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To determine the influence of slaughter transports carried out under commercial conditions, 162 pigs weighing 98 kg and of both sexes were studied. A total of seven transports were performed in summer and in winter conditions, with durations of 1 h and 13 h 15 min within each season. Cortisol, glucose, creatine phosphokinase (CPK), lactate dehydrogenase (LDH), albumin and total protein serum concentrations were measured. All variables increased during transport and decreased during lairage (<i>P</i> < 0.001), with cortisol values being 3.47 ± 0.19, 8.52 ± 0.28, and 6.96 ± 0.18 µg/dl at loading, unloading and exsanguinations, respectively, except for glucose (0.54 ± 0.03, 0.44 ± 0.04, and 0.86 ± 0.03 g/l). Short journeys did not allow the total recovery from the loading stress. A certain level of dehydration was observed, especially during lairage on the longest journeys (increase of 6.87 ± 1.29 g/l for total proteins; <i>P</i> < 0.01). Winter transports were slightly more stressful (<i>P</i> < 0.01 for cortisol and LDH, and <i>P</i> < 0.001 for CPK), with poorer recovery during lairage (CPK decrease being –141 ± 559 and –2 906 ± 730 IU/l for winter and summer journeys, respectively; <i>P</i> < 0.01). Females showed higher stress reactivity. Genetics modulated the effect of the rest of influencing factors, with Nn individuals showing a rougher reaction in short and winter conditions, but with lower dehydration levels. Under Mediterranean commercial conditions, stress in transported slaughter pigs was largely determined by season and genetics, so that an adaptation of handling procedures to these seasonal variations appears crucial if transport stress is to be reduced. Also, an improvement in stress resistance could be obtained by controlling the halothane gene of pigs.

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ABSTRACT

Several multivariate statistical methods (principal component, discriminant (linear, quadratic and nearest neighbour)