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

The aim of this study was to evaluate the acute and longer-term behavioural and physiological responses caused by administering clove oil under the horn bud of calves and compare these with the responses caused by cautery disbudding. Forty female Friesian-cross calves (mean ± SD: 3.5 ± 2.72 d of age) were allocated to one of four treatments (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). Lying behaviour was recorded continuously using accelerometers, while other behaviours were recorded from video for the same 2 h periods on 3 days relative to treatment: baseline (day before), D0 (0-24 h after) and D1 (24-48 h after). Pain sensitivity adjacent to the horn bud was measured using pressure algometry, and blood samples were collected to measure complete blood cell counts and serum amyloid A concentrations, before and 48 h after administration of treatments. CAUT calves tended to perform more head shakes than CON and CLOV calves during the first 2 h after treatment (change from baseline, no./2 h: CON: −0.3, CAUT: 4.7, LA + CAUT: 3.0, CLOV: −0.4, SED = 2.33, P = 0.096). Compared to baseline, CLOV calves spent less (P < 0.05) time head rubbing than LA + CAUT calves on D0, however, on D1 all treatments rubbed their heads less (P < 0.05) compared to CON calves. Compared to baseline, CAUT and LA + CAUT calves spent less (P < 0.05) time running than CON calves on D0, but the time spent running did not differ between CON and CLOV calves. Mean daily lying times after administration of treatments were greater in CLOV compared to CON and CAUT calves, and CLOV and LA + CAUT calves did not differ (change from baseline (min/24 h): CON: −14.8, CAUT: 25.1, LA + CAUT: 64.2, CLOV: 94.8, SED = 31.77; P = 0.016). Overall, all treatments displayed more sensitivity in response to pressure algometry than CON calves (change from baseline (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 blood constitutes. Our results suggest that injecting clove oil under the horn bud was initially less painful, and in the 48 h after treatment, did not cause more pain than cautery disbudding. Unlike cautery disbudding, injecting clove oil does not involve tissue removal nor is there a risk of thermal damage to the brain. Therefore, clove oil could be an alternative to cautery disbudding, if this method is found to efficaciously prevent horn growth.