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

¹ Clemson University, Clemson, SC
² ARS, USDA, Beaver, WV
³ University of Georgia, Athens
⁴ Virginia Polytechnic Institute and State University, Blacksburg, VA

^* To whom correspondence should be addressed. E-mail: sducket{at}clemson.edu.

	Abstract

Angus-cross steers (n = 198; 270 kg; 8 mo) were used in a three-year study to assess the effects of winter stocker growth rate and finishing system on 9-10-11^th rib composition, color and palatability. During the winter months (December to April), 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 allotted randomly within each stocker growth rate to either a high concentrate (CONC) or pasture (PAST) finishing system. All steers were finished to an equal time endpoint to minimize confounding due to animal age. At the end of the finishing phase, steers were transported to a commercial packing plant for slaughter and primal rib (NAMP 107) was removed from one side of each carcass. The 9-10-11^th rib section was dissected into lean, fat and bone and LM samples were analyzed 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 9-10-11^th rib section weight were greater (P = 0.01) for HIGH than LOW or MED. Winter stocker growth rate did not alter 9-10-11^th 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 9-10-11^th 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 9-10-11^th 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 9-10-11^th 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.

Key Words: Beef, Forage, Stocker, Carcass Composition, Meat Quality