Abstract
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.
Highlights
Hot-iron disbudding, a routine procedure that prevents horn bud growth through cauterization, is painful for calves
A place conditioning paradigm has been used to demonstrate that calves will avoid an area where they experienced disbudding without post-operative pain control compared to an area where they received a sham procedure[10] or were disbudded with the use of an NSAID11
We assessed whether a conditioned place preference test would reveal ongoing pain in the hours immediately after disbudding (Day 0), and 3 weeks later, during healing (Day 20)
Summary
Hot-iron disbudding, a routine procedure that prevents horn bud growth through cauterization, is painful for calves. A common disbudding practice is to cauterize the horn-growing tissue with a heated iron when calves are 0 to 2 months of age This procedure is unequivocally painful; the post-operative period is associated with wound-directed behaviors such as ear flicks, head shakes, and head rubbing, as well as physiological changes including increased plasma cortisol and heart rate. Given its important implications for cattle welfare, research is needed to address whether calves experience ongoing pain in the weeks after disbudding Operant measures, such as the conditioned place preference paradigm, have been developed to unmask ongoing pain in rodent injury models. This paradigm is based on the premise that an animal will choose to spend more time in an environment in which a previously rewarding experience (e.g., administration of pain relief) occurred[8]. Since wounds vary in healing time[4,5], we documented the tissue types present in the wound bed to verify the healing stage at these timepoints
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