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Electroencephalographic and cardiovascular responses to castration in Bos indicus bull calves and the mitigating effects of lidocaine or meloxicam administration

Lehmann, Heidi (2017) Electroencephalographic and cardiovascular responses to castration in Bos indicus bull calves and the mitigating effects of lidocaine or meloxicam administration. Other thesis, Murdoch University.

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Abstract

Australian Bos indicus cattle are legally able to be castrated without anaesthesia or analgesia up to the age of 12 months. Castration surgery is known to cause pain to cattle, though a reliable and consistent assessment of pain must be first optimised before analgesic therapies can be tested for this procedure. Studies in conscious cattle have demonstrated the difficulty in isolating pain responses from the stress of handling and human contact.

This study aimed to investigate electroencephalographic and cardiovascular responses indicative of nociception in Bos indicus bull calves undergoing surgical castration whilst under general anaesthesia. Further, the mitigating effects of administration of local anaesthetic or systemic meloxicam on these electroencephalographic and cardiovascular responses were investigated.

A total of 36 six-to-eight month old Bos indicus bull calves were included in this prospective, randomised, experimental study. Animals were randomly allocated to three groups of twelve (groups L – 260 mg of 2% lidocaine subcutaneously and intratesticularly five minutes prior to castration, M - 0.5 mg kg-1 of meloxicam subcutaneously 30 minutes prior to castration and C – no preoperative analgesia administered). Anaesthesia was induced and maintained with halothane (0.9-1.1%) in oxygen. Electroencephalogram, heart rate (HR) and mean blood pressure (MAP) were recorded for 300 seconds prior to (baseline, B) and from the start of surgery (first testicle incision, T1). HR and MAP were compared at ten-second intervals for 90 seconds from the start of T1. Median frequency (F50), spectral edge frequency (F95) and total power of the electroencephalograph (Ptot) were analysed using area-under-the-curve comparing T1 to B.

All electroencephalographic variables were significantly different between B and T1. No differences in F50 were found between groups during T1. F95 and Ptot were significantly different between group L and groups C and M during T1. There were transient significant changes in HR and MAP in groups L and M compared to group C during the 20-50 second periods.

This study is the first description of electroencephalographic and cardiovascular responses to castration in Bos indicus cattle, and the effect of two different analgesic strategies in reducing these responses. Administration of lidocaine prior to castration significantly attenuated the acute post-operative nociceptive response. In addition, the preoperative administration of meloxicam attenuated the cardiovascular, but not the electroencephalographic, responses to castration in the peracute period. These findings provide support for the preoperative administration of lidocaine and give impetus for further research into the peracute anti-nociceptive effects of meloxicam for castration in Bos indicus bull calves.

Publication Type: Thesis (Other)
Murdoch Affiliation: School of Veterinary and Life Sciences
Notes: Research Masters with Training
Supervisor: Musk, Gabrielle, Drynan, Eleanor and Laurence, Michael
URI: http://researchrepository.murdoch.edu.au/id/eprint/40738
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