Genetic variability of muscle glycolytic potential in pigs

Abstract

This review presents the current state of knowledge on the genetic variability of muscle glycolytic potential (GP) in pigs. This trait refers to the intra vitam glycogen content of muscle, and is defined as the potential of lactic acid production during post mortem glycolysis. Muscle GP depends on the muscle considered, and is higher in white than in red muscles. Muscle GP also depends on the time of measurement : it is higher when the muscle sample is removed by biopsy on resting live animals than when it is removed from the carcass within one hour after slaughter. The relationship of ultimate pH of meat with GP is linear, up to a plateau occurring beyond a muscle-dependent GP threshold value. Muscle GP is strongly influenced by the RN major gene (« acid meat » gene) which is at the origin of the particular position occupied in this respect by the Hampshire breed(« Hampshire effect »). The RN– allele, responsible for the large increase in GP (+ 70 %) in fast-white muscles (e.g. Longissimus dorsi), is almost completely dominant. Independently of the RN gene, GP shows an appreciable polygenic variability (heritability of 20-25 %). This trait is positively related to carcass lean to fat ratio and to residual glycogen content of meat, whereas it is negatively related to ultimate pH and cooking yield of meat. The RN– carriers show an increased water to protein ratio in muscle. There are indications that the energetic metabolism of muscle is more oxidative in animals with a genetically higher GP. Muscle glycolytic potential, which can be assessed on the live animal (Longissimus dorsi biopsy), is a criterion of selection to be taken into consideration for genetic improvement of pig meat quality.