Rendement Napole gene effects and a comparison of glycolytic potential and DNA genotyping for classification of Rendement Napole status in Hampshire-sired pigs

The purpose of the present study was to compare Rendement Napole (RN) classification from glycolytic potential (GP) and DNA techniques, and to study the effect of the RN gene on performance, carcass, muscle quality, and sensory traits. Progeny (N = 118) from the mating of 15 purebred Hampshire sires to York x Landrace females were classified for RN gene status using the GP of the loin and polymerase chain reaction-restriction fragment length polymorphism sequence methodology. Females mated in the study (N = 32) were considered normal (rn+/rn+) based on a loin GP measurement taken on samples collected by live press biopsy. Progeny were randomly selected for harvest within a litter for each sire. Observed mean, standard deviation, and range of progeny loin GP values were 132.2, 30.7, and 70.0 to 193.0 micromol/g, respectively. The GP data were not normally distributed. Peak numbers of observations occurred between 120 and 129 micromol/g and 160 to 169 micromol/g. Pigs with a loin GP of > 150 micromol/g were classified RN-/rn+ based on the observed valley between the peak values, resulting in 37 pigs classified as RN-/rn+ and 81 pigs classified as rn+/rn+. Using DNA procedures, 81 RN-/rn+ and 37 rn+/rn+ pigs were observed. All classification errors occurred when GP values were < or = 150 micromol/g, with 30 of 44 and 14 of 44 classification errors occurring when loin GP values were between 121 and 150 micromol/g and 70 and 120 micromol/g, respectively. Gene effects, based on DNA results, were evaluated using mixed-model procedures with fixed effects of DNA genotype and gender, and random sire and litter effects. No RN genotype differences for growth rate,10th-rib backfat, or loin muscle area were observed. Loins from the RN-/rn+ pigs had significantly (P < 0.05) lower ultimate pH (0.16 units), greater GP (50.3 micromol/g), greater drip loss (0.93%), paler objective color (L*, 1.66 units), paler visual color (0.31 units), and lower firmness (0.61 units) scores. Additionally, loins from RN-/rn+ pigs had significantly (P < 0.05) lower marbling scores (0.68 units) and intramuscular fat content (0.25%) and greater cooking loss (2.51%). Cooked moisture, juiciness score, and mechanical and sensory tenderness measures did not differ between genotypes. The GP-based classification did not correctly classify RN genotype in the present study, emphasizing the importance of the direct DNA analysis for estimation of gene frequency and effects. The DNA-based genotype results clearly indicate the RN- allele has negative effects on muscle quality measures.