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This study was conducted to identify the origin of Escherichia coli O157:H7 contamination on steer hides at the time of harvest. Samples were collected from the feedlot, transport trailers, and packing plant holding pens and from the colons and hides of feedlot steers. A total of 50 hide samples were positive for E. coli O157:H7 in two geographical locations: the Midwest (25 positive hides) and Southwest (25 positive hides). Hide samples were screened, and the presence of E. coli O157: H7 was confirmed. E. coli O157:H7 isolates were fingerprinted by pulsed-field gel electrophoresis and subjected to multiplex PCR procedures for amplification of E. coli O157:H7 genes stx1, stx2, eaeA, fliC, rfbEO157, and hlyA. Feedlot water trough, pen floor, feed bunk, loading chute, truck trailer side wall and floor, packing plant holding pen floor and side rail, and packing plant cattle drinking water samples were positive for E. coli O157:H7. Pulsed-field gel electrophoresis banding patterns were analyzed after classifying isolates according to the marker genes present and according to packing plant. In this study, hide samples positive for E. coli O157:H7 were traced to other E. coli O157:H7-positive hide, colon, feedlot pen floor fecal, packing plant holding pen drinking water, and transport trailer side wall samples. Links were found between packing plant side rails, feedlot loading chutes, and feedlot pens and between truck trailer, different feedlots, and colons of multiple cattle. This study is the first in which genotypic matches have been made between E. coli O157:H7 isolates obtained from transport trailer side walls and those from cattle hide samples within the packing plant.

Data from a serial slaughter of 324 steers were used to determine the effects of feeder-cattle frame size (Large, L; Medium, M; Small, S) and muscle thickness (No. 1, No. 2, No. 3) on absolute growth and carcass development. Yearling feeder steers representing nine frame-size • musclethickness subclasses were backgrounded 28 d; subsamples of steers (n = 6) from each subclass were slaughtered at 28~d intervals (O, 28, 56, 84, 112 or 140 d) during a 140-d finishing period. One side from each carcass was dissected into muscle, bone and fat. Absolute growth during finishing was linear. Allometric growth coefficients for muscle, bone and fat were similar for all nine subclasses. Frame size was related (P<.01) to differences in absolute growth rate (L>S), compositional maturity at a common carcass weight (S>M>L) and slaughter weight at a constant carcass-fat percentage (L>M>S). Muscle thickness did not influence absolute growth rate, but was associated with differences (P<.01) in carcass muscle-to-bone ratio at a common bone weight and in muscle percentage when carcass fatness was statistically standardized. The effects of muscle thickness on carcass composition were most pronounced within the large-framed group. Relationships of these results to the USDA feeder-carrie grading principles are discussed.

Samples from steers fed a highenergy diet for 185 days prior to slaughter were used to compare collagen solubility and palatability of beef from youthful and mature carcasses. Carcasses representing the two maturity classes were selected specitically to have similar levels of intramuscular and subcutaneous fat, but distinctly different maturity indicators. Under the conditions of this study, maturity class had no effect on sensory properties or shear force values of cooked rib steaks. Total collagen content of samples from the longissimus muscle was higher for mature carcasses, but maturity class means for percentage of soluble collagen were not different. The relationships of these findings to preslaughter feeding regimen and collagen metabolism are discussed.

This study involved a comparison of the antimicrobial efficacy of several beef hide decontamination interventions to identify those that more effectively reduced levels of Escherichia coli O157:H7 and Salmonella. Whole beef hides were inoculated with E. coli O157:H7 and Salmonella and decontaminated with sprays of solutions of acetic acid (AA; 10%, 55 degrees C), lactic acid (LA; 10%, 55 degrees C), sodium hydroxide (SH; 3%, 23 degrees C), sodium metasilicate (SM; 4%, 23 degrees C), or sodium hydroxide (1.5%), followed by high-pressure washing with chlorinated (0.02%) water (SHC; both applied at 23 degrees C) or water (W; 23 degrees C) or by deluging with solutions of potassium cyanate (PC; 2.4%, 30 degrees C) or sodium sulfide (SS; 6.2%, 30 degrees C). All spraying treatments (AA, LA, SH, SM, and SHC) resulted in removal of visual organic material, whereas the dehairing treatments (PC and SS) successfully removed hair along with visual organic material. The PC, SS, and SHC treatments resulted in the greatest reductions of E. coli O157:H7 (P < 0.05), by 5.1, 4.8, and 5.0 log CFU/cm2, respectively. The SS and SHC treatments decreased Salmonella by 4.2 and 4.4 log CFU/cm2, respectively, compared with the water treatment, which reduced levels by 1.7 log CFU/cm2 (P < 0.05). The SH, AA, and LA treatments also lowered both E. coli O157:H7 and Salmonella by at least 2.0 log CFU/cm2. The treatments that were effective in this study deserve further consideration for commercial implementation as hide decontamination interventions.

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