Contraception of African elephants using porcine zona pellucida vaccine

by Earth Org · Published November 21, 2008 · Updated June 14, 2014

There is a valid and workable alternative to culling.

1. Veterinary Wildlife Studies, Department of Production Animals Studies, University of Pretoria, Private Bag X04, Ondestepoort 0110, RSA email: henk.Bertschinger@up.ac.za
2. Makalali Private Game Reserve, Hoedspruit, RSA.
3. The Science and Conservation Center, ZooMontana, Billings, USA
4. CatchCo Africa, Naboomspruit, RSA

The use of antigens to control of fertility is known as immunocontraception or immuno-fertility control. A number of antigens have been employed in the past with varying degrees of success. The most commonly used antigen has been porcine zona pellucida (pZP) proteins to control fertility of females. Zona pellucida proteins isolated from ovaries of pigs (pZP) have been shown to be effective for the immunocontraception of horses3,6,9 and a range of wild and zoo herbivores4,5,7,8. In these species the vaccine was shown to be safe and, where tested, also reversible. Other methods have looked at the use of sperm antigens to control both male and female fertility but the results have been disappointing, particularly in the female. A third approach is to use hormones as antigens. One hormone (GnRH) in particular has been used successfully as a vaccine to control reproduction in domestic animals. This paper reports on a project that was carried out in three phases to investigate the use pZP vaccine to contracept some elephants in the Kruger National Park (KNP) and, following on this initial work, a number of projects in private game reserves.

In order to understand how pZP vaccine works as a contraceptive we need to look at the process of fertilisation of the egg by a sperm. This is explained in Fig 1 (A-C). Blocking of all sperm receptor sites relies on antibody concentrations that are sufficiently high to achieve this and should the concentrations fall below a critical level, which happens over time, the cow will once again be fertile. pZP only targets the zona pellucida of the cow and has no direct effect on behaviour. Because the cow does not fall pregnant she will continue to show an oestrous cycle which is 15-17 weeks long. This means that she will come on heat 2-3 times a year.

Kruger park: Phase 1

This phase was designed to establish homology between porcine and African elephant zona pellucida proteins. In 1995, during the last cull that took place in the KNP, ovaries were collected from several elephant cows. After fixation ovarian blocks were embedded in paraffin and sectioned. Sections were then processed for immunocytochemistry. They were first treated with rabbit-anti-pZP (primary antibody) followed by the secondary antibody labelled with colloidal gold and finally enhanced with silver. Histological examination of the sections showed distinct immunogold staining of the zona pellucida of oocytes in primary, secondary and tertiary follicles. The results were confirmed in samples examined with TEM. This proved that there are shared epitopes between the ZP proteins of the two species and that antibodies to pZP should recognise elephant zona pellucida proteins (Fayrer-Hosken et al., 2000).

Kruger Park: Phase 2
Phase 2 was designed to establish a PZP vaccination regime for African elephants. Two elephant cows (both at zoos in the USA) were vaccinated with 400 g of pZP and 5mg of synthetic trehalose dicorynnomycolate adjuvant. Boosters (400 or 600 g) were administered after 4 weeks and 10 months, respectively. The antibody concentrations achieved after the second booster in these cows were comparable to those of horses that had been successfully contracepted with pZP vaccine (Fayrer-Hosken et al., 2000).

Kruger Park: Phase 3
The objective of Phase 3 was to test the contraceptive efficacy of the pZP vaccine in a sample of free-ranging elephant cows in the KNP. In 1996 41 cows (21 treatment and 20 controls) were selected for the first trial. Selection criteria were a small calf (< 1 m high) and a negative trans-rectal ultrasound pregnancy result. The Treatment Group was vaccinated with 600 g of pZP and the same adjuvant as described above. The controls were injected with placebo. All treated cows were radio-collared and 6 weeks later they were located and darted with a booster from a helicopter using dropout darts. The procedure was repeated 6 months after the primary vaccination.

Twelve months after the primary vaccination 19 Treatment and 18 Controls were located, immobilised and examined for pregnancy. One cow in the Treatment Group was excluded as the results showed that she was already pregnant at the time of the primary vaccination. Of the remaining Treatment Group 8 (44 %) were pregnant compared to 16 (89 %) in the controls. Although the difference was significant the results were disappointing compared to those achieved in free-ranging horses. A second trial with 10 vaccinated cows was thus planned. This time the vaccination intervals between the primary vaccination and first booster and the first and second boosters were 2 and 4 weeks, respectively. The results showed a significant improvement with only 2 (20 %) cows falling pregnant. The trials also showed that the vaccine is safe to use in pregnant elephants, that contraception can be maintained by administration of an annual booster and, if a booster is not used, that cows return to fertility. These are important qualities when selecting a contraceptive method for wildlife species

Private Game Reserves
Since the Kruger Park project we have been using the pZP vaccine on elephants in private game reserves. The vaccination protocol has changed in that we now make use of modified Freunds for the primary and incomplete Freunds adjuvant for the booster vaccinations. This has resulted in a 100 % efficacy in the cows that have passed the critical inter-calving period since vaccination was first introduced. The reserves, number of cows and the year in which vaccination was implemented are Makalali (n = 23; 2000), Mabula (n = 4; 2002), Shambala (n = 4; 2004), Phinda (n = 19; 2004) and Thaba Tholo (n = 8; 2004). The vaccine used during 2003 and 2004 was produced by our laboratory where we manufacture about 1 500 doses a year. The number of doses can be increased if necessary to about 10 000/annum or more.

Makalali is the only private reserve where the project has been running long enough to provide data on the efficacy of the vaccine and possible effects on behaviour. Twenty-three cows have been vaccinated. The protocol employed for most of the cows was a primary vaccination followed by two boosters at 3-4 weeks intervals during the first year. A single annual booster for each cow followed this. Darting was performed from the ground during the first two years of vaccination but in 2003-2004, 17 and 21 cows were darted from the helicopter. At no time was immobilisation of animals necessary to perform vaccinations. Total time taken for helicopter vaccination was about 30 min and the herds settled down much quicker (1-2 days) then if darted from the ground. The success rate has been encouraging to say the least. Ten cows have passed the 53-month inter-calving period of the reserve with no early calving indicating 100 % reproductive control so far.

The elephants at Makalali have been monitored intensively almost on a daily basis. To date, no anomalies in terms of aggressive or indifferent behaviour with regards to nursing time, nursing behaviour and calf proximity have been noted. No change in the cows social hierarchy has been noted. Since January 2003, a total of 15 heats were observed in 10 cows (9 in 2003 and 6 in 2004) with four mating episodes. For the same period, thirty-eight musth occasions were seen in 5 bulls (26 in 2003 and 12 in 2004). These occasions include musth displayed in the same bull during consecutive days, or within the same musth cycle. The greatest occurrence of musth was recorded in the largest, dominant bull. Bulls were not observed harassing or separating cows off from their herds or calves as a result of increased oestrous frequency. Thus, the Makalali program demonstrates that pZP does not cause herd fragmentation, harassment by bulls, change in rank and other negative behaviours normally associated with hormonal contraceptives.

This coming year we will treat the first elephant cows with a so-called one-shot vaccine. This means that the vaccination protocol for the first year can be reduced to a single darting. This will make a big difference to the cost of contraception and will make it feasible to treat much larger populations of elephants. Even without the one-shot vaccine it is possible to contracept large populations.

In conclusion we feel that it is important to emphasise the following points:

The pZP vaccine can be used successfully to contracept African elephants
The Vaccine is safe during pregnancy and has no negative effect on birth or calf raising
It has no side effects other than occasional lumps at the site of vaccination
It is reversible
Other than an increased incidence of heat no behavioural side effects were seen
Administration of the vaccine is carried out remotely by darting and does not require immobilisation

NB: Cost for a private Game Reserve that covers all the costs is R 800-900 per cow per single vaccination