A multilevel logistic regression model was used to identify and quantify the effects of factors affecting the mortality of pigs being transported to slaughter under commercial conditions. A survey of 739 journeys to 37 slaughterhouses in five eu countries was carried out, and information potentially related to the welfare and mortality of the pigs and the number of injuries were recorded. The average temperature during the journey, its duration, the average loading time per pig, the recorded injuries, fasting before transport, and the interaction between fasting and journey duration were used in the final model. The average mortality was 0.11 per cent and the average proportion of injured pigs was 0.36 per cent, and these figures were significantly correlated (P<0.001). In 29 per cent of the journeys the pigs were not fasted before being loaded, which doubled the risk of mortality irrespective of whether the pigs were injured or not. The risk of mortality increased with average temperature. In journeys with fasted pigs that did not have any recorded injury, average temperature was more important than the duration of the journey. The risk of mortality increased as the average time taken to load them decreased, and the risk was highest when the pigs were not fasted and when injuries were recorded. Other factors such as the country, loading density, availability of drinking water and type of ventilation did not affect the risk of mortality.
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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