Effects of vaccination against gonadotrophin‐releasing hormone (GnRH) on the social status of brushtail possums in captivity

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Abstract
Options for the biological control of brushtail possums (Trichosurus vulpecula) are being evaluated in the hope of finding a cost‐effective, long‐term solution to the problem of reducing numbers of possums as hosts of bovine tuberculosis and as threats to conservation values. Methods of inhibiting possum reproduction by affecting sex steroid levels are among the options. However, this may result in behavioural changes. In some species, a loss of status by dominant animals allows subordinates to breed more successfully. This paper describes how social hierarchies in captive groups of possums are affected by vaccination of dominant females against gonadotrophin‐releasing hormone (GnRH) to block all centrally controlled steroid hormone release. Ten groups consisting of two females and one male were established in pens, and the dominance status of each animal was measured by recording the outcome of social interactions during monthly observations. The dominant female in each pen was vaccinated against GnRH with a series of three immunisations. Social hierarchies remained unchanged over the 2–4 months after vaccination of the dominant females. We therefore conclude that methods of biological control that disrupt sex steroid production could be considered for possum control once these findings are confirmed by similar observations on wild possums.