In recent years, injection of clove oil was investigated as potential alternative to the use of a hot iron for disbudding due to its cytotoxic and anaesthetic properties. Isoeugenol, the isomer of the main component of clove oil, is available as a pure substance and has some advantages as compared to clove oil, but its effects were studied rarely. In this paper we investigated behaviour, heart rate, heart rate variability and surface temperature around the horn bud of 40 calves in four treatments (N = 10/treatment): injection under each horn bud of 1.5ml clove oil (CLOV), isoeugenol (ISO) or saline (CON), or hot-iron disbudding (BURN) with local anaesthesia and sedation. Behaviour, heart rate (HR) and heart rate variability (HRV) as well as surface temperature around the horn buds were measured before and at different time points after the treatment up to 7 days post treatment; behaviour was also observed during the treatment. Behavioural observations were performed real-time or per video recording. HR and HRV were analysed during undisturbed lying periods and post-treatment changes relative to baseline were calculated. The maximum surface temperature in the region around each of the two horn buds was used for further analysis. LMM, ANOVA or, for behaviour during treatment, non-parametric tests were used for statistical analysis. There was a treatment*time point interaction (LMM, p<0.05) for behaviours associated with pain (ear flicking, head shaking, head scratching) as well as for self-grooming. HR or HRV changes from baseline did not differ between treatments, but sample size was strongly reduced due to lack of data. The development of the maximum surface temperature around the horn buds differed clearly between treatments. Our findings suggest that the injection of clove oil and especially isoeugenol causes less pain compared to the use of a hot iron without analgesia, but more pain compared to the injection of saline solution.

Calves are frequently disbudded to reduce the number of injuries due to horns to other animals and farm workers. The most commonly used method is thermal disbudding which is increasingly causing animal welfare concerns (Stafford and Mellor, 2011; Sutherland et al., 2013, Cozzi et al., 2015). The objective of our study was to evaluate alternative disbudding methods either by injection of clove oil or its synthetic analogue isoeugenol. Forty Simmental calves (26 male, 14 female) aged between 1 and 5 days were treated using 4 different methods (n = 10): injection of 1.5 mL clove oil, injection of 1.5 mL isoeugenol, injection of 1.5 mL isotonic NaCl solution (control group) and thermal disbudding. For thermal disbudding sedation and local anesthesia were legally required. Horn growth of all calves was repeatedly measured. Computer tomography (CT) of the horn bud region and histological examination of biopsy samples taken from the horn bud region were performed. Additionally, saliva cortisol concentrations were measured before and after intervention. Significant differences in horn growth were found between isoeugenol treatment and control group ( P = 0.001), between clove oil treatment and control group ( P = 0.001) and between thermal dehorning and control group ( P < 0.001). After clove oil injection 10/10 calves showed signs of inflammation and swelling of the horn bud region including the upper eye lid area. CT images of animals after thermal disbudding showed complete destruction on the horn buds but also severe local damage to the frontal bone. CT images of animals after clove oil or isoeugenol injection showed complete or partial destruction of the horn bud. Histological examination was performed at 1 horn bud per animal of 5 per each group. Eight biopsy samples showed normal unchanged epidermis and dermis (3 isoeugenol, 5 control group), in 6 samples normal vital skin side by side with necrotic epidermis and/or dermis was found (2 isoeugenol, 2 clove oil, 3 thermal dehorning). In one sample (thermal dehorning) necrotic bone with osteomyelitis was detected. In 3 samples (thermal dehorning) dystrophic calcification was present. After clove oil treatment necrotic epidermis and dermis as well vital skin with a purulent crust was detected.

Disbudding of calves is a common, painful intervention. Due to cytotoxic and anesthetic properties, the injection of clove oil or its component isoeugenol may be less detrimental to animal welfare. We investigated mechanical nociceptive threshold (MNT), possible tissue alterations and horn growth for up to 12 weeks after injection of 1.5 mL clove oil (CLOV), isoeugenol (ISO) or saline (CON) or after hot-iron disbudding (BURN; with local anesthesia and sedation, n = 10/treatment). MNT was measured using von Frey filaments and a pressure algometer at four locations around the horn bud. There was a treatment*time point interaction (linear mixed model, p < 0.05). MNT decreased most strongly and for the longest time for BURN in most calves at least for 3 weeks. For ISO, the decrease was less distinct and most calves’ values returned to baseline after 1–2 weeks. MNT in CLOV was intermediate, with decreased values up to 3 weeks in some animals. 12 weeks after the treatment, horn growth was prevented in about 50% of the horns in CLOV and ISO. Tissue alterations such as swellings of the eyelids often occurred in CLOV, but less so in ISO. Our results suggest that injection of isoeugenol causes less pain and thus seems to be beneficial compared to hot-iron disbudding, while clove oil was not advantageous. Regarding the effectiveness of isoeugenol to prevent horn growth, more studies are needed.