Physiological and behavioural responses of young horses to hot iron branding and microchip implantation.

Branding is the traditional and well-established method used to mark horses, but recently microchip transponders for implantation have become available. In this study, behaviour, physiological stress vari- ables and skin temperature in foals were determined in response to hot-iron branding (n = 7) and micro- chip implantation (n = 7). Salivary cortisol concentrations increased in response to branding (1.8 ± 0.2 ng/mL) and microchip implantation (1.4 ± 0.1 ng/mL), but cortisol release over time did not differ. In response to both manipu- lations there was a transient increase in heart rate (P < 0.001) and heart rate variability (P < 0.01). Brand- ing and microchip implantation induced a comparable aversive behaviour (branding, score 3.86 ± 0.85; microchip, score 4.00 ± 0.82). Both techniques thus caused similar physiological and behavioural changes indicative of stress. Acutely, implantation of a microchip was as stressful as branding in foals. Branding caused a necrotising skin burn lasting at least 7 days. Moreover branding, but not microchip implantation (P < 0.001), was accompanied by a generalized increase in skin temperature which was comparable to low degree post-burn hypermetabolism in humans.