Morphine with or without Acepromazine in Horses: A Kinematic Evaluation

SIMPLE SUMMARY: Morphine is an opioid agonist drug and produces a significant analgesic effect in horses but besides the evidenced analgesic effect, the use of morphine is not routine due to the potential excitatory effects described in the literature. To minimize these effects, neuroleptanalgesia, or the combination of opioids and sedative drugs, is encouraged. Our aim was to describe changes occurring in the locomotor pattern after co-administration of a tranquilizer, acepromazine, and morphine in horses. Six mature horses were used and received four different treatments with saline solution, morphine, acepromazine, or a combination of morphine and acepromazine. A three-dimensional accelerometric device was used to collect data and objectivize those findings moreover the sedative effect of the treatments was also measured. Significant differences were observed when comparing all the treatments in the majority of accelerometric variables, except the regularity of the pattern, some energetic parameters, and tranquilization. An evident counteraction of the effects caused by both morphine and acepromazine was observed. Due to these effects, the possibility of adding acepromazine to an additional analgesic treatment with morphine in the clinical setting ensures the absence of the supplemental instability caused by other sedatives and minimizes the potential opioid excitatory effects. ABSTRACT: The objective was to demonstrate walking locomotor pattern alterations after co-administration of acepromazine and morphine in horses. Six mature horses receiving four different treatments were used. Treatments consisted of a single dose of saline solution, 0.2 mg/kg bwt of morphine hydrochloride, 0.02 mg/kg bwt of acepromazine maleate, and a combination of 0.2 mg/kg bwt of morphine hydrochloride with 0.02 mg/kg bwt of acepromazine maleate. A three-dimensional accelerometric device was used to collect data. Walking tests were performed 10 min prior to injection, and then at 5, 10, 15, and 20 min after the injection, and then every 10 min for 3 h. Eight variables were calculated including stride kinematic, coordination, and energetic parameters; moreover ground-to-lip distance (GLD), as a tranquilization parameter, was also measured. A significant interaction was observed in all the variables studied but regularity, mediolateral power, the propulsive part of the power, and the GLD. An evident counteraction of the effects caused by both, opioids and phenothiazines, in the gait pattern was observed. The co-administration of acepromazine and morphine could allow a safe opiate administration while minimizing the possible central nervous system (CNS) excitation and reducing potential locomotor adverse effects.