Stress status at slaughter. The experiment was performed
with 32 Normand cull cows (48 to 60 months old, mean live
weight 642 kg) selected for their live weight, age and body
fat score for a 100-day finishing period as described by
Gobert et al. (2009). Animals were randomly assigned to
three isoenergetic and isonitrogenous rations. All rations
were given a straw (30%) and concentrate (70%)-based diet
supplemented with lipids (40 g oil/kg DM diet) provided by
extruded linseed (n 56) or by extruded linseeds (1/3) and
rapeseeds (2/3; n 510), or by extruded linseeds associated
with antioxidants (vitamin E and plant extracts rich in polyphenols
from rosemary, grape, citrus and marigold; 155 IU/kg
and 0.7 g/kg DM diet; n516) during their finishing period.
Two slaughter conditions were used as described in Bourguet
et al. (2010). Half of the cows from each feeding group were
slaughtered at the Experimental INRA slaughterhouse under
limited stress (LS) conditions (7-min transport to the abattoir
located at 2 km from the experimental farm). Cows under LS
conditions (LS group; n516) were accompanied in the lorry
by a non-experimental companion to avoid social isolation
stress. They were immediately slaughtered after unloading.
The other half of the cows from each feeding group were
submitted to stress conditions (S group; n 516). Stress conditions
consisted in additional physical exercise and psychological
stress. Cows were individually transported towards
an unfamiliar farm (15min transport) and unloaded at the
entrance of a labyrinth and taken through three times (28min
accompanied by two purposely noisy experimenters), and
finally they were individually transported to the abattoir
(15-min transport) where they were immediately slaughtered.
The Longissimus thoracis (LT) and ST muscles, which differ
in their contractile and metabolic properties (Talmant et al.,
1986), were excised and treated as described above.
In all experimental designs, experimental procedures and
animal holding facilities respected French animal protection,
and were approved by the French veterinary services.