Behavioural and physiological responses to clove oil injected under the horn bud of calves

The aim of this study was to evaluate the behavioural and physiological responses caused by administering clove oil into the horn bud region of calves and compare them with the responses to cautery disbudding. At approximately 1 wk of age, 40 female Friesian-cross calves were allocated to one of four treatment groups (n = 10 calves/treatment): 1) control handling (CON), 2) administration of 0.5 mL of clove oil under each horn bud (CLOV), 3) cautery disbudding (CAUT) or 4) local anaesthetic plus cautery disbudding (LA+CAUT). Behaviour was video recorded continuously for 24 h before (baseline, D-1) and 48 h after administration of treatments. Additionally, lying behaviour was recorded continuously using accelerometers. Pain sensitivity adjacent to the horn bud was measured using pressure algometry before and 48 h after administration of treatments. Blood samples were collected before and 48 h after administration of treatments to measure complete blood cell counts and serum amyloid A concentrations. Compared to D-1, CLOV calves spent less time head rubbing than LA+CAUT calves on D0 (0 to 24 h after treatment; P < 0.05). All disbudding treatments (CAUT, LA+CAUT and CLOV) spent less time head rubbing compared to CON calves on D1 (24 to 48 h after treatment; P < 0.05). Compared to D-1, CAUT and LA+CAUT calves spent less time running than CON calves on D0, but the time spent running did not differ between CON and CLOV calves (P = 0.053). Compared to D-1, CLOV calves spent more time lying than CON and CAUT calves over the entire 48 h post-treatment period, however lying times did not differ between CLOV and LA+CAUT calves (change [48 h post-treatment – D-1] in lying time (min/24 h): CON: -14.8, CAUT: 25.1, LA+CAUT: 64.2, CLOV: 94.8, SED = 31.77; P = 0.016). CAUT, LA+CAUT and CLOV calves displayed more sensitivity in response to pressure algometry than CON calves (change [48 h post-treatment – D-1] in mechanical nociceptive threshold (kg of force): CON: -0.3, CAUT: -2.2, LA+CAUT: -1.8, CLOV: -1.5, SED = 0.46; P = 0.003). There was no treatment effect on any blood constitutes measured. Overall, our results suggest that injecting clove oil into the horn bud region did not cause more pain than cautery disbudding. Moreover, unlike cautery disbudding, injecting clove oil did not involve tissue removal or the risk of thermal damage to the brain. Therefore, if this method is found to efficaciously prevent horn growth it may provide an alternative to cautery disbudding.