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Two studies were conducted to evaluate the effects of corn (CDG) and sorghum (SDG) wet distillers grains with solubles on feedlot cattle performance, carcass characteristics, and apparent total tract digestion of nutrients. In Exp. 1,224 steers were used in a randomized complete block design (initial BW 391.1 [+ or -] 9.51 kg) and fed steam-flaked corn (SFC)-based diets consisting of (DM basis) 0% distillers grains (CON), 15% SDG, 30% SDG, 15% CDG, 30% CDG, 15% of a 50:50 blend of SDG and CDG, and 30% of a 50:50 blend of CDG and SDG. Decreased carcass-adjusted final BW and HCW (P [less than or equal to] 0.05) were noted as the inclusion amount of distillers grains increased in the diet. Body weight gain efficiency did not differ among the CDG, 50:50 SDG and CDG blend, and CON treatments, but G:F was numerically less with either amount of SDG than for CON, and decreased (P [less than or equal to] 0.05) as distillers grains were increased from 15 to 30%. Cattle fed CON had greater carcass yield grades than those fed the distillers grain diets (P [less than or equal to] 0.05). In Exp. 2, crossbred beef steers (n = 36; initial BW 567.3 [+ or -] 53.1 kg) were used in a generalized randomized block design and fed SFC-based diets with 0% distillers grains (CON) and 15% (DM basis) CDG or SDG. Digestibility was determined with a pulse dose of [Cr.sub.2][O.sub.3]. Feeding steers 15% CDG or SDG increased intakes of CP and NDF (P [less than or equal to] 0.05), but intakes of DM, OM, and starch did not differ among treatments (P [greater than or equal to] 0.07). Apparent total tract digestibilities of DM, OM, CP, NDF, and starch (P [greater than or equal to] 0.25) did not differ among the 3 treatments. Fecal pH averaged over all sampling times was not affected by treatment, nor were average fecal pH values for prefeeding samples (0, 24, 48, and 72 h after the pulse dose) or for samples taken after feeding (12, 36, and 60 h after the pulse dose; P [greater than or equal to] 0.11). Results suggest that with 15% distillers grains in the DM, G:F was similar for cattle fed the CDG, 50:50 SDG and CDG blend, and CON diets. Feeding 30 vs. 15% distillers grains decreased G:F, but including 15% CDG or SDG in SFC-based diets did not affect apparent total tract digestibilities in feedlot steers. Key words: beef cattle, digestibility, distillers grains with solubles, feedlot doi: 10.2527/jas.2009-2487

The effects of wet distillers grains with solubles (WDG) on in vitro rate of gas production, IVDMD, [H.sub.2]S production, and VFA were evaluated. Five substrate treatments that were balanced for ether extract content were arranged in a 2 x 2 + 1 factorial. Factors were concentration (15 or 30%; DM basis) and source of WDG (corn or sorghum WDG; CDG and SDG, respectively) plus a 0% WDG control in substrates with steam-flaked corn as the basal grain. Control substrates had greater (P < 0.01) IVDMD and total gas production per gram of substrate DM than WDG-based substrates, and IVDMD was greater (P = 0.03) for CDG than for SDG substrates. Increasing WDG inclusion from 15 to 30% decreased IVDMD and total gas production (P < 0.05), but [H.sub.2]S production ([micro]mol/g of fermentable DM) increased (P = 0.01) as inclusion of WDG increased. There were no differences (P [greater than or equal to] 0.10) among treatments in proportions of major VFA, acetate:propionate ratio, and total VFA concentration. These results suggest that including WDG in the substrate decreased IVDMD and gas production, which was particularly evident as WDG increased from 15 to 30% of substrate DM. In addition, CDG seemed to be more digestible than SDG. Hydrogen sulfide production increased with increasing WDG in the substrate, reflecting greater S concentrations in WDG, but in vitro VFA profiles were not affected by WDG concentration or source. Key words: beef cattle, distillers grains with solubles, hydrogen sulfide, in vitro fermentation, volatile fatty acid doi: 10.2527/jas.2009-2486

Effects of varying bulk densities of steam-flaked corn (SFC) and level of inclusion of roughage in feedlot diets were evaluated in 3 experiments. In Exp. 1, a total of 128 beef steers were used in a 2 x 2 factorial arrangement to evaluate the effects of bulk density of SFC (335 or 386 g/L) and roughage concentration (6 or 10% ground alfalfa hay, DM basis) on performance and carcass characteristics. No interactions were observed between bulk density and roughage concentration for performance data. From d 0 to the end, cattle fed the 335 g/L SFC had greater overall G:F (P = 0.04) than those fed the 386 g/L SFC, with tendencies (P < 0.10) for improved G:F with the lighter flake weight evident at all 35-d intervals throughout the feeding period. Dry matter intake was less for cattle fed 6 vs. 10% roughage from d 0 to 35 (P = 0.03) and d 0 to 70 (P = 0.05), but not for the overall feeding period. Feeding 6 vs. 10% ground alfalfa as the roughage source tended (P = 0.09) to improve overall G:F. Treatment effects on carcass measurements were generally not significant (P > 0.20). In Exp. 2, the effects of bulk density of SFC (283, 335, or 386 g/L) and 6 or 10% ground alfalfa hay on IVDMD and in vitro pH were evaluated at 6, 12, 18, and 24 h of incubation. With a reduced-strength buffer in vitro fermentation system, pH increased (P < 0.01) with increasing bulk density at 6 and 12 h, and IVDMD decreased (P < 0.03) as bulk density increased. In contrast, in a normal-strength buffer system, there were no treatment differences (P > 0.23) for IVDMD. In Exp. 3, two diets that varied in bulk density of SFC and roughage concentration (335 g/L SFC with 6% alfalfa hay vs. 386 g/L SFC with 10% alfalfa hay) were compared for their effects on the pattern of feed intake and the acid-base balance in Holstein steers (12/treatment). No differences (P > 0.10) between treatments were noted for blood gases or urine pH; however, day effects (P < 0.02) were detected for blood pH, partial pressure of C[O.sub.2], and urine pH, which generally decreased (P < 0.05) with an increasing time on feed. The 2 treatments had little effect on the pattern of feed intake within the sampling days, with the exception that the 386 g/L SFC with 10% alfalfa hay diet increased (P < 0.05) the percentage of total DMI consumed at 1 and 6 h after feeding on d 14. Within the ranges of bulk density and roughage level studied, 335 g/L SFC with 6% alfalfa hay yielded the optimal animal performance, with limited effects on in vitro fermentation and the acid-base balance. Key words: acid-base balance, bulk density, feedlot cattle, in vitro dry matter disappearance, roughage, steam-flaked corn doi:10.2527/jas.2009-2400

Effects of 3 ionophores and 2 antibiotics on in vitro [H.sub.2]S production, IVDMD, total gas production, and VFA profile with or without added S were examined. In Exp. 1, ruminal fluid from 2 ruminally cannulated steers fed a steam-flaked corn-based diet (75% concentrate) without ionophore and antibiotics for 28 d before collection was used to inoculate in vitro cultures. Treatments were control (no ionophore or antibiotic), 3 ionophores (lasalocid sodium and monensin sodium at 5 mg/L or laidlomycin propionate at 1.65 mg/L), and 2 antibiotics (chlortetracycline hydrochloride at 5 mg/L and tylosin tartarate at 1.25 mg/L). Cultures also had 0 or 1.75 mg of S/L (from sodium sulfate). No S x ionophore-antibiotic treatment interactions were noted (P > 0.53) for IVDMD, total gas production, and [H.sub.2]S production. Hydrogen sulfide ([micro]mol/g of fermentable DM) was increased (P < 0.001), and total gas production tended (P = 0.09) to be increased with additional S; however, IVDMD was not affected by added S (P = 0.90). Production of [H.sub.2]S was not affected by ionophores or antibiotics (P > 0.18). On average, IVDMD (P = 0.05) was greater for ionophores than for antibiotics, whereas total gas production was less for ionophores than for control (P < 0.001) and antibiotics (P < 0.001). Molar proportions of acetate (P < 0.01) and acetate:propionate (P < 0.01) were decreased and propionate was increased (P < 0.001) in ionophore treatments when no S was added but when S was added there were no differences (P > 0.20) in acetate, propionate, or acetate:propionate between ionophores and control (S x treatment interaction, P = 0.03). In Exp. 2, the effects of ionophore-antibiotic combinations with added S were examined using the same procedures as in Exp. 1. Treatments were control, monensin plus tylosin (MT), and lasalocid plus chlortetracycline (LCTC), with concentrations of the ionophores and antibiotics as in Exp. 1. No differences were observed among treatments for [H.sub.2]S production (P > 0.55). Treatments MT and LCTC tended (P = 0.06) to increase IVDMD and decreased (P = 0.02) gas production vs. control. Proportion of acetate (P = 0.01) an(1 acetate:propionate (P < 0.01) were decreased and propionate increased (P = 0.01) for both MT and LCTC compared with control. These data suggest that when S is approximately 0.42% of substrate DM, the 3 ionophores and 2 antibiotics we evaluated did not affect production of [H.sub.2]S gas in an in vitro rumen culture system. Key words: antibiotic, beef cattle, hydrogen sulfide, ionophore, sulfur

British and British x Continental steers (n = 560; initial BW = 339.4 [+ or -] 1.76 kg) were used in a serial slaughter study with a completely random design to evaluate effects of zilpaterol hydrochloride (ZH; 8.33 mg/kg of dietary DM basis) on performance and carcass characteristics. Treatments were arranged in a 4 x 4 factorial (112 pens; 7 pens/treatment; 5 steers/ pen) and included duration of ZH feeding (0, 20, 30, or 40 d before slaughter plus a 3-d ZH withdrawal period) and days on feed (DOF) before slaughter (136, 157, 177, and 198 d). No duration of ZH feeding x slaughter group interactions were detected for the performance measurements (P > 0.10). Final BW did not differ (P = 0.15) between the 0-d group and the average of the 3 ZH groups, but ADG was greater for the average of the 3 ZH groups during the period in which ZH diets were fed (P < 0.01) and for the overall feeding period (P = 0.05). As duration of ZH feeding increased, DMI decreased (P = 0.01) and G:F increased linearly (P < 0.01). With the exception of KPH (P = 0.022), no duration of ZH feeding x slaughter group interactions (P > 0.10) were detected for carcass characteristics. Regardless of the duration of ZH feeding, cattle fed ZH had greater HCW (P < 0.01), greater dressing percent (P < 0.01), less 12th-rib fat (P < 0.01), larger LM area (P < 0.01), less KPH (P = 0.03), and lower yield grade (P < 0.01) than the 0-d cattle. The 0-d group had greater marbling scores (P < 0.01) than cattle fed ZH diets, with a tendency for a linear decrease in marbling score (P = 0.10) as duration of ZH feeding was extended. A greater percentage of carcasses in the 0-d group graded USDA Choice or greater (P < 0.01) than in the 3 ZH groups, whereas the percentage of Select carcasses was greater (P = 0.01) for the 3 ZH groups. From d 0 to end (P = 0.04) and during the last 43 d on feed (P < 0.01), ADG responded quadratically to DOF before slaughter. No differences were detected among slaughter groups for DMI for the entire trial period; however, a quadratic response (P = 0.02) was observed for the final 43 d before slaughter. A quadratic response was also detected for the final 43 d before slaughter (P < 0.01) and from d 0 to end (P = 0.02) for G:F. Final BW, HCW, dressing percent, and 12th-rib fat increased linearly (P < 0.01) as DOF before slaughter increased. Our results indicate that no substantial effects on performance and carcass measurements were observed when ZH was fed for 30 or 40 d as opposed to 20 d, and that effects of ZH generally did not interact with DOF before slaughter. Key words: B-adrenergic receptor agonist, cattle, feedlot, performance, zilpaterol