Correction

is probably the most widely used opioid in general equine practice. Corletto and others (2005) showed that butorphanol improved the quality of sedation and surgical conditions for field castration in ponies. However, butorphanol is an antagonist at the μ opioid receptor and exerts its effects through the κ opioid receptor. Its analgesic efficacy is therefore considered lower than that of the μ agonists. At the same time, at clinically relevant doses, the duration of its analgesic action is short (Kalpravidh and others 1984). In the UK, buprenorphine, a partial μ agonist opioid, has received market authorisation for use in horses that are not intended for human consumption (October 2013). Although its use in horses had already been described by Nolan and Hall (1984), a multitude of additional studies has been published over the past few years. Buprenorphine was shown to provide superior analgesia compared to butorphanol in a thermal threshold model (Love and others 2012) and compared to placebo in the postoperative period after castration in ponies (Love and others 2013). The latter observation is consistent with reports on the pharmacokinetics and pharmacodynamics of buprenorphine, which suggest a duration of analgesic action of six to 12 hours (Carregaro and others 2007, Love and others 2014). Conflicting results have been reported on the effects of buprenorphine on the quality of sedation with detomidine. Buprenorphine did not seem to improve the level of sedation obtained with detomidine, and at higher doses actually reduced the degree of sedation in a study by Love and others (2011), while a more recent study showed that buprenorphine enhanced and prolonged the sedation produced by detomidine (Taylor and others 2014). When administered epidurally in combination with detomidine in horses undergoing stifle arthroscopy, buprenorphine provided similar intraand postoperative effects to morphine (Fischer and others 2009). However, epidural morphine seemed to be a more effective analgesic with a longer duration of action than epidural buprenorphine in a synovitis model of the thoracic limb in ponies (Freitas and others 2011). A study by Rigotti and others (2014), summarised on p 623 of this issue of Veterinary Record, further investigated the effects of buprenorphine in equids. The results are relevant as the effects of the only two opioids that are licensed for equine use in the UK, that is, butorphanol and buprenorphine, were compared in ponies undergoing the most commonly performed surgical procedure in this species. The results indicated that ponies that received buprenorphine before induction of anaesthesia required less supplementary ketamine and rescue drugs than those which had received butorphanol, suggesting better intraoperative analgesia with buprenorphine. At the same time, a higher level of locomotor activity after anaesthesia was observed in the buprenorphine group, but this consisted of only moderate walking, without excitement or dangerous behaviour. Traditionally, there have been concerns about the use of opioids in horses, mainly because early studies reported excitation after administration of high doses of opioids in healthy horses (Combie and others 1979), as well as reduced propulsive gastrointestinal motility, while most studies had not provided convincing evidence that systemically administered opioids consistently and effectively relieved pain in horses (Bennett and Steffey 2002). However, in a review that included more recent literature, Clutton (2010) illustrated a widening role for opioid analgesics in equine pain management. The study by Rigotti and others (2014) indeed supports the perioperative use of the μ agonist buprenorphine in ponies or horses. These results are encouraging for future research on the effects of opioids in equids.