Incidence of pre-slaughter stress on meat quality of non sensible pigs

Pigs (n=186) of the same genetic strain at the RN and HAL loci, i.e. rn(+)rn(+) / NN, were slaughtered in two abattoirs (referred to as A1 et A2). All pigs were anaesthetised with CO2, using a mixture of air (30 %) and CO2 (70 %). One hundred and twenty-eight pigs were slaughtered in A1 (corusinga restrainer) and fifty-eight pigs were slaughtered in A2 (backloading) at a rate of 720 pigs per hour per slaughterline. In A1, the pigs were led in a single file to the restrainer which introduced them individually into the stunning machine. In A2, the pigs walked 5 or 6 abreast towards the stunning machine, being pushed by a sliding door from the piggery to the cradle of the machine without human intervention. The pH was measured at 40 min, 2h30 and 24h after slaughter in the semimembranosus muscle (SM). Colorimetric values (L*, a* and b*) were measured after deboning on the internal surface of the SM. The hams were graded as follows: 1, no PSE zone; 2, doubtful; 3, PSE zones in the SM and sometimes in the internal flexor muscle; 4, PSE zones in all the flexor muscles; each one of these grades being squared with pre-thresholded gaps of luminance. The muscle pH value was higher in A2 than in A1 at pH1 (40min). L* and a* value (P < 0.001) were higher in A1 than in A2. There was a remarkable difference between the two abattoirs in the proportion of hams graded 3-4, with 17,7% in A1,vs. 5 % in A2. Waiting-time before slaughter affected the pH value at 24h. The values of pH 1 and PH 2.5 decreased with the increase in the meat quality score in the two abattoirs. The result of the present study indicate that the method of handling the pigs to the stunning device affects the frequency and importance of PSE-zones in the ham. The stressless automated driving of groups of animals to the stunning machine, combined with the backloading of a nacelle, (compared to a traditional system driving pigs in single file, using electrical goads and a queue up restrainer) is beneficial with respect to both meat quality and animal welfare.