Can emotional reactivity predict stress responses at slaughter in sheep?

The slaughter period is very complex and may represent different types of stress for the animal. The way and extent animals react to these stress factors depend on their individual emotional reactivity. The objective of the present study was to determine in sheep relationships between reactivity profiles measured during rearing, plasma cortisol levels in blood collected at exsanguination, and metabolic activity in the post-mortem muscle. During the rearing period INRA401 lambs (n = 267) showed coherence in their responses to situations representing different contexts of novelty, social isolation and presence of man. Vigilance and high-pitched bleating were the most often occurring behaviours. Highest levels of these behaviours were observed during novelty and social isolation. Lambs with higher plasma cortisol levels at exsanguination produced meat with lower pH 3 h (r = −0.19, p = 0.003) and 24 h post-mortem (r = −0.13, p = 0.05). Multiple regression analysis found that more socially attracted lambs and lambs performing more high-pitched bleating had higher muscle temperature 3 h post-mortem (p < 0.001), explaining 23.5% of variability. More vigilant lambs had higher pH (r = 0.14, p = 0.02) 3 h post-mortem. Multiple regression including both cortisol and vigilance as explanatory variable was significant (p < 0.01) and explained 12.8% of variability of pH 3 h post-mortem. In the present study, slaughter day, that is, day-to-day variations in the slaughter context, explained 18.4% of the variability in cortisol levels and 25.0–72.7% of variability in post-mortem muscle measurements. When analyses were based on averages per category created according to cortisol levels at exsanguination, to reduce the variability due to slaughter days, behavioural traits (vigilance and social attractiveness of flock-mates) explained statistically about 50% of variability in cortisol levels at exsanguination, and pre-slaughter cortisol levels explained up to 50% of variability of ultimate pH. Relationships between post-mortem muscle metabolism and expressions of social distress and reactivity to novelty suggest that reactivity profile may predict stress reactions during slaughter period and that social disturbances and novel environment in the slaughterhouse may be major causes of stress.