Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

Systematic review of nonsteroidal anti-inflammatory drug-induced adverse effects in dogs

The aim of this systematic review was to identify, assess, and critically evaluate the quality of evidence of nonsteroidal anti-inflammatory drug (NSAID)-induced adverse effects in dogs. Original prospective studies published in peer-reviewed journals in English (1990-2012) that reported data on the safety of NSAIDs administration in dogs were searched. For each study, design type (I, II, III, or IV) and assessment of quality (+, Ø, -) were rated. For each drug, quantity and consistency rating (***, **, *) and strength of evidence (high, moderate, low, or extremely low) were identified and evaluated. The strength of evidence was defined in terms of how applicable and relevant the conclusions were to the target population. Sixty-four studies met the inclusion criteria. Thirty-five (55%) research studies and 29 (45%) clinical trials were identified. A high strength of evidence existed for carprofen, firocoxib, and meloxicam; moderate for deracoxib, ketoprofen, and robenacoxib; and low for etodolac. Quality and consistency rating were as follows: carprofen (***/***), deracoxib (**/***), etodolac (*/unable to rate), firocoxib (***/**), ketoprofen (**/***), meloxicam (***/***), and robenacoxib (**/**), respectively. Adverse effects were detected in 35 studies (55%) and commonly included vomiting, diarrhea, and anorexia. Three studies (5%) reported a power analysis related to adverse effects of ≥80%. In randomized, placebo-controlled, blinded studies (n = 25, 39%), the incidence of adverse effects was not statistically different between treated and control dogs. Finally, most studies were not appropriately designed to determine the safety of NSAIDs, and involved a healthy nongeriatric population of research dogs.

Pro-apoptotic effects of tepoxalin, a cyclooxygenase/lipoxygenase dual inhibitor, on canine synovial fibroblasts

Canine osteoarthritis occurs frequently and causes secondary synovitis. Administration of nonsteroidal anti-inflammatory drugs (NSAIDs) is one of the major therapeutic options for pain management of joint diseases. Tepoxalin has an unique property as an NSAIDs that suppresses both cyclooxygenase and lipoxygenase. The purpose of this study was to evaluate antiproliferative effects of tepoxalin on cultured canine synovial cells. Cytotoxic effects of tepoxalin, carprofen, meloxicam and AA-861 on cultured canine synoviocytes were evaluated by MTT colorimetric assay. Apoptosis was detected by morphological observations with Giemsa or annexin V/Hoechst 33342 staining and by the inhibition of caspase-3 activity with N-Ac-Asp-Glu-Val-Asp-CHO (Ac-DEVD-CHO). Cytotoxic effects of tepoxalin were evident in comparison with the effects of carprofen or meloxicam. The same tendency of cytotoxicity was observed when 5-lipoxygenase was inhibited by AA-861. The morphological findings and contradictory effects of Ac-DEVD-CHO with regard to the cytotoxicity proved the proapoptotic effects of tepoxalin. In conclusion, tepoxalin might control osteoarthritic synovitis by inducing apoptosis in proliferating synoviocytes, while most NSAIDs that selectively inhibit cyclooxygenase-2 most likely would not suppress synovial proliferation.

Induction of VEGF by tepoxalin does not lead to increased tumour growth in a canine osteosarcoma xenograft

The purpose of this study was to determine the impact of the non-steroidal anti-inflammatory drug tepoxalin on canine tumour cell growth and describe the changes associated with tepoxalin treatment. In vitro experiments were performed to assess tepoxalin-associated alterations in tumour cell growth. Clinically achievable tepoxalin concentrations did not significantly alter tumour cell growth in vitro. Vascular endothelial growth factor (VEGF) production and hypoxia-inducible factor-1α dose-dependently increased in vitro in the presence of tepoxalin. A canine osteosarcoma xenograft was used to determine in vivo effects of tepoxalin on tumour growth and angiogenesis. Despite increased VEGF in vitro, there was a significant growth delay associated with tepoxalin treatment. Normal dogs were administered tepoxalin to assess effects on systemic VEGF production, but not found to have significantly increased VEGF. These data suggest that tepoxalin may moderately inhibit tumour growth and may be administered as an analgesic to tumour-bearing dogs.