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The objective was to investigate the influence of cattle origin and region of finishing on the prevalence of Salmonella , Escherichia coli O157:H7, and select antimicrobial resistance in E. coli populations. Yearling heifers ( n  = 190) were utilized in a 2 × 2 factorial arrangement. After determining fecal Salmonella prevalence, heifers were sorted into one of four treatments: heifers originating from South Dakota (SD) and finished in SD (SD-SD); heifers originating from SD and finished in Texas (SD-TX); heifers originating from TX and finished in SD (TX-SD); and heifers originating from TX and finished in TX (TX-TX). Fecal, pen, and water scum line samples were collected longitudinally throughout the study; hide swab and subiliac lymph node (SLN) samples were collected at study end. A treatment × time interaction was observed ( p  ≤ 0.01) for fecal Salmonella prevalence, with prevalence being greatest for TX-TX and TX-SD heifers before transport. From day (d) 14 through study end, prevalence was greatest for TX-TX and SD-TX heifers compared with SD-SD and TX-SD heifers. Salmonella prevalence on hides were greater ( p  ≤ 0.01) for heifers finished in TX compared with SD. Salmonella prevalence in SLN tended ( p  = 0.06) to be greater in TX-TX and SD-TX heifers compared with TX-SD and SD-SD. Fecal E. coli O157:H7 prevalence had a treatment × time interaction ( p  = 0.04), with SD-TX prevalence being greater than TX-SD on d 56 and SD-SD and TX-TX being intermediate. A treatment × time interaction was observed for fecal trimethoprim-sulfamethoxazole-resistant and cefotaxime-resistant E. coli O157:H7 prevalence ( p  ≤ 0.01). Overall, these data suggest that the region of finishing influences pathogenic bacterial shedding patterns, with the initial 14 d after feedlot arrival being critical for pathogen carriage.

Aims: Our objective was to determine how injectable antimicrobials affected populations of Salmonella enterica, Escherichia coli and Enterococcus spp. in feedlot cattle., Methods and Results: Two arrival date blocks of high-risk crossbred beef cattle (n = 249; mean BW = 244 kg) were randomly assigned one of four antimicrobial treatments administered on day 0: sterile saline control (CON), tulathromycin (TUL), ceftiofur (CEF) or florfenicol (FLR). Faecal samples were collected on days 0, 28, 56, 112, 182 and study end (day 252 for block 1 and day 242 for block 2). Hide swabs and subiliac lymph nodes were collected the day before and the day of harvest. Samples were cultured for antimicrobial-resistant Salmonella, Escherichia coli and Enterococcus spp. The effect of treatment varied by day across all targeted bacterial populations (p ≤ 0.01) except total E. coli. Total E. coli counts were greatest on days 112, 182 and study end (p ≤ 0.01). Tulathromycin resulted in greater counts and prevalence of Salmonella from faeces than CON at study end (p ≤ 0.01). Tulathromycin and CEF yielded greater Salmonella hide prevalence and greater counts of 128ERY R E. coli at study end than CON (p ≤ 0.01). No faecal Salmonella resistant to tetracyclines or third-generation cephalosporins were detected. Ceftiofur was associated with greater counts of 8ERY R Enterococcus spp. at study end (p ≤ 0.03). By the day before harvest, antimicrobial use did not increase prevalence or counts for all other bacterial populations compared with CON (p ≥ 0.13)., Conclusions: Antimicrobial resistance (AMR) in feedlot cattle is not caused solely by using a metaphylactic antimicrobial on arrival, but more likely a multitude of environmental and management factors., (© 2022 The Authors. Journal of Applied Microbiology published by John Wiley & Sons Ltd on behalf of Society for Applied Microbiology.)

Bovine respiratory disease (BRD) is the primary animal health concern facing feedlot producers. Many antimicrobial mitigation strategies are available, but few studies have compared feedlot performance during both the receiving and finishing periods following application of different antimicrobials used as metaphylaxis at arrival. The objective of this study was to compare antimicrobial metaphylaxis methods on clinical health and growth performance across both the receiving and finishing periods. A total of 238 multiple-sourced steers in two source blocks were used in a generalized complete block design. The four treatments included: 1) a negative control, 5 mL of sterile saline injected subcutaneously (CON); 2) subcutaneous administration of florfenicol at 40 mg/kg of BW (NUF); 3) subcutaneous administration of ceftiofur in the posterior aspect of the ear at 6.6 mg/kg of BW (EXC); and 4) subcutaneous administration of tulathromycin at 2.5 mg/kg of BW (DRA). The morbidity rate for the first treatment of BRD was decreased for the DRA and EXC treatments compared to CON and NUF (P <  0.01). Additionally, average daily gain (ADG), dry matter intake (DMI), and gain-to-feed (G:F) were greater (P  ≤ 0.02) in the DRA treatment during the receiving period compared to all other treatments. The ADG was also greater (P  < 0.05) for EXC than the CON treatment throughout the finishing period. Nonetheless, other growth performance variables did not differ among metaphylactic treatments during the finishing period (P ≥  0.14). Likewise, no differences in carcass characteristics or liver abscess score were observed (P ≥  0.18). All complete blood count (CBC) variables were affected by day (P ≤  0.01) except mean corpuscular hemoglobin concentration (P  = 0.29). Treatment × time interactions were observed for platelet count, white blood cell (WBC) count, monocyte count and percentage, and lymphocyte percentage (P ≤  0.03). However, there were no observed hematological variables that differed among treatment (P ≥  0.10). The results indicate that some commercially available antimicrobials labeled for metaphylactic use are more efficacious than others in decreasing morbidity rate. [ABSTRACT FROM AUTHOR]

The objective was to investigate the influence of cattle origin and region of finishing on the prevalence of Salmonella, Escherichia coli O157:H7, and select antimicrobial resistance in E. coli populations. Yearling heifers (n = 190) were utilized in a 2 × 2 factorial arrangement. Heifers (n = 98) in the northern region were sourced from South Dakota (SD) while heifers (n = 92) in the southern region were sourced from Texas (TX). After feedlot arrival in each respective region, fecal Salmonella prevalence was determined, and heifers were sorted into 1 of 4 treatments: heifers sourced from SD and finished in SD (SD-SD); heifers sourced from SD and finished in TX (SD-TX); heifers sourced from TX and finished in SD (TX-SD); heifers sourced from TX and finished in TX (TX-TX). Transport for SD-TX and TX-SD heifers occurred on d 0. Fecal, pen, and water scum line (WSL) samples were collected longitudinally throughout the study; hide and subiliac lymph node (SLN) samples were collected at study end (d 78 for heifers finished in TX and d 90 for heifers finished in SD). A treatment × time interaction was observed (P = 0.01) for fecal Salmonella prevalence, with prevalence being greatest for TX-TX and TX-SD heifers before transport. From d 14 through study end, prevalence was greatest for TX-TX and SD-TX heifers compared with SD-SD and TX-SD heifers. The TX-SD heifers had a 72% decrease in Salmonella prevalence from d 1 to harvest, whereas the SD-TX heifers had a 2,200% increase in Salmonella prevalence from d 1 to harvest. Salmonella prevalence on hides were greater (P = 0.01) for heifers finished in TX compared with SD. Salmonella prevalence in SLN tended (P = 0.06) to be greater in TX-TX and SD-TX heifers compared with TX-SD and SD-SD. Fecal E. coli O157:H7 prevalence had a treatment × time interaction (P = 0.04), with SD-TX prevalence being greater than TX-SD on d 56 and SD-SD and TX-TX being intermediate. A treatment × time interaction was observed for fecal trimethoprim-sulfamethoxazole-resistant and cefotaxime-resistant E. coli O157:H7 prevalence (P ≤ 0.01). Overall, these data suggest region of finishing influences pathogenic bacterial shedding patterns, with the initial 14 d after feedlot arrival being critical for pathogen carriage. [ABSTRACT FROM AUTHOR]