Thermal, mechanical and electrical stimuli in antinociceptive studies in standing horses: an update

Antinociceptive and wound healing effects of a commercial formulation of lidocaine, bupivacaine, adrenaline and cetrimide applied topically to superficial skin wounds in horses

BACKGROUND

Post-traumatic distal limb wounds cause discomfort and heal gradually by second intention. The topical application of Tri-Solfen (lidocaine hydrochloride, bupivacaine hydrochloride, adrenaline acid tartrate and cetrimide [LBAC]) produces effective postsurgical cutaneous analgesia in lambs, calves and piglets; however, its effect on wounds in horses is unknown.

METHODS

The antinociceptive effect, measured by mechanical threshold (MT), and the wound healing impacts of LBAC compared with saline were investigated on surgically created 20 × 20 mm distal limb wounds in 10 horses. Treatment was applied once daily for 7 days following wounding on day 0. Mechanical thresholds were measured after treatment on days 1, 2 and 3. Healing was observed for 25 days.

RESULTS

The topical application of LBAC immediately following wounding and its reapplication 24 hours later increased the average MT on the first post-traumatic day by 3 Newtons. However, no antinociceptive benefit was observed on days 2 or 3. Treatment with LBAC did not adversely affect wound healing when compared with saline.

LIMITATIONS

Methodological differences preclude absolute MT comparisons between studies. The experimental design did not include a model of contaminated or naturally occurring wounds.

CONCLUSION

LBAC may provide an early antinociceptive benefit when applied to uncontaminated surgically created wounds without compromising healing.

Morphine in donkeys: Antinociceptive effect and preliminary pharmacokinetics

BACKGROUND

Morphine is the prototypical μ-opioid receptor agonist used to provide analgesia in veterinary species. Its effects are well-described in horses but not donkeys.

OBJECTIVES

To determine the antinociceptive effects of two doses of morphine in donkeys. To describe preliminary pharmacokinetic parameters of morphine in donkeys.

STUDY DESIGN

In vivo experiment.

METHODS

Eight adult castrated male donkeys were given intravenous (IV) 0.9% saline, morphine 0.1 mg/kg bwt (LDM), or morphine 0.5 mg/kg bwt (HDM) in a randomised order with a minimum 1-week washout period. Mechanical nociceptive thresholds (MNTs) were determined by a blinded investigator pre-injection and 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 300, and 360 min post-injection. Venous blood samples were collected pre-injection and 2, 5, 10, 15, 30, 45, 60, 90, and 120 min post-injection. Data were analysed using Friedman's test with Dunn's post hoc test for multiple comparisons. Pharmacokinetic parameters were calculated for the HDM treatment.

RESULTS

Baseline MNT was [median (interquartile range)] 8.9 (7.1-10.3) N and did not differ between treatments. Peak MNTs occurred at 60 min for both LDM (16.2 N) and HDM (25.0 N) treatments. MNTs after HDM treatment were higher than saline (p < 0.04) at 15, 60, 90, 120, 150, 180, 240, and 300 min post-injection. MNTs after LDM treatment were higher than baseline (p < 0.05) at 45 and 60 min post-injection. Terminal half-life for HDM was (mean ± SD) 51.0 ± 10.7 min, the volume of distribution at steady-state 2.07 ± 0.33 L/min and clearance 49.2 ± 4.16 ml * min/kg using noncompartmental analysis. The concentration of morphine-3-glucuronide (M3G) was higher than morphine-6-glucuronide (M6G) at all sampled time points.

MAIN LIMITATIONS

Short duration of plasma sampling for pharmacokinetic analysis; lack of objective measure of gastrointestinal function.

CONCLUSIONS

The HDM treatment provided mechanical antinociception in donkeys with no significant adverse effects.

The Clinical Pharmacology and Therapeutic Evaluation of Non-Steroidal Anti-Inflammatory Drugs in Adult Horses

This review firstly examines the underlying pathophysiology of pain and inflammation associated with orthopedic disease and endotoxemia. Then, it reviews the clinical pharmacology (pharmacokinetics and pharmacodynamics) of both conventional and non-conventional NSAIDs in the adult horse, and finally provides an overview of different modalities to evaluate the therapeutic efficacy of NSAIDs in research.

The Antinociceptive Effect of Magnesium Sulphate Administered in the Epidural Space in Standing Horses

To study the antinociceptive properties of epidural magnesium sulphate (MgSO₄) in standing horses Experimental, placebo-controlled, masked, cross-over A group of six healthy horses Through an epidural catheter, 1 mg kg ^-1 MgSO₄ (treatment Mg) diluted to a volume of 15 mL or the same volume of saline (treatment S) was administered over 15 minutes. Electrical, thermal and mechanical nociceptive thresholds were determined on the pelvic limb before and 20, 40, 60, 80, 100, 120, 140, 160 and 180 minutes after the start of the injection. Heart rate (HR) and respiratory frequency (f_R) were recorded every 10 minutes. Blood samples were collected before treatment and every 30 minutes throughout the study period. Data were assessed for normality using a Shapiro-Wilk test. A linear mixed model with horse as random effect and time, treatment and their interaction as fixed effects was used. Treatments were compared at 20, 60, 120 and 180 minutes using the Wilcoxon rank sum test stratified for horse (global α = 0.05, with Bonferroni correction α = 0.0125). Epidural MgSO₄ caused a significant increase in the electrical threshold (mA) (P = .0001), but no significant differences in thermal and mechanical nociceptive thresholds. During the injection of MgSO_4, two horses collapsed. One stood up within 20 minutes and was able to continue the study, the second one was excluded. A significant difference was found for HR at T180 (Mg 44 ± 23 beats minute^-1; S 32 ± 9 beats minute^-1) (P = .0090). Epidural administration of MgSO₄ caused an increase in the electrical threshold of the pelvic limbs of horses. Caution is warranted however, as with the current dose, 2 horses collapsed.

Facial Expressions of Horses Using Weighted Multivariate Statistics for Assessment of Subtle Local Pain Induced by Polylactide-Based Polymers Implanted Subcutaneously

Simple Summary

Facial expression (FE) has been used for pain diagnosis in horses. The current study aimed to identify pain in horses undergoing under-skin polylactide-based polymer implantation. Five statistical methods for analyzing FE were used, including conventional and new approaches. First, we scored the seven FEs separately. Subsequently, the scores of the seven FEs were added (SUM). Subsequently, principal component analysis (PCoA) was performed using the scores of the seven FEs obtained using the first method. Afterwards, weights were created for each FE based on each variable’s contribution variability obtained from the PCoA (SUM.W). Finally, we applied a general score to the animal’s face (GFS). The horses were filmed before and 24 and 48 h after implantation. The tissue sensitivity to mechanical stimulation and skin temperature of the horses were assessed at the same time points. The results show no changes in the FEs analyzed separately or jointly. The horses with incision and suture but no polymer implant displayed a higher pain-related FE 48 h after implantation, while the horses implanted with polymers displayed more apparent alterations in the mechanical skin sensitivity and temperature. Our findings show that the five statistical methods used to analyze the faces of the horses were not able to detect low-grade inflammatory pain.

Abstract

Facial-expression-based analysis has been widely applied as a pain coding system in horses. Herein, we aimed to identify pain in horses undergoing subcutaneously polylactide-based polymer implantation. The sham group was submitted only to surgical incision. The horses were filmed before and 24 and 48 h after implantation. Five statistical methods for evaluating their facial expressions (FEs) were tested. Primarily, three levels of scores (0, 1, and 2) were applied to the seven FEs (ear movements, eyebrow tension, orbicularis tension, dilated nostrils, eye opening, muzzle tension, and masticatory muscles tension). Subsequently, the scores of the seven FEs were added (SUM). Afterwards, principal component analysis (PCoA) was performed using the scores of the seven FEs obtained using the first method. Subsequently, weights were created for each FE, based on each variable’s contribution variability obtained from the PCoA (SUM.W). Lastly, we applied a general score (GFS) to the animal’s face (0 = without pain; 1 = moderate pain; 2 = severe pain). The mechanical nociceptive threshold (MNT) and cutaneous temperature (CT) values were collected at the same moments. The results show no intra- or intergroup differences, when evaluating each FE separately or in the GFS. In the intragroup comparison and 48 h after implantation, the control group showed higher values for SUM, PCoA, and SUM.W, although the horses implanted with polymers displayed more obvious alterations in the CT and MNT. Our findings show that the five statistical strategies used to analyze the faces of the horses were not able to detect low-grade inflammatory pain.

Comparative Study of the Sedative and Anti-nociceptive Effects of Sacrococcygeal Epidural Administration of Romifidine, Lidocaine, and Romifidine/Lidocaine in the Dromedary Camel

In a randomized prospective study, comparative sedative and anti-nociceptive effects of epidural administration of romifidine (RO), lidocaine (LD), and a combination of romifidine-lidocaine (ROLD) in camel were evaluated. Eighteen healthy adult dromedary camels were assigned randomly to three treatment groups (n = 6), each receiving 50 μg/kg of RO, 0.30 mg/kg of LD, or a combination of both RO and LD. All treatments were expanded in 0.9% sterile normal saline solution to a final dose volume of 20 ml and administered directly into the sacrococcygeal space. After epidural injection of each treatment, the onset time, duration, anatomical extension of anti-nociception, and sedation were documented. Anti-nociception was tested at different areas using a pinprick test and artery forceps pinching at the perineum and inguinal area. RO and ROLD treatments resulted in mild to severe sedation and complete bilateral analgesia with loss of sensation in the tail, perineum, scrotum in males, vulva in females, the caudal aspect skin of the upper hind limb, and inguinal region (udder in females and the prepuce in males). The anatomic extent of anti-nociception reached the chest cranially and the footpad distally. Camels who received LD showed the shortest duration (P &lt; 0.001) to the onset of perineal anti-nociception (3.67 ± 0.33 min) followed by those who received RO LD (4.00 ± 0.37 min) and RO (6.67 ± 0.33 min), respectively. RO and ROLD resulted in significantly (P &lt; 0.001) longer periods of analgesia (158.33 ± 4.01 min and 165 ± 3.87 min, respectively) than LD (75.83 ± 3.27). An epidural RO and ROLD would appear to produce a very effective and acceptable anti-nociceptive effect in the perineal and inguinal regions of camels.

Nociceptive pain and anxiety in equines: Physiological and behavioral alterations

Pain and anxiety are two of the most important concerns in clinical veterinary medicine because they arise as consequences of multiple factors that can severely affect animal welfare. The aim of the present review was to provide a description and interpretation of the physiological and behavioral alterations associated with pain and anxiety in equines. To this end, we conducted an extensive review of diverse sources on the topic. The article begins by describing the neurophysiological pathway of pain, followed by a discussion of the importance of the limbic system in responses to pain and anxiety, since prolonged exposure to situations that cause stress and pain generates such physiological changes as tachycardia, tachypnea, hypertension, hyperthermia, and heart rate variability (HRV), often accompanied by altered emotional states, deficient rest, and even aggressiveness. In the long term, animals may show deficiencies in their ability to deal with changes in the environment due to alterations in the functioning of their immune, nervous, and endocrinologic systems. In conclusion, pain and anxiety directly impact the homeostasis of organisms, so it is necessary to conduct objective evaluations of both sensations using behavioral scales, like the horse grimace scale, complemented by assessments of blood biomarkers to analyze their correlation with physiological parameters: Heart rate, respiratory rate, HRV, theparasympathetic tone activity index, lactate and glucose levels, and temperature. Additional tools - infrared thermography, for example - can also be used in these efforts to improve the quality of life and welfare of horses.

Heat hypersensitivity at a site proximal to a surgically induced osteochondral fracture in horses

OBJECTIVE

To evaluate thermal nociceptive thresholds (TNTs) before and after inducing a standardized radiocarpal bone osteochondral fracture (OCF) in horses.

STUDY DESIGN

Prospective, controlled, randomized, masked study.

ANIMALS

A group of 10 Thoroughbred fillies aged 2 years.

METHODS

Skin temperature and TNTs were measured on the skin over the triceps brachii muscle in both the thoracic limbs before (week 0) and weekly (weeks 1-8) after unilateral arthroscopic induction of a radiocarpal OCF (n = 4) or sham surgery (n = 6) followed by a standardized exercise programme. The contralateral, non-operated thoracic limb was used as a control within each horse. Percentage thermal excursion (%TE) defined as %TE = 100 ∗ (TNT - skin temperature)/(cut-off temperature - skin temperature) was calculated. Data were analysed with a mixed-effects model followed by Dunnett's and Tukey's tests for within and between-limbs comparisons, respectively; p < 0.05 was considered significant.

RESULTS

Skin temperature in the control limb of OCF horses was significantly higher at week 7 than at week 0 (p = 0.0125). At week 1, TNTs and %TE values in operated limbs of OCF horses were significantly reduced compared with their baseline values at week 0 (p ≤ 0.0153) and their values in contralateral control limbs (p ≤ 0.0024) and operated limbs of sham-operated horses (p ≤ 0.0162). At week 2, TNTs and %TE values in operated limbs of OCF horses remained significantly reduced compared with values in operated limbs of sham-operated horses (p ≤ 0.0248).

CONCLUSIONS AND CLINICAL RELEVANCE

Creation of an OCF in a radiocarpal bone induced transitory (<2 weeks) ipsilateral heat hypersensitivity proximal to the surgery site (skin over the triceps brachii muscle) in horses. Surgically induced OCF may cause somatosensory abnormalities consistent with secondary thermal hyperalgesia.