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Intramuscular lipid contributes to overall eating quality of fresh pork. The objective of this trial was to determine the utility of ultrasound image analysis in prediction of intramuscular lipid in pork. Cross sectional ultrasonic images of the longissimus dorsi were taken at approximately the tenth rib on 50 pigs of market weight at the Western Illinois University Swine Testing Station. Both purebred and crossbred animals were represented in the group, which were pigs entered by private individuals in the Illinois State Fair Classic competition. Thus the animals represented a wide range of genetic backgrounds. Two ultrasound technicians collected images on each pig. All images were taken one day prior to slaughter. A computer program specifically designed to analyze color shading was written to analyze the pixel fields of the images to determine the percent of pixels in a specific color range. Images were analyzed for pixel shading from a range of 140, which represented a small range of values between white and black, to a value of 70, which offered a much broader range of gray shades. A sample of the loin was taken from the 10-12th rib region for quality and composition analysis. Pork quality traits measured included pH at 24 h, subjective quality scores, Warner-Bratzler shear force (WBS), Hunter color values and lipid content. Intramuscular lipid ranged from 0.5 to 5.45% and was significantly correlated (P < .01) with loin firmness (r= .429) and marbling score (r=.872), but not with WBS measured on samples aged 5 days postmortem. Predicted lipid content from images collected by both ultrasound operators was not significantly correlated with WBS or color of pork loins. However, the correlation between marbling and predicted lipid content from ultrasound operator 1 approached significance (r=.273; P Key Words: Pork, Intramuscular Lipid, Ultrasound

Bone-in loins (n=72) from halothane negative (HH) and carrier (Hh) pigs fed diets supplemented with either 0, 1.25, or 2.5% magnesium mica (MM) were used to test the interactive effect, if any, of genotype and dietary magnesium on quality traits of vacuum-packaged pork during extended storage at 2 C. At 48 h postmortem, the blade and sirloin portions were removed, and loins were fabricated into 3 equal-length sections, vacuum-packaged, and assigned randomly to 0, 3 or 6 weeks of storage. At each allotted storage time, loins were removed from vacuum-bags and processed into longissimus muscle (LM) chops. A 2-g sample of LM was removed from the center of the loin section and homogenized in 20 mL of distrilled, deionized water for pH measurements. Subjective and objective color data were collected on two 2.5-cm thick chops after a 45-min bloom period, and two 3-cm thick chops were used to measure drip loss percentages (DL%). Loins from pigs fed 2.5% MM had lower (P0.10) effect on pork quality. Muscle pH values for HH- and Hh-pigs were similar (P>0.10) at 0 and 3 weeks of storage; however, after 6 weeks of storage LM pH from HH-pigs was higher (P0.05) after 3 and 6 weeks of storage. Both American and Japanese color scores for LM chops from Hh-pigs were lower (P0.10) after 3 and 6 weeks of storage. In agreement with previous results from our laboratory, long-term supplementation of swine diets with MM had no appreciable effect on pork quality during storage. Initial (0 week) pork color and water-holding capacity of Hh-pigs were inferior to HH-pigs; however, quality traits were similar among genotypes as storage was extended to 6 weeks. Key Words: Halothane, Magnesium mica, Pork quality

Duroc pigs from two genetic lines representing the progeny of the sixth generation of pigs selected for increased leanness and growth efficiency (LEAN) or a control line maintained from the base population (CON) were tested to determine carcass and muscle quality traits. Thirty-one pigs of mixed sex were randomly sampled from each genetic line and slaughtered in two slaughter groups (N = 62 pigs) when they reached 114 kg. Postmortem temperature and pH were measured in the longis-simus (LM) and semimembranosus (SM) muscles at 0.5, 1, 2, 3, 4, and 22 to 24 h postmortem. Midline fat at the first rib, last rib, and last lumber vertebrae, tenth rib fat (measured 3/4 of the distance across the LM edge), LM area, carcass length, and muscle conformation scores were determined. Chops were removed from the LM, SM, and biceps femoris (BF) for determination of visual color, firmness/wetness, and marbling scores, Hunter L*, a*, and b* values, and drip loss. Hot carcass weight and LM area did not differ (P > 0.15) between LEAN and CON pigs. However, carcass length (79.4 vs 77.1 cm) and muscle conformation scores (6.0 vs 4.7) were higher (P < 0.001) and fat thickness measurements measured at the first rib (40.0 vs 45.1 mm), tenth rib (23.0 vs 32.7 mm), last rib (21.7 vs 27.0 mm), and last lumbar vertebrae (25.9 vs 30.2 mm) were lower (P < 0.015) for LEAN compared to CON pigs. Postmortem muscle pH was not affected by genotype, muscle, or their interaction with time postmortem (P > 0.10). Muscle temperature did not differ (P > 0.05) between genotypes in the SM at any time postmortem, but LM temperature was lower (P < 0.05) in LEAN pigs compared to CON pigs at 2, 3, and 4 hours postmortem. Genotype did not affect drip volume, percent drip loss, Hunter L*, a*, visual color, firmness, or marbling (P > 0.11). Hunter b* values were lower (P = 0.009) for LEAN than CON pigs across all muscles. These data suggest that selecting Duroc pigs for lean growth efficiency improved leanness without negatively affecting muscle quality. Key Words: Pork Quality, Growth Efficiency, Genetic Selection

Crossbred pigs were used to determine the effect of feeding magnesium mica (MM) on longissimus muscle (LM) quality of pigs heterozygous for the halothane gene. Pigs were blocked by weight, penned in groups of 6, and pens (3 pens/diet) were randomly assigned to either a control corn-soybean meal or the control diet supplemented with 2.5% MM. Diets were fed during the grower (0.95% lysine; 43.6 to 68.6 kg) and finisher (0.85% lysine; 68.6 to 102.8 kg) periods, and MM was included in the diet at the expense of corn. At the conclusion of the feeding trial, 12 pigs from each dietary treatment were randomly selected and subjected to either no stress (NS) or 3 h of transportation stress (TS). Upon completion of TS, pigs were harvested at 45-min intervals with TS pigs harvested first, followed by NS pigs. Immediately following stunning and at 0.75, 1.5, 3, 6, 12, and 24 h postmortem, samples from the LM were aseptically excised from left sides for pH, glycogen, and lactate determinations. At 48-h postmortem, right sides were fabricated into wholesale cuts, and subjective and objective measurements of pork quality were obtained from the LM after a 45-min bloom period. Dietary MM had no effect (P>0.10) on ADG or ADFI; however, gain-to-feed ratio was improved during the grower phase when pigs were fed MM-supplemented diets (0.365 vs. 0.351; P0.10) by dietary MM or TS. Dietary MM appears to elevate early postmortem pH, possibly explaining the lack of discernable change in pork quality traits of stressed pigs. Key Words: Magnesium, Stress, Pork Quality