A retrospective analysis of risk factors associated with bovine respiratory disease treatment failure in feedlot cattle.

The objective of this project was to identify risk factors associated with the probability of failing to resolve clinical signs of bovine respiratory disease (BRD) after initial antimicrobial treatment. A retrospective data analysis was performed with 194,062 animals treated for BRD with an antimicrobial from 10 U.S. feedlots from 2005 to 2009. A binary variable classified cattle as a treatment failure if they were retreated for BRD or died following an initial BRD treatment. A generalized logistic mixed model was created to evaluate associations of quarter of the year at feedlot arrival, arrival weight, sex, risk classification (high vs. low), days on feed at first BRD treatment, and rectal temperature at first BRD treatment and all 2-way interactions with the probability of first treatment failure for BRD. A total of 64,683 out of 194,062 (33.3%) of cattle initially treated for BRD were classified as treatment failures due to death or retreatment. Multiple 2-way interactions were present. High-risk calves had greater probability of first treatment failure compared with low-risk calves, but this effect was modified by quarter of arrival, days on feed at first treatment, and rectal temperature category. The effect of arrival weight category was modified by days on feed at first treatment of BRD and quarter of arrival for probability of first treatment failure. Multiple arrival and treatment characteristics were associated with the probability of first BRD treatment failure. Knowledge of these factors can lead future prospective studies to improve the prediction of treatment failure and provide baseline results for the industry.

A mixed treatment comparison meta-analysis of metaphylaxis treatments for bovine respiratory disease in beef cattle.

The objective of this project was to evaluate the effects of antimicrobials approved for parenteral metaphylactic use in feeder and stocker calves on morbidity and mortality for bovine respiratory disease with the use of a mixed treatment comparison meta-analysis. An initial literature review was conducted in April 2016 through Pubmed, Agricola, and CAB (Commonwealth Agricultural Bureau) for randomized controlled trials for metaphylaxis antimicrobial administered parentally to incoming feedlot or stocker calves within 48 h of arrival. The final list of publications included 29 studies, with a total of 37 trials. There were 8 different metaphylactic antimicrobials. Final event outcomes were categorized into bovine respiratory disease (BRD) morbidity cumulative incidence d 1 to ≤ 60 of the feeding period, BRD morbidity cumulative incidence d 1 to closeout of the feeding period, BRD mortality cumulative incidence d 1 to closeout of the feeding period, and BRD retreatment cumulative incidence morbidity d 1 to closeout of the feeding period. Network meta-analysis combined direct and indirect evidence for all the event outcomes to determine mean odds ratio (OR) with 95% credibility intervals (CrIs) for all metaphylactic antimicrobial comparisons. The "upper tier" treatment arms for morbidity d 1 to ≤ 60 included tulathromycin, gamithromycin, and tilmicosin. For BRD mortality cumulative incidence d 1 to closeout and BRD retreatment morbidity d 1 to closeout, classifying the treatment arms into tiers was not possible due to overlapping 95% CrIs. The results of this project accurately identified differences between metaphylactic antimicrobials, and metaphylactic antimicrobial options appear to offer different outcomes on BRD morbidity and mortality odds in feedlot cattle.

Interpreting statistics from published research to answer clinical and management questions.

Appropriate statistical analysis is critical in interpreting results from published literature to answer clinical and management questions. Internal validity is an assessment of whether the study design and statistical analysis are appropriate for the hypotheses and study variables while controlling for bias and confounding. External validity is an assessment of the appropriateness of extrapolation of the study results to other populations. Knowledge about whether treatment or observation groups are truly different is unknown, but studies can be broadly categorized as exploratory or discovery, based on knowledge about previous research, biology, and study design, and this categorization affects interpretation. Confidence intervals, -values, prediction intervals, credible intervals, and other decision aids are used singly or in combination to provide evidence for the likelihood of a given model but can be interpreted only if the study is internally valid. These decision aids do not test for bias, study design, or the appropriateness of applying study results to other populations dissimilar to the population tested. The biologic and economic importance of the magnitude of difference between treatment groups or observation groups as estimated by the study data and statistical interpretation is important to consider in clinical and management decisions. Statistical results should be interpreted in light of the specific question and production system addressed, the study design, and knowledge about pertinent aspects of biology to appropriately aid decisions.

A stochastic model to determine the economic value of changing diagnostic test characteristics for identification of cattle for treatment of bovine respiratory disease.

Bovine respiratory disease is an economically important syndrome in the beef industry, and diagnostic accuracy is important for optimal disease management. The objective of this study was to determine whether improving diagnostic sensitivity or specificity was of greater economic value at varied levels of respiratory disease prevalence by using Monte Carlo simulation. Existing literature was used to populate model distributions of published sensitivity, specificity, and performance (ADG, carcass weight, yield grade, quality grade, and mortality risk) differences among calves based on clinical respiratory disease status. Data from multiple cattle feeding operations were used to generate true ranges of respiratory disease prevalence and associated mortality. Input variables were combined into a single model that calculated estimated net returns for animals by diagnostic category (true positive, false positive, false negative, and true negative) based on the prevalence, sensitivity, and specificity for each iteration. Net returns for each diagnostic category were multiplied by the proportion of animals in each diagnostic category to determine group profitability. Apparent prevalence was categorized into low (<15%) and high (≥15%) groups. For both apparent prevalence categories, increasing specificity created more rapid, positive change in net returns than increasing sensitivity. Improvement of diagnostic specificity, perhaps through a confirmatory test interpreted in series or pen-level diagnostics, can increase diagnostic value more than improving sensitivity. Mortality risk was the primary driver for net returns. The results from this study are important for determining future research priorities to analyze diagnostic techniques for bovine respiratory disease and provide a novel way for modeling diagnostic tests.

Effect of Mannheimia haemolytica pneumonia on behavior and physiologic responses of calves during high ambient environmental temperatures.

The objective of this study was to determine the effect of pneumonia during conditions of high (maximum ≥ 32°C) ambient temperatures on physiological and behavioral responses of calves. Eighteen black beef heifers averaging 240 kg were blocked by BW and randomly assigned to 1 of 2 treatment groups: 1) pneumonia induced by bronchoselective endoscopic inoculation with Mannheimia haemolytica (MH; n = 10) and 2) noninoculated controls (CN; n = 8). Nasal passage and rectal temperatures were measured every 2 h for 24 h after challenge and then twice daily for 9 d. Accelerometers, pedometers, and positioning devices monitored cattle behavior within the pen for 9 d after challenge. Blood samples were collected on trial d 0, 0.5, 1, 2, 3, 7, and 9 and were analyzed to determine the concentration of substance P, cortisol, haptoglobin, and metalloproteinase. All calves in the MH group were euthanized and necropsied on trial d 9. All MH calves became clinically ill postchallenge. A treatment × time interaction (P < 0.05) was evident for nasal and rectal temperatures, behavior, weight, and blood analysis. Rectal temperatures in MH were higher (P < 0.01) than CN during the period from 6 to 24 h after challenge. Conversely, nasal passage temperatures were less in MH calves compared with CN at 12 to 22 h after challenge. Calves in MH spent less time at the grain bunk, less time at the hay feeder, and more time lying down during the early pneumonia period compared with CN calves. Also, MH calves had significantly greater concentrations of blood biomarkers of pain (substance P) on d 0.5 (P < 0.01); stress (cortisol) on d 0.5 and 1 (P < 0.01); haptoglobin on d 0.5, 1, 2, 3, 7 (P < 0.01); and metalloproteinase on d 1, 2, and 3 (P < 0.01) compared with CN calves. At necropsy, all MH calves had right cranioventral bronchopneumonia (median lung lesions = 6.8%). Mannheimia haemolytica pneumonia caused significantly more changes in behavior and increased biomarkers during high (maximum ≥32°C) ambient temperatures compared with control calves. The results of this study may guide research in the development of objective assessment tools for management of cattle affected with bovine respiratory disease during extreme summer conditions.

Effect of castration method on neurohormonal and electroencephalographic stress indicators in Holstein calves of different ages.

As public concern for food animal welfare increases, a need to validate objective pain assessment tools exists in order to formulate animal welfare policies and facilitate regulatory approval of compounds to alleviate pain in livestock in the United States. The aims of this study were (1) to compare the physiological response to pain induced by surgical and nonsurgical (band) castration in calves and (2) to elucidate age-related differences in pain response of calves subjected to different castration methods. Seventy-six Holstein bull calves were blocked by age (≤8-wk and ≥6-mo-old) and randomly assigned to 1 of 4 treatment groups: control (n=20), castration by banding (n=18), cut-and-clamp surgical castration (n=20), and cut-and-pull surgical castration (n=18). Measurements included electroencephalogram, heart rate variability, infrared thermography, electrodermal activity, and concentrations of serum cortisol and plasma substance P before, during, and within 20min following castration. Electroencephalogram recordings showed desynchronization for all treatments, consistent with increased arousal; yet the magnitude of desynchronization was greatest for 6-mo-old calves castrated by cut-and-clamp. Additionally, older calves in the cut-and-pull group showed greater desynchronization than younger calves in the same group. Based on the heart rate variability analysis, 6-mo-old calves in the control or cut-and-pull castration groups showed greater sympathetic tone than younger calves in the same treatment groups. Overall, younger calves showed lower electrodermal activity than older calves. Regardless of treatment, concentrations of cortisol and plasma substance P were greater in 6-mo-old calves relative to their younger counterparts, indicating a more robust response to all treatments in older calves. In summary, neurohormonal and electroencephalographic stress responses of calves to castration were age-specific. Castration by cut-and-clamp showed the most pronounced stress response in 6-mo-old calves. These findings provide evidence that support welfare policies recommending castration at an early age and the use of analgesic compounds at the time of surgical castration especially in older calves. However, the potential long-term negative consequences of early untreated pain must be considered and warrant further investigation.