1366 Comparison of the effects of laidlomycin propionate plus chlortetracycline vs. monensin plus tylosin and multiple β-agonist feeding strategies on feedlot performance and carcass characteristics

One hundred ninety-two steers (initial BW = 354 ± 23.5 kg) were used in randomized complete block design to examine the effect of various ionophore and ractopamine hydrochloride (RH) supplementation strategies on performance and carcass characteristics. Twelve pens of 4steers were assigned to each of the following treatments: unsupplemented control (CON), laidlomycin propionate plus chlortetracycline (CTC) with or without RH (LP and LPRH, respectively), and monensin sodium plus tylosin with RH (MON). Steers were fed for a total of 151 d, of which RH supplemented treatments received the β-agonist for the final 32 d. Laidlomycin propionate and CTC were removed during this period for the LPRH treatment, as no combination clearance exists for the commercially applied β-agonist (Actogain; Zoetis LLC, Florham Park, NJ). When included in the diet, LP, CTC, monensin, tylosin, and RH were supplemented at 10.7 g/ton, 343 mg/(head · d), 32.0 g/ton, 10.7 g/ton, and 255 mg/(head · d) (DM basis), respectively. Upon harvest, carcass data was collected by trained personnel. Before RH supplementation (d 0 to 118), both LP and LPRH treatments had greater ADG (P< 0.02) and G:F (P< 0.01) than CON, while MON was intermediate. During the RH supplementation period (d 119 to 150), LP maintained greater DMI (P< 0.01) than both RH treatments; however, over the same period, MON treated cattle had improved G:F (P< 0.02) compared to LP supplemented cattle and CON. Feeding LP without RH increased final BW (P= 0.02) over CON, and all ionophore supplemented treatments had improved ADG (P< 0.05) and G:F (P< 0.05) over the entire 151 d feeding period. Hot carcass weight was significantly greater (P= 0.04) in cattle fed LP with no β-agonist than CON, where LP cattle yielded an average of 12 kg more HCW, while both RH supplemented treatments were intermediate. Monensin plus tylosin with RH yielded significantly greater LM area (P= 0.03) than unsupplemented controls; however LP and LPRH treatments were unaffected. All other carcass characteristics were not significantly different. The results of this study indicate that LP supplementation without the use of a β-agonist may yield similar live performance and carcass responses associated with the administration of RH. These results also suggest that performance and carcass characteristics for cattle fed LP plus CTC are similar to those of cattle fed monensin plus tylosin throughout the feeding period.