Young Blond d’Aquitaine, Angus and Limousin bulls differ in emotional reactivity: Relationships with animal traits, stress reactions at slaughter and post-mortem muscle metabolism

• Young bulls of different breeds differed in stress reactivity when tested in standardised tests.
• At slaughter, breed differences did not result in different stress levels between breeds.
• The above lack of differences may be explained by the relatively short slaughter period.
• Stress reactions at slaughter explained part of the variability in early post-mortem pH decline between bulls.
• Relationships between stress reactions at slaughter and early post-mortem pH decline were breed-independent.

The present study investigated relationships between reactivity during tests, stress reactions at slaughter and animal traits in young Blond d’Aquitaine (BA), Limousin (LI) and Angus (AN) bulls. Behavioural and physiological reactivity of animals was evaluated during rearing using a “Human test” (exposure to human presence and handling) and an “Umbrella test (exposure to a sudden event, the opening of an umbrella). During both tests, bulls were also subjected to social isolation and novelty. Three weeks after the tests, bulls were slaughtered in an experimental abattoir and stress reactions were evaluated using ante-mortem behavioural and physiological measurements, and indicators of post-mortem muscle (Longissimus dorsi: LD and Semitendinosus: ST) metabolism. Animal traits (morphological measures, basal cortisol level and testosterone level) were also recorded. BA reacted more strongly to the tests than AN, while LI had often intermediate levels. In the Human test, BA and LI spent more time vigilant than AN. In the Umbrella test, BA turned their head backwards more often, were further away from the umbrella and expressed more startle responses than AN. At slaughter, AN showed lower LD pH3h and higher LD and ST pH30h after bleeding. Regression analyses showed that up to 25.3 and 39.7% of the variability between individuals in early post-mortem ST and LD pH40min was explained by differences in heart rate minutes before slaughter, and stress reactions during the reactivity tests, respectively, at least partly removing breed effects. Ultimate pH was more strongly related to physical traits, specifically dressing percentage. Models are in accordance with existing knowledge on the biological relationships between these traits and post-mortem metabolism. Overall, results show that the breeds differed in stress reactions during reactivity tests and in post-mortem pH decline. A considerable part of the breed effects on early post-mortem pH decline was explained by certain stress reactions during the reactivity tests or immediately before slaughter (pH40min, pH3h) and physical traits (pH30h).