B. B. Karisch

Effects of steer breed composition on feedlot performance and carcass traits1

Records of steers (n = 3,554) of known breed composition were used to assess the effect of breed composition on feedlot performance and carcass traits. Feedlot ADG was greater (P ≤ 0.01) for Angus and Red Angus than for Brangus and Polled Hereford steers. Longissimus muscle area ranged from 81.6 cm2 for Beefmaster carcasses to 85.7 cm2 for Red Angus carcasses and was affected by breed (P < 0.01). Marbling score was greatest (P = 0.03) in Angus carcasses and greater (P < 0.05) in Brangus than in Polled Hereford and Beefmaster carcasses. All following results are relative to a British base. Direct additive effects for backfat thickness in Continental (P < 0.01), American (P < 0.01), and Zebu (P < 0.05) breeds were − 0.6, − 0.2, and − 0.1 cm. Marbling score and USDA QG direct additive effects (P < 0.01) were large negative values for American, Continental, and Zebu. The Continental direct additive effect (P < 0.01) for LM area was 9.7 cm2 . Calculated YG direct additive effects (P < 0.01) were − 0.2 and − 1.0 for American and Continental breeds, respectively. Direct heterosis effects (P < 0.01) in British × American steers were present for ADG and marbling score, whereas Continental crosses tended to exhibit direct heterosis effects (P < 0.05) for LM area and backfat thickness. Steer breed composition influenced finishing performance and carcass traits. This information is important for breed selection, finishing, and marketing decisions.

Multidrug resistant Mannheimia haemolytica isolated from high-risk beef stocker cattle after antimicrobial metaphylaxis and treatment for bovine respiratory disease

Antimicrobial resistance (AMR) in bacterial respiratory pathogens in high-risk stocker cattle has been poorly characterized. The objective of this study was to describe the prevalence of multidrug resistant (MDR; resistance to > 3 antimicrobial classes) respiratory pathogens in 50 conventionally managed stocker cattle over 21 days after arrival. Cattle received tildipirosin metaphylaxis on day 0 and were eligible to receive up to 3 additional antimicrobials for bovine respiratory disease (BRD): florfenicol, ceftiofur and enrofloxacin. Nasopharyngeal swabs were collected on days 0, 7, 14, and 21 for bacterial culture and antimicrobial susceptibility testing using disc diffusion and broth microdilution. Mannheimia haemolytica was isolated from 5 of 48, 27 of 50, 44 of 50, and 40 of 50 cattle on days 0, 7, 14, and 21, respectively. One of 5, 27 of 27, 43 of 44, and 40 of 40 M. haemolytica were MDR on days 0, 7, 14, and 21, respectively. Pasteurella multocida was isolated from 6 of 48 cattle on day 0 and none were MDR; no other pathogens were isolated. Twenty-four cattle required at least one BRD treatment; M. haemolytica was isolated before treatment from 13 of 24 cattle; all were MDR. One hundred-eighteen M. haemolytica isolates were subjected to pulsed-field gel electrophoresis (PFGE); multiple genotypes were identified. Whole genome sequencing of 33 isolates revealed 14 known AMR genes. Multidrug resistant M. haemolytica can be highly prevalent and genetically diverse in stocker cattle; additional research is necessary to determine factors that influence prevalence and the impact on cattle health.

Effect of a DNA-based immunostimulant on growth, performance, and expression of inflammatory and immune mediators in beef calves abruptly weaned and introduced to a complete ration

The effect of a DNA immunostimulant on inflammatory and immune responses, performance, and health in calves following abrupt weaning and introduction to a concentrate diet was tested. Sixty-four single source Angus crossbred steers were weaned on day 1 and assigned to receive a DNA immunostimulant (TRT) or saline (CON) on days 0, 2, 4, and 6. On day 0, steers received clostridial and respiratory vaccines and anthelmintic; they were then transported 2 h, allocated to pens (n = 8 per pen), and introduced to total mixed ration. Daily intake, ADG, and feed efficiency were measured. Serum haptoglobin, tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β) were assayed by ELISA or AlphaLISA on days 0, 2, 4, 6, 14, and 28; serum-neutralizing antibodies (SNA) to bovine herpesvirus-1 and bovine viral diarrhea virus-1 (BVDV-1) were quantified on days 0, 28, 68, and 135. In a subset of cattle (n = 6 to 8 per treatment group), the percent macrophages and activated gamma delta (γδ) T cells in blood was determined by flow cytometry on days 2 and 6, and expression of mRNA for TNF-α, interferon-gamma (IFN-γ), IL-4, and IL-10 by stimulated blood mononuclear cells was assessed by real-time reverse transcriptase PCR on day 6. After 70 d, cattle were shipped 1,205 km to a feedlot and performance and health were followed. There was a significant effect of time on serum TNF-α, IL-1β, haptoglobin, and SNA (P < 0.001); the range in concentration among cattle on each day was large. The ratio of IFN-γ to IL-4 expression was significantly higher (P = 0.03) for TRT cattle, suggesting that treatment activated T-helper type 1 cells. There was a trend toward an improved feed conversion (P = 0.10) for TRT steers over the 70-d backgrounding period. There was no effect of treatment on feedlot performance or carcass merit (P > 0.10). During backgrounding, 1 TRT steer died of enterocolitis. In spite of backgrounding, cattle experienced an outbreak of bovine respiratory disease (BRD) in the feedlot and 1 of 31 TRT cattle and 5 of 32 CON cattle died of BRD. The immunostimulant modified some immune responses during backgrounding. Large variability in inflammatory responses during backgrounding indicated that events around weaning induce systemic inflammation that varies substantially among cattle.