Velvet antler removal from red deer : a thesis presented in partial fulfilment of the degree of Doctor of Philosophy in Veterinary Medicine at Massey University, Manawatu, New Zealand

Abstract

Antlers are unique structures specific to deer that are cast and regrown annually. The harvest of velvet antler is a surgical procedure requiring analgesia and haemostasis. Analgesia is provided by lignocaine ring blocks around the base of the antler in adult stags or compression analgesia with a rubber (NaturOTM) ring in yearlings. Stags are often sedated with xylazine for velvet removal. This thesis covers four topics requiring refinement or further understanding: variability in local analgesia using lignocaine; the efficacy or noxiousness of NaturOTM rings; lignocaine residues in antlers; and post- xylazine stag death. In a video observational study of antler harvest on commercial velvet farms, successful analgesia was characterised by fewer “gaps” in the ring block, greater volume of lignocaine per antler, greater time taken to inject lignocaine, greater number of injections, lower stag age, and other stag factors. There was significant confounding in the data and multiple variables are likely to be important. In a series of studies investigating the use of NaturOTM rings, the rings prevented behavioural responses and partially prevented EEG responses to antler removal. On application of the NaturOTM ring, some animals demonstrated behavioural and EEG responses indicative of noxious sensation. NaturOTM rings provide analgesia during antler removal and may cause discomfort on application. It is believed that lignocaine reaches the antler via the blood stream, resulting in tissue residues. Blood flow to the antler was investigated using acrylic models, fluorescent microspheres and cineangiography. Different tourniquet types were tested to determine whether they could prevent lignocaine residues. The arterial supply to the antler is elaborate and tourniquets minimised arterial flow at tensions less than 2kg but did not prevent lignocaine residues. Occasionally, stags die within 48 hours of sedation with xylazine. In an epizoological survey, this was not related to drug or environmental factors. Reactions involved either acute respiratory distress or delayed death with severe pulmonary oedema. During observations of yearlings sedated with xylazine most demonstrated hypoxaemia that could be reversed by oxygen supplementation or yohimbine administration. This work provides indicators of how best practice in velvet antler removal may be improved.