Use and Efficacy of Analgesic Agents in Sheep (Ovis aries) Used in Biomedical Research

Abstract

Sheep (Ovis aries) are widely used as large animal models in biomedical research. However, current literature on the use of analgesics in sheep generally focuses on an industry or farm level of use. This structured review evaluates use and efficacy of analgesics administered to sheep in a biomedical research setting. Electronic databases were searched with terms related to analgesia in research sheep. After application of exclusion criteria, 29 peer-reviewed publications were evaluated from 1995 to 2018. Drugs used for analgesia in sheep include opioids, α2 agonists, NSAID, local anesthetics, NMDA receptor antagonists, and calcium channel blockers. Opioid agonists have previously been considered short acting and of questionable efficacy in sheep, but newer modalities may provide effective analgesia. NSAID may exhibit an analgesic effect only when inflammatory pain is present and may not be beneficial for use in acute pain models. α2 agonists provide effective yet short-lived analgesia; however, side effects are of concern. Local anesthetics were previously widely used as stand-alone agents, as alternatives to the use of general anesthetics in sheep. These agents have since fallen out of favor as sole agents. Despite this, they provide a valuable analgesic effect when used as adjuncts to general anesthetic regimes. The NMDA antagonist ketamine provided good analgesia and is likely underutilized as an analgesic agent in sheep. Future controlled studies should further evaluate the analgesic properties of ketamine in sheep.

Effects of the natural sweetener rebaudioside A on intake, nutrient digestion, rumen fermentation, and blood biochemical parameters in adult goats during summer

“…On d 20 to 21 of each period, rumen fluid samples were collected using an esophageal tube at 0, 2.5, and 6 hr after morning feeding (Jasmin et al., 2011; Wang, Wang, et al., 2016). The first 10‐mL ruminal fluid was discarded to minimize false elevation of ruminal pH.…”

Pain, Pathophysiological Mechanisms, and New Therapeutic Options for Alternative Analgesic Agents in Sheep: A Review and Investigation

“…In the wake of the achievements of theoretical sciences, exogenous substances that mimic the effects of endogenous endorphins were soon developed. Some of the obtained opiate substances proved to be 1000–80,000 times more potent in analgesic tests than their protoplast, morphine [ 1 , 10 ]. However, these substances have certain adverse effects in some species, particularly ruminants [ 1 , 11 ].…”

“…Strong analgesics (narcotics) in veterinary medicine are used as a premedication and, to a lesser extent, during the postoperative period (in which NSAIDs are mostly utilized and have no effect on neoplastic processes) [ 1 , 12 ]. The domain of the use of analgesics (in the strict sense) in combating visceral, post-traumatic (acute), chronic, and cancer pain is neglected [ 1 , 10 ]. The adverse consequence of omitting antinociceptive therapy in animals is increased stress, especially increased symptoms associated with an alarm reaction (increased levels of ACTH, E, NE, cortisol, vasopressin, renin, angiotensin II, aldosterone, and glucose and decreased levels of insulin and testosterone in blood).…”

“…Animals need humane treatment based on the modern achievements of veterinary neuropharmacology. High-intensity pain requires the use of a narcotic analgesic, which should not be used during the manifestation of symptoms of patients’ increased suffering, but in advance, to avoid dilemmas concerning which drugs to use such as analgesics, anxiolytics, sedatives, or muscle relaxants [ 10 ]. Medical care for the animal should be carried out in such a manner, to meet all the conditions of its welfare [ 27 ].…”

Comparison of pulmonary function in isoflurane anaesthetized ventilated sheep (Ovis aries) following administration of intravenous xylazine versus medetomidine

“…In this setting it is imperative that anaesthetic and analgesic protocols optimize animal welfare but do not interfere with study findings by impairing perfusion and tissue oxygenation of vital organs. Opioids are the most frequently used analgesic agents in other species, however the analgesic efficacy of opioids has been questioned in sheep, 3,4 while alpha 2 adrenoreceptor agonists have been shown to have good analgesic efficacy in sheep. 5,6 Alpha 2 adrenoreceptor agonists, which the remainder of this paper will be referred to as alpha 2 -agonists, offer alternatives for providing analgesia in this species.…”