Effects of ractopamine administration and castration method on the response to preslaughter stress and carcass and meat quality in pigs of two Piétrain genotypes1

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 preslaughter stress and carcass and meat quality of 2 Piétrain genotypes. A total of 1,488 male pigs (115 ± 5 kg BW) were distributed according to a 2 × 2 × 2 factorial arrangement of treatments. The first factor was ractopamine supplementation with 2 groups of pigs (376 and 380 pigs each) receiving 7.5 mg/kg 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 surgical castrates (SC) and 744 immunized males (IM), and the third factor was the genotype with 2 crossbreeds 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, whereas 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 SC-GA pigs showed a greater gastrointestinal tract temperature during unloading (P = 0.05) and lairage time (P = 0.03). Blood creatine kinase (CK) concentrations were greater (P = 0.04) in SC compared with IM, and no difference was found in the concentrations of stress hormones in urine collected postmortem. 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 LM (P = 0.05). Warner-Bratzler shear force values were slightly greater in the LM from RAC-GB pigs and from IM compared with 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.

Use of electromyography to detect muscle exhaustion in finishing barrows fed ractopamine HCl1

“…Rocha et al (2013) reported RAC barrows required more physical contact to move during handling and transportation. Additionally, MarchantForde et al (2003) found pigs fed RAC took longer to voluntarily exit pens during weekly weight measurements, thus making them more difficult to handle.…”

Ractopamine supplementation improves leanness and carcass yield, minimally affecting pork quality in immunocastrated pigs

“…Under stress, there is intense muscle glycogen degradation, producing high levels of lactic acid that are released into the bloodstream. As RAC is similar to natural catecholamine, it may cause physiological changes in animals, inducing stress (Rocha et al, 2013). However, in this study, the cortisol levels in the blood were not altered by either immunocastration or the addition of RAC, suggesting that these treatments did not induce stress in the animals.…”

Veterinary Drug Residues in Meat-Related Edible Tissues

“…In a metaanalysis of results obtained in 23 studies from 1990 to 2006, it was concluded that, except for increased shear forces, dietary administration of ractopamine (5-20 ppm) has generally no deleterious effect on pork quality parameters such as color, firmness, water holding capacity, marbling score, and intramuscular fat content. Although the 7.5 ppm ractopamine dose improved carcass leanness, it also increased drip loss and toughness of pork (Rocha et al, 2013). It has been reported that even low doses (5 ppm) of ractopamine in the diet reduced tenderness slightly, as determined by both mechanical and taste panel evaluation, although there was no effect on other sensory properties such as flavor or juiciness (Patience et al, 2009).…”