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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A portion of horses vaccinated against WNV may respond poorly. Vaccination every 6 months may be indicated in certain horses and in areas of high vector activity. Other preventative methods such as mosquito control are warranted to prevent WNV infection in horses.

Campylobacter is a leading cause of foodborne gastroenteritis. Recent studies have indicated a rise in fluoroquinolone-resistant (FQ-R) Campylobacter in cattle, where FQ is used to control bovine respiratory disease (BRD). To assess the effect of danofloxacin treatment on the development of FQ-resistance in C. jejuni, 30 commercial calves were divided into Group 1, Group 2, and Group 3 (n = 10), and were all inoculated orally with FQ-susceptible (FQ-S) C. jejuni; seven days later, Group 3 was challenged with transtracheal Mannheimia haemolytica, and one week later, Group 2 and Group 3 were injected subcutaneously with danofloxacin. Rectal feces were collected to determine relative percentages of FQ-R Campylobacter via culture. Before oral inoculation with C. jejuni, 87% of calves were naturally colonized by FQ-R C. jejuni. Two days after the inoculation, FQ-R C. jejuni decreased substantially in the majority of calves. Within 24 h of danofloxacin injection, almost all C. jejuni populations shifted to an FQ-R phenotype in both FQ-treated groups, which was only transitory, as FQ-S strains became predominant during later periods. Genotyping indicated that the spike seen in FQ-R C. jejuni populations following the injection was due mainly to enrichment of preexisting FQ-R C. jejuni, rather than development of de novo FQ resistance in susceptible strains. These results provide important insights into the dynamic changes of FQ-resistant Campylobacter in cattle in response to FQ treatment.

Determination of Escherichia coli O157 prevalence immediately prior to shipment and harvest is an important facet of the ecology of this organism, which requires further elucidation. As part of a larger study to measure the effects of within-pen prevalence of E. coli O157 on subsequent carcass contamination, fecal samples from 15 pens of cattle in each of 12 different feedlots in three states (Colorado, Nebraska, and Montana) were collected from June through September 2002. Thirty fresh fecal samples were collected from each pen floor within 36 h of shipment to slaughter. Fecal samples underwent standard enrichment, immunomagnetic separation, and isolation procedures for E. coli O157. Multivariable logistic regression was used to determine which factors best predicted pen-level positive culture results, and to estimate the magnitude of association between each factor and the outcome, while adjusting for other factors in the model. Thirteen (86.7%) of the 15 pens had at least one positive sample, and the within-pen prevalence of E. coli O157 in positive pens ranged from 3.3% to 77.8%. The odds of E. coli O157 positive fecal samples from cattle fed brewers grains were six times that for cattle not fed brewers grains. The odds of E. coli O157 positive fecal samples from pens of cattle from Central Nebraska was nine times that for pens of cattle from Eastern Colorado. These data demonstrate that the presence of E. coli O157 in fecal samples from finished feedlot cattle is associated with feeding of brewers grain and geographic location. Additional studies to further characterize geographic distribution of E. coli O157 and to investigate pen-level intervention strategies should be conducted.

Transportation of cattle from the feedlot to the slaughter plant could influence hide contamination of Escherichia coli O157. A study was initiated to investigate the influence of transportation and lairage on shedding and hide contamination of E. coli O157. Fecal and hide samples were obtained from 40 pens of harvest-ready beef cattle at the feedlot prior to transport and again at the slaughter plant immediately after slaughter. Potential risk factors for hide contamination at the feedlot, during transport, and at slaughter were evaluated. A multilevel Poisson regression model was used to evaluate if transportation and lairage were associated with hide contamination by E. coli O157 in finished beef cattle. Lots of cattle held in E. coli O157-positive lairage pens had eight times greater risk of having positive slaughter hide samples compared with cattle held in culture-negative pens (relative risk, 8.0; 95% confidence interval, 1.6 to 38.8). Lots of cattle that were held in lairage pens contaminated with feces had three times greater risk for positive slaughter hide samples compared with cattle held in clean pens (relative risk, 3.1; 95% confidence interval, 1.2 to 7.9). Lots of cattle that were transported for long distances (> 160.9 km) had twice the risk of having positive hide samples at slaughter compared with cattle transported a shorter distance (relative risk, 2.4; 95% confidence interval, 1.1 to 5.1). These findings suggest that transportation and lairage should be considered in E. coli O157 control strategies.

Background A randomized, masked, 2‐arm parallel trial was conducted to assess the efficacy of a Moraxella bovis (M. bovis) autogenous vaccine to prevent naturally occurring infectious bovine keratoconjunctivis (IBK) in beef calves. Hypothesis The null hypothesis was that treatment group was not associated with either risk of IBK or last observed weight. Animals The trial was conducted between May and November 2009 and 2010 on a university‐owned farm in Iowa. The vaccine contained 2 randomly selected M. bovis from IBK cases that occurred at the farm in 2008. Calves born between January and May 2009 and 2010 without visible corneal lesions were randomly allocated to receive vaccine (n = 191) or placebo (n = 178). Methods Two SC doses were administered 21–28 days apart. Allocation to treatment was concealed using bottles marked A or B. Staff observing the animals for IBK could not determine the treatment grouping. The herd met the “at‐risk” criteria (ie, >15% IBK in unvaccinated calves and M. bovis detection in IBK cases). Analysis was “per‐protocol”. Results The risk of IBK was 58/185 (31%) in vaccinated calves and 66/173 (38%) in unvaccinated calves (adjusted risk ratio = 0.78; 95% CI, 0.49–1.24). Average weight before sale did not differ between the vaccinated calves (196.6 kg, SD ± 39.9) and unvaccinated calves (198.1 kg, SD ± 42.7) (P value = .19). No adverse effects were noted. Conclusion and Clinical Importance Combination of the study results with previous studies suggests that autogenous M. bovis vaccines often are ineffective in controlling naturally occurring IBK.

This study reports normal data for the STT I and rebound tonometry in calves. This data may be useful in complete ophthalmic examinations of cattle, guiding diagnosis of glaucoma, uveitis, and keratoconjunctivitis sicca. However, results of these diagnostic modalities must be interpreted in light of clinical signs, given the wide range of normal values obtained in this study.