Practical analgesia for livestock husbandry: the role of topical anaesthesia

M. Sheil ^AB, S. Lomax^A, H.A. Dickson^A, P. Windsor^A.

^{A. Faculty of Veterinary Science, The University of Sydney
B. Animal Ethics Pty. Ltd.}

• Procedure
• Results
• Discussion
• Conclusion
• Acknowledgments
• References
  
  

Husbandry procedures in livestock cause significant pain and suffering, yet are invariably performed without analgesia. This is a major welfare omission with important social and trade implications. Whilst the ideal solution is to breed animals that do not require these procedures or to find painless alternative practices, this is likely to take time. A mechanism is needed to address welfare concerns in the interim while long term solutions are pursued. In every other field of medicine this ‘interim’ role is filled by the use of analgesia, yet this is an option that is unavailable for the vast majority of farm animals.

There is a virtual absence of medications licenced for use in farm animals and a lack of practical or affordable methods of delivery, such that farmers have few options available to treat pain in their animals. This has set the scene for conflict between animal advocacy groups and farmers as is evidenced by mulesing-related boycotts of Australian wool, and retailer boycotts of meat from piglets castrated without analgesia in the EU.

The vast majority of veterinary administered general or local anaesthetic regimens are impractical or commercially unviable for use in farming practices. To address pain in livestock, new analgesic regimens are required which meet the practical and economic constraints of farming practice. A step-wise approach is needed to ensure that analgesic regimens develop in a viable and sustainable manner.

The use of topical anaesthesia shows promise as a “first step” to begin to address farm animal pain. This has been exemplified by the success of Tri-Solfen® , which is the first “farmer applied” analgesic product to become commercially available to alleviate pain associated with Mulesing. It is a multifunction spray-on topical anaesthetic, haemostatic and antiseptic agent that is applied to numb the wound immediately post mulesing. It has a significant analgesic effect eliminating or significantly reducing wound pain and pain-related behaviour up to, and including, 8 hours post mulesing. It also lowers peak cortisol response, reduces bleeding and speeds up wound healing^1,2. Subsequent research has identified that pre-operative administration of a non-steroidal antiinflammatory agent (Carprofen) significantly enhances the analgesic effect such that the combination not only abolishes pain-related behaviour up to and including 12 hours post mulesing, but also abolishes the acute cortisol response.2 In terms of pain alleviation and mitigation of stress response, this exceeds that which is achieved during equivalent surgical procedures in pets, such as ovariohysterectomy (spaying) of cats and dogs^3,4, and provides a means to perform the procedure humanely while genetic breeding and other long term alternative solutions are pursued.

Similarly effective and sustainable “farm based” analgesic regimens are required for other husbandry procedures. Topical anaesthesia is being investigated to alleviate pain associated with other husbandry procedures including castration, tail docking and dehorning. This paper discusses the use of topical anaesthesia as a potential sustainable “first step” to alleviate pain associated with castration and tail docking in sheep.

Procedure

Randomised, placebo-controlled trials were performed on 8 groups of 6-12 week old lambs (n=8 in each group) undergoing routine castration and tail docking. Castration with surgical or hot knife tail docking was performed with and without topical anaesthetic or placebo application, and compared with ring castration and tail docking or handled but unmarked controls.

In treated lambs, Tri-Solfen® or placebo gel was applied by spray-on metered dose directly to the tail docked wounds and onto each of the exteriorized spermatic cords (prior to their being severed), as well as to the scrotal sac and cut skin edge immediately post castration.

Wound pain was assessed using 10 and 75 gram calibrated Von-Frey monofilaments to determine response to light touch and pain stimulation over a 4 hour period. Pain-related behaviour was assessed by trained, blinded observers using a numerical rating scale over a 5 hour period. Wound healing was assessed by veterinary inspection and palpation 14 and 28 days following the procedures.

Plasma lignocaine and bupivacaine levels were determined using HPLC from jugular venous blood samples collected at 0, 30, 90 and 120 minutes following the procedures.

Results

Castration wound pain: Rapid (1min) and prolonged (up to 4 hr) primary hyperalgesia developed in untreated and placebo treated sheep but not in Tri-Solfen® treated sheep (p=<0.0001).