Effects of ractopamine administration and castration method on the response to pre-slaughter stress and carcass and meat quality in pigs of two Piétrain genotypes.

Rocha, L.M., Bridi, A.M., Foury, A., Mormède, P., Weschenfelder, A.V., Devillers, N., Bertoloni, W., and Faucitano, L. (2013). "Effects of ractopamine administration and castration method on the response to pre-slaughter stress and carcass and meat quality in pigs of two Piétrain genotypes.", Journal of Animal Science, 91(8), pp. 3965-3977. doi : 10.2527/jas.2012-6058  Access to full text

Abstract

The objective of this study was to evaluate the effects of ractopamine supplementation, castration method and their interaction on the behavioral and physiological response to pre-slaughter stress and carcass and meat quality of 2 Piétrain genotypes. A total of 1,488 male pigs (115±5 kg live weight) were distributed according to a 2 × 2 × 2 factorial design. The first factor was ractopamine supplementation with 2 groups of pigs (376 and 380 pigs each) receiving 7.5 ppm of ractopamine (RAC) or not (NRAC) in their diet during the last 28 d of the finishing period. The second factor was castration method with 744 surgically castrates (SC) and 744 immunized males (IM), and the third factor was the genotype with 2 crossbreds containing 50% (genotype A; GA; n = 744) or 25% (genotype B; GB; n = 744) Piétrain genetics. Surgical castration took place at 2 d of age, while immunization against gonadotropin-releasing factor (GnRF) was performed through 2 subcutaneous injections of GnRF analog (Improvest, 2 mL) at 10 and 4 wk before slaughter. At loading more vocal stimulation was needed by the handler to drive GB pigs forward through the farm alley (P = 0.01) and RAC-fed-GB pigs through the ramp (P = 0.02). Feeding RAC to IM increased the number of fights in lairage compared with SC (P = 0.03). Feeding RAC shortened fighting bouts compared with NRAC pigs (P = 0.05). The pigs SC-GA showed a greater gastro-intestinal tract temperature during unloading (P = 0.05) and lairage time (P = 0.03). Blood creatine kinase (CK) levels were greater (P = 0.04) in SC compared to IM and no difference was found in the levels of stress hormones in urine collected post-mortem. Dressing yield was greater (P = 0.01) in RAC and SC-GB pigs. Carcasses from RAC pigs and IM were leaner than those from NRAC and SC pigs (P < 0.001 and P = 0.002, respectively). Feeding RAC to IM increased drip loss in the Longissimus muscle (LM; P = 0.05). Warner-Bratzler shear force (WBSF) values were slightly greater in the LM from RAC-GB pigs and from IM compared to SC (P = 0.01 and P <0.001, respectively) and in the Semimembranosus muscle of RAC pigs (P = 0.006). In conclusion, immunization against GnRF more than the use of Piétrain genotypes appears to be a viable alternative to the use of ractopamine, as it seems to promote production of lean carcasses without compromising animal welfare and pork quality.

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