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Objective: Various opioids are available for use in equine medicine. Studies directly comparing their analgesic effects and side effects are rare. Therefore, the aim of this study was to compare the antinociceptive effect and the duration of analgesia of two different doses of morphine, butorphanol and levomethadone in horses., Material and Methods: Eight adult, healthy horses were used for this randomized, placebo-controlled, blinded cross-over trail. Each horse received placebo (P = 0.9% saline) and morphine (M 0.1  = 0.1 mg/kg; M 0.2  = 0.2 mg/kg), butorphanol (B 0.1  = 0.1 mg/kg; B 0.2  = 0.2 mg/kg) and levomethadone (L 0.1  = 0.1 mg/kg; L 0.2  = 0.2 mg/kg) in a low and a high dose and with a wash-out period of 14 days. Thermal thresholds were determined by incremental contact heat applied to the skin at the withers. Single stimulations were performed 15 minutes prior and 10, 30, 60, 90, 120, 180, 240, 300, 360, 420, 540 and 1350 minutes after treatment. Threshold values, gastrointestinal auscultation score and horses' behavior were recorded. Data were analyzed with analysis of variance for repeated measurements (p < 0.05)., Results: In group M 0.1 , changes in thermal thresholds did not reach significance. Thermal threshold increased significantly in the groups M 0.2 , B 0.1 , B 0.2 , L 0.1 and L 0.2 for 240, 90, 90, 60 and 300 minutes, respectively. Behavioural changes, increased locomotion and decreased bowel sounds as well as delayed time until defecation were noticed in all groups., Conclusions: Levomethadone induced a dose-dependent increase and prolongation of analgesia, whereas with butorphanol there was no difference between dosages regarding duration and intensity of analgesia. Morphine provided detectable analgesia only in the high dose of 0.2 mg/kg., Clinical Relevance: Levomethadone and morphine in the low dose (0.1 mg/kg) produced only minor and short lived anti-nociception and further studies are necessary to give a profound dose recommendation for the use of these drugs in horses.

Objective: In most ocular procedures, a central position of the eye is necessary. This can be achieved using a deep plane of anaesthesia, locoregional blocks or with neuromuscular blocking agents. The aim of this study was to evaluate the influence of atracurium on cardiovascular parameters, and on recovery quality and duration in horses., Material and Methods: Thirty-four warmblood horses undergoing in total 50 vitrectomies were divided into two groups. Premedication, induction and maintenance were identical in all patients. After 20 minutes, horses of group A received atracurium (0.1 mg/kg) while in the control group (group K) the depth of anaesthesia was adapted to keep the bulbus in a central position. Dobutamine and fluids were administered to maintain the mean arterial blood pressure (MAP) above 70 mmHg. Cardiac output (CO), heart rate (HR), MAP, respiratory rate, end-expiratory isoflurane concentration (ETIso) and dobutamine requirements were determined. Position and movement of the globe during the surgical procedure were scored. Time and quality of the recovery period was scored., Results: Horses of group K required significantly higher concentrations of isoflurane (group A: 1.08 ± 0.1%; group K: 1.34 ± 0.2%) and had an overall lower MAP (group A: 88.4 ± 10.3 mmHg; group K: 76.6 ± 11.6 mmHg) and CO (group A: 36.9 ± 11.7 l/min; group K: 28.5 ± 7.2 l/min) but needed significantly more dobutamine (group A: 0.37 ± 0.17 μg/kg/min; group K: 0.99 ± 0.46 μg/kg/min) compared to group A. Complete relaxation occurred 9.5 ± 2.5 minutes after atracurium bolus and lasted for 25 ± 7.1 minutes. The score of the bulbus position and movement was significantly lower in group A, resulting in a better quality for the surgical procedure. In group A, the recovery time to standing was significantly shorter (group A: 18.1 ± 5.4 min; group K: 31.5 ± 7.1 min), with no difference in quality., Conclusion and Clinical Relevance: The use of atracurium resulted in a better cardiovascular condition, probably because of the isoflurane-sparing effect. The recovery time was shorter in these horses without negative effects on recovery quality. No signs of residual atracurium effects were detected.