elucidate the effect of the GnRH vaccine treatment on the oestrous cycle over the 12 month monitoring period in this study. We would recommend extending the observation period to two to three years in sites with seasonal variation and additionally using a progestagen EIA method to assess in-the-field ovarian activity as described by Freeman (2011) [53 in order to optimize the vaccination by applying it during the luteal phase . It is reported that five adult captive elephant cows (four of which had calved previously) treated in Zimbabwe with the same vaccine and dose as a means of contraception did not show behavioural oestrus for a period of two years following treatment (Bertschinger, personal communication). The cows that were housed with three adult bulls were initially vaccinated three times at intervals of 5 weeks. This was followed by boosters administered every 6 months. Differences that could account for the positive response include the additional initial booster and administration of vaccine by hand-injection.
All 12 monitored females showed some evidence of ovarian cyclicity during the 14-month study, although most (75%) of the cycles did not fall within the reported normal 13-17 weeks oestrous cycle range reported for African elephants . Three (2 treatment, 1 control) females from the Lower Escarpment showed a period of anoestrus which after the vaccination and onset of the rainy season was followed by a prolonged luteal phase (25.86, 15.86 and 16.86 weeks, respectively) (Table 2). The Upper Escarpment herd had higher mean luteal, inter-luteal and peak FPM concentrations compared to the Lower Escarpment herd in both treatment and control group, which may be attributed to the different habitats and the resource availability, more pronounced in the Upper Escarpment through the seasons with a higher average rainfall and nutritionally poorer vegetation compared to the Lower Escarpment. Factors including the lack of changes in group dynamics, absence of mature males and a fenced environment preventing seasonal movements may have contributed to the high incidence of cyclic abnormalities observed in EPGR elephant herds. The potential effects of pZP vaccine on variability of the oestrous cycles of the four treated cows (numbers 1, 2, 8, 9) cannot be completely excluded. All four cows showed luteal activity (Cow 1: Figure 1 a) and their LP and ILP FPM concentrations were similar to those of their herd mates on the Lower Escarpment. As reported by Ahlers et al. (2012) [19, ovarian function did not appear to be disrupted by pZP treatment.
In wild elephants, we presume that sexually-receptive periods in females result in mating and pregnancy. These females subsequently will not cycle again two to three years after a gestation period of 22 months [34, 35, 54]. Repeated oestrous cycles are thus an abnormal feature of reproduction in free-ranging elephants [7, 55, 56]. Abnormal cycles in female elephants are currently not well understood . With the exception of reports by Ahlers et al. (2012) [19 and Ghosal et al. (2012) [58, limited information is available which our data can be compared to. In a one-year study conducted on a wild herd of African elephants in South Africa 42.9% of females treated with pZP vaccine failed to cycle and 14.3% had irregular cycles . Three distinctive types of hormone profiles were observed in semi-captive Asian elephant (Elephas maximus) females . These were normal oestrous cycles, acyclic patterns or progestagen profiles with high values indicative of a pregnant animal. In captive populations in North America, 43% of African elephants also showed abnormal cycles. The proposed causes in these captive elephants include reproductive tract pathology, alteration in the secretion of pituitary gonadotropins and thyroid hormones and hyperprolactinaemia [57, 59]. Other studies report social and environmental variables affecting ovarian cyclicity[57, 60].
The effect of seasonal changes on reproductive hormonal activity in non-pregnant free-ranging African elephants has been previously documented [10, 11, 19]. In our study the effect of the dry season (starting May through September) on FPM levels was evident in nearly all study animals (6 treatment, 4 control). They either had lower FPM levels or a period of hormonal flat-lining (anoestrus). In the latter case cyclic activity resumed during the wet season (October through April). A comparison of FPM concentrations for the three-month period before and after treatment revealed a significant increase. This effect, however, was present in treated and control individuals and most probably can be attributed to the onset of the rainy season. The four Upper Escarpment females (Females No. 11, 12, 13, and 14) as well as four females (Females No. 4, 5, 7, and 8) from the Lower Escarpment appeared to experience a period of seasonal anoestrus during the dry season 2009. Following the onset of the subsequent dry season (post-treatment) in May 2010, the FPM levels decreased, and in almost all treated animals (5 of 6; Females No. 1, 2, 3, 8, and 9) from the Lower Escarpment herd, the levels were lower than the previous dry season. This might reflect either an incomplete effect of the GnRH vaccine causing a reduced secretion of progestins, or lower rainfall received during the previous season resulting in limited abundance of resources. In general, the average monthly FPM concentrations closely followed rainfall patterns and confirmed the relationship reported in the literature between ecological variation and ovarian activity [10, 11, 19]. Thus African elephants appear to optimize the timing of oestrus in order to maximize use of seasonal availability of resources to coincide with the energetic investment needed for reproduction .