Aims: To evaluate the pharmacokinetics of dexmedetomidine (DEX) administered I/V at a dose of 5 µg/kg bodyweight in dairy calves and to compare the sedative effects of anaesthetic protocols involving DEX and xylazine.
Methods: Nine dairy calves, aged 17-20 days, were treated with 5 µg/kg I/V dexmedetomidine. For pharmacokinetic evaluation, blood samples were collected over 12 hours and serum samples were analysed by high performance liquid chromatography-mass spectrometry. Another nine dairy calves, aged 16-20 days, were treated with 0.2 mg/kg I/V xylazine. After both treatments, heart rate, respiratory rate and rectal temperature were measured for 20 minutes. Sedation quality and recovery times were also assessed.
Results: The kinetics of DEX was best described by a two-compartment model. The distribution and elimination half-lives were 8.7 (SD 5.0) and 83.5 (SD 67.5) minutes, respectively. Mean maximum concentration and body clearance were 12.5 (SD 8.6) ng/mL and 27.9 (SD 13.1) mL/minute/kg, respectively; the mean volume of distribution at steady state was 2,170.8 (SD 1,657.5) mL/kg. A decrease in heart rate was observed after treatments with both DEX and xylazine. No differences in heart or respiration rate, or rectal temperature were observed between the two treatment groups. The onset of sedation occurred after 2.7 (SD 0.67) minutes for calves treated with DEX and 2.8 (SD 0.78) minutes for calves treated with xylazine, and was characterised by a similar degree of deep sedation and ease of handling of the calves. All recoveries were eventless, and no adverse reactions were noted.
Conclusions and clinical relevance: Dexmedetomidine treatment resulted in a reliable and long lasting sedation in calves, a transient decrease in heart rate and no modification in respiratory rate or rectal temperature. The results were comparable to xylazine, the most popular alpha-2-agonist among bovine practitioners. The use of DEX in dairy calves for rapid procedures such as dehorning or castration could be suggested.
Keywords: Dexmedetomidine; dairy calf; pharmacokinetics; sedative effects; xylazine.