Carcass traits and M. longissimus lumborum palatability attributes of calf- and yearling-finished steers.

A 2-yr experiment was conducted to compare carcass characteristics and meat palatability attributes of steers ((3/4) British, (1/4) Continental) finished postweaning as calves or yearlings. Calves and yearlings of the same contemporary group were designated to a finishing system at weaning. Calves (n = 73) were finished in the feedlot (191 d) on a high-concentrate diet. Yearlings (n = 84) grazed crop residues after weaning, followed by spring and summer pasture grazing, and concluded with a short finishing period (91 d) in the feedlot. All steers were fed to a constant, fat thickness endpoint of 1 cm. The M. longissimus lumborum steaks from each production system were aged for 7, 14, or 21 d for Warner-Bratzler shear force determination and for 7 or 14 d for in-house sensory panel evaluation. Insoluble, percent soluble, and total collagen were determined. Yearlings produced heavier (P < 0.001) carcasses with larger (P < 0.001) LM areas and lower (P < 0.001) marbling scores and quality grades. Calves possessed greater amounts of total collagen (P < 0.001), with a significantly greater percentage of soluble collagen compared with yearlings (39.72 vs. 24.38%). Calves produced steaks with lower (P < 0.001) shear force values and greater (P < 0.001) sensory ratings for flavor. The USDA Choice steaks from the calves were more (P < 0.001) tender and more (P < 0.050) palatable than Choice steaks from yearlings, and USDA Select steaks from calves were rated more tender (P < 0.001), juicy (P = 0.012), and desirable (P < 0.001) than Select steaks from yearlings. As expected, increasing aging time from 7- to 14- to 21-d produced steaks with lower (P < 0.001) shear force values, regardless of the production system. Risk probabilities showed 1.24% of the steaks from calf-finished steers and 21.22% of steaks from yearling-finished steers to be tough. Sensory rating probabilities showed the steaks from the calves were most likely to be desirable for tenderness, whereas steaks from the yearlings were most likely to be undesirable for tenderness, juiciness, flavor, and overall acceptability. Thus, calf-finished steers produce carcasses superior in quality and palatability compared with those from yearling-finished steers. However, yearling-finished steers can produce tender beef with extended aging.

Accelerated wound repair, cell proliferation, and collagen accumulation are produced by a cartilage-derived growth factor.

Cartilage-derived growth factor (CDGF), a cationic polypeptide of approximately 18,000 mol wt, was prepared from bovine articular cartilage; other sources were bovine and human scapular and costal cartilage. Previous studies have shown that CDGF stimulates the proliferation of cultured mouse fibroblasts as well as chondrocytes and endothelial cells from various sources. In this study, CDGF was shown to stimulate dose-dependently the accumulation of DNA and collagen by rat embryo fibroblasts and a population of fibroblasts derived from granulation tissue. CDGF also stimulated the proliferation of cultured bovine capillary endothelial cells dose-dependently. To evaluate the effects of CDGF in vivo, we implanted polyvinyl alcohol sponges subcutaneously in rats. 6 d postimplantation, sponges were injected with 300 micrograms of partially purified CDGF, a dose which takes into account the cell numbers in the sponges as compared with cell cultures. CDGF rapidly disappeared from the sponges and only approximately 10% of the initial dose was present at 4 h. Despite its transient presence, CDGF caused a relative increase in sponge DNA content of 2.6-fold at 48 h and 2.4-fold at 72 h. We repeated the sponge experiment by using 500-ng injections of CDGF purified to near homogeneity by heparin-Sepharose chromatography. Purified CDGF caused significant increases in sponge collagen, protein, and DNA content at 48 and 72 h after a single injection. The effects of CDGF were abolished by heat and unaffected by reduction of disulfide linkages. Morphologically, CDGF did not evoke an inflammatory response, and its effect on proliferating endothelial cells and fibroblasts was, therefore, probably direct. However, increases in DNA content of sponges could not be fully accounted for by increased DNA synthesis, which suggests that recruitment may be an important component of the in vivo response. Taken together, the effects of CDGF on cultured cells and granulation tissue suggest that the sustained presence of CDGF in vivo may greatly enhance its effects upon wound repair.

The intracellular degradation of poly(epsilon-caprolactone).

Poly(epsilon-caprolactone) [PEC], a biodegradable aliphatic polyester, undergoes a two-stage degradation process: The first lengthy phase involves nonenzymatic hydrolytic cleavage of ester groups, the second phase beginning when the polymer is more highly crystalline, and of low molecular weight. The cellular events of the second phase were examined by implanting gelatin capsules containing 25 mg of low molecular weight (Mn 3000) PEC powders, 106 to 500 micron, in rats. PEC fragments ultimately were degraded in phagosomes of macrophages and giant cells, the process requiring less than 13 days for completion at some sites. PEC was also identified within fibroblasts. These studies support the intracellular degradation of PEC as the principal pathway of degradation once the molecular weight of the aged polymer is reduced to 3000 or less.