Effects of dietary fat and crude protein on feedlot performance, carcass characteristics, and meat quality in finishing steers fed differing levels of dried distillers grains with solubles

The objective of this study was to evaluate the influence of dietary protein and fat from distillers dried grains with solubles (DDGS) on feedlot performance, carcass characteristics, and meat quality in finishing steers. Angus-cross steers (n = 105; 443 ± 20 kg of BW) were blocked by BW and randomly assigned to 1 of 5 dietary treatments: 1) corn-based diet with DDGS included at 25% of DM (CON), 2) CON with DDGS included at twice the amount of CON (50% of DM; 50DDGS), 3) CON with added corn protein to equal the CP in the 50DDGS diet (CON+CP), 4) CON with added vegetable oil to equal the fat in the 50DDGS diet (CON+VO), and 5) CON with protein and fat added to equal the CP and fat in the 50DDGS diet (CON+CPVO). Steers were fed to a common 12th-rib fat depth endpoint (1.3 ± 0.2 cm; 68 to 125 d on trial). Loins and rounds were collected from 44 carcasses for Warner-Bratzler shear force (WBSF), ether extract, and case-life analyses. Data were analyzed using the MIXED procedure of SAS. Contrasts between 1) CON vs. elevated CP diets (50DDGS, CON+CP, and CON+CPVO; EP), 2) CON vs. elevated fat diets (50DDGS, CON+VO, and CON+CPVO; EF) and 3) CON vs. diets with elevated CP and fat (50DDGS and CON+CPVO; EPF) were analyzed. There were no differences in days on feed or DMI among treatments. Steers fed CON had greater ADG (P [less-than or equal to] 0.03) than EP, EF, and EPF diets. Steers fed CON also had greater G:F (P [less-than or equal to] 0.04) than EP and EPF steers. Final BW was greater for CON than EP and EPF diets (P [less-than or equal to] 0.03). Likewise, CON steers had heavier HCW than EPF steers (P = 0.04). Dressing percent, 12th-rib fat depth, LM area, KPH, and yield grade were not affected by treatment (P greater-than-or-equal 0.06). Steers fed the CON diet had greater marbling scores (P [less-than or equal to] 0.03) and quality grades (P [less-than or equal to] 0.02) compared with those fed EP, EF, and EPF diets. There were no differences in WBSF, ether extract, or lipid oxidation due to treatment (P greater-than-or-equal 0.44). However, CON steers had greater (P = 0.02) L* values than EF-fed steers and greater b* values than EP, EF, and EPF steers (P [less-than or equal to] 0.02) during retail display of ground product. Data from this study illustrate that live animal performance, marbling and quality grade, and color stability of ground product during retail display are negatively affected when DDGS are increased from 25 to 50% of the diet DM. This response appears to be due to elevated dietary fat, elevated CP, and a combination of elevated fat and protein within in the diet.