A field test of the anaesthetics, surgical methods and radio-transmitters required for producing Judas pigs for an eradication programme

Judas pigs (Sus scrofa) will be integral to the success of the proposed Auckland Island (45 891 ha) pig eradication. Judas pigs must be permanently unable to breed and reliably retain a radio-transmitter to enable tracking and retrieval. This study tested the techniques and practical requirements to undertake the procedures required to produce a Judas pig in a remote location. Four adult female wild pigs were captured using a netgun from a helicopter and processed at a base site in the field. They were anaesthetised using intramuscular injection of one of two anaesthetic protocols (Zoletil™, ketamine and xylazine; or medetomidine, ketamine and butorphanol). Surgical sterilisation consisted of tubal ligation and resection via a ventral midline incision. Pigs received either a subcutaneous or intra-abdominal implanted radio-transmitter and had a radio-collar and radioear tag attached. The anaesthetic was reversed prior to release close to the capture location. Radio-tracking at 10 and 104 days showed all pigs had survived and radio-tracking was effective using all the transmitter types. Pigs were humanely dispatched and necropsied on day 104. No adverse events were detected from the surgeries or radio-transmitters. All transmitter types except one subcutaneous transmitter model were shown to be secure and had an effective radio range for a Judas pig programme. Pig growth rates implicate a limited humane collaring period and ear transmitters may be at greater risk of transmitter loss. Implantable intra-abdominal radio transmitters provide the most security, but multiple transmitters are advised. Surgical sterilisation by tubal ligation and resection under general anaesthesia using an intramuscular injection containing medetomidine, butorphanol and ketamine and reversed with atipamezole was shown to be feasible in field conditions.