Antinociceptive and selected physiological effects of morphine and xylazine on tiletamine-zolazepam anesthesia in llamas

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Abstract

Objective

Evaluate antinociception, anesthesia, and recovery in llamas given tiletamine-zolazepam (TZ) with either morphine, xylazine, morphine and xylazine, or saline.

Study design

Randomized crossover experimental study.

Animals

Six healthy, adult intact male llamas.

Methods

Llamas were given each of four treatments intramuscularly with a 1-week washout: TZ (2 mg kg−1) combined with either morphine (0.5 mg kg−1; M), xylazine (0.15 mg kg−1; X), morphine (0.5 mg kg−1) and xylazine (0.15mg kg−1) (MX), or saline (C). Llamas breathed room air during the experiment. Characteristics of anesthesia, recovery, and selected cardiopulmonary variables were recorded. Antinociception was assessed by clamping a claw at 5-minute intervals. Data were analyzed using a mixed-model anova and Tukey-Kramer test, and are expressed as least squares mean ± SEM. Significance was set at p < 0.05.

Results

No llama in the control group demonstrated antinociception. Antinociception was longest with treatment MX, followed by treatments X and M, respectively. Heart rates in llamas given treatments X and MX were significantly lower than with other treatments. The respiratory rate in llamas given treatment C was greater (p < 0.05) than for all other treatments, however, the respiratory rate was not significantly different among treatments X, M and MX. The PaO2 for llamas given MX remained <60 mmHg throughout the 20 minute period of blood gas analysis. Mean arterial blood pressure in llamas in treatment MX was less than for treatments M or C.

Conclusion and clinical relevance

The combination of morphine (0.5 mg kg−1) and xylazine (0.15 mg kg−1) increased the duration of antinociception compared with xylazine alone, in TZ-anesthetized llamas. Treatments X, M and MX were associated with hypoxemia (PaO2 < 60 mmHg).

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