Long-term effects of disbudding: stress reactivity, behaviour and meat quality in young fattening cattle

Abstract

Disbudding, referring to the removal or destruction of the horn bud in young calves, usually using a hot iron, is a common management practice in cattle farming. Associated short-term effects have been well investigated and include physiological, behavioural and emotional stress reactions. Little is known about possible long-term effects of horned versus disbudded cattle. There is evidence that horn status influences the social rank and the quantity and quality of social interactions. Previous social and non-social experiences during rearing may impact stress reactivity, which can be investigated from both physiological and behavioural points of view. Physiological short-term stress reactions include an increase in catecholamine and cortisol concentrations through activation of both the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. In case of prolonged experience of adverse stimuli, a modified HPA axis reactivity comprising of an altered adrenal cortisol responses to adrenocorticotropic hormone [ACTH] may occur. Behavioural stress reactivity can be evaluated by challenging individuals to experimental, mainly fear-eliciting situations. Being highly variable between individuals and stable across time and contexts, individual behavioural stress reactivity may also impact reactions to pre-slaughter stress and, therefore, its influences on meat quality. The present study investigated possible long-term effects of disbudding in fattening cattle by focusing on possible differences between horned and disbudded cattle regarding to HPA axis reactivity, behaviour, pre-slaughter stress just before slaughter and meat quality. We used 81 bulls (experiment 1 [E1]) and 71 heifers (experiment 2 [E2]) reared under different conditions: groups of i) exclusively horned cattle (H+), ii) exclusively disbudded cattle (H-) and, additionally for E1, iii) mixed cattle (half horned, half disbudded, M). At slaughter, half of the bulls of each rearing condition were slaughtered under one of two slaughter conditions: with limited stress (LS) or with supplementary stress (SS) during the 30 minutes before slaughter. During rearing, we investigated the HPA axis reactivity and its repeatability using repeated ACTH challenges (first challenge before disbudding, the second and third at 11 months) and spontaneous (general activity and synchrony) and reactive (during novel object and food competition tests (NOT and FCT, respectively)) behaviours. At slaughter, we studied physiological stress reactivity and meat quality (physical, chemical and sensory traits). The repeatability of adrenal cortisol responses was weak and moderate, when the physiological state between challenges varied or did not change, respectively. Although standardizing the time of day of ACTH challenges improved the repeatability, the readout remains questionable. Horned bulls of unmixed rearing groups showed greater cortisol responses after disbudding than unmixed H- bulls. Compared to H- animals, horned bulls and heifers showed greater general activity in the field (E1 and E2) and greater levels of agonistic behaviour during FCT, due to higher levels of agonistic interactions with contact (E1) and without contact (E2). During NOTs, H+ bulls of unmixed and mixed groups showed more exploration and less locomotion, possibly indicating less fearfulness, than H- bulls, whereas the opposite effect was found for heifers in E2. A supplementary stress at slaughter increased the physiological stress response, especially in unmixed rearing groups, and decreased meat juiciness. In unmixed groups, horned bulls had colder carcasses, shorter sarcomeres (also within mixed groups), and less tender meat than H- bulls. Our study revealed several novel long-term effects of disbudding. Only if reared in unmixed groups, horned and disbudded cattle differed in HPA axis reactivity and behaviour, pre-slaughter stress levels and meat quality. Additionally, supplementary pre-slaughter stress just before slaughter affected pre-slaughter stress levels and meat quality. Further research is needed to refine our understanding of these results, improve the assessment parameters and extend these findings of the horn status to other contexts, including, for example, dairy cows, on-farm experiments and human– animal relationships.