Management of Elephant Populations in Private South African Game Reserves with Porcine Zona Pellucida Vaccine
Control of African elephant populations has become an absolute necessity in a number of game reserves in southern Africa. The two main methods used to control populations so far are culling and translocation. Culling, besides being regarded as inhumane and unacceptable in many quarters, is not suitable for smaller populations. It requires that whole family units are culled simultaneously which could mean that in reserves with 10 to 50 elephants a considerable portion, if not the entire population, is killed. As far as translocation is concerned, limited new space is available for elephants. The only alternative to the two above options is to control the rate of reproduction. The porcine zona pellucida (pZP) vaccine has been used to successfully contracept wild horses6,7,9 and other wildlife species8. Work on the contraception of African elephants was initiated in the Kruger National Park in 1995 when the potential for using the porcine zona pellucida (pZP) was investigated.4 Subsequently the first field trials on wild elephants were carried out in Kruger and the results clearly showed that elephants could be contracepted with the pZP vaccine, although the efficacy achieved was 80%.5 During these field trials safety and reversibility were be demonstrated.
In 2000 an elephant contraceptive program was initiated at Makalali Private Game Reserve, RSA, which has become the flagship model for immunocontrol in African elephants. The preliminary findings have been reported in three publications.1-3 During the first year, all 18 cows that were individually identified and older than 12 years of age were treated. During the next 4 years the number of cows contracepted increased to 23 as young animals were added to the program. The standard vaccination procedure during the first year consisted of a primary vaccination (600 µg or 400 µg pZP with 0.5 ml Freund’s modified complete adjuvant) followed by boosters (200 µg pZP with 0.5 ml Freund’s incomplete adjuvant) at 3 to 6-week intervals. Annual boosters to maintain antibody titers and contraceptive effect followed. To date, the success rate on cows that have passed reserve-specific intercalving period of 56 months has been 100%. The population stabilized within 3 years by which time all cows that had been pregnant at the time of first vaccination in 2000 had calved.1,3 Once again safety during pregnancy (14 cows pregnant at 2–21 months gestation when first treated gave birth to normal healthy calves) as well as side effects that were limited to occasional lumps at the site of vaccination could be shown. Following ground darting, behavioral patterns returned to pre-darting status within 2 days. During 2003 and 2004 most boosters were administered from a helicopter, whereas, previously they had been done from a vehicle or on foot. In all cases, drop-out darts were used. Time taken for vaccination from helicopter take-off to landing was about 30 min (1.5 min per cow; 30 min for total time). This required prior knowledge of the locations of family units or that an individual in each unit is radio-collared. Herds settled down much more quickly (1–2 days) than if darted from the ground.
Since then, we have vaccinated another 107 elephant cows in eight game reserves. The cow populations have ranged from 4 to 43. In one of the reserves, Mabula, RSA, two of the four cows vaccinated have passed the mean intercalving intervals of the reserve with neither of them producing a calf. Treatment at the remaining reserves was initiated in 2004 or 2005 and it is too early to evaluate results. The most difficult reserve in terms of the vaccination process was Welgevonden, RSA, (35 000 ha) with 43 cows. The reserve is mountainous and heavily wooded. None of the elephants were collared and individuals could not be easily identified on the day of primary vaccination. The total flying time during which individuals were identified and vaccinated was 4.5 hours. Administration of the first booster took about 2 hours to locate and vaccinate each cow. Between the first and second booster the first rains occurred, followed by the spring flush of the vegetation. By the time the second booster was attempted late in November, the trees all had foliage. Only half the cows were located and darted because the elephants were very difficult to spot under the tree canopies. The valuable lessons we learned from this were: 1) that helicopter vaccinations should be performed when most trees are bare, and 2) when larger populations are vaccinated repeatedly during the first year, one cow in each family unit should be radio-collared. This makes rapid location of each unit possible and cuts down on the major cost factor that is flying time.
Elephant behavior is being monitored in all eight reserves where contraception is being applied. Because most of them have been contracepted recently, only the data from Makalali is available.3 The elephants at Makalali have been monitored intensively almost on a daily basis. To date, no anomalies in terms of aggressive or indifferent behavior with regards to nursing time, nursing behavior 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 (nine in 2003 and six in 2004) with four mating episodes. For the same period, 38 musth occasions were seen in five 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 estrous frequency. Thus, the Makalali program demonstrates that pZP does not cause herd fragmentation, harassment by bulls, change in rank and other negative behaviors normally associated with hormonal contraceptives.
In conclusion we feel that it is important to emphasize 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 swelling at the site of vaccination
- It is reversible
- Other than an increased incidence of heat no behavioral side effects were seen
- Administration of the vaccine is carried out remotely by darting and does not require immobilization
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