Efficacy of articaine hydrochloride for disbudding in goat kids and velvet antler removal in red deer, and novel disbudding methods for goat kids : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand

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Painful husbandry procedures are routinely performed in farm animals all over the world. Most of these procedures can be humanely performed under local anaesthesia. Lignocaine is the most commonly used local anaesthetic in veterinary medicine. Even though lignocaine is a cheap and effective local anaesthetic, its use in goat kids and deer has been a concern. In goat kids, lignocaine has been reported to produce toxicity following cornual nerve block. In deer, the presence of lignocaine residue in the harvested velvet antlers following ring block has been a concern as one of its metabolites, 2,6-dimethylaniline (DMA) has been classified as a possible carcinogen in humans. Articaine hydrochloride is an amide-type local anaesthetic with unique pharmacological properties such as rapid hydrolysis in plasma to an inactive metabolite and high lipid solubility. It is widely used in humans for local and regional nerve blocks in dentistry. Several studies in humans suggested that articaine hydrochloride was effective and safer than lignocaine. Given concerns on the use of lignocaine in goat kids and deer, a series of studies were conducted to evaluate the safety and efficacy of articaine hydrochloride as an alternative to lignocaine hydrochloride for disbudding in goat kids and velvet antler removal in deer. As there is a paucity of data on the toxicity of lignocaine in goat kids, the thesis has also investigated the toxicity of lignocaine hydrochloride in goat kids. In addition, novel analgesic and disbudding techniques for goat kids were evaluated. The dose-ranging studies in goat kids suggested that doses up to 8 mg kg–1 and 7 mg kg–1 of articaine hydrochloride and lignocaine hydrochloride, respectively, can be safely used for perineural injections. Pharmacokinetic studies demonstrated that articaine hydrochloride was rapidly hydrolysed and eliminated in goat kids. The elimination half-life of articaine (1.26 ± 0.34 hours) was determined to be shorter than the elimination half-lives of lignocaine (1.71 ± 0.51 hours) and lignocaine’s metabolite, monoethylglycinexylidide (3.19 ± 1.21 hours) in goat kids. The total dose of articaine (16.24 ± 1.79 mg kg–1) required to produce convulsions in goat kids was higher than that of lignocaine (12.31 ± 1.42 mg kg–1). The mean convulsive plasma concentrations of articaine and lignocaine were 9.90 ± 2.38 µg mL–1 and 13.59 ± 2.34 µg mL–1, respectively. Both pharmacokinetic and toxicity data indicate that articaine has a greater margin of safety than lignocaine in goat kids. Cornual nerve block (0.5 mL/site) using articaine hydrochloride (1.5%) and lignocaine hydrochloride (1%) alleviated the acute pain during disbudding in goat kids. However, both the drugs provided analgesia only for a short time which necessitates the use of non-steroidal anti-inflammatory drugs (NSAIDs) for postoperative analgesia. In addition, the injection of these drugs at four sites to anaesthetise both the horn buds caused stress and pain in goat kids. Therefore, it is recommended to use sedatives and NSAIDs along with local anaesthetics for disbudding goat kids. However, future studies should evaluate the safety and efficacy of this protocol for disbudding in goat kids. Similar to goat kids, articaine was rapidly hydrolysed to the inactive metabolite, articainic acid, and rapidly eliminated in red deer. A ring block around the base of the antlers using 4% articaine hydrochloride (1 mL/cm pedicle circumference) provided effective analgesia for velvet antler removal in red deer. The results of the studies in red deer suggested that articaine could be a safe and effective local anaesthetic for velvet antler removal. Residue analysis of harvested antlers using liquid chromatography–mass spectrometry (LC–MS) method revealed that the concentrations of articaine and lignocaine in the harvested velvet antlers were similar. Further studies to evaluate the safety of articaine and its metabolites are warranted in target species before recommending articaine hydrochloride as an alternative to lignocaine hydrochloride for velvet antler removal. The analgesic efficacy of methoxyflurane and a novel topical local anaesthetic formulation for disbudding in goat kids were evaluated. Both methoxyflurane and the novel topical formulation provided cutaneous analgesia but did not provide sufficient analgesia for disbudding in goat kids. Further research is required to evaluate the efficacy of these novel analgesic techniques. The efficacy of mepacrine and eugenol for disbudding in goat kids were investigated following subcutaneous injection (0.2 mL) under the horn buds. Both eugenol and mepacrine produced necrosis of horn buds in goat kids but failed to stop horn bud growth. Injection of these compounds using a needle (26 G) and syringe was painful but no pain-related behaviours were seen after the injection. Future studies should evaluate different injection volumes and different non-invasive or minimally invasive administration techniques to increase the efficacy of this novel technique. Refinement of this novel technique might provide a simple, fast, safe and effective way to stop horn bud growth in goat kids.
Animal anesthesia, Dehorning, Kids (Goats), Surgery, Red deer, Antlers