Bovine respiratory disease (BRD) is an economically important disease of cattle and continues to be an intensely studied topic. However, literature summarizing the time between pathogen exposure and clinical signs, shedding, and seroconversion is minimal. A structured literature review of the published literature was performed to determine cattle responses (time from pathogen exposure to clinical signs, shedding, and seroconversion) in challenge models using common BRD viral and bacterial pathogens. After review a descriptive analysis of published studies using common BRD pathogen challenge studies was performed. Inclusion criteria were single pathogen challenge studies with no treatment or vaccination evaluating outcomes of interest: clinical signs, shedding, and seroconversion. Pathogens of interest included: bovine viral diarrhea virus (BVDV), bovine herpesvirus type 1 (BHV-1), parainfluenza-3 virus, bovine respiratory syncytial virus, Mannheimia haemolytica, Mycoplasma bovis, Pastuerella multocida, and Histophilus somni. Thirty-five studies and 64 trials were included for analysis. The median days to the resolution of clinical signs after BVDV challenge was 15 and shedding was not detected on day 12 postchallenge. Resolution of BHV-1 shedding resolved on day 12 and clinical signs on day 12 postchallenge. Bovine respiratory syncytial virus ceased shedding on day 9 and median time to resolution of clinical signs was on day 12 postchallenge. M. haemolytica resolved clinical signs 8 days postchallenge. This literature review and descriptive analysis can serve as a resource to assist in designing challenge model studies and potentially aid in estimation of duration of clinical disease and shedding after natural pathogen exposure.

Bovine respiratory disease (BRD) diagnosis during the postweaning phase of beef production is an important component of effective preventive health and treatment programs. Although identification of diseased animals based on signs of clinical illness (CI) is a common method in the beef industry for identifying BRD, very little information is available on the accuracy of this method. Previous investigators hypothesized that monitoring pulmonary lesions at harvest (LU) could be a more reliable indicator of disease status during the postweaning phase. A structured literature review was conducted to identify research that compared CI and LU. Because there is no true gold standard for diagnosing BRD, Bayesian methods were used to estimate the sensitivity and specificity of each diagnostic method relative to a BRD diagnosis at any time during the postweaning phase. Results from the current study indicate that the estimated diagnostic sensitivity and specificity of CI were 61.8% (97.5% probability interval [PI]: 55.7, 68.4) and 62.8% (97.5% PI: 60.0, 65.7), respectively. Use of LU for a BRD diagnosis was estimated to have a sensitivity of 77.4% (97.5% PI: 66.2, 87.3) and a specificity of 89.7% (97.5% PI: 86.0, 93.8). Further analysis revealed that the probabilities of LU having higher sensitivity and specificity than CI were 99.4% and 100%, respectively. The present research indicates that neither method was perfect, and both methods were relatively poor at correctly classifying truly diseased animals (sensitivity) but that LU was more accurate than CI for BRD diagnosis. Results from the present study should be considered when these diagnostic methods are used to evaluate BRD outcomes in clinical and research settings.

Objective—To evaluate plasma concentrations of substance P (SP) and cortisol in calves after castration or simulated castration. Animals—10 Angus-crossbred calves. Procedures—Calves were acclimated for 5 days, assigned to a block on the basis of scrotal circumference, and randomly assigned to a castrated or simulated-castrated (control) group. Blood samples were collected twice before, at the time of (0 hours), and at several times points after castration or simulated castration. Vocalization and attitude scores were determined at time of castration or simulated castration. Plasma concentrations of SP and cortisol were determined by use of competitive and chemiluminescent enzyme immunoassays, respectively. Data were analyzed by use of repeated-measures analysis with a mixed model. Results—Mean ± SEM cortisol concentration in castrated calves (78.88 ± 10.07 nmol/L) was similar to that in uncastrated control calves (73.01 ± 10.07 nmol/L). However, mean SP concentration in castrated calves (506.43 ± 38.11 pg/mL) was significantly higher than the concentration in control calves (386.42 ± 40.09 pg/mL). Mean cortisol concentration in calves with vocalization scores of 0 was not significantly different from the concentration in calves with vocalization scores of 3. However, calves with vocalization scores of 3 had significantly higher SP concentrations, compared with SP concentrations for calves with vocalization scores of 0. Conclusions and Clinical Relevance—Similar cortisol concentrations were measured in castrated and control calves. A significant increase in plasma concentrations of SP after castration suggested a likely association with nociception. These results may affect assessment of animal well-being in livestock production systems.

Failure to adhere to standard item-writing guidelines may render examination questions easier or more difficult than intended. Item complexity describes the cognitive skill level required to obtain a correct answer. Higher cognitive examination items promote critical thinking and are recommended to prepare students for clinical training. This study evaluated faculty-authored examinations to determine the impact of item-writing flaws and item complexity on the difficulty and discrimination value of examination items used to assess third year veterinary students. The impact of item-writing flaws and item complexity (cognitive level I-V) on examination item difficulty and discrimination value was evaluated on 1925 examination items prepared by clinical faculty for third year veterinary students. The mean (± SE) percent correct (83.3 % ± 17.5) was consistent with target values in professional education, and the mean discrimination index (0.18 ± 0.17) was slightly lower than recommended (0.20). More than one item-writing flaw was identified in 37.3 % of questions. The most common item-writing flaws were awkward stem structure, implausible distractors, longest response is correct, and responses are series of true-false statements. Higher cognitive skills (complexity level III-IV) were required to correctly answer 38.4 % of examination items. As item complexity increased, item difficulty and discrimination values increased. The probability of writing discriminating, difficult examination items decreased when implausible distractors and all of the above were used, and increased if the distractors were comprised of a series of true/false statements. Items with four distractors were not more difficult or discriminating than items with three distractors. Preparation of examination questions targeting higher cognitive levels will increase the likelihood of constructing discriminating items. Use of implausible distractors to complete a five-option multiple choice question does not strengthen the discrimination value.