Effect of Tranquilization or Sedation on the Gait of Lame Horses

Opioid-free sedation for atlantoaxial cerebrospinal fluid collection in adult horses

BACKGROUND

Atlantoaxial (AA) cerebrospinal fluid (CSF) collection in standing horses utilizes the controlled narcotic morphine, thereby limiting feasibility in field practice settings.

OBJECTIVES

To compare AA CSF collection time and reaction scores in horses sedated with morphine-containing and opioid-free sedation protocols: detomidine + morphine (DM), detomidine + xylazine (DX), detomidine + detomidine (DD), detomidine alone (D0); To develop a novel method for assessing sedation in standing horses using open-source motion-tracking software.

ANIMALS

Six healthy adult horses.

METHODS

Randomized crossover. Atlantoaxial CSF collections were performed weekly for 4 weeks. Horses received sedation protocols in random order. Procedure time and procedure reaction scores were compared between groups using Friedman test. Associations between procedure reaction scores and motion tracking variables (total distance and farthest excursion traveled by horse's head) were examined using scatter diagrams.

RESULTS

Procedure times were D0 (median = 120 seconds, range XXXX), DM (48, range xxx to yy), DX (36 range), or DD (49, range); (P = .25). Procedure reaction scores were lower in horses sedated with DX (median score = 1.0, range xx to yy), compared to DD (2.8; range cc to vv, P = .04) or DO (3.0 range; P = .01). Reactions to dura mater puncture were recorded in 3 of 6 horses in D0 and DD groups, and 0 of 6 horses in DX and DM groups. Positive associations were observed between reaction score vs total distance or farthest excursion distance from baseline.

CONCLUSIONS AND CLINICAL IMPORTANCE

Both opioid-free and morphine-containing sedation protocols are acceptable for AA CSF collection. Motion-tracking software represents a novel method for assessing sedation in standing horses.

Tranquilizer effect on the Lyapunov exponents of lame horses

Tranquilization of horses with acepromazine has been used to suppress erratic head movements and increase the accuracy of a lameness examination. Some equine clinicians believe that tranquilization with acepromazine will make lameness more evident by causing the horse to focus on adjusting its gait to avoid limb pain rather than its surroundings. The aim of this study was to investigate the effect of acepromazine on the Lyapunov exponents of lame horses. Ten lame horses were trotted in a straight line for a minimum of 25 strides. Kinematic data created by head movement were analyzed. Nonlinear analysis methods were applied to lame horse locomotion. The effect of acepromazine on the largest Lyapunov exponents of the lame horses were investigated. There was no statistically significant effect of acepromazine on the maximum value of Lyapunov exponents. The nonlinear dynamic methods can be used to analyze the gait in horses. Local stability of horse gait remains unchanged after the administration of acepromazine.

Effects of acepromazine and xylazine on subjective and objective assessments of forelimb lameness

BACKGROUND

To facilitate lameness evaluation, sedatives such as xylazine and acepromazine are regularly used in the clinical setting, despite concerns that they may confound lameness assessment.

OBJECTIVES

The objective of this study was to determine the effect of low doses of acepromazine and xylazine on subjective and objective lameness assessment.

STUDY DESIGN

Randomised, blinded, crossover study.

METHODS

Six horses with experimentally induced solar pain were evaluated over a 1-hour period after treatment with intravenous xylazine (0.1 or 0.2 mg/kg), intravenous acepromazine (0.02 or 0.04 mg/kg), intravenous saline (1 mL) or local analgesia (4 mL 2% mepivacaine administered subcutaneously). Lameness was assessed objectively with inertial sensors and subjectively on a scale from 0 to 5. Lameness assessments were compared with logistic regression analysis to account for the repeated measures and cross-over study design (P < .05).

RESULTS

Xylazine (0.1 and 0.2 mg/kg) or acepromazine (0.02 and 0.04 mg/kg) did not result in significant differences in objective lameness assessment (vector sum) or average subjective lameness grade. Local analgesia was associated with a decrease in subjective lameness grade (OR 0.32 [0.11-0.92], P = .03). Objective measures of lameness (vector sum) were significantly decreased 45 minutes (vector sum 41.8, P = .04) and 60 minutes (vector sum 47.3, P = .03) following local analgesia administration compared with baseline (vector sum 121.4).

MAIN LIMITATIONS

Extrapolation of the experimental model of moderate lameness used in this study to broad range of clinical lameness situations should be performed carefully.

CONCLUSIONS

These results support the use of low doses of xylazine or acepromazine to facilitate forelimb lameness evaluation up to 1 hour in duration.

Evaluation of the effects of commonly used α2-adrenergic receptor agonists alone and in combination with butorphanol tartrate on objective measurements of lameness in horses

OBJECTIVE

To determine the effects of 3 α₂-adrenergic receptor agonists (α₂-ARAs), alone or in combination with butorphanol tartrate, on objective measurements of lameness in horses.

ANIMALS

17 adult polo horses with naturally occurring forelimb or hind limb lameness (or both).

PROCEDURES

In a crossover design, each horse received each protocol (saline [0.09% NaCl] solution [2 mL, IV] or xylazine hydrochloride [0.33 mg/kg, IV], detomidine hydrochloride [0.007 mg/kg, IV], or romifidine hydrochloride [0.033 mg/kg, IV] alone or in combination with butorphanol [0.007 mg/kg, IV]) in random order, with a washout period (≥ 7 days) between protocols. Horses were assessed immediately prior to (baseline) and 10, 15, 20, 30, and 40 minutes after administration of each protocol for degree of sedation, mechanical nociceptive threshold (MNT), and objective lameness measurements.

RESULTS

Compared with baseline values, sedation scores and MNTs were significantly higher at all evaluated time points following administration of all sedation protocols except xylazine alone; following administration of xylazine alone, sedation scores and MNTs were significantly higher at ≤ 30 minutes and ≤ 20 minutes, respectively. Significant differences in objective forelimb lameness measurements were noted after administration of the 3 α₂-ARA-butorphanol combinations. Most significant differences in objective measurements of hind limb lameness were detected after administration of detomidine or romifidine, alone or in combination with butorphanol.

CONCLUSIONS AND CLINICAL RELEVANCE

In the study horses, xylazine alone had the least impact on objective lameness measurements. The administration of α₂-ARAs, particularly detomidine or romifidine, alone or in combination with butorphanol, resulted in small but significant effects on objective lameness measurements.

A kinematic comparison of the locomotor pattern of horses sedated with detomidine alone and in combination with low doses of butorphanol

BACKGROUND

Chemical restraint is often used to perform diagnostic and minor surgical procedures; α₂ -adrenoceptor agonists are the most commonly used drugs; however, the combination with an opiate can induce a profound sedation. There is a lack of kinematic studies examining the effects of the combination of these drugs on locomotor patterns.

OBJECTIVES

The objective of the study was to evaluate the duration of the effects of sedation with detomidine and detomidine combined with a low dose of butorphanol on the movement patterns of horses.

STUDY DESIGN

The study was a controlled, randomised, blinded and crossover experiment.

METHODS

Each of six horses was injected intravenously with saline (0.9%) solution (10 mL), detomidine diluted in saline solution (0.01 mg/kg bwt) or a combination of detomidine (0.01 mg/kg bwt) and butorphanol (0.02 mg/kg bwt) diluted in saline solution, in a random order. A single accelerometer positioned at the sacrum was used for gait assessment 15 min before (baseline) and 5, 15, 30, 45, 60, 75, 90, 105 and 120 min after each injection. Eight variables were measured, including speed, stride frequency, stride length, regularity, dorsoventral power, propulsive power, mediolateral power and total power; force of acceleration and the three components of power were calculated. The degree of sedation was measured by the ground-to-lip distance.

RESULTS

There were significant differences among groups, with shorter effects after the injection of the combination of drugs, for most parameters.

MAIN LIMITATIONS

A small number of horses were involved in the study.

CONCLUSIONS

The combination of detomidine and butorphanol produces a shorter effect on almost all accelerometric parameters, probably due to the excitement produced by the opioid drug causing a quicker return to normal values. Accelerometry offers a method of objectively monitoring gait abnormalities in walking sedated horses.