Pig meat quality: influence of breed, RN genotype and environment.

The purpose of this thesis was to study the influence of genetic and environmental factors on pig meat quality. Meat quality traits studied were: daily gain, carcass composition and muscle distribution, technological and sensory qualities. The dominant allele for the RN gene (Rendement Napole) is known to increase the glycogen content of glycolytic muscles in Hampshire and Hampshire crossbreeds. The allele frequency for the dominant allele (RN) was estimated to 0.61 in purebred Swedish Hampshire pigs. By analysing the sum of glucose and glucose-6-phosphate in meat juice, it was found possible to predict the animals' RN phenotype. This is a quicker method than analysis of the estimated level of glycogen in the muscles (glycolytic potential, GP), as is commonly used to classify by RN phenotype. In crossbred animals, the RN allele gave higher daily gain and leaner carcasses, and a larger proportion of glycolytic ham muscle (M. biceps femoris, M. gluteus and M. semimembranosus), at the expense of M. quadriceps femoris. No effect on the RN allele on carcass traits was found in purebred Hampshire animals, but purebred RN carriers were leaner than either Yorkshire or Landrace pigs. The effects of the RN allele on technological meat quality were consistent in both purebred and crossbred animals. In comparison with non-carriers and purebred Yorkshire, RN carriers hand lower values for ultimate pH, water-holding capacity, techological yield, crude protein content and dry matter, and higher glycolytic protential, cooking loss and internal reflectance values. In a sensory test, fresh loin from RN carriers was more acidic than either non-carriers or purebred Yorkshire, and was more tender than Yorkshire. Cured cook ham from RN carriers was also more juicy than that from non-carriers. In comparison with Duroc-sired pigs, Yorkshire-sired pigs had a significantly leaner carcass and meat with lower IMF content and marbling scores and higher shear force values and water content. Concerning sensory properties, meat from Duroc crosses was less acid, more tender and gained higher overall acceptance scores. Moderate indoor exercise during raising gave shorter carcasses, paler meat and higher drip loss in the loin, and in the ham, a lower proportion of intramuscular fat and dry matter and higher pigment content. Outdoor rearing gave lower daily gain and leaner carcasses and meat with lower pH, higher drip loss, shear force values and internal reflectance values, compared with indoor rearing in ordinary pens. Meat from outdoor-reared pigs contained more lactate and crude protein and had a higher glycolytic potential, less IMF and less water. Regarding the sensory qualities, outdoor rearing impaired tenderness, juiciness and overall acceptance.