No abstract

Experimental oral challenge studies with three different genotypes of Escherichia coli O157:H7 were conducted in cattle to determine the genotype-specific variability in shedding frequencies and concentrations and the frequency and extent of contamination of the environment. The results indicated that the E. coli O157:H7 genotype and ecological origin maybe important factors for the occurrence and concentration in the cattle host. Four groups of six young Holstein steers each were orally challenged with 10 6 CFU of one of three E. coli O157:H7 strains: FRIK 47 (groups 1 and 2), FRIK 1641 (group 3), and FRIK 2533 (group 4). Recto-anal mucosal swabs (RAMS) and environmental samples were taken on alternate days over 30 days. The numbers of E. coli O157:H7 cells and generic E. coli cells per sample were determined. Also, the presence and absence of 28 gene targets were determined for 2,411 isolates using high-throughput real-time PCR. Over the study period, strains FRIK 47, FRIK 1641, and FRIK 2533 were detected in 52%, 42%, and 2% of RAMS, respectively. Environmental detection of the challenge strains was found mainly in samples of the hides and pen floors, with strains FRIK 47, FRIK 1641, and FRIK 2533 detected in 22%, 27%, and 0% of environmental samples, respectively. Based on the panel of 28 gene targets, genotypes of enterohemorrhagic E. coli (EHEC) and generic E. coli from the experimental samples were clustered into three subgroups. In conclusion, the results suggested that the type and intensity of measures to control this pathogen at the preharvest level may need to be strain specific.

This study reports analysis of faecal shedding dynamics in cattle for three Escherichia coli O157:H7 (ECO157) strains (S1, S2 and S3) of different genotype and ecological history, using experimental inoculation data. The three strains were compared for their shedding frequency and level of ECO157 in faeces. A multistate Markov chain model was used to compare shedding patterns of S1 and S2. Strains S1 and S2 were detected seven to eight times more often and at 104 larger levels than strain S3. Strains S1 and S2 had similar frequencies and levels of shedding. However, the total time spent in the shedding state during colonization was on average four times longer for S1 (15 days) compared to S2 (4 days). These results indicate that an ECO157 strain effect on the frequency, level, pattern and the duration of faecal shedding may need to be considered in control of ECO157 in the cattle reservoir.

Bovine digital dermatitis (DD) is a contagious and multifactorial disease that leads to painful, ulcerative lesions of the skin near the heel-horn border of the foot, most commonly in dairy cattle. With regard to beef cattle, the pathogenesis and etiology of DD has not been widely reported or studied over the past several decades. A longitudinal field trial in a commercial feedlot was conducted to compare prevalence and effects of DD in beef steers provided a diet supplemented with a novel formulation of inorganic and organic trace mineral sources (OTM diet) compared to a diet provided with similar levels of trace minerals solely from inorganic sources (CON diet). A secondary objective was to evaluate the prevalence of DD and the potential effects on growth performance and carcass yield and quality. One thousand seventy-seven steers were assigned to 1 of the 2 treatment groups (CON diet or OTM diet) based on location of their home pens which were situated in 1 of 2 barns. All pens in the B barn (group B) were assigned to the OTM diet, and all pens in the A barn (group A) were assigned to the CON diet. The study was conducted in 2 phases: adaptation phase (AP) comprising the initial 60 d of feeding CON and OTM diets and postadaptation phase (PAP) which lasted until cattle were sent to harvest. In the AP, pens in group B had a greater proportion of steers (54.03%) with DD lesions compared to pens in group A (26.72%). During the PAP, the relative risk of observing an increased DD prevalence was significantly ( < 0.05) higher in CON group compared to OTM group. Growth performance, final live weight, and hot carcass weight were negatively impacted when steers were observed to have active DD lesions (M2 lesions) compared to steers with no M2 lesions over the study period. For ADG, a calculated loss per steer of 0.08 kg/d from type I (no M2 lesions) to type II (one M2 lesion; SE = 0.028; = 0.003) and loss of 0.14 kg/d from type I to type III (multiple M2 lesions; SE = 0.038; = 0.0003) were observed. A significant BW loss of approximately 10.06 kg (SE = 4.18; = 0.022) and a mean reduction of 5.5 kg per steer in HCW (SE = 2.74; = 0.043) were also found between type I and type II steers.

Bovine digital dermatitis (DD) is a severe infectious cause of lameness in cattle worldwide, with important economic and welfare consequences. There are three treponeme phylogroups (T. pedis, T. phagedenis, and T. medium) that are implicated in playing an important causative role in DD. This study was conducted to develop real-time PCR and loop-mediated isothermal amplification (LAMP) assays for the detection and differentiation of the three treponeme phylogroups associated with DD. The real-time PCR treponeme phylogroup assays targeted the 16S-23S rDNA intergenic space (ITS) for T. pedis and T. phagedenis, and the flagellin gene (flaB2) for T. medium. The 3 treponeme phylogroup LAMP assays targeted the flagellin gene (flaB2) and the 16S rRNA was targeted for the Treponeme ssp. LAMP assay. The real-time PCR and LAMP assays correctly detected the target sequence of all control strains examined, and no cross-reactions were observed, representing 100% specificity. The limit of detection for each of the three treponeme phylogroup real-time PCR and LAMP assays was ≤ 70 fg/μl. The detection limit for the Treponema spp. LAMP assay ranged from 7–690 fg/μl depending on phylogroup. Treponemes were isolated from 40 DD lesion biopsies using an immunomagnetic separation culture method. The treponeme isolation samples were then subjected to the real-time PCR and LAMP assays for analysis. The treponeme phylogroup real-time PCR and LAMP assay results had 100% agreement, matching on all isolation samples. These results indicate that the developed assays are a sensitive and specific test for the detection and differentiation of the three main treponeme phylogroups implicated in DD.