Intramuscular adipose tissue from the fifth-eighth thoracic vertebrae region of the longissimus dorsi muscle, and portions of the overlying subcutaneous adipose tissue, were obtained at 16 and 18 months of age from Angus steers fed ad libitum either a corn silage (low energy) or ground corn (high energy) diet. Carcass weight, backfat thickness, and kidney, pelvic and heart fat were significantly greater in the steers fed the high energy diet; however, there were no significant differences in marbling scores between diet groups. Additionally, feeding steers the high energy diet did not result in differences in adipocyte diameter or number of adipose cells per gram tissue in either adipose tissue depot. Intramuscular adipocytes had a peak diameter (the diameter represented by the greatest number of cells) of 104 +/- 2 microns; peak diameter in subcutaneous adipose tissue was 141 +/- 5 microns. The activities of ATP-citrate lyase and NADP-malate dehydrogenase increased with age in the subcutaneous adipose tissue; feeding steers the high energy diet increased enzyme activities further. Age and diet had no effect on enzyme activities in intramuscular adipose tissue. A similar pattern was observed for the incorporation of lipogenic precursors into fatty acids. Acetate provided 70-80% of the acetyl units to in vitro lipogenesis in subcutaneous adipose tissue, but only 10-25% in intramuscular adipose tissue. Conversely, glucose provided 1-10% of the acetyl units in subcutaneous adipose tissue, but 50-75% in the intramuscular depot.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological tenderness differences between longissimus muscles (LM) from Bos indicus and Bos taurus breeds were evaluated. Steers and heifers of Hereford x Angus (H x A, n = 10), 3/8 Sahiwal x H, A or H x A (3/8 SAH, n = 6) and 5/8 Sahiwal x H, A or H x A (5/8 SAH, n = 11) crosses were utilized. Muscle temperature and pH were monitored every 3 h for the first 12 h and at 24 h. Samples were obtained within 1 h and at 24 h postmortem from the LM for determination of calcium-dependent protease (CDP) -I and -II and CDP inhibitor (INH) activities. At 1 and 14 d postmortem, LM samples were removed for determining cathepsin B and B + L activity, soluble and total collagen, sarcomere length, muscle-fiber histochemistry, shear force and sensory-panel traits. Data were analyzed using least squares procedures with fixed effects of breed cross, sex and their interaction. No significant breed cross effects were observed for carcass traits or rates of pH and temperature decline. Steaks from H x A had lower (P less than .05) shear-force values and higher (P less than .05) sensory scores for tenderness at 1 and 14 d postmortem than steaks from 3/8 and 5/8 SAH. Correspondingly, 5/8 SAH had lower (P less than .05) myofibril fragmentation indices than H x A at 1, 3, 7 and 14 d postmortem. Breed cross effects were not significant for sarcomere length, fiber types, soluble and total collagen, cathepsin B and B + L specific activity, CDP-I and -II activity and INH activity within 1 h postmortem. However, INH total activity/100 g of muscle was greater (P less than .01) at 24 h postmortem for 5/8 SAH (208.8 +/- 14.8) and 3/8 SAH (195.6 +/- 19.3) than for H x A (136.3 +/- 14.9). For H x A, SDS-PAGE revealed that by d 1 desmin had been subjected to proteolysis, and by d 14 desmin could not be detected, but a 30,000-dalton component was clearly evident. However, in 5/8 SAH, desmin remained visible at d 14 without a 30,000-dalton component appearing. This reduced protein hydrolysis may account for less tender meat in SAH; INH apparently influences this process.

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Carcass and longissimus thoracis palatability traits from 888 steers obtained from mating Hereford and Angus cows to Hereford or Angus (HA), Charolais (Ch), Gelbvieh (Gb), Pinzgauer (Pz), Shorthorn (Sh), Galloway (Gw), Longhorn (Lh), Nellore (Ne), Piedmontese (Pm), and Salers (Sa) sires were compared. Data were adjusted to constant age (426 d), carcass weight (324 kg), fat thickness (1.2 cm), fat trim percentage (23%), and marbling (small00) end points. At a constant age of 426 d, carcasses from Ch steers were heaviest (P < .05) and Gw and Lh carcasses were lightest (P < .05). Adjusted fat thickness was greatest (P < .05) on carcasses from HA and least (P < .05) on carcasses from Ch, Gb, Lh, and Pm steers. USDA numerical yield grades were lowest (P < .05) for carcasses from Pm and highest (P < .05) for carcasses from HA, Ne, and Sh steers. Marbling scores were highest (P < .05) for carcasses from HA, Pz, and Sh and lowest (P < .05) for carcasses from Ch, Ne, and Pm steers. Longissimus thoracis from Pz had a lower (P < .05) shear force than that from all other breeds except HA, Gb, and Pm. Longissimus thoracis of carcasses from Ne steers was least (P < .05) tender. Adjustment of traits to various end points resulted in some changes in sire breed differences depending on the end point and the trait being considered but had little effect on palatability traits. Carcasses from Pm-sired steers provided the most desirable combination of carcass and longissimus palatability traits.

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Postmortem aging of carcasses obtained from Angus-Hereford (n = 8) and 5/8 Brahman crossbred (n = 8) heifers was investigated to determine the cause of variation in meat tenderness. Raw longissimus muscle (LM) myofibril fragmentation index was lower and cooked LM Warner-Bratzler shear force was greater for the 5/8 Brahman crossbreds (P less than .05). The activities of calcium-dependent protease (CDP) -I and -II were not affected (P greater than .05) by breed; however, CDP inhibitor activity was higher (P less than .05) in the 5/8 Brahman carcasses. The activities of cathepsins B and B + L were not affected by breed or postmortem storage time (0, 1, 3, 7 or 14 d). Hereford-Angus carcasses were fatter opposite the 12th rib and had higher USDA yield grades and marbling scores (P less than .05). Hereford-Angus crossbreds had less dark, coarse band formation around the exterior of the LM and lighter, finer-textured lean (P less than .05). Cooking loss (%) and cooking rate (g/min) were not affected by breed or postmortem aging (P greater than .05). The increased toughness in the 5/8 Brahman carcasses may be due to increased CDP inhibitor activity.

Ovine carcasses were arterially infused with a volume equal to 10% of the live weight after electrical stimulation. The infusion solutions contained .075 M, .15 M or .3 M calcium chloride. Results indicated that .3 M calcium chloride treatment was the most effective concentration of CaCl2 to reduce the shear force value measured at 24 h postmortem. To examine the contribution of ionic strength to tenderization that occurs by infusion of carcasses with .3 M CaCl2, ovine carcasses were infused with CaCl2 and NaCl solutions of identical ionic strength. Results indicated that the tenderization that occurred by infusion of carcasses with CaCl2 was not due to ionic strength of the CaCl2 solution. Results also indicated that, compared to control animals, NaCl-infused carcasses were more tender after 6 d of postmortem storage (but not after 1 d, as observed with CaCl2-infused carcasses). Evidence is presented that indicates that activation of calcium-dependent proteases could be responsible for the observed tenderization (reduction in shear force) due to infusion of ovine carcasses with CaCl2.