Lubabegron (Experior; Elanco, Greenfield, IN, USA) is the first U.S. Food and Drug Administration approved feed additive for reducing gas emissions from feedlot animals or their waste; it does not have live or carcass performance claims. Our primary objective was to determine the effect of lubabegron on feedlot performance and carcass traits in finishing beef steers compared to ractopamine hydrochloride (Optaflexx; Elanco, Greenfield, IN, USA). A commercial feedlot trial using cross-bred beef steers (n = 2,117; 373 +/- 15 kg initial body weight [BW]) was completed with a randomized complete block design. Treatments consisted of two feed additives: (1) OPT targeted to deliver 300 mg/animal/d of ractopamine hydrochloride for 28 +/- 7 d out from harvest and (2) EXP targeted to deliver 36 mg/animal/d of lubabegron 56 +/- 7 d out from harvest and a 4-d preslaughter withdrawal period. Twenty 70 to 142 hd pens with 10 pens per treatment were used. Cattle were weighed at arrival processing and at harvest and fed for an average of 167 d. Data were used to calculate production metrics, partial budgets, and estimated greenhouse gas emissions using published methods, and were analyzed using linear mixed models with pen as the experimental unit and block as a random intercept. A statistical significance threshold of alpha = 0.05 was determined a priori. There was no evidence for statistically significant differences between treatments for initial BW (P = 0.70), health-related outcomes (P values >= 0.43), or mobility scores (P = 0.09). Cattle-fed EXP had increased final BW, ADG, G:F, and decreased dry matter intake (P values <= 0.01) compared to OPT. Carcasses were 11 +/- 1.76 kg (hot carcass weight) heavier in EXP group (P < 0.01), and differed between treatments for both yield grades (YG) and quality grades distributions (P values <= 0.01). Cattle-fed EXP had a shift toward more YG 1 and 2, select and sub-select carcasses compared to OPT, which had as shift toward more YG 3, 4, 5, prime and choice carcasses. With increased beef production and efficiency compared to OPT, the estimated CO2 equivalent emissions from production were reduced by 6.2% per unit of carcass weight for EXP (P <= 0.01). Estimated net returns/animal shipped were $56.61 +/- 9.37 more for EXP than OPT (P <= 0.01). In conclusion, when cattle were fed for the same total number of days, feeding EXP compared to OPT increased net returns, feedlot performance, and efficiency, but resulted in carcass yield and quality characteristics that may impact marketing programs. Lay Summary Lubabegron (Experior), the first Food and Drug Administration approved feed additive for reducing gas emissions from feedlot animals, was studied for its impact on feedlot performance and carcass traits in beef steers compared to feeding ractopamine hydrochloride (Optaflexx). In a commercial feedlot trial with 2,117 cross-bred beef steers, lubabegron (EXP) demonstrated advantages over ractopamine hydrochloride (OPT) in final body weight, average daily gain, feed efficiency, and reduced dry matter intake. Carcasses from EXP were heavier, with shifts towards decreased yield and quality grades. The feeding of EXP resulted in a 6.2% reduction in estimated CO2 equivalent emissions per unit of carcass weight, and a $56.61 higher estimated net returns per animal shipped compared to OPT. This study indicates that feeding Experior instead of Optaflexx in commercial feedlot steers enhances feedlot performance and efficiency while influencing carcass characteristics that may impact marketing programs.

The objective of this research was to evaluate the effects of two implant programs and differing days-on-feed (DOF) on net returns of beef feedlot heifers using sensitivity analyses of key economic factors. Crossbred beef heifers [n = 10,583; initial weight 315 kg (+/- 20.1 SD)] were enrolled across three trials (one Kansas, two Texas feedlot trials). Heifers were blocked by arrival and randomly allocated to one of six pens, resulting in a total of 144 pens and 24 blocks. Pen was randomly assigned to treatment as a 2 x 3 factorial. Implant programs were: IH + 200-Revalor-IH at initial processing, and a terminal implant after approximately 90 DOF (Revalor-200), or, XH-a single implant at initial processing (Revalor-XH). The DOF treatments were: heifers fed to a standard baseline endpoint (BASE) or heifers fed for an additional + 21 or + 42 d beyond BASE. Pen-level partial budgets were used for economic sensitivity analyses, which varied price points of single pricing components with all other components fixed. Variable components were live-fed cattle prices, base carcass prices (i.e., dressed), Choice-Select spread (CS-spread), and feed and yardage prices (FYP). For each, a Low, Mid-Low, Middle, Mid-High, and High price was chosen. Linear mixed models were fit for statistical analyses (alpha = 0.05). There were no significant two-way interactions (P-values >= 0.14). Regardless of the variable component evaluated, XH heifers had poorer net returns than IH + 200 at all prices (P <= 0.04). Selling live, the + 21 and (or) + 42 heifers had lower net returns than BASE at every fed cattle price point (P < 0.01). Selling dressed, the + 21 and (or) + 42 heifers had lower returns than BASE at Low, Mid-Low, and Middle fed cattle base prices (P < 0.01); there were no significant DOF differences at Mid-High, or High prices (P >= 0.24). Net returns were lower for + 42 than BASE at all CS-spreads (P <= 0.03), while BASE and + 21 did not differ significantly. Longer DOF had lower net returns than BASE when selling live at every FYP (P < 0.01) except at the Low price (P = 0.14). Selling dressed, there was no significant effect of DOF at Low or Mid-Low FYP (P >= 0.11); conversely, extended DOF had lower net returns than BASE at Middle, Mid-High, and High FYP (P < 0.01). Overall, there was minimal economic evidence to support extending feedlot heifer DOF beyond the BASE endpoint, and when feeding longer, larger reductions in return were observed when marketing live as opposed to dressed.

The objectives were to evaluate the effects of metaphylaxis (META) and pull-and-treat (PT) programs on health, antimicrobial use, beef production, economics, and greenhouse gas emissions in cattle at medium risk for bovine respiratory disease (BRD). A randomized complete block design was used at two US commercial feedlots. Steers and heifers [2366 total; 261 (±11.0) kg initial weight] were blocked by sex and feedlot arrival, and allocated to one of two pens within a block (16 pens total, eight blocks). Pens were randomly assigned to treatment: META, tulathromycin injection at initial processing; or PT, tulathromycin injection only for first clinical BRD treatment. Data were analyzed with linear and generalized linear mixed models. There was greater BRD morbidity in PT than META cattle (17.2% vs. 7.3% respectively; p < 0.01), and greater total mortality (2.5% vs. 1.1% respectively; p = 0.03). Per animal enrolled, 1.1 antimicrobial doses were used for META compared to 0.2 for PT (p < 0.01). Per animal enrolled, final live (p = 0.04) and carcass (p = 0.08) weights were greater for META than PT; however, net returns ($/animal) were not significantly different (p = 0.71). Compared to PT, total lifetime estimated CO2 equivalent emissions from production were reduced by 2% per unit of live weight for META (p = 0.09). While antimicrobial use was reduced with PT, there may be substantial negative impacts on other outcomes if META was not used in this type of cattle population.

Pulmonary disease is often associated with feedlot cattle mortality, and the most common syndromes include bronchopneumonia, acute interstitial pneumonia, and bronchopneumonia with an interstitial pneumonia. The study objective was to utilize gross necropsy and histopathology to determine the frequency of pulmonary lesions from three major syndromes and agreement between gross and histopathological diagnosis. A cross sectional, observational study was performed at six U.S. feedyards using a full systematic necropsy to assess mortalities during summer 2022. A subset of mortalities had four lung samples submitted for histopathological diagnosis. Gross necropsy was performed on 417 mortalities, 402 received a gross diagnosis and 189 had a histopathological diagnosis. Descriptive statistics were used to evaluate pulmonary diagnosis frequency based on method (gross/histopathology), and generalized linear mixed models were used to evaluate agreement between histopathological and gross diagnoses. Using gross diagnosis, bronchopneumonia represented 36.6% of cases with acute interstitial pneumonia and bronchopneumonia with an interstitial pneumonia representing 10.0% and 35.8%, respectively. Results identified bronchopneumonia with an interstitial pneumonia as a frequent syndrome which has only been recently reported. Histopathological diagnosis had similar findings; bronchopneumonia represented 32.3% of cases, with acute interstitial pneumonia and bronchopneumonia with an interstitial pneumonia representing 12.2% and 36.0%, respectively. Histopathological diagnosis tended (p-VALUE = 0.06) to be associated with gross diagnosis. Pulmonary disease was common and both diagnostic modalities illustrated three primary syndromes: bronchopneumonia, acute interstitial pneumonia, and bronchopneumonia with an interstitial pneumonia with similar frequencies. Improved understanding of pulmonary pathology can be valuable for evaluating and adjusting therapeutic interventions.

Research objectives were to evaluate effects of two implant programs for beef heifers fed three different durations (days-on-feed; DOF) on carcass weight and composition (primary outcomes) and feedlot performance (secondary outcomes) at commercial feedlots. Data from a randomized trial in Kansas were analyzed separately and also pooled with data from two previously published trials conducted in Texas. Heifers were randomly allocated to pens within a block, and pens were randomized to treatments in a 2 x 3 factorial randomized complete block design. Implant programs were IH + 200 - an initial Revalor-IH implant [80 mg trenbolone acetate (TBA) and 8 mg estradiol (E-2)] and a re-implant after a mean of 98-d (+/- 10.8 SD) with Revalor-200 (200 mg TBA and 20 mg E-2), or XH - Revalor-XH, a single extended-release implant (200 mg TBA and 20 mg E-2). Heifers were fed to a baseline endpoint (BASE; pooled mean 166-d +/- 11.9 SD), +21, or +42 additional DOF. A total of 10,583 crossbred heifers with mean initial body weight (BW) 315 kg (+/- 20.1 SD) were enrolled in 144 pens in 24 blocks (treatment replications) across the three trials. General and generalized linear mixed models accounting for clustering of trials, blocks, and pens were used to test for effects of treatments, with significance set at alpha = 0.05. The only implant program x DOF interaction in pooled analyses was for dry matter intake (DMI; P < 0.01); IH + 200 heifers had lower mean DMI than XH when fed +42 DOF. Gain:feed was higher for IH + 200 compared to XH with dead and removed animals excluded (P < 0.01) or included (P = 0.03). For IH + 200, hot carcass weight (HCW) increased (P < 0.01), USDA Yield Grade (YG) distributions shifted towards lower numerical categories (P < 0.01), and Prime carcasses decreased while Select increased compared to XH (P < 0.01). For each incremental increase in DOF, final BW (P < 0.01) and HCW increased (P < 0.01), while daily gain (P < 0.01) and gain:feed (P < 0.01) decreased. Categories of YG were affected by DOF (P < 0.01); there were fewer YG 1 and 2 and more YG 4 and 5 carcasses for +42 compared to BASE and +21. USDA Quality Grade (QG) distributions differed by DOF (P < 0.01); each incremental increase in DOF resulted in more Prime and fewer Select carcasses. Without meaningful interactions, tested implant programs likely have a consistent effect when heifers are fed to similar DOF, while changes in HCW, QG, and YG may influence marketing decisions when extending DOF.

The objective was to investigate the effects of inorganic or amino acid-complexed sources of trace minerals (zinc and copper) on performance of beef heifers during a grazing period following a receiving trial. Crossbred beef heifer calves (n = 287, initial body weight = 231 ± 0.49 kg) were used in a 42-day receiving trial. Any cattle that failed to gain at least 0.45 kg/d, and(or) received 3 doses of antibiotic therapy during the receiving trial were removed from the study. Remaining cattle were kept within their respective pen and treatment and were randomly retained for the grazing phase. If there were not enough eligible calves/pen, calves on the same treatment that had been randomly removed from other pens were added to achieve equal pen counts. Cattle (n = 204; initial body weight = 262 ± 1.44 kg) grazed at 2 different locations in Arkansas; in Fayetteville, cattle (12 pens; 6 pens/treatment) grazed 6-acre stockpiled mixed grass pastures (n = 8 calves/pasture); in Batesville, cattle (12 pens; 6 pens/treatment) grazed 5-acre stockpiled novel-endophyte fescue pastures (n = 9 calves/pasture). Treatments consisted of supplemental zinc (540 mg/d) and copper (90 mg/d) from complexed (Availa, Zinpro Corp. Eden Prairie, MN) or inorganic sources (sulfates). Cattle grazed for at least 114 days until reaching a weight goal of 341 kg. Cattle had ad libitum access to water and were offered bermudagrass hay when forage was limited. Body weights were measured on 28-day intervals. A subset of calves (3/pen) were liver biopsied at the end of receiving and grazing phases to compare liver mineral concentrations. Following grazing, calves were removed from treatments and sent to a Kansas feedlot (n = 198) where they were commingled and fed in a single pen for 141 days. Morbidity and mortality data were recorded, and after slaughter, carcass data were collected. Statistical analyses were performed using MIXED and GLIMMIX procedures of SAS 9.4 with location as a random effect and pen within location specified as subject. There was no treatment (P = 0.14) or treatment × day interaction (P = 0.92) for body weights during the grazing phase. Overall average daily gain was not different between treatments (P = 0.94; 0.69, SE = 0.04). Treatment did not affect liver mineral concentrations (P ≥ 0.17). There were no differences in feedlot morbidity, mortality, or carcass characteristics (P ≥ 0.28). In conclusion, although complexed sources of trace minerals (zinc, copper, manganese, and cobalt) improved body weight gain and decreased morbidity treatments during the receiving phase, there were no significant differences from grazing to slaughter when supplementing amino acid complexed versus inorganic mineral sources of zinc and copper during the grazing period.

Bovine respiratory disease (BRD) is a frequent disease in feedlot cattle, but little is known on the role of pen housing conditions. The objective of this research is to use a retrospective analysis with data from 10 U.S. feedlots to determine potential associations between BRD risk during the first 45 days after arrival with pen-level management factors including the number of water sources, shared water sources, and shared fence lines. Generalized linear mixed models were used to evaluate associations between management factors, cattle demographics, and BRD incidence. The effect of shared water sources on BRD risk was modified by arrival weight and cohort size (p < 0.05). Cattle with two water sources had lower BRD morbidity (5.55% ± 0.98) compared to cattle with one water source (8.80% ± 1.50) when arrival weight was 227 kg to 272 kg, while there were few differences in heavier weight cattle. Cattle with two water sources had lower BRD morbidity (3.11% ± 0.56) compared to one water (5.50% ± 0.10) when cohort size was 100–175 head, but there were no BRD morbidity differences when bigger or smaller cohorts were evaluated. Shared fence lines and water sources were associated with BRD risk; however, no biologically meaningful results were identified. The number of water sources was associated with BRD risk, and effects were modified by cohort size and arrival weight.

The objective of this study was to evaluate the effectiveness of a direct-fed microbial (DFM) product in reducing fecal shedding ofEscherichia coli O157:H7 in finishing commercial feedlot cattle in Kansas (KS) and Nebraska (NE). Utilizing a randomized complete block design within the feedlot (KS, n = 1; NE,n = 1), cattle were randomly allocated to 20 pens, grouped in blocks of two based on allocation date, and then, within the block, randomly assigned to a treatment group (DFM or negative control). The DFM product was included in the diet at a targeted daily dose of 1 x 10(9) colony-forming units (CFU) of theLactobacillus acidophilusandLactobacillus caseicombination per animal for at least 60 d before sampling. Feedlots were sampled for four consecutive weeks; weekly sampling consisted of collecting 20 pen floor fecal samples per pen. Fecal samples were subjected to culture-based methods for detection and isolation of E. coli O157, and positive samples were quantified using real-time polymerase chain reaction. Primary outcomes of interest were fecal prevalence ofE. coli O157:H7 and E. coli O157 supershedding (>= 10(4)CFU/g of feces) prevalence. Data for each feedlot were analyzed at the pen level using mixed models accounting for the study design features. Model-adjusted meanE. coli O157:H7 fecal prevalence estimates (standard error of the mean [SEM]) for DFM and control groups were 8.2% (SEM = 2.2%) and 9.9% (SEM = 2.5%) in KS and 14.6% (SEM = 2.8%) versus 14.3% (SEM = 2.6%) in NE; prevalence did not differ significantly between treatment groups at either site (KS,p = 0.51; NE,p = 0.92). MeanE. coliO157 supershedding prevalence estimates for DFM and control groups were 2.2% (SEM = 0.7%) versus 1.8% (SEM = 0.7%) in KS (p = 0.66) and 6.7% (SEM = 1.5%) versus 3.2% (SEM = 1.0%) in NE (p = 0.04). In conclusion, administering the DFM product in the finishing diet of feedlot cattle did not significantly reduceE. coliO157:H7 fecal prevalence or supershedding prevalence in study pens at either commercial feedlot.

The objective of this study was to compare feedlot performance and carcass traits between two implant programs in heifers harvested at 3 different days on feed (DOF; 179, 200, or 221 d). Crossbred beef heifers (n = 3,084; 291 + 3.9 kg) were used in a 2×3 factorial arrangement of treatments in a randomized complete block design. Revalor-IH (80 mg TBA and 8 mg E2) was administered on arrival followed by Revalor-200 (200 mg TBA and 20 mg E2) 94 d before harvest (IH/200) or Revalor-XH (80 mg TBA and 8 mg E2, uncoated; 120 mg TBA and 12 mg E2, coated) was administered on arrival (XH). No implant × DOF interaction was detected (P ≥ 0.09) for any parameter. Heifers subjected to IH/200 had greater (P ≤ 0.01) final BW, ADG (P < 0.01) and G:F (P = 0.01). As DOF increased, BW increased (P ≤ 0.01) while ADG (P<0.01) and G:F (P ≤ 0.01) decreased. Hot carcass weight was greater (P = 0.01) for IH/200 compared with XH (367 vs. 361 kg, respectively). Heifers receiving XH had greater marbling scores (P = 0.02; 582 vs. 568) and BF (P = 0.01; 1.78 vs 1.70 cm) compared with IH/200 while re-implanted heifers had increased (P = 0.01) REA (86.5 vs. 83.2 cm2). Heifers implanted with XH tended to be fatter than those implanted with IH/200 having a greater (P = 0.01) proportion of USDA Prime and fewer (P<0.01) USDA Select. Increasing DOF increased (P ≤ 0.03) HCW, DP, BF, REA, marbling, and proportion of USDA Prime carcasses. Growth performance and HCW were increased for IH/200 compared with XH heifers. Increasing DOF resulted in poorer ADG and G:F but increased HCW.

Lucas M. Horton,1 MS; Brandon E. Depenbusch,2 MS, PhD; Dustin L. Pendell,1,3 MS, PhD; David G. Renter,1 DVM, PhD 1 Center for Outcomes Research and Epidemiology and the Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506 2 Innovative Livestock Services, Inc., Great Bend, KS 67530 3 Department of Agricultural Economics, College of Agriculture, Kansas State University, Manhattan, KS 66506 Corresponding author: Dr. David Renter; drenter@vet.k-state.edu

Our objectives were to describe revenue received for feedlot cattle culled for slaughter and associations with reported weekly prices from US beef markets. Observational data on feedlot culls (N = 2,992) were collected from 4 Kansas feedlots over 2 years (2018 to 2020). Weekly prices from various US beef markets were used to evaluate correlations with prices received for culled animals. Descriptive statistics, and linear and generalized linear mixed models, were used to evaluate characteristics of feedlot culls. Musculoskeletal/trauma (49.7%) and respiratory disease (40.9%) were the most common reasons for culling. Culls returned revenue 98.1% of the time; those culled for respiratory disease or “other” reasons returned revenue significantly less frequently (96.7 or 96.3%, respectively) than those culled for musculoskeletal/trauma (99.1%). Mean revenue received [± 95% CI] was 434.81 [427.22 to 442.40] $/animal (culls returning no revenue included); and mean carcass price was 87.40 [86.70 to 88.10] $/hundredweight. Revenue was significantly correlated with several market indices, but most correlations were relatively weak. In this population, national cull cow (Breaker [75% lean]; over 500 lb [227 kg]) prices appeared to be the overall best indicator of feedlot cull prices, with feedlot cull carcasses averaging 74.6% of the weekly cull cow carcass price.

A total of 1,866 cross-bred heifers (268 ± 9 kg initial BW) were used in a 181-d finishing study to evaluate the effects of time of terminal implant administration on growth and carcass measures. All heifers received an initial implant containing 80 mg of trenbolone acetate and 8 mg of estradiol (Revalor-IH, Merck Animal Health, Madison, NJ) at initiation of the experiment. Cattle were fed in 24 pens using a randomized complete block design. There were a total of six blocks, with arrival date serving as the blocking factor. The four treatments were achieved by administration of a subsequent implant containing 200 mg of TBA and 20 mg of estradiol (Revalor-200) at 160, 120, 80 or 40 d before harvest (DBH). Marketing dates of blocks of heifers were determined at initiation of the experiment and were based on expected growth performance of the heifers using historical data for the facility. All animals that died or were removed from the study were excluded from the analysis. Dry matter intake was similar (P ≥ 0.12) between all treatments. A quadratic response to treatment was observed for G:F (P = 0.02), HCW (P = 0.03), and LM area (P = 0.01), and a tendency for a quadratic response to treatment was observed for ADG (P = 0.07) and dressing percentage (P = 0.06). For all of these variables, the greatest numeric treatment values were observed for the 120 and 80 DBH treatments. Based on an axis of symmetry analysis for the regression lines, HCW was optimized at 94 DBH and G:F was optimized at 90 DBH. In addition to these observations, linear increases in marbling score (P = 0.03) and percentage of carcasses grading USDA Prime (P = 0.02) were observed as DBH treatment decreased. These results indicate that the optimal time to give a terminal implant to heifers based on G:F and HCW is between 90 and 94 DBH. However, the earlier in the finishing period that the terminal implant was given, the greater the negative impact on intramuscular fat deposition.

Animal agriculture continues to look for new, non-antibiotic feed solutions that can be used in conventional and natural feedlot systems to help improve cattle health and performance. Therefore, crossbred heifers (n = 1,495; 359 ± 10.75 kg; 20 pens total) were used in a randomized complete block design study at a commercial feedlot to determine the effects of a proprietary Saccharomyces cerevisiae fermentation prototype on performance, carcass characteristics, and liver abscess prevalence when monensin, tylosin, and direct-fed microbials were not included in the diet. Heifers were fed a diet containing (1) monensin, tylosin, and a direct-fed microbials (PC) or (2) a Saccharomyces cerevisiae fermentation prototype (PRT; NaturSafe, Diamond V, Cedar Rapids, IA) at 18 g/head daily without PC. Diets were fed twice daily with heifers receiving half of the daily dose of treatment in the TMR at each feeding. Pen BW were collected on d 0 and before slaughter. Daily measurements recorded while cattle were in the feedlot included feed intake, morbidity, and mortality. Cattle were shipped to slaughter on d 125 and 146 (5 pens per treatment per day). Carcass data collected included HCW, DP, QG, YG, KPH, rib fat thickness, LM area, marbling score, and liver abscess scores. Data were analyzed with the MIXED procedure (continuous) and GLIMMIX procedure (categorical) of SAS. Treatments were similar (P ≥ 0.16) for final BW (580 vs. 580 kg), ADG (1.64 vs. 1.63 kg/d), G:F (0.159 vs. 0.156 kg/kg), HCW (366 vs. 367 kg), other carcass characteristics, morbidity (0.3 vs. 0.0%), and mortality (0.77 vs. 0.70%). Heifers fed PRT had a numerically lower (P = 0.27) prevalence of liver abscesses with fewer livers having less severe (i.e., A−) abscesses. Replacing monensin, tylosin, and direct-fed microbials in conventional feedlot diets with NaturSafe resulted in similar growth performance, carcass characteristics, and liver abscess prevalence in feedlot cattle.

Three experiments evaluated initial implant strategies for finishing cattle. In Exp. 1, heifers (n = 1,405; initial BW = 282 kg) were given (1) Revalor-IH followed by Revalor-200 (REV-IH/200), (2) Revalor-H followed by Revalor-200 (REV-H/200), or (3) Revalor-200 followed by Revalor-200 (REV-200/200). Intake, ADG, and G:F were not affected (P ≥ 0.14) by implant strategies, nor were HCW and LM area (P ≥ 0.16). Percent USDA Choice was greater (P < 0.01) for Rev-IH/200 compared with Rev-H/200 and Rev-200/200. Experiment 2 used steers (n = 1,858; initial BW = 250 kg) given (1) Revalor-IS reimplanted with Revalor-200 (Rev-IS/200), (2) Revalor-XS followed by Revalor-IS (Rev-XS/IS), (3) Revalor-XS followed by Revalor-S (Rev-XS/S), or (4) Revalor-XS followed by Revalor-200 (Rev-XS/200). Implanting strategies did not affect (P ≥ 0.32) DMI or G:F. Carcass traits were not different (P ≥ 0.18) among treatments, except steers implanted with Rev-XS/200 had greater (P < 0.01) LM area. In Exp. 3, steers (n = 1,408; initial BW = 305 kg) were given (1) Rev-IS/200, (2) Rev-200/200, or (3) Rev-XS/200. Gain and G:F did not differ (P ≥ 0.36) among the 3 implant strategies, nor did HCW or marbling score (P ≥ 0.15). Steers given Rev-XS/200 had greater (P < 0.01) LM area and decreased (P ≤ 0.05) 12th-rib fat and YG compared with Rev-200/200 and Rev-IS/200. Using Rev-200/200 and Rev-XS/200 increased (P = 0.03) USDA Select compared with Rev-IS/200. Using greater-initial-dose implant strategies may not affect ADG or G:F but appears to increase leanness.

Angus crossbred steers (n = 40; 563 ± 44 kg) were used to examine the effects of handling method and fat thickness on the blood chemistry and physiology of market steers. Steers were blocked by backfat (BF) thickness and were randomly assigned to treatment groups: low-stress handling (LSH) and aggressive handling (AH). Cattle were then ran¬domly assigned to one of 5 blocks containing 4 steers from the LSH and AH treatments. Steers in the LSH treatment were walked and AH cattle were run through a course of 1,540 m. Blood samples were obtained via jugular venipuncture before handling (BASE), at 770 m (LAP1), at 1,540 m (LAP2), and at1 h (1H) and 2 h (2H) after finishing the course. Blood samples were analyzed for plasma lactate (LAC), creatinine kinase (CK), base excess (BE), blood pH (pH), serum cortisol (CORT) concentrations, and venous carbon dioxide (PvCO2) and oxygen (PvO2) pressures. Heart rate (HR), respiratory rate (RR), and rectal temperature (TEMP) were measured at the same intervals. Cattle in the AH treatment had greater ( < 0.05) LAC than those in LSH at BASE (4.1 vs. 3.0 mmol/L), LAP1 (16.5 vs. 2.3 mmol/L), LAP2 (22.3 vs. 2.4 mmol/L), 1H (7.2 vs. 2.7 mmol/L), and 2H (4.0 vs. 2.5 mmol/L), respectively. Creatinine kinase and RR were not different (P > 0.14). Blood pH in AH cattle was decreased compared with that in LSH cattle ( < 0.05) at LAP1 (7.25 vs. 7.45) and LAP2 (7.19 vs. 7.48) but was not different ( > 0.13) at BASE, 1H, or 2H. Heart rate and TEMP were increased in AH cattle compared to LSH ( > 0.01). Serum cortisol was increased ( < 0.05) in AH compared to that in LSH cattle at LAP1 (87.5 vs. 58.9 nmol/L), LAP2 (144.4 vs. 93.1 nmol/L), and 1H (113.5 vs. 53.1 nmol/L). Although RR was not differ¬ent between LSH and AH, PvCO2 was decreased in AH compared to that in LSH ( < 0.05) at LAP2 (30.6 vs. 39.3 mmHg) and PvO2 was increased at LAP1 (42.7 vs. 33.5 mmHg) and at LAP2 (51.5 vs. 36.6 mmHg). Lactate was increased in AH cattle in the thicker BF group at 1H ( < 0.05), and blood pH was decreased at LAP1, LAP2, and 1H ( < 0.05) compared to the thinner BF cohorts. Four AH steers became exhausted (EXH) and did not complete the course. Increased CK, decreased PvCO2, and muscle tremors occurred in EXH steers compared to non-exhausted AH cohorts. Results of this study show that AH causes physiologic and blood chemistry changes in steers, which can be potentially detrimental to cattle, emphasizing the need for low-stress handling practices.

With the mandatory implementation of VFD on the horizon, as well as retailer and consumer demands for reduced antibiotic usage, cattle feeders are considering other technologies that can mitigate liver abscesses and maintain growth performance when standard industry technologies are removed from the diet. In this study, cross-bred heifers (N = 1495; 359 ± 3.4 kg) were utilized in a randomized complete block design at a commercial feedlot to determine the effects of a Saccharomyces cerevisiae fermentation product (NaturSafe, Diamond V, Cedar Rapids, IA) on performance, carcass characteristics, and liver abscesses when monensin, tylosin, and direct fed microbials (DFM) were not included in the diet. Upon arrival, heifers were allowed ad libitum access to water and long-stemmed hay. During processing, they received a feedlot tag and growth implant, and were vaccinated and treated for parasites. Heifers were then blocked by arrival BW and randomly assigned to one of 2 treatments (10 pens/treatment, approximately 75 heifers/pen). Treatments consisted of a diet containing: (1) monensin, tylosin, and Bovamine Defend (positive control, PC) or (2) NaturSafe at 18 g/head/d without monensin, tylosin, and the DFM. Diets were fed twice daily with heifers receiving half of the daily dose of treatment in the TMR at each feeding. Pen BW were collected on d 0 and at harvest on d 125 and 146 (5 pens per treatment per day). Feed intake, morbidity and mortality were monitored daily. Cattle were vaccinated and implanted a second time approximately 74 d before harvest. Hot carcass weight, dressing percentage, quality grade, yield grade, percent kidney-pelvic-heart fat percentage, rib fat thickness, rib-eye area, marbling score and liver abscess scores were determined. Performance, carcass characteristics and liver abscess scores were analyzed using the MIXED procedure of SAS with pen as the experimental unit. Performance, carcass characteristics, morbidity and mortality were similar (P > 0.05) between treatments. Heifers fed NaturSafe had a numerically lower (P = 0.11) incidence of liver abscesses compared with PC (14.5% vs. 19.3%, respectively) with fewer (P = 0.02) livers condemned that had less severe (i.e., A-) abscesses (3.3% vs. 6.9%, respectively). Results from this study suggest that NaturSafe has the potential to reduce liver abscesses and maintain growth performance when standard industry technologies like monensin, tylosin, and DFM are removed from conventional production diets.

With more judicious use of antibiotics in the future, the beef industry will need new science-based strategies to mitigate foodborne pathogens, especially as standard industry technologies are removed from the diet. In this study, cross-bred heifers (N = 1495; 359 ± 3.4 kg) were utilized in a randomized complete block design at a commercial feedlot to determine the effects of a Saccharomyces cerevisiae fermentation product (NaturSafe; Diamond V, Cedar Rapids, IA) on foodborne pathogens when monensin, tylosin, and direct fed microbials (DFM) were not included in the diet. Upon arrival, heifers were allowed ad libitum access to water and long-stemmed hay. During processing, they received a feedlot tag and growth implant and were vaccinated and treated for parasites. Heifers were then blocked by arrival BW and randomly assigned to one of 2 treatments (10 pens/treatment, approximately 75 heifers/pen). Treatments consisted of a diet containing 1) monensin, tylosin, and Bovamine Defend (positive control, PC), or 2) NaturSafe at 18 g/head/d without monensin, tylosin, and the DFM. Diets were fed twice daily with heifers receiving half of the daily dose of treatment in the TMR at each feeding. Cattle were harvested on d 125 and 146 (5 pens per treatment per day). At the abattoir, fecal swabs and subiliac lymph nodes were obtained from 400 animals (200/treatment, 20/pen). Fecal samples were subjected to selective culture for Salmonella and E. coli O157:H7 enumeration. Only Salmonella were enumerated from the lymph nodes. Salmonella isolates from feces and lymph nodes were analyzed for virulence (in vitro assay) and antibiotic (ceftiofur, enrofloxacin, and florfenicol) susceptibility. Statistical analyses were performed using ANOVA with Tukey's test for multiple comparisons. Compared to PC, cattle fed NaturSafe had a lower (P < 0.05) concentration of Salmonella in the feces (74%) and lymph nodes (86%). The fecal concentration of E. coli O157:H7 was decreased (P < 0.05) by 58%. Salmonella isolates from feces and lymph nodes were less (P < 0.05) virulent (68% and 66%, respectively) and associated with a decreased expression of hilA, a genetic regulator of Salmonella invasion into eukaryotic cells. Salmonella resistance to select antibiotics was decreased by 17 to 100% (fecal isolates) and 42 to 75% (lymph node isolates). Results from this study indicate that NaturSafe can be used as a pre-harvest food safety intervention in beef cattle when standard industry technologies like monensin, tylosin, and DFM are removed from conventional production diets.

This study evaluated the influence of the Programmed Nutrition Beef Program and exogenous growth promotants (ExGP) on water holding capacity characteristics of enhanced beef strip loins. Sixty, frozen strip loins, arranged in a 2×2 factorial treatment arrangement with dietary program serving as the first factor and use of ExGP as the second factor, were thawed, injected with an enhancement solution, and stored for 7days. Loins from ExGP cattle possessed the ability to bind more (P<0.05) water before pumping and bind less (P<0.05) water after pumping and storage. Loin pH across treatments was similar (P>0.10) before injection, but increased post-injection and after storage (P<0.01). Treatments did not affect loin purge loss, steak cook loss, and expressible moisture (P>0.10). The Programmed Nutrition Beef Program and use of ExGPs minimally impacted water holding capacity of enhanced frozen/thawed beef strip loins.

The objective of this study was to examine the effects of alternative finishing strategies on feedlot performance and carcass characteristics. Beef steers (64 pens; 8 steers/pen) were allocated to a randomized complete block design with a 2 × 2 factorial treatment arrangement. Factor 1 consisted of diet, with cattle fed a conventional (CON) diet or a diet consisting of Programmed Nutrition Beef Program (PN) supplements. The PN treatment included Programmed Nutrition Beef Receiver fed from d 1 through 20 of feeding and Programmed Nutrition Beef Finisher fed from d 21 to harvest. Factor 2 evaluated the presence (EGP+) or absence (EGP-) of exogenous growth promotants (ExGP) in the production system. Steers in the EGP+ treatments were initially implanted with Component E-S, reimplanted with Component TE-IS, and fed 400 mg·animal·dof ractopamine hydrochloride for the final 28 d before harvest. Steers were harvested on d 175, and strip loins were removed from 2 carcasses selected at random from each pen for transport to Kansas State University. One 1.27-cm-thick steak was removed from the anterior face for proximate and long-chain fatty acid analysis. There were no diet × ExGP interactions ( > 0.10) for feedlot performance except for DMI ( = 0.02). Steers in the PN/EGP+ treatment consumed more feed than all other treatments ( < 0.05). Both diet and ExGP affected DMI ( < 0.05), with PN and EGP+ steers consuming more feed than their contemporaries. Gain:feed and ADG were unaffected ( > 0.10) by diet, but ExGP improved these measures ( < 0.01). There were no diet × ExGP interactions for carcass characteristics except KPH fat and percentages of yield grade 3 and 4 carcasses ( < 0.05). Diet affected total incidence of liver abscesses because PN steers had a greater ( = 0.05) incidence of liver abscesses than steers in the CON treatment. Diet did not affect the other carcass characteristics ( > 0.10). Use of ExGP increased ( < 0.05) HCW, LM area, and 12th-rib fat but did not affect ( > 0.10) marbling score. Using ExGP reduced the percentage carcasses grading Premium Choice ( < 0.05). No diet × ExGP interactions or diet effects were detected for long-chain fatty acid profiles ( > 0.10). Use of ExGP increased ( < 0.05) the ratio of saturated:unsaturated fatty acids. In summary, the alternative feeding strategy presented in this study produced similar feedlot performance and carcass characteristics compared with a conventional feedlot system.

A database of daily feed deliveries for steers and heifers fed at 3 commercial feedyards in Kansas between January 1, 2010, and January 31, 2012 (n = 1,515 pens), was used to investigate the prevalence and extent of changes in DMI after initiation of feeding zilpaterol hydrochloride (ZIL) at 8.3 mg/kg (DM) for 20 d. Season affected the percentage of pens experiencing a decrease in DMI post-ZIL (P < 0.01), but there were significant (P < 0.01) season × sex, season × feedyard, season × pre-ZIL DMI, season × days post-ZIL, and season × period post-ZIL interactions. Average DMI decreased within 1 d after initiation of ZIL feeding in all seasons; however, this initial decrease was greater (P < 0.01) in the summer (-0.30 kg) and winter (-0.27 kg) than in the spring (-0.05 kg) or fall (-0.06 kg). The decrease in DMI averaged across all days post-ZIL was greater in summer than during other seasons for both steers and heifers, and the change in intake was greater in steers than heifers in all seasons but fall. Size of intake change within each season varied by feedyard and by season. The percentage of pens that had a large DMI decrease (≥ 0.9 kg/d) was greatest during the summer (33%), and the percentage of pens with no decrease was the least (15%); during the fall, 34% of pens had no DMI decrease and only 8% of pens had a large decrease in DMI. Intake before ZIL initiation affected size and prevalence of DMI decrease; with increasing pre-ZIL DMI, the percentage of pens with a decrease increased from 62% for pens with pre-ZIL DMI of less than 7.7 kg/d to 82% for pens consuming greater than 10.5 kg/d pre-ZIL (P < 0.01). Of those pens with greater than 10.5 kg/d pre-ZIL DMI, 27% had DMI decrease of greater than 1.4 kg/d compared to only 3% for pens consuming <8.7 kg/d pre-ZIL. The average dosage of ZIL consumed per animal with an average DMI of 7.3, 8.2, 9.1, 10.0, and 10.9 kg/d was calculated to be 61, 68, 76, 83, and 91 mg/animal daily, which may be related to the differences in DMI decrease. Pre-ZIL DMI contributed to DMI decrease during ZIL administration, but the increased occurrence and size of DMI decrease during the summer may indicate an additional physiological mechanism.