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The interpretation of muscle structure by scanning electron microscopy (SEM) has not been consistent among various studies. Consequently, the literature is confusing with respect to the identity of T-tubules, transverse ridges, Z-disks, and intermyofibrillar connections. The objective of this research was to evaluate the effects of different methods of sample preparation and imaging on ultrastructural details of previously identified transverse structures and intermyofibrillar connections and to verify or disprove the commonality of these structures under different viewing conditions. Scanning electron microscopy coupled with a cold stage, SEM at room temperature, and transmission electron microscopy (TEM) of thin sections were most appropriate for exposing detail of inter- and intracellular structures and for measuring sarcomere length and spacing of intermyofibrillar connections. Scanning electron microscopy of samples mounted on a cold stage, fractured, and sublimed provided excellent images of meat and muscle ultrastructure and may be used in correlative microscopy. Sarcomere length and spacing between intermyofibrillar connections were similar among most specimen preparation techniques and were affected similarly by heat treatments. Results indicate that the regularly spaced transverse structures viewed by conventional SEM and the intermyofibrillar connections viewed by low-temperature SEM are Z-disks.

Alternate right or left sides of eight Holstein-Friesian steer carcasses were electrically stimulated (ES, 550 V) approximately 40 min postmortem, with the nonstimulated (NS) sides serving as the experimental control. Temperature and pH of the longissimus muscle (LM) from both sides were monitored at 1, 3, 6, 12, 24 and 48 h poststimulation. At 12, 24 and 48 h, the LM was sectioned for visual evaluation and for measurements of pH and temperature at three locations across the muscle surface and for measurements of color using a Hunter Color Difference Meter. A significant correlation (r=.792, P<.0001) was found between the pH of the dorsal surface of the muscle [the position at which a dark, coarsely textured outer band (DCB) or "heat-ring" is normally located] and DCB score; pH was elevated in those muscle areas where the DCB was most pronounced. Electrical stimulation lowered (P<.05) both the incidence and severity of the DCB at 12 h postmortem, and totally eliminated this phenomenon by 24 h. At 24 h, however, the DCB severity in NS sides was less than at 12 h. Muscle color, as measured objectively and visually, was brighter in the stimulated muscles through 24 h postmortem.

Four experiments using 580 barrows and 580 gilts (Study 1) and seven experiments using 500 barrows and 500 gilts (Study 2) were conducted at various geographical locations in the United States to determine the dose response of a pelleted form of porcine somatotropin (pST) relative to ADG, feed/gain (F/G), and percentage of carcass protein. Average initial weights for Studies 1 and 2 were 67.6 and 72.6 kg, respectively, and four pigs/pen were slaughtered when they achieved weights of 106.5 to 111.0 kg. In Study 1, pigs were implanted subcutaneously with pelleted pST doses of 0, 12, 24, 36, or 48 mg/wk and self-fed a corn-soybean meal diet containing 13.75% CP. Study 2 included two control groups self-fed a diet containing either 13.75 or 17% CP with added lysine. The pST-treated pigs were administered 12, 24, or 36 mg/wk, and all were offered the 17% CP diet. The pST treatments in Study 1 resulted in a linear reduction (P< .05) in average daily feed intake (ADFI) and a quadratic (P< .05) improvement in F/G and percentage of carcass protein. The pST treatments in Study 2 resulted in a linear reduction in ADFI (P< .05), a linear improvement in F/G, and a quadratic increase in the percentage of carcass protein (P< .05). Average daily gain was not affected in either study with this form of pST. The greatest increase in efficiency of lean gain was observed with the 36-mg dose for both Study 1 (9.4%) and Study 2 (10.8%). In Study 1, the force required to shear cores of the longissimus muscle was increased linearly with pST treatment (P< .05). There was a similar linear increase in Study 2 with pST treatment (P< .05); however, there was also an effect of sex (P< .05) on shear force (gilts > barrows) that was similar in magnitude to that observed for pST treatment. Differences in sensory evaluation because of pST were minor and of the same magnitude as those observed between barrows and gilts. It was therefore concluded that weekly administration of pST improved F/G and percentage of carcass protein with no detrimental effects on palatability of cooked lean pork.

Carcasses and(or) tissues of 510 boars and 510 barrows were analyzed for lean content, muscle quality, incidence of objectionable odor, 5α-androstenone concentration and skatole concentration. Boars and barrows differed (P< .01) in warm carcass weight (73.5 vs 80.1 kg), longissimus muscle area (36. vs 35. cm2), 10th rib fat depth (1.80 vs 2.57 cm), estimated percent muscle (56.1 vs 51.3%) and marbling score (1.73 vs 1.97). No difference (P> .05) was found for muscle color score (2.51 vs 2.45). Although odor panel scores were higher (P< .01) for boars than for barrows (1.74 vs 1.56), both scored quite low. The correlation coefficients between panel scores and 5α-androstenone content (.13) and between panel scores and skatole content (−.14) were nonsignificant (P> .05). These results indicate that boars reared in U.S. commercial production facilities produce lean meat more efficiently than barrows do and they have a low incidence of offensive odor. Concentration of 5α-androstenone and skatole in backfat proved unrelated to odor intensity.

Three hundred sixty-one market-weight barrow and gilt carcasses were physically dissected into bone, skin, fat and muscle. A three-variable multiple linear regression equation containing the same independent variables (warm carcass weight, 10th rib loin muscle area and 10th rib fat depth) used (U.S.) to determine pork carcass lean weight was found to be the most practical means for predicting weight of muscle standardized to 10% fat. Multiple linear regression equations containing more than three independent variables produced only slight improvements in R2values; however, the standard deviation about the regression line was not greatly improved by the addition of more independent variables to this three-independent-variable regression model. A single multiple linear regression equation using the three independent variables above may not be adequate to describe variation over the entire live-weight range for all hogs marketed in the U. S. For most accurate muscle weight prediction, different equations should be used for weight subclasses with one equation for carcasses under 100 kg and another for those heavier than 100 kg. A single prediction equation for muscle weight was adequate for carcasses of both barrows and gilts.

On-line techniques for estimating carcass composition and value with potential for eventual application in the packing industry must be accurate, rapid, dependable in a plant environment and cost-efficient. Several potential technologies are discussed and data are presented to establish the relative accuracy of real-time ultrasound imaging, electromagnetic scanning and optical electronic fat-lean probes. Market-weight barrows and gilts were subjected to ultrasound image analysis prior to slaughter. Carcasses were evaluated for composition using electromagnetic scanning, ultrasound image analysis, optical probe analysis and direct measurement of loin muscle area and fat depth with a dot grid and ruler. Carcasses were fabricated into standard U.S. primal cuts and each cut was dissected into lean, fat, bone and skin. Multiple linear regression analyses to predict weight of total dissected carcass lean revealed that the electronic signal from the electromagnetic scanner, carcass length and temperature combined gave an R2of .89 (RSD 1.74). Carcass ultrasound images of fat depth and loin muscle area at the 10th rib and warm carcass weight gave an R2of .79 (RSD 2.20). The electronic probe for fat and muscle depth at the 10th rib of chilled carcasses and chilled carcass weight gave an R2of .79 (RSD 2.19). The R2is .81 (RSD 2.07) when actual loin muscle area and fat depth were determined by direct measurement in ribbed carcasses and combined with carcass weight.