Efficacy of xylazine in neonatal calves via different routes of administration.

Intramuscular (IM) injections may be more aversive than subcutaneous (SC) and intra-nasal (IN) routes. Xylazine is commonly used as a sedative for cattle, but little is known about efficacy via these routes. The first aim of this study was to compare efficacy using these different routes of administration. The second aim was to determine whether a simple behavioural assessment was associated with physiological responses. Using a within-subject design, the effects of xylazine (0.2mg/kg) were assessed in 12 Holstein calves (6.2±2.8days old) administered via IM, SC, IN drip tube (IN) and IN spray (INs). Sedation was assessed on a scale based on recumbency and eyeball rotation. Heart rate (HR), respiratory rate (RR) and rectal temperature (RT) were recorded for 2h after treatment. Intramuscular and SC routes produced an equivalent mean±standard deviation (SD) onset of sedation (IM: 4.8±2.0min vs. SC: 6.8±2.2min) and duration of sedation (IM: 60.3±25.5min vs. SC: 61.9±23.3min). IN treatments produced less consistent and longer onset times (IN: 33.0±26.9min, and INs: 31.0±15.1min) and a shorter duration of sedation (IN: 42.0±31.5min, and INs: 26.7±21.8min). Behaviour scores were moderately correlated with changes in HR (r=-0.52; CI -0.60, -0.43) and changes in RR (r=-0.42; CI -0.51, -0.32), but not with changes in RT (r=-0.09, CI -0.20, 0.02). We conclude that SC is a viable alternative to the more aversive IM route, and that a simple clinical scale can be useful for assessing xylazine sedation.