Morphine has significant clinical and analgesic effects in horses, but its impact on the gastrointestinal tract requires further understanding. This study assessed the analgesic and gastrointestinal effects of morphine in horses undergoing elective orchiectomy in the quadrupedal position. Thirty uncastrated male horses were randomly assigned to three groups: orchiectomy without morphine and sedation protocol (OSM), orchiectomy with morphine and sedation protocol (OM), and administration of morphine alone in the absence of orchiectomy (M). The anesthetic protocol involved acepromazine (0.05 mg/kg IV) and detomidine (10 mcg/kg IV) sedation in groups OSM and OM, with morphine sulfate (0.05 mg/kg IV) given to OM and M, and NaCl to OSM. The team measured clinical parameters, pain, and sedation using the EQUUS-FAP scale, while they monitored bowel motility and gastric dilation through abdominal ultrasound. These assessments were performed on the previous day (m1), 20 min before surgery (m2), and at various time points following the administration of morphine or saline solution: one hour (m3), two hours (m4), four hours (m5), six hours (m6), and eight hours (m7) post-procedure for all three groups. There was no significant difference in pain score between OSM and OM, though OM had better sedation. Ultrasound revealed decreased colon contractions and minor gastric dilation in OSM and OM, normalizing within 6 h. Group M showed reduced motility and significant gastric dilation lasting 8 h. In conclusion, while morphine enhanced sedation without causing greater gastrointestinal dysfunction than OSM, its administration alone resulted in a more pronounced reduction in gastrointestinal motility and an increased risk of gastric dilation.

A multimodal approach is recommended to optimize perioperative pain control in animals, although opioid use in horses remains limited due to the risks of central nervous system (CNS) stimulation and reduced intestinal motility. A group of 19 healthy, male, mixed-breed horses were divided into two groups and medicated with acepromazine (0.05 mg kg⁻¹) and detomidine (10 µg kg⁻¹), with methadone (0.05 mg kg⁻¹) (ADM) or saline (ADS) administered intravenously (IV). Physiological variables, intestinal motility, gastric distention, and facial pain (EQUUS-FAP) were evaluated one day before (DB), before the surgical procedure (BS), and at 1, 2, 4, 6, and 8 h (T1h–T8h) after administration (ADM-ADS). Results are presented as means with standard deviation or medians with an interquartile range. Analysis of variance, the Mann–Whitney, and Durbin tests were applied (p < 0.05). Intestinal motility was reduced at T1h and T2h, returning to baseline by T6h and T8h in both groups. Ultrasonographic examination revealed reduced motility, with less significant changes in the left ventral colon (LVC), right ventral colon (RVC), and cecum. Gastric dilatation was more pronounced in the ADM group at T1, 4, 6, and 8h. EQUUS-FAP scores were significantly lower in ADM at T2, 4, and 6h. ADM protocol may aid chemical restraint and analgesia without increasing hypomotility.

The objective was to compare the linear, spatial, and temporal variables of the Marcha Batida (MB) and Marcha Picada (MP) gaits, aiming to characterize and identify their differences. 135 ridden Mangalarga Marchador horses were evaluated. The following variables were measured: speed, length, frequency, and duration of strides; distribution of stride time in each type of support; time and position of the diagonal dissociation; type and distance of the lateral limb footprints. At the same speed (3.88 m/s), MB and MP presented the same frequency, duration, and length of strides. MB showed a predominance of diagonal supports, followed by thoracic tripedal, pelvic tripedal, lateral bipedal, quadrupedal and pelvic monopedal supports, while MP showed a predominance of lateral supports, followed by diagonal supports, thoracic and pelvic tripedal supports, and pelvic unipedal support. All MP animals showed dissociation starting with the thoracic limb and were more dissociated than the MB. Most MB horses showed overstepping, while in the MP, the predominance was of animals with overstepping and an average distance of 17.68 centimeters. It is concluded that MB and MP presented differences in the kinematic variables analyzed, and the values found showed divergence from the description of the current breed standard.