Effects of non-steroidal anti-inflammatory drugs on the hyperalgesia to noxious mechanical stimulation induced by the application of a tourniquet to a forelimb of sheep

Can Lambs in Pain Identify Medicated Feed?

Lambs in Australia undergo painful husbandry procedures as part of common husbandry. The magnitude and duration of pain are difficult to assess in lambs. Most currently used methods rely on behavioral expressions and physiological markers that may fail to detect the state of pain an animal experience. This study examined motivation of 12-week-old lambs experiencing chronic pain to self-medicate by consumption of feed containing an analgesic agent as an indicator of pain in lambs. In this study, 36 male Merino lambs were individually penned and acclimated to pelleted feed and two artificial odors: strawberry and banana. Once acclimated to odored feed, lambs were tested for their individual preference for the odors. Lambs were then assigned to one of two groups: Sham—sham handled day 0 and 7 or Ring—Ring castrated day 0 and tail docked day 7. To enable self-medication testing, lambs underwent a conditioning period (day 0–3) followed by the self-medication period (day 7–12). On day 0 lambs were castrated or sham handled, and then offered only medicated feed that contained an odor cue (either strawberry or banana). On day 7, lambs underwent tail-docking or sham handling and were offered both the conditioned medicated feed and non-medicated feed. Amount of each feed consumed was recorded 1 and 12 h after offer each day. Blood samples were taken for cortisol and white blood cell analysis and behavioral observations were recorded for 12 h following treatment. There was no difference in preference for medicated feed between Ring and Sham lambs during the self-medication phase (P = 0.18). Lambs in both groups displayed a significant preference for strawberry cued medicated feed during the self-medicated period when compared to the other testing periods (P = 0.05). Ring lambs displayed more active pain behaviors (mean = 15.1) than Sham (mean = 0.4, P < 0.05). Following castration, Ring lambs had a higher neutrophil/lymphocyte ratio at 6, 24, 48, and 72 h. This study was not able to demonstrate that lambs can self-medicate for a state of pain.

Pain Management in Small Ruminants and Camelids: Analgesic Agents

Small ruminants are increasing in popularity as both production and companion animals in the United States. Among sheep, goats, and camelids, there are many disease processes and management techniques that have the potential to result in painful or noxious stimuli. In these species, many medications and therapeutic techniques can be used to reduce or eliminate the long-term consequences of pain. This review focuses on the commonly used medications available for pain management of small ruminants and discusses the benefits and negative aspects of their use.

Pain Management in Small Ruminants and Camelids: Applications and Strategies

Small ruminants are increasing in popularity as production and companion animals in the United States, and among sheep, goats, and camelids there are many disease processes and management techniques that have the potential to result in painful or noxious stimuli. In these species, many medications and therapeutic techniques can be used to reduce or eliminate the long-term consequences of pain. In this second portion of the review, we focus on the application of pain management in these species. These strategies include mono- and multimodal and the use of precision pain management, such as epidural drug administration, regional perfusions, and transdermal applications.

Pharmacokinetics and antinociceptive effects of tramadol and its metabolite O-desmethyltramadol following intravenous administration in sheep

Although sheep are widely used as an experimental model for various surgical procedures there is a paucity of data on the pharmacokinetics and efficacy of analgesic drugs in this species. The aims of this study were to investigate the pharmacokinetics of intravenously (IV) administered tramadol and its active metabolite O-desmethyltramadol (M1) and to assess the mechanical antinociceptive effects in sheep. In a prospective, randomized, blinded study, six healthy adult sheep were given 4 and 6 mg/kg tramadol and saline IV in a cross-over design with a 2-week wash-out period. At predetermined time points blood samples were collected and physiological parameters and mechanical nociceptive threshold (MNT) values were recorded. The analytical determination of tramadol and M1 was performed using high performance liquid chromatography. Pharmacokinetic parameters fitted a two- and a non-compartmental model for tramadol and M1, respectively. Normally distributed data were analysed by a repeated mixed linear model. Plasma concentration vs. time profiles of tramadol and M1 were similar after the two doses. Tramadol and M1 plasma levels decreased rapidly in the systemic circulation, with both undetectable after 6 h following drug administration. Physiological parameters did not differ between groups; MNT values were not statistically significant between groups at any time point. It was concluded that although tramadol and M1 concentrations in plasma were above the human minimum analgesic concentration after both treatments, no mechanical antinociceptive effects of tramadol were reported. Further studies are warranted to assess the analgesic efficacy of tramadol in sheep.

Physiological and behavioural assessment of pain in ruminants: principles and caveats

Pain elicits a range of physiological and behavioural responses. These are commonly used to assess the impact of pain-inducing stimuli on animals, to determine whether or not significant pain is experienced and to devise strategies for alleviating pain. This paper outlines a range of principles and caveats to guide the evaluation of physiological and behavioural responses to painful stimuli, so that they can be better used to minimise pain in the experimental context. Although this advice is based on studies of farm animals responding to painful husbandry practices, it is more generally applicable.

Assessment and management of pain in small ruminants and camelids

Many disease processes and management procedures of small ruminants have the potential to result in painful or noxious stimuli. There are a variety of medications and interventions that can be used to minimize the long-term consequences of pain in these species. The first portion of this article focuses on the commonly used medications available for pain management of small ruminants and discusses the benefits and side effects to their use. The second portion of the article focuses on the management of pain associated with common diseases or procedures of these species.

Ketoprofen in piglets: enantioselective pharmacokinetics, pharmacodynamics and PK/PD modelling

The chiral pharmacokinetics and pharmacodynamics of ketoprofen were investigated in a placebo-controlled study in piglets after intramuscular administration of 6 mg/kg racemic ketoprofen. The absorption half-lives of both enantiomers were short, and S-ketoprofen predominated over R-ketoprofen in plasma. A kaolin-induced inflammation model was used to evaluate the anti-inflammatory, antipyretic and analgesic effects of ketoprofen. Skin temperatures increased after the kaolin injection, but the effect of ketoprofen was small. No significant antipyretic effects could be detected, but body temperatures tended to be lower in the ketoprofen-treated piglets. Mechanical nociceptive threshold testing was used to evaluate the analgesic effects. The piglets in the ketoprofen-treated group had significantly higher mechanical nociceptive thresholds compared to the piglets in the placebo group for 12-24 h following the treatment. Pharmacokinetic/pharmacodynamic modelling of the results from the mechanical nociceptive threshold testing gave a median IC(50) for S-ketoprofen of 26.7 μg/mL and an IC(50) for R-ketoprofen of 1.6 μg/mL. This indicates that R-ketoprofen is a more potent analgesic than S-ketoprofen in piglets. Estimated ED(50) for racemic ketoprofen was 2.5 mg/kg.

Effects of a topical anaesthetic formulation and systemic carprofen, given singly or in combination, on the cortisol and behavioural responses of Merino lambs to castration

OBJECTIVE

To determine the effectiveness of a topical anaesthetic formulation (Tri-Solfen) with or without the administration of a non-steroidal anti-inflammatory drug (carprofen) on the pain and distress response associated with ring or surgical castration of ram lambs.

PROCEDURES

Merino ram lambs (n = 78) were allocated to 10 treatment groups: 4 groups of knife-castrated lambs and 4 groups of ring-castrated lambs received carprofen (4 mg/kg SC) and Tri-Solfen; 2 control groups (sham) received carprofen at 0 or 4 mg/kg SC. Measurements included plasma cortisol and haptoglobin concentrations, haematology, and behaviour, including posture.

RESULTS

Knife-castrated lambs had higher peak cortisol and integrated cortisol responses for the first 6 h after treatment and greater concentration s of circulating acute phase proteins than ring-castrated lambs, both of which were significantly different from the sham controls. Tri-Solfen applied to the knife castration wound significantly reduced both the peak plasma cortisol concentration and the integrated cortisol response for the first 6 h and improved lying behaviour in the first 12 h. Carprofen reduced the cortisol response to knife castration at 30 min, but elevated the cortisol responses at 24 and 48 h. Carprofen nearly halved the number of acute pain behaviours associated with ring castration. There were no significant additive or synergistic effects from combining the analgesic treatments. Tri-Solfen applied to the tail wound provided no detectible benefits during ring castration + tail docking.

CONCLUSIONS

The physiological and behavioural responses suggest that ring castration has less impact on the lamb than knife castration. The specific analgesic treatments can provide modest amelioration of the pain and discomfort associated with castration. Alternative doses or application methods may enhance their efficacy.

Effectiveness of non-steroidal anti-inflammatory drugs and epidural anaesthesia in reducing the pain and stress responses to a surgical husbandry procedure (mulesing) in sheep

In this study, we examined the potential of several widely used non-steroidal anti-inflammatory drugs (NSAIDs) and other analgesics to reduce pain and stress in sheep after surgery. Because mulesing involves a greater degree of tissue trauma than other surgical husbandry procedures such as castration or tail-docking, it provides a more rigorous and conservative test to identify potentially useful analgesic strategies in sheep. Merino lambs (5 weeks of age) were randomised into eight treatment groups: (1) carprofen; (2) flunixin; (3) ketoprofen; (4) buprenorphine; (5) xylazine; (6) lignocaine epidural; (7) saline control; (8) sham control. The NSAIDs were administered 1.5 h before mulesing, buprenorphine 0.75 h and xylazine and lignocaine 0.25 h before mulesing. Pain- and discomfort-related behaviours were recorded for 12 h after mulesing, and plasma cortisol concentrations were measured before mulesing and 0.5, 6, 12, 24 and 48 h after mulesing. The results indicated that no single analgesic treatment provided satisfactory analgesia during both the surgical mulesing procedure and the ensuing period of pain associated with the inflammatory phase. However, there were indications that two NSAIDs (carprofen and flunixin) showed good potential as analgesics during the inflammatory phase. A combination of short- and long-acting analgesics may be needed to provide more complete pain relief. In conclusion, the administration of some NSAIDs offers the potential for good analgesia in sheep for the inflammatory phase following the tissue trauma of surgical husbandry procedures. Other analgesic options need to be considered if the acute stress response to the procedure is to be reduced.

The effect of a topical anaesthetic formulation, systemic flunixin and carprofen, singly or in combination, on cortisol and behavioural responses of Merino lambs to mulesing

OBJECTIVE

To determine the pain responses of lambs to mulesing, and the effectiveness of potential analgesic treatments.

PROCEDURES

Merino lambs (n=64) were allocated at 5 weeks of age to eight treatment groups: 1) sham mules; 2) conventional mules; 3) topical anaesthetic, incorporating lignocaine, bupivicaine, adrenaline and cetrimide, applied immediately after mulesing; 4) flunixin + topical anaesthetic, with flunixin administered 2.5 mg/kg s.c. 90 min before mulesing; 5) carprofen + topical anaesthetic, with carprofen administered 4 mg/kg s.c. 90 min before mulesing; 6) carprofen, administered as above; 7) flunixin, administered as above; and 8) carprofen + flunixin, administered as above. Plasma cortisol was measured at 0, 0.5, 6, 12 and 24 h relative to mulesing. Animal behaviour, including posture, was recorded for 12 h after mulesing.

RESULTS

The conventional mules lambs exhibited large increases in plasma cortisol, reduced lying and increased standing with a hunched back compared with sham mules animals. Topical anaesthetic reduced the cortisol peak to mulesing and hunched standing, and increased lying compared with the conventional mules treatment, but generally did not result in values equivalent to sham mules animals. Carprofen, flunixin, and carprofen + flunixin treatments did not reduce the cortisol response to mulesing but substantially ameliorated some changes in behavioural postures. Flunixin + topical anaesthetic reduced the cortisol peak following mulesing and substantially ameliorated most changes in behavioural postures. Carprofen + topical anaesthetic abolished the cortisol peak following mulesing and substantially ameliorated most changes in behavioural postures. All mulesed animals lost weight in the week after mulesing regardless of analgesic administration, but there were no significant differences in growth rate between any of the eight treatments over the 3 weeks after mulesing.

CONCLUSIONS

Analgesics can moderate the pain response of lambs to mulesing. The welfare outcome for lambs of mulesing could be improved by use of a combination of local anaesthetic and long acting non-steroidal anti-inflammatory drug.

Responses of rats to noxious mechanical stimulation of their tails during tail reperfusion following transient ischaemia

We investigated whether conscious rats exhibit hyperalgesia to noxious mechanical stimuli during tail reperfusion following transient tail ischaemia. Mechanical stimuli were delivered by three mechanical algometers, differing in contact area, geometry and rate of application. Tail ischaemia was induced by applying a pneumatic tourniquet to the base of the tail until the rats exhibited escape behaviour. Control animals had a sham tourniquet placed on their tails. During tail reperfusion, there was significant hyperalgesia when the noxious mechanical stimulus was applied by a narrow bar transverse to the tail, less when applied by a rubber piston, and there was no hyperalgesia when the stimulus was punctate, similar to a von Frey hair. Repeated application of the mechanical stimuli themselves, at 30-min intervals, did not induce hyperalgesia. Rats subjected repetitively to the combination of the bar algometer and tail ischaemia at intervals of at least 48 h, for a total period of three weeks, exhibited progressively enhanced hyperalgesia to the bar algometer, and also enhanced hyperalgesia to noxious ischaemic and thermal stimuli. Rats therefore do exhibit hyperalgesia to mechanical stimuli following conditioning ischaemia, but the nature of the hyperalgesia depends critically on the geometry of the algometer, and the time course of the hyperalgesia was different to that which manifests to a noxious thermal stimulus.

An assessment of the peripheral antinociceptive potential of remoxipride, clonidine and fentanyl in sheep using the forelimb tourniquet

A modification of the intravenous regional anaesthesia technique was used to assess the peripheral antinociceptive effect of remoxipride, clonidine and fentanyl. Drugs administered intravenously via peripheral catheters were restricted to the distal limb and nociceptive threshold test site by prior inflation of a tourniquet proximal to both the catheter and a threshold-testing device. Lignocaine (1 mg/kg) induced peripheral antinociception during tourniquet inflation. Clonidine (6 micrograms/kg) only induced significant elevations in thresholds after tourniquet deflation. A low dose of remoxipride (2 mg/kg), which had no systemic antinociceptive effect, produced antinociception after its restriction to the periphery. Peripheral administration of saline and tourniquet-induced restriction of blood flow to the distal limb did not alter threshold values. Peripheral administration of fentanyl was used to test a further modification of the injection protocol designed to reduce the incidence of leakage into the systemic circulation. Fentanyl administration (11.2 micrograms/kg) failed to elicit an increase in thresholds when it was restricted to the distal limb test site. The contribution of a peripheral mechanism to the antinociception induced by systemic administration of a higher remoxipride dose (7.5 mg/kg) was investigated using an inflated tourniquet to exclude remoxipride from the periphery. Exclusion of remoxipride from the periphery reduced its antinociceptive effect, i.e. threshold values were lower than if remoxipride was allowed free access to the limb prior to tourniquet inflation. The technique described here was effective in demonstrating that the increase in noninflammatory nociceptive thresholds seen with clonidine and fentanyl is not peripherally mediated whilst that seen with remoxipride has a peripheral component.

Effects of four analgesic treatments on the behavioural and cortisol responses of 3-week-old lambs to tail docking

The behavioural and cortisol responses of groups of seven or eight lambs were used to determine which of three methods of tail docking (rubber ring, Burdizzo and rubber ring combined, or heated docking iron) produced the least signs of pain in the first 3 h after use and which of four analgesic treatments (1.0 ml bupivacaine subcutaneously, 0.5 ml bupivacaine epidurally, a topical cold analgesic spray or diclofenac 1.5 mg kg-1) was most effective in reducing these signs. Amputation with a heated docking iron produced levels of behaviour and cortisol responses which did not differ markedly from those of handled controls. The rubber ring method produced the greatest increase in all parameters (total active behaviour 110 +/- 91 counts; 51 +/- 23 min spent in abnormal postures; peak cortisol 93 +/- 51 nmol l-1). Subcutaneous bupivacaine, administered immediately prior to application of the ring, appeared to be the analgesic treatment most effective at reducing these responses (23 +/- 15 counts; 24 +/- 22 min.; 44 +/- 20 nmol l-1).