Adcock, S., Tucker, C. B. 2020. Conditioned place preference reveals ongoing pain in calves 3 weeks after disbudding. Scientific Reports 10(1), 3849.
Hot-iron disbudding, a routine procedure that prevents horn bud growth through cauterization, is painful for calves. The resulting burns remain sensitive to touch for weeks, but it is unknown whether calves experience ongoing, non-evoked pain. We evaluated conditioned place preference for analgesia in 44 calves disbudded or sham-disbudded 6 hours (Day 0) or 20 days (Day 20) before testing (n = 11/treatment). Calves were conditioned to associate the effects of a lidocaine cornual nerve block with the location and pattern of a visual stimulus, and a control injection of saline with the contrasting stimulus. On Day 0, disbudded calves tended to prefer the lidocaine-paired stimulus over the saline-paired one, suggesting that they found analgesia rewarding. On Day 20, sham calves avoided the lidocaine-paired stimulus, consistent with humans’ experience of this drug being painful. Disbudded calves on Day 20 did not show this aversion, suggesting that they traded off the short-term pain of the lidocaine with the longer-term analgesia provided. Day 0 sham calves did not avoid the lidocaine-paired stimulus, likely because they received less than half the dose of Day 20 calves during conditioning. Thus, higher doses of lidocaine are aversive to uninjured animals, but disbudded calves are willing to engage in this cost. We conclude that calves experience ongoing pain 3 weeks after disbudding, raising additional welfare concerns about this procedure.