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By use of likelihood ratios, the threshold of serum IgG1 concentration for optimal health and performance of calves was higher than values reported previously. Implementation and maintenance of management and intervention strategies designed for early detection and treatment of calves at risk for failure of passive transfer will likely result in increases in preweaning health and performance parameters.

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bIn the United States, the bla CMY-2 gene contained within incompatibility type A/C (IncA/C) plasmids is frequently identified in extended-spectrum-cephalosporin-resistant (ESC r ) Escherichia coli strains from both human and cattle sources. Concerns have been raised that therapeutic use of ceftiofur in cattle may increase the prevalence of ESC r E. coli. We report that herd ESC r E. coli fecal and hide prevalences throughout the residency of cattle at a feedlot, including during the period of greatest ceftiofur use at the feedlot, were either not significantly different (P > 0.05) or significantly less (P < 0.05) than the respective prevalences at arrival. Longitudinal sampling of cattle treated with ceftiofur demonstrated that once the transient increase of ESC r E. coli shedding that follows ceftiofur injection abated, ceftiofur-injected cattle were no more likely than untreated members of the same herd to shed ESC r E. coli. Pulsed-field gel electrophoresis (PFGE) genotyping, antibiotic resistance phenotyping, screening for presence of the bla CMY-2 gene, and plasmid replicon typing were performed on 312 ESC r E. coli isolates obtained during six sampling periods spanning the 10-month residence of cattle at the feedlot. The identification of only 26 unique PFGE genotypes, 12 of which were isolated during multiple sampling periods, suggests that clonal expansion of feedlot-adapted bla CMY-2 E. coli strains contributed more to the persistence of bla CMY-2 than horizontal transfer of IncA/C plasmids between E. coli strains at this feedlot. We conclude that therapeutic use of ceftiofur at this cattle feedlot did not significantly increase the herd prevalence of ESC r E. coli. Extended-spectrum cephalosporins (ESC) are critically important to human medicine and are frequently prescribed for the treatment of invasive Escherichia coli and Salmonella enterica infections (1-3). The bla CMY-2 gene, encoding the AmpC-like ␤-lactamase CMY-2, is frequently harbored by large (Ͼ120-kbp) incompatibility type A/C (IncA/C) plasmids in ESC-resistant (ESC r ) E. coli and ESC r S. enterica strains isolated from human and animal sources in the United States (4-13). IncA/C plasmids are considered broad-host-range plasmids since they have been identified in many bacterial species, including Aeromonas, Escherichia, Klebsiella, Photobacterium, Salmonella, Vibrio, and Yersinia (14,15). IncA/C plasmids possess conserved backbone sequences, but the sequences of genetic element insertions carrying antibiotic resistance genes are often divergent (14,(16)(17)(18). However, the insertions carrying genes conferring resistance to tetracyclines (tetA), phenicols (floR), and streptomycin (aadA2) are generally conserved between bla CMY-2 IncA/C plasmids harbored in E. coli and S. enterica hosts (17, 18). Thus, it has been hypothesized that commensal E. coli populations in the lower gastrointestinal systems of cattle may serve as a reservoir of bla CMY-2 IncA/C plasmids, which could then be transferred to more virulent food-borne pathogens, inclu...

Hetero-yellow (HY), red (RED) and brown (BR, high tannin) sorghums were fed dry-rolled or reconstituted (RED and BR only) to evaluate the effect of variety and reconstitution on the site and extent of starch and protein digestion in steers fitted with ruminal, duodenal and ileal cannulae. Processed grains were incorporated into 88% sorghum (DM basis) diets fed at 2% of body weight in a 5 X 5 Latin square. Ruminal fermentation of organic matter, starch and protein tended to be lower for the dry-rolled RED than for either the dry-rolled HY or BR sorghum. Digestion of organic matter (OM) and starch in the small intestine was very low for dry-rolled sorghums. Total tract starch digestibility was lower for the dry-rolled RED sorghum (86.9%) than the BR (90.8%) and HY (91.4%). Nitrogen (N) digestibility ranged from 53.1% for the dry-rolled BR to 64.5% for the HY. Tannins were extensively (95.2%) degraded in the rumen, which may have enhanced fermentation of the BR sorghum. Reconstitution increased (P less than .05) total-tract starch digestion of the RED and tended to increase starch digestion of the BR as well. Total N flow to the duodenum tended to increase with reconstitution, with most of the increase being due to greater (P less than .05) microbial-N. Reconstitution also increased (P less than .05) total-tract N digestibility of the RED. The response to reconstitution for the RED sorghum appeared to be due primarily to an increase (P less than .10) in the extent of fermentation of organic matter and starch in the rumen. Reconstitution of BR, however, enhanced disappearance of starch from the small intestine. In both cases, most (97.3%) of the digestible starch of the reconstituted sorghums had disappeared before the terminal ileum. In contrast, 14.5% (621 g) of the digestible starch of dry-rolled RED disappeared in the large intestine. Sorghum grain variety and reconstitution appear to alter site and extent of starch and protein digestion, which may result in variable performance of cattle fed sorghum grain diets.

Comparisons of enrichment methods (with or without antibiotics and with or without a preenrichment step) using gram-negative (GN) broth or tryptic soy broth (TSB) were conducted with feeds inoculated with Escherichia coli O157:H7. TSB was more sensitive than GN broth, and TSB with a preenrichment step followed by TSB with antibiotics was more sensitive than plain TSB enrichment, in detecting E. coli O157 in inoculated feeds. Feed samples were collected from feed bunks from 54 feedlots to determine the prevalence of E. coli O157 in cattle feeds. TSB preenrichment followed by TSB with antibiotics and the standard GN broth enrichment were used for each feed sample. All samples underwent immunomagnetic separation and were plated onto sorbitol MacConkey agar with cefixime and potassium tellurite. Identification of E. coli O157 was based on indole production, positive latex agglutination for O157 antigen, API 20E test strip results, PCR for the eaeA gene, and the presence of at least one Shiga toxin. E. coli O157 was detected in 52 of 504 feed samples (10.3%) by using GN broth enrichment and in 46 of 504 feed samples (9.1%) by using TSB followed by TSB supplemented with cefixime and vancomycin. E. coli O157 was detected in 75 of 504 feed bunk samples (14.9%) by one or both methods. There was no correlation between E. coli O157 prevalence and generic coliform counts in feeds. The prevalence of E. coli O157 in cattle feed warrants further studies to increase our knowledge of the on-farm ecology of E. coli O157 in order to develop strategies to prevent food-borne disease in humans.The source of Escherichia coli O157 that colonizes cattle is unknown. Feeds commonly contain coliforms (7) and generic E. coli (25), suggesting fecal contamination of feedstuffs. Individual cattle can be transiently colonized and shed E. coli O157 in their feces (15) for 30 to 60 days (3). The reported prevalence in cattle has generally been low in winter and high in summer (1,15,29), although some studies have found similar prevalences in winter and summer (11). On a herd basis, fecal shedding usually occurs in clusters, followed by relatively longer periods of low or no fecal shedding (13, 15). E. coli O157 can survive for an extended period in bovine feces (18,33), providing opportunity for feed contamination.E. coli O157 has rarely been detected in cattle feeds; in two previous studies, it was not detected (14, 25) and in a third it was detected in only 3 out of 32 (9.4%) feed samples taken from a farm over a 5-month period (36). Recently, 0.5% of feeds that were purchased and stored in certain farms were found to contain E. coli O157 (11). Certain conditions appear to support growth of generic E. coli and E. coli O157 in cattle feeds, such as increased concentrations of lactate and decreased concentrations of propionate (25) and high pH in poorly fermented silage (7). This ability of E. coli O157 to survive and grow in feed under appropriate conditions (7, 25), as well as the temporal clustering of fecal shedding in cattle, suggests that c...