Sixty-one animals with different Halothane genes (homozygous halothane positive, n=34; and homozygous halothane negative, n=27) were fed with three diets (control group, with no supplement; magnesium (Mg) group with 1.28g MgCO 3 /kg and tryptophan (Trp) group with 5g L -Trp/kg) during the last 5 days before slaughter.Animals were submitted to minimal stress ante mortem conditions. Pig behaviour was recorded at the experimental farm, raceway to the CO 2 stunning system and during the stunning period. Corneal reflexes were recorded after stunning as well. There were no differences in feed intake among diets (p>0.05) during the 5 days of treatment. The halothane positive (nn) group had lower intake than the halothane negative (NN) group (p<0.01). The behaviour of the pigs in the raceway did not differ (p>0.05) among treatments or halothane genotype. A significant (p<0.001) interaction diet*halothane was found in the time to appear the first retreat attempt during the exposure to the CO 2 system. In the nn group, the time of performing the first retreat attempt was later in the Mg (p<0.05) than the Control group. Moreover, in the Mg group, the nn had a later (p<0.05) first retreat attempt than the NN. Thus, Mg supplementation could have a positive effect on welfare of nn pigs. The nn had a lower proportion of animals that showed corneal reflexes after stunning than NN, indicating a higher effectiveness of the stunning method in nn pigs. Neither Mg nor Trp affected carcass quality and meat quality parameters, although significant differences were found between genotypes.
IntroductionThe pre-slaughter handling of fattening pigs is one of the most stressful events and it has an important effect on the final carcass and pork quality (Gispert et al., 2000a). It includes mixing unfamiliar animals, fasting, loading, transport, abattoir lairage and the stunning procedure. All of these are stressful factors which sometimes are difficult to alleviate. The most unpleasant situation for the pigs takes place during handling and transport before slaughter (Gispert et al., 1996). Inappropriate handling results in lower animal welfare shown by skin damage and a higher mortality among the pigs.Moreover, it can lead to poorer pork quality such as PSE (Pale Soft and Exudative) and DFD (Dark Firm and Dry) meat.Likewise, the stunning procedure used should be considered because it may modify the final carcass and pork quality (EFSA, 2004). In some countries, including Spain, the CO 2 stunning method has increased in popularity due to its positive effects on meat quality compared with the electrical method (Velarde et al., 2001). In the CO 2 stunning dip-lift system, pigs are lowered directly into the maximum carbon dioxide concentration at the bottom of the pit inducing their unconsciousness (EFSA, 2004). It is a statutory requirement in Europe to use a minimum of 70% CO 2 (Directive 93/119/EC), however many slaughterhouses use between 83 and 90% CO 2 to increase throughput. Nevertheless, the use of carbon dioxide is questioned o...
