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Title: Effects of winter stocker growth rate and finishing system on: II. 9-10-11th rib composition, muscle color, and palatability

Author
item DUCKETT, SUSAN - CLEMSON UNIVERSITY
item Neel, James
item SONON, JR., ROBERTO - UNIVERSITY OF GEORGIA
item FONTENOT, JOSEPH - VIRGINIA TECH
item Clapham, William

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2007
Publication Date: 9/20/2007
Citation: Duckett, S.K., Neel, J.P., Sonon, Jr., R.N., Fontenot, J.H., Clapham, W.M. 2007. Effects of winter stocker growth rate and finishing system on: II. 9-10-11th rib composition, muscle color, and palatability. Journal of Animal Science. 85:2691-2698.

Interpretive Summary: Consumer markets for natural, forage-finished beef products are expanding in the U.S. The Southeastern U.S. is an ideal location for production of forage-finished beef due to the climate, abundance of forages and near year-round grazing season. Therefore, the objective of this research was to evaluate changes in rib composition, color, and palatability of beef from steers finished to a similar time endpoint on concentrate diet or forage diet after stockering at three growth rates during the winter period. Growth rate during the winter stocker period did not influence rib composition, color, or beef palatability. Finishing cattle on forages increased percentage lean yield and reduced percentage of fat trim by 42%. Finishing cattle on concentrates increased carcass weight and produced carcasses with brighter lean color and whiter fat color. Finishing system did not alter shear force or sensory attributes. Off-flavor ratings were higher for steaks from forage-finished beef; however, the values were relatively low. Finishing steers on forage reduced fat percentages in the rib and LM without altering tenderness of beef steaks. Winter performance can very greatly without impacting meat quality for both forage- and feedlot- finished cattle. Cattle finished on forages were shown to produce quality, highly palatable beef.

Technical Abstract: Angus-cross steers (n = 198) were used in a three-year study to assess the effects of winter stocker growth rate and finishing system on rib composition, color and palatability. During the winter months, steers were randomly allotted to three stocker growth rates: low (0.23 kg/d; LOW), medium (0.45 kg/d; MED), or high (0.68 kg/d; HIGH). At the completion of the stockering phase, steers were randomly allotted within each stocker growth rate to either a high concentrate (CONC) or pasture (PAST) finishing system. All steers regardless of finishing treatment were finished to an equal time endpoint to minimize confounding due to animal age or environmental factors. At the end of the finishing phase, steers were transported to a commercial packing plant for slaughter and rib (NAMP 107) obtained from one side of each carcass. The 9-10-11th rib section was dissected into lean, fat and bone and LM samples obtained for palatability and collagen content. Data were analyzed in a completely randomized design with stocker growth rate, finishing system, and two-way interaction as fixed effects and year as a random effect. Hot carcass weight and 9-10-11th rib section weight were greater (P = 0.01) for HIGH than LOW or MED. Winter stocker growth rate did not alter 9-10-11th rib composition. The percentage of fat-free lean including the LM and other lean trim was greater (P = 0.001) for PAST than CONC. Total fat percentage of the 9-10-11th rib section was 42% lower (P = 0.001) for PAST than CONC due to lower percentages of s.c., intermuscular, and i.m. fat. The percentage of total bone in the 9-10-11th rib section was greater (P = 0.001) for PAST than CONC. Finishing beef cattle on PAST increased (P = 0.001) the percentage of lean and bone, and reduced (P = 0.001) the percentage of fat in the carcass based on published prediction equations from 9-10-11th rib dissection. Stocker growth rate did not influence the objective color scores of LM or s.c. fat. Longissimus muscle color of PAST was darker (lower L*; P = 0.0001) and less red (lower a*; P = 0.002) than CONC. Juiciness scores were higher (P = 0.02) for CONC than PAST. Initial and overall tenderness scores as well as Warner-Bratzler shear force values did not differ (P > 0.28) among finishing systems. Beef flavor intensity was lower (P = 0.0001) and off-flavor intensity higher (P = 0.0001) for PAST than CONC. Total collagen content was greater (P = 0.0005) for PAST than CONC; however, there were no differences in percentage soluble or insoluble collagen. Growth rate during the winter stocker period did not influence rib composition, color, or beef palatability. Finishing steers on forage reduced fat percentages in the rib and LM without altering tenderness of beef steaks.