The aim of this study was to compare the effects of subarachnoid administration of hyperbaric solutions of bupivacaine or ropivacaine in xylazine-sedated calves undergoing surgery. Subarachnoid anaesthesia was performed with either 20 mg of hyperbaric bupivacaine (bupivacaine group (BG), n=10) or 30 mg of hyperbaric ropivacaine (ropivacaine group (RG), n=10) into the lumbar dural space of 20 calves in a randomised, prospective clinical trial. Systolic (SBP), diastolic (DBP) and mean (MBP) blood pressure, heart rate (HR), respiratory rate, rectal temperature were recorded after sedation (time 0), and up to 120 minutes after injection. Onset, duration and magnitude of sensory block (scale 1–4) were determined using the pin-prick test throughout surgery. Data were analysed using analysis of variance and non-parametric tests (P<0.05). Bodyweight, age, duration of surgery, SBP, DBP, MBP, HR were not significantly different between groups. Onset of anaesthesia (mean±sd; BG, 5±1 minutes; RG, 7±1 minutes) and duration of anaesthesia (mean±sd; BG, 153±32 minutes; RG, 86±12 minutes) were significantly different between groups. Analgesic scores were significantly higher than baseline from 5 to 120 min, and from 7 to 85 min in BG and RG, respectively. Subarachnoid administration of hyperbaric solutions of bupivacaine produced faster onset and longer duration of anaesthesia than ropivacaine.