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Effects of supplementation of OMNIGEN-AF and ractopamine hydrochloride on feedlot performance and carcass characteristics
Crossbred steers (n = 336; initial BW = 309 ± 22 kg) were utilized in a feedlot finishing trial in a 3 x 2 factorial complete randomized block design with the objective of identifying any possible interaction between OmniGen – AF (OM), a commercial feed additive containing B- complex vitamins and live yeast cells, and ractopamine hydrochloride (RAC). Factors were duration of OM supplementation (0, 28, or 56 d) during the final stage of feedlot production at 4 g / 45.5 kg BW and supplementation of RAC at 300 mg∙ steer-1d-1 for the last 28 d of finishing (RAC) or no beta agonist supplementation (NORAC). Steers were blocked by BW, stratified, and assigned randomly within block to pen (n = 42; 8 steers / pen). Ultrasound data measurements of rump fat thickness, 12th rib fat thickness, LM area, and intramuscular fat were collected on each steer 56 and 1 d prior to harvest and the difference between these time points was calculated. The day of harvest HCW were recorded. After a 48 – h chill, 12th rib fat depth, LM area, and marbling score were recorded. Data were analyzed using the Glimmix Procedure of SAS as a completely randomized block design with pen was the experimental unit and block treated as a random effect. There were no OM by RAC interaction observed in this study for any of the feedlot performance, carcass characteristics or ultrasound variables measured (P > 0.42). There was no significant effect of OM supplementation on any feedlot performance or carcass characteristics (P ≥ 0.10). Over the entire feeding period, steers supplemented RAC experienced a 0.5 kg/ d increase in ADG (1.81 and 1.76 kg/ d; P = 0.02), resulting in 10.0 kg greater FBW (625 and 615 kg; P < 0.01) and a 7.0 kg heavier carcass (394 and 387 kg; P < 0.01) compared to steers that received NORAC. Analysis of ultrasound time point differences reveals RAC steers experienced a 2.1 cm2 greater increase in steer’s LM area (6.6 and 4.6 cm2, respectively; P = <0.01) and reduction in the increase of intramuscular fat percentage (0.26 and 0.48%, respectively; P = 0.02) compared to NO RAC. These data would suggest that there is no effect on overall steer feedlot performance or carcass characteristics due to Omnigen – AF supplementation during the final 56 d of feedlot finishing.
Keywords:
Beef, Omnigen – AF, ractopamine hydrochloride