July 15, 2014
Disbudding and dehorning of cattle in the United States is not currently regulated. The Canadian Veterinary Medical Association recommends that disbudding be performed within the first week of life.10 In the United Kingdom, disbudding with a hot iron is preferred to dehorning and it is advised that this should be performed before cattle reach the age of 2 months.11 Application of caustic paste is acceptable in cattle up to 7 days old,12 but anesthesia is required if cattle are dehorned after this period.12,13 Australian and New Zealand authorities recommend disbudding at the youngest age possible, and chemical dehorning is not deemed to be acceptable unless it is performed within the first few days after birth.14-17 In Australia, dehorning without local anesthesia or analgesia is restricted to animals less than 6 months old.2,12 The New Zealand Code of Welfare for Painful Husbandry Procedures mandates a 9 month age limit for dehorning without attention to pain relief.17 The 1992 Animal Rights Law in Sweden requires that dehorning via cautery be performed under anesthesia/sedation.6,12 In Denmark, calves up to 4 weeks old can be dehorned without application of a local anesthetic.12
Dehorning cattle conveys advantages. Horns are the single major cause of carcass wastage due to bruising,16 and trim associated with bruising for carcasses from horned cattle is approximately twice that for carcasses from hornless cattle.12 Dehorned cattle require less feeding trough space; are easier and less dangerous to handle and transport; present a lower risk of interference from dominant animals at feeding time; pose a reduced risk of injury to udders, flanks, and eyes of other cattle; present a lower injury risk for handlers, horses, and dogs; exhibit fewer aggressive behaviors associated with individual dominance; and may incur fewer financial penalties on sale.1,2,8,13,17,19-21
Physiologic and behavioral indicators have been used to assess acute distress responses to potentially painful husbandry procedures. Tissue damage (e.g., from disbudding and dehorning) results in activation and release of intracellular contents from damaged cells, inflammatory cells, and nerve fibers.22 Physiologic, neuroendocrine, and behavioral changes indicative of pain and distress are observed following dehorning.5,23
Physiologic indicators—Although responses vary slightly according to dehorning method, plasma cortisol concentrations increase rapidly 30 to 60 minutes after dehorning, decline slightly, plateau level for 3 to 4 hours, and then return to baseline values approximately 6 to 8 hours after the procedure.24-30 Assessment of the catecholamine (fight or flight) response allows evaluation of the acute responses to painful procedures, but this response is short-lived and relevant only to the earliest phases of the distress response.26 Adrenaline (epinephrine) concentration was increased 5 minutes after scoop dehorning of 10-week-old calves, was not affected by use of local anesthesia, and returned to baseline within 10 minutes.26 Noradrenaline (norepinephrine) concentrations may also rise due to tissue release of noradrenaline in response to injury; increased noradrenaline concentrations were observed 10 minutes after dehorning, but had returned to baseline levels within 60 minutes.26 Eye temperature drops either during dehorning or after local anesthesia wore off due to sympathetic activity leading to vasoconstriction and redirection of the blood.
Sedation—Although sedation with xylazine and/or butorphanol reduced the occurrence of avoidance behaviors during disbudding/dehorning, sedation alone was not effective in reducing the cortisol response to hot-iron disbudding.43 Cortisol may not be a reliable indicator of stress in xylazine-sedated calves and xylazine alone does not effectively control pain from hot-iron disbudding.44 Calves administered sodium salicylate in conjunction with a xylazine/ketamine/butorphanol (XKB) mixture spent more time lying down post-surgery than those that received only XKB.45 The addition of ketamine to more traditional chemical restraint formulas (“ketamine stun”) can increase patient cooperation, and has been shown to lower stress response to both dehorning and castration in calves. These sedative techniques may be more stably administered via constant-rate or drip infusion than by bolus injection.46
Cauterization—Cauterization of the wound following scoop dehorning with a local anesthetic virtually abolished the cortisol response for 24 hours in 3- to 4-month-old calves.47 In addition, blood loss was minimal and no complications were observed during wound healing. Cauterization after scoop dehorning of 5- to 6-month-old calves produced a transient rise in plasma cortisol concentration associated with the pain of the cautery procedure; however, when combined with local anesthesia, the cortisol response was virtually abolished throughout the 9-hour postoperative observation period.43
Local anesthesia—Many sources now recommend that local anesthesia be provided. Anesthesia reduces avoidance behaviors during the disbudding/dehorning procedure.12,20,48 Investigation of the benefits of local anesthesia (in the form of a preoperative cornual nerve block with lidocaine or bupivicaine) has produced conflicting results. Local administration of lidocaine prior to electric dehorning of 7- to10- and 14- to 16-week-old calves did not significantly reduce plasma cortisol levels, suggesting that the anesthetic did not reduce stress associated with dehorning.49 McMeekan et al25 observed that local anesthesia prevented an increase in plasma cortisol concentrations in 3- to 4-month-old calves undergoing dehorning only for the duration of effect of the anesthetic; once the anesthetic wore off, a marked increase in plasma cortisol concentrations was observed. Similar results were observed in 6- to 8-week-old calves,8 10-week-old calves,26 and 3- to 4-month-old calves.34 Local anesthesia virtually abolished behavioral indicators of pain for the duration of its action; after the anesthetic wore off, however, calves displayed behavioral changes similar to those displayed by calves dehorned without local anesthesia. Overall cortisol response was not significantly reduced, but a rise in plasma cortisol concentrations was delayed by administration of bupivicaine; preoperative administration of bupivicaine attenuated the increase in cortisol concentrations for 4 hours, but a marked rise in plasma cortisol concentration was observed once the effects of the bupivicaine wore off.37 Administration of bupivicaine locally prior to scoop dehorning, followed by a second dose 4 hours later almost abolished the cortisol response for 8 hours.50 Application of local anesthetic prior to disbudding/dehorning with caustic paste did not attenuate behavioral indicators of distress, possibly because the basic pH of the caustic paste negatively affected the action of the local anesthetic.5 Disbudding using caustic paste in 10- to 35-day-old calves resulted in fewer behavioral changes than disbudding using a hot iron.5 Recently, a preoperative cornual nerve block with 100% ethanol has been shown to provide superior analgesia when compared to a cornual nerve block with 2% lidocaine.51
Analgesia—Administration of nonsteroidal anti-inflammatories (NSAIDs) results in prolonged postoperative analgesia.22 Oral administration of ketoprofen prior to and 7 hours after hot-iron dehorning of 4- to 8-week-old calves significantly reduced head shaking, ear flicking, and head rubbing for at least 24 hours.13 In addition, the investigators observed a tendency toward greater weight gain on the first day after surgery compared with control calves.13 Calves administered meloxicam at the time of hot-iron dehorning spent more time on average lying down at five52 and ten53 days after surgery when compared with control groups. Intramuscular administration of ketoprofen to 3- to 4-month-old calves prior to scoop dehorning slightly reduced the initial plasma cortisol peak, but abolished the plateau phase.25 Intramuscular administration of ketoprofen to calves 2 days to 2 weeks old produced a slight, transient reduction in cortisol concentration after disbudding with a butane dehorner.19 The investigators speculated that ketoprofen may be more effective in older calves and calves disbudded using other devices. Sodium salicylate administered either alone or in conjunction with sedation (intramuscular xylazine, ketamine, butorphanol), also significantly reduced the cortisol response associated with simultaneous castration and dehorning.54 In addition, sodium salicylate reduced the decrease in ADG from simultaneous castration and dehorning.54 One study has shown that intravenous tramadol alone is not effective in reducing acute pain from dehorning, but may provide late post-operative analgesia by reducing non-acute pain following dehorning.55 The combination of a local anesthetic and ketoprofen administered prior to scoop dehorning of 3-to 4-month-old calves virtually abolished the rise in plasma cortisol concentration routinely observed after dehorning.25 In studies using local anesthesia in conjunction with NSAIDS other than ketoprofen, Meloxicam was found to effectively alleviate pain following dehorning by cauterization,28,56,57 but phenylbutazone31 did not reduce the cortisol response to scoop dehorning. Carprofen combined with local anesthesia can reduce cortisol levels and pain-related behaviors for up to 24 hours after hot-iron disbudding.58 Another study found that flunixin meglumine administered with a local anesthetic effectively reduced pain behavior associated with caustic paste disbudding.59
Availability and use of pharmaceuticals—Although combined use of an anesthetic and analgesic appears to represent the most effective method for controlling pain associated with dehorning, regulatory access and cost remain obstacles to practical application. Studies of pharmaceutical pain management have borne little evidence of increased production yield; however, most of these studies have been too short to permit an adequate assessment. In a survey of producers, the most commonly cited factor for decisions regarding pain mitigation was cost.60 Ketoprofen is not currently FDA-approved for labeled use in livestock in the United States. The only approved NSAID is flunixin meglumine, which has not been demonstrated to have equivalent analgesic efficacy and is approved only for intravenous delivery for the treatment of respiratory disease, mastitis, or endotoxemia. The use of pharmaceuticals can burden producers in terms of both direct and indirect costs; the latter are associated with time delays and a potential need for more veterinary assistance. Extralabel use of anesthetics and analgesics, while potentially an option, is not ideal. Knowledge of effectiveness for these drugs is not as great as it is for drugs approved for particular species and purposes. Extralabel use can also discourage research and development necessary to approve drugs for specific purposes. Extralabel drug use in the United States is only permitted under certain conditions, among which is that the veterinarian is able to establish a necessary meat and/or milk withdrawal period.61
Selection and breeding of polled stock has been proposed as an alternative because it eliminates both animal pain and production expenses associated with dehorning. Polledness is a dominant autosomal trait.12,62,63 that appears in all offspring of homozygous polled bulls. In the past it was believed the production characteristics of horned cattle were intrinsically superior to those of polled cattle. More recent reviews, however, acknowledge that polled individuals have existed in cattle populations throughout recorded history,64 and that polled genes in Bos taurus have a simple inheritance and are apparently not linked to production performance or behavioral traits.65,66 Polled beef bulls already demonstrate behavior,65 growth,67 carcass quality67 and reproductive68 performance62,63,69 equivalent to their horned counterparts. Further work is required with dairy bulls where polled sires are rare in many breeds including Holstein (~1%).70
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