Assessing physiological and behavioural parameters of stress in pZP vaccinated elephants

Abstract

Management of protected elephant populations in South Africa has long been a challenge. In the absence of poaching and with the provision of extra water holes, elephant populations have increased at unexpectedly high rates and show no signs of reaching a plateau. Various methods of population control have been considered to control elephant numbers, including culling or translocation of family groups and habitat expansion; none has proved entirely satisfactory. More recently, attention has focused on methods of contraception and amongst these immunocontraception with a porcine zona pellucida (pZP) vaccine has been proven effective and safe. However, there are still concerns that pZP vaccination may have unexpected long term side-effects on fertility or social structure and behaviour. For example, the expected effect of pZP vaccination is temporary infertility despite continuing cyclicity. As a result, it is anticipated that bulls (in musth) would visit and disturb a herd considerably more frequently because cows would have considerable more estrous periods; this might endanger young calves and is likely to be a source of extra stress to the herd. In the period of 14/7/08 - 4/10/08 behavioral observations of the elephant families in The Greater Makalali Private Game Reserve (GMPGR) were made to evaluate several factors that might indicate an increase in stress levels in pZP vaccinated elephants. In addition, fecal samples were collected to determine the cortisol concentrations, which should give an indication of physiological stress experienced during the preceding 48 hours. In GMPGR, the presence of adult bulls with a matriarchal herd had little if any effect on behavior and was not a clear cause of stress related behavioural patterns. On the other hand, the annual aerial pZP vaccination by darting did result in a transient increase in fecal cortisol and diminished water and food availability during winter was also associated with rising fecal cortisol concentrations. Overall, the physiological effects of contracepting elephants with the pZP vaccine appear to be associated with minimal social disruption and related stress. However, the darting process itself is clearly stressful.