One hundred beef carcasses were selected at three packing plants and were used to determine the relationship between glycolytic potential (GP) and dark, firm, and dry (DFD) beef and to determine the effects of DFD status and GP on cooked beef palatability. Eight individual muscles were excised from one hindquarter of each carcass at d 7 postmortem: longissimus lumborum, psoas major, gluteus medius, tensor fasciae latae, rectus femoris, semimembranosus, biceps femoris, and semitendinosus. Ultimate pH, colorimeter readings, and Warner-Bratzler shear force were determined for all eight muscles at d 7 postmortem. A nine-member trained sensory panel evaluated cooked longissimus lumborum, gluteus medius, and semimembranosus steaks. Traits determined solely for the longissimus lumborum were GP (2 x [glycogen + glucose + glucose-6-phosphate] + lactate) and ether-extractable fat. A curvilinear relationship existed between GP and ultimate pH within the longissimus muscle. There appeared to be a GP threshold at approximately 100 micromol/g, below which lower GP was associated with higher ultimate pH and above which GP had no effect on ultimate pH. The greatest pH and muscle color differences between normal and DFD carcasses were observed in the longissimus lumborum, gluteus medius, semimembranosus, and semitendinosus muscles. Cooked longissimus from DFD carcasses had higher shear force values (46% greater) and more shear force variation (2.3 times greater variation) than those from normal carcasses. Dark cutting carcasses also had higher shear force values for gluteus medius (33% greater) and semimembranosus (36% greater) than normal carcasses. Sensory panel tenderness of longissimus, gluteus medius, and semimembranosus was lower for DFD carcasses than for normal carcasses. Longissimus and gluteus medius flavor desirability scores were lower for DFD than for normal carcasses. Steaks from DFD carcasses had more off-flavor comments than steaks from normal carcasses, specifically more "peanutty," "sour," and "bitter" flavors. The DFD effect of higher shear force values was approximately five times greater (+3.11 kg vs +0.63 kg) for carcasses with "slight" marbling scores than for carcasses with "small" marbling scores. In general, higher GP was associated with increased tenderness, even among normal carcasses. In conclusion, low GP was associated with DFD beef and resulted in substantially less-palatable cooked steaks.

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.