Influence of yeast cell wall supplementation during the finishing phase on feedlot steer performance, carcass characteristics and post-mortem tenderness

Objectives were to evaluate benefits of yeast cell wall (YCW) supplementation on performance, carcass traits and tenderness of steers finished with zilpaterol hydrochloride (ZH). A randomized complete block design was used. British X Continental steers (n = 72; initial BW = 305±13 kg) were blocked by BW and allotted randomly to 24 pens (8 pens/treatment; 3 pens/block; 3 steers/pen). Treatments were: 1) control (CON); 2) YCW containing 100,000 IU vitamin D2/g (5.0 g•hd-1•d-1) (Y-D); 3) YCW C (5.0 g•hd-1•d-1) (Y-C). Steers were supplemented with respective treatments for 55 d, of which ZH was fed d 30-49. Cattle were weighed at d 0, 21, and 55. Carcass data was collected at the plant, and strip loins were obtained. Strips were cut into steaks and assigned to one of four aging periods (7, 14, 21 or 28 d). Tenderness was examined using Warner-Bratzler shear force (WBSF). Shrunk performance showed no differences. Carcass adjusted average daily gain (ADG) from d 21-55 was 0.29 kg greater for Y-D and 0.35 kg greater for Y-C when compared to CON (P = 0.04 and 0.01, respectively). Additionally, YCW increased G:F from d 21-55 with a 20.77% improvement for Y-D and 28.46% for Y-C over CON (P = 0.06 and 0.01, respectively). Carcass data revealed no differences, yet there was a trend for a 6 kg increase in HCW by both Y-D and Y-C compared to CON (P = 0.16 and 0.12). The treatment × aging interaction with the WBSF data was not significant (P = 0.20) and no differences were found in cooking loss (P = 0.88). Treatment Y-C displayed WBSF values 0.30 kg higher than CON and 0.29 kg greater than Y-D (P = 0.0062 and 0.0075). Within the 7 d aging period, Y-C steaks were 0.62 kg (P = 0.005) and 0.54 kg (P = 0.014) less tender than CON or Y-D, respectively. For 14 d steaks, Y-C WBSF values were 0.58 kg greater than CON (P = 0.008). No differences were found in the 21 or 28 d aging periods. The frequency distribution of WBSF values consistently displayed a trend for tougher Y-C steaks within each aging period. These data indicate yeast cell wall supplementation could increase performance of finishing steers while vitamin D2 supplementation at the current dosage yielded no beneficial effects on tenderness.