Background: 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 and potential differences between horned and disbudded cattle. There is evidence that horn status influences 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 stress reactions include, for example, an increase in catecholamine and cortisol concentrations through activation of the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis in the short term or, in case of prolonged experience of adverse stimuli, modified HPA axis reactivity (e.g. altered adrenal cortisol responses to injected adrenocorticotropic hormone [ACTH]). Behavioural stress reactivity is 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 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) behaviours. At slaughter, we studied physiological stress reactivity and meat quality (physical, chemical and sensory traits).

Results: Repeatability of adrenal cortisol responses was weak and moderate, depending on the change in physiological state between challenges (marked or no change, respectively). Standardisation of the time of day of ACTH challenges improved repeatability. Horned bulls of unmixed rearing groups showed greater cortisol responses after disbudding than unmixed H-bulls. Horned bulls and heifers showed generally more activity in spontaneous behaviour (E1 and E2) than H-cattle and had a greater propensity for agonistic interactions during food competition, while H+ heifers additionally expressed more behaviour without contact than H-heifers. During novel-object tests, H+ bulls of unmixed and mixed groups showed more exploration and less locomotion, possibly indicating less fearfulness, than H-bulls, whereas the opposite was found for heifers in E2. Supplementary stress at slaughter increased physiological stress levels, especially in unmixed rearing groups, and decreased meat juiciness. Horned bulls had colder carcasses, shorter sarcomeres and their meat was judged as less tender than that of H-bulls.

Our study revealed several long-term effects of disbudding: Horned and disbudded cattle differed in HPA axis reactivity, 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 better understand these results and extend our knowledge of horn status in other contexts, including, for example, dairy cows, on-farm experiments and humananimal relationships.

iii Zusammenfassung Hintergrund: Das Enthornen von Kälbern ist ein weitverbreiteter Routineeingriff in der Rinderhaltung, der das Entfernen oder Zerstören der Hornanlage, meist durch einen heißen Brennstab, bedeutet. Kurzzeitfolgen der Enthornung beinhalten sowohl physiologische und verhaltensassoziierte als auch emotionale Reaktionen. Über mögliche Langzeitfolgen der Enthornung und somit potentielle Unterschiede zwischen be-und enthornten Rindern ist bisher nur wenig bekannt. Es gibt Hinweise, dass der Hornstatus den sozialen Rang und die Quantität und Qualität sozialer Interaktionen beeinflusst. Frühe soziale und nicht-soziale Erfahrungen während der Aufzucht können spätere Stressreaktionen beeinflussen, welche auf physiologischer und Verhaltens-Ebene untersucht werden können