Respiratory Disease In Feedlot Cattle Research Articles

Mycoplasma bovis and Mannheimia haemolytica dynamics during acute bovine respiratory disease in feedlot cattle

Mycoplasma bovis is a bacterium member of the family Myco­plasmataceae, characterized by a small genome, lack of cell wall, and high nutritional requirements for in vitro growth (Li et al., 2011; Parker et al., 2018; Dudek et al., 2020). Traditionally, M. bovis has been linked to chronic BRD cases and treatment failures (Booker et al., 2008; Hermeyer et al., 2012; Gershwin et al., 2015; Becker et al., 2020). Several virulence factors have been implicated in M. bovis ability to persist in the lungs of cat­tle with BRD, such as variable surface proteins (Vsp), adhesins, nucleases, H2O2 production and biofilm formation (Burki et al., 2015; Perez-Casal, 2020). Due to the difficulties of growing M. bovis in the lab, the inherent culture bias (Prakash et al., 2021) could have shaped our current knowledge of M. bovis in BRD.
 Recent evidence has emerged linking M. bovis presence in the upper respiratory tract with acute BRD status (Timsit et al., 2018; Centeno-Martinez et al., 2022). However, the association between M. bovis and other BRD agents, especially Mannheim­ia haemolytica, over time remains unknown during the first month on the feedlot. A more comprehensive understanding of the dependencies among BRD pathogens over time will help develop new non-antibiotic control strategies and subsequently reduce the burden of BRD on beef cattle production. Therefore, this study aimed to evaluate the association of M. bovis and M. haemolytica during acute BRD in feedlot cattle.

Using Efficiency-Corrected quantitative PCR to assess risk of respiratory disease in feedlot cattle

Using Efficiency-Corrected quantitative PCR to assess risk of respiratory disease in feedlot cattle

Evaluation of First Treatment Timing, Fatal Disease Onset, and Days from First Treatment to Death Associated with Bovine Respiratory Disease in Feedlot Cattle

Bovine respiratory disease (BRD) is a frequent beef cattle syndrome. Improved understanding of the timing of BRD events, including subsequent deleterious outcomes, promotes efficient resource allocation. This study's objective was to determine differences in timing distributions of initial BRD treatments (Tx1), days to death after initial treatment (DTD), and days after arrival to fatal disease onset (FDO). Individual animal records for the first BRD treatment (n = 301,721) or BRD mortality (n = 19,332) were received from 25 feed yards. A subset of data (318-363 kg; steers/heifers) was created and Wasserstein distances were used to compare temporal distributions of Tx1, FDO, and DTD across genders (steers/heifers) and the quarter of arrival. Disease frequency varied by quarter with the greatest Wasserstein distances observed between Q2 and Q3 and between Q2 and Q4. Cattle arriving in Q3 and Q4 had earlier Tx1 events than in Q2. Evaluating FDO and DTD revealed the greatest Wasserstein distance between cattle arriving in Q2 and Q4, with cattle arriving in Q2 having later events. Distributions of FDO varied by gender and quarter and typically had wide distributions with the largest 25-75% quartiles ranging from 20 to 80 days (heifers arriving in Q2). The DTD had right-skewed distributions with 25% of cases occurring by days 3-4 post-treatment. Results illustrate temporal disease and outcome patterns are largely right-skewed and may not be well represented by simple arithmetic means. Knowledge of typical temporal patterns allows cattle health managers to focus disease control efforts on the correct groups of cattle at the appropriate time.

Isolation and Genetic Characterization of a Bovine Coronavirus KBR-1 Strain from Calf Feces in South Korea.

Bovine coronavirus (BCoV) causes severe diarrhea in neonatal calves, winter dysentery in adult cattle, and respiratory disease in feedlot cattle, resulting in economic losses. A total of 16/140 calf diarrheic feces samples collected in South Korea between 2017 and 2018 were positive for BCoV. Phylogenetic analysis of the complete spike and hemagglutinin/esterase genes revealed that the 16 Korean BCoV strains belonged to group GIIa along with Korean strains isolated after 2000, whereas Korean BCoV strains isolated before 2000 belonged to group GI. Mice and goats inoculated with an inactivated KBR-1 strain (isolated from this study) generated higher antibody titers (96 ± 13.49 and 73 ± 13.49, respectively) when mixed with the Montanide01 adjuvant than when mixed with the Carbopol or IMS1313 adjuvants. Viral antigens were detected in the large intestine, jejunum, and ileum of calves inoculated with inactivated KBR-1 vaccine (104.0 TCID50/mL) at 14 days of post-challenge (DPC). However, no viral antigens were detected in calves vaccinated with a higher dose of inactivated KBR-1 strain (106.0 TCID50/mL) at 14 DPC, and they had high antibody titers and stable diarrhea scores. Currently, the group GIIa is prevalent in cows in South Korea, and although further research is needed in the future, the recently isolated KBR-1 strain has potential value as a new vaccine candidate.

Mycoplasma bovis is associated with Mannheimia haemolytica during acute bovine respiratory disease in feedlot cattle.

Bovine Respiratory Disease (BRD) represents a significant burden to the health of feedlot cattle and the profitability of the beef industry in the US. Mannheimia haemolytica is widely regarded as the primary bacterial pathogen driving acute BRD. While Mycoplasma bovis is most commonly implicated in chronic cases of BRD, this agent's potential role in acute stages of BRD is unclear. Therefore, this study aimed to evaluate potential associations between M. bovis and M. haemolytica during acute BRD in feedlot cattle. Nasal swabs (n = 1,044) were collected over time from feedlot cattle (n = 270) enrolled in an experiment assessing the effect of vaccination for Bovine Respiratory Syncytial Virus (BRSV). Swabs were analyzed for detection of M. bovis, M. haemolytica, Pasteurella multocida, Histophilus somni, and BRSV via multiplex qPCR assays. Data were analyzed using inverse conditional probability weighted (ICPW) logistic regression models to investigate potential effects of M. bovis presence on arrival (d0), day seven (d7) and day 14 (d14) post-arrival on M. haemolytica prevalence on day 28 (d28) post-arrival, adjusting for the previous history of P. multocida, H. somni, BRSV, BRD morbidity, and body weight. The potential association between time-to-BRD detection and M. bovis presence on d0, d7, and d14 post-arrival, was inferred via an ICPW time-to-event model. The presence of M. bovis in nasal swabs collected on d7 post-arrival was significantly associated with an increase in the prevalence of M. haemolytica on d28 (prevalence difference: 45%; 95% Confidence Interval: 31%, 60%; P-value < 0.001). Significant time-varying coefficients for M. bovis presence were detected at d0, d7, and d14 post-arrival in the ICPW time-to-event model (P-value < 0.001). The shortest median time-to-BRD detection was 29 days in cattle that were M. bovis positive on d0, d7, and d14 post-arrival and in those that were positive on d0 and d14 post-arrival. Under the conditions of this study, our findings suggest that M. bovis may be influencing the respiratory environment during the acute phase of BRD, increasing the abundance of M. haemolytica, which could have important impacts on the occurrence of BRD.

Evaluation of reticulorumen temperature boluses for the diagnosis of subclinical cases of bovine respiratory disease in feedlot cattle.

Bovine respiratory disease (BRD) is the most important and costly health issue of the feedlot industry worldwide. Remote monitoring of reticulorumen temperature has been suggested as a potential tool to improve the diagnostic accuracy of BRD. The present study aimed to evaluate 1) the difference and degree of reticulorumen hyperthermia episodes between healthy and subclinical BRD feedlot steers, and 2) determine the correlation between reticulorumen hyperthermia and lung pathology, performance, and carcass traits. Mixed-breed feedlot steers (n = 148) with a mean arrival weight of 321 ± 3.34 kg were administered a reticulorumen bolus at feedlot entry and monitored for visual and audible signs of BRD until slaughter when lungs were examined and scored for lesions indicative of BRD. Post-slaughter animals with no record of BRD treatment were assigned to one of three case definitions. Healthy steers had no visual or audible signs of BRD (i.e., CIS=1), and total lung consolidation score < 5% or pleurisy score < 3 at slaughter. Subclinical BRD cases had a CIS of 1, and a lung consolidation score ≥ 5% or a pleurisy score of 3 at slaughter. Mild CIS cases had at least one CIS of 2, and a lung consolidation score < 5% and a pleurisy score < 3 at slaughter. Subclinical BRD and mild CIS cases had longer total duration of reticulorumen hyperthermia, more episodes and longer average episode duration above 40.0 °C compared to healthy steers (P < 0.05). A moderate positive correlation was found between lung consolidation and total duration (r = 0.27, P < 0.001), episode duration (r = 0.29, P < 0.001), and number of episodes (r = 0.20, P < 0.05). Pleurisy score was also found to be moderately and positively correlated with total duration (r = 0.23, P < 0.01), episode duration (r = 0.37, P < 0.001), and number of episodes (r = 0.26, P < 0.01). Moderate negative correlations were found between reticulorumen hyperthermia and carcass traits including hot standard carcass weight (HSCW) (-0.22 ≤ r ≤ -0.23, P < 0.05) and P8-fat depth (-0.18 ≤ r ≤ -0.32, P < 0.05). Subclinical BRD reduced carcass weight by 22 kg and average daily gain (ADG) by 0.44 kg/day compared to healthy steers (P < 0.05), but mild CIS cases had no effect on performance (P > 0.05). The reticulorumen bolus technology appears promising for detection of subclinical BRD cases in feedlot cattle as defined by lung pathology at slaughter.

Economic impact of digital dermatitis, foot rot, and bovine respiratory disease in feedlot cattle.

Digital dermatitis (DD) has emerged in North American feedlots, although production and economic impacts are not fully understood. Objectives of this study were to: (1) estimate the economic impact of a single case of DD, foot rot (FR), and bovine respiratory disease (BRD) in feedlot cattle and (2) determine its impact on average daily gain (ADG). Feedlot cattle health and production records were available from two feedlots for a 3-yr interval. The dataset consisted of 77,115 animal records, with 19.3% (14,900) diagnosed with a disease. Diseased animals were categorized into five groups: DD, FR, BRD, other diseases (OT), and two or more diseases (TM), with a treatment cumulative incidence of 6.0%, 59.1%, 10.7%, 12.7%, and 11.5%, respectively. FR was the disease with the highest cumulative incidence in both heifers and steers (58.8% and 59.6%, respectively). Of all fall-placed cattle diagnosed with any disease, 48.1% of the cases were FR. DD affected the partial budget in five out of the eight groups of cattle, with the highest impact of DD seen in grass yearling heifers and grass yearling steers: $-98 and $-96 CAD, respectively, relative to their healthier counterparts. Healthy cattle had a significantly higher ADG when compared with DD cattle in five of the eight categories, ranging from 0.11 kg/d in winter-placed heifers to 0.17 kg/d in fall-placed steers. In the economic analysis, it was concluded that on an individual animal basis, BRD was the most impactful of all analyzed diseases, whereas DD was second, marking the importance of controlling and mitigating this foot condition. Identifying differential effects of diseases on a partial budget analysis and ADG of the types of cattle stratified by sex enables feedlot producers to focus control and mitigation strategies on specific groups.

Efficacy of statistical process control procedures to monitor deviations in physical behavior for preclinical detection of bovine respiratory disease in feedlot cattle

Opportunities exist to improve the efficacy of antimicrobial treatment and animal welfare standards through use of remote sensor technologies for early detection of bovine respiratory disease (BRD). A post-hoc analysis using statistical process control (SPC) procedures was performed on continuously-recorded physical activity data collected from BRD-diagnosed and healthy calves from Pillen et al. (2016). We hypothesized that SPC models that monitor physical activity traits (step count, motion index, standing time, lying bouts) would yield higher diagnostic accuracies compared to methods based on visual observation of clinical signs of illness for detecting the onset of BRD. Crossbred steers and bulls (n = 266; initial BW = 180 kg) at high risk for BRD were fitted with leg-attached accelerometers (IceQube, IceRobotics, Ltd.) upon arrival at a commercial feedlot and evaluated for 56 d Overall, calves experienced 48% morbidity, with the average day of first treatment occurring 16 d post-feedlot arrival. Shewhart charts were used to evaluate daily changes in each trait as univariate models and combined traits in principal component analysis (PCA)–constructed multivariate models, relative to the day of BRD diagnosis. Diagnostic test sensitivity and specificity were calculated for each model and compared. The univariate models had relatively low sensitivities (< 40%), with specificities ranging from 23 to 81%, and chart signaling occurred up to 2 d prior to visual diagnosis of BRD. The univariate model for step count had the highest accuracy (52.3%), while lying time had the lowest accuracy (32%). The multivariate models that included all 4 physical activity traits or only lying bout behavior had moderate sensitivities (44 to 57%), but low specificities (< 37%), and chart signaling occurred 2 d prior to visual diagnosis. The relatively low diagnostic test accuracies of the SPC models reported in this study may have been due to substantial within-animal daily variation in the physical activity traits and(or) the limited time for adequate model training prior to the onset of BRD cases. Future research should investigate SPC analysis of multifactorial algorithms using physical activity and feeding behavior traits to improve the accuracy of preclinical detection of BRD.

Diagnosis of Bovine Respiratory Disease in feedlot cattle using blood 1H NMR metabolomics

Current diagnosis methods for Bovine Respiratory Disease (BRD) in feedlots have a low diagnostic accuracy. The current study aimed to search for blood biomarkers of BRD using 1H NMR metabolomics and determine their accuracy in diagnosing BRD. Animals with visual signs of BRD (n = 149) and visually healthy (non-BRD; n = 148) were sampled for blood metabolomics analysis. Lung lesions indicative of BRD were scored at slaughter. Non-targeted 1H NMR metabolomics was used to develop predictive algorithms for disease classification using classification and regression trees. In the absence of a gold standard for BRD diagnosis, six reference diagnosis methods were used to define an animal as BRD or non-BRD. Sensitivity (Se) and specificity (Sp) were used to estimate diagnostic accuracy (Acc). Blood metabolomics demonstrated a high accuracy at diagnosing BRD when using visual signs of BRD (Acc = 0.85), however was less accurate at diagnosing BRD using rectal temperature (Acc = 0.65), lung auscultation score (Acc = 0.61) and lung lesions at slaughter as reference diagnosis methods (Acc = 0.71). Phenylalanine, lactate, hydroxybutyrate, tyrosine, citrate and leucine were identified as metabolites of importance in classifying animals as BRD or non-BRD. The blood metabolome classified BRD and non-BRD animals with high accuracy and shows potential for use as a BRD diagnosis tool.

Review of health and performance effects of bovine viral diarrhea virus and testing for persistently infected feedlot cattle

Bovine viral diarrhea virus (BVDV) is an important pathogen commonly associated with bovine respiratory disease in feedlot cattle, and has varying effects on animal health and performance outcomes. The objective of this paper is to provide a review of the literature evaluating the effects of continued exposure to cattle persistently infected (PI) with BVDV, as well as testing and removing PI cattle from pen cohorts, on calf health and performance outcomes. Nine studies evaluated health and performance outcomes of cattle exposed to a PI-BVDV calf in their pen vs pens of cattle not exposed. Two additional studies evaluated the effects of testing and removal of PI animals from pens on health and performance outcomes compared to leaving a Pi-positive animal(s) in the pen with cohorts for varied periods of time. The literature evaluating the effects of testing and removing PI-BVDV calves from pen cohorts is limited, but does not suggest improvement in health and/or performance in calves by testing and removing PI-BVDV calves after arrival into the feedlot. Additional research is needed to evaluate the effect of testing and removing PI-BVDV calves prior to incorporating the practice in the field.

Brazilian strain of bovine respiratory coronavirus is derived from dual enteric and respiratory tropism

Bovine coronavirus (BCoV) is a pathogen related to enteric and respiratory diseases in cattle worldwide. Enteric (BECoV) strains of BCoV are predominant in South America, and genetic investigations have been conducted to identify its relationship with isolates of respiratory origin (BRCoV). In this study, we used a BRCoV strain (BR-UEL11) derived from an outbreak of respiratory disease in feedlot cattle in southern Brazil, and compared the partial sequence of the polymorphic region of Spike (which was detected and sequenced by two distinct reverse transcription-polymerase chain reactions) with those of other BCoV strains. The phylogenetic relationship of BR-UEL11 with Brazilian BCoV, which is associated with calf diarrhea and winter dysentery (enteric, BECoV; respiratory, BRCoV), and classical reference prototypes was analyzed. The analysis showed that the BRCoV strains from Brazil clustered with a clade that was distinct from most isolates associated with calf diarrhea (BECoV) and ancestral prototype strains such as Mebus, Nebraska, and LYVB. Furthermore, the BRCoV strains from Brazil clustered with a clade that contained recent strains associated with winter dysentery, showing 98-99% nucleotide identity with those strains. These results suggested that the Brazilian BCoV evolved from being solely enteric to a dual enteric and respiratory tropic virus.

Metagenomic characterization of the virome associated with bovine respiratory disease in feedlot cattle identified novel viruses and suggests an etiologic role for influenza D virus.

Bovine respiratory disease (BRD) is the most costly disease affecting the cattle industry. The pathogenesis of BRD is complex and includes contributions from microbial pathogens as well as host, environmental and animal management factors. In this study, we utilized viral metagenomic sequencing to explore the virome of nasal swab samples obtained from feedlot cattle with acute BRD and asymptomatic pen-mates at six and four feedlots in Mexico and the USA, respectively, in April-October 2015. Twenty-one viruses were detected, with bovine rhinitis A (52.7 %) and B (23.7 %) virus, and bovine coronavirus (24.7 %) being the most commonly identified. The emerging influenza D virus (IDV) tended to be significantly associated (P=0.134; odds ratio=2.94) with disease, whereas viruses commonly associated with BRD such as bovine viral diarrhea virus, bovine herpesvirus 1, bovine respiratory syncytial virus and bovine parainfluenza 3 virus were detected less frequently. The detection of IDV was further confirmed using a real-time PCR assay. Nasal swabs from symptomatic animals had significantly more IDV RNA than those collected from healthy animals (P=0.04). In addition to known viruses, new genotypes of bovine rhinitis B virus and enterovirus E were identified and a newly proposed species of bocaparvovirus, Ungulate bocaparvovirus 6, was characterized. Ungulate tetraparvovirus 1 was also detected for the first time in North America to our knowledge. These results illustrate the complexity of the virome associated with BRD and highlight the need for further research into the contribution of other viruses to BRD pathogenesis.

Associations between prior management of cattle and risk of bovine respiratory disease in feedlot cattle

Bovine respiratory disease (BRD) is the major cause of clinical disease and death in feedlot populations worldwide. A longitudinal study was conducted to assess associations between risk factors related to on-farm management prior to transport to the feedlot and risk of BRD in a population of feedlot beef cattle sourced from throughout the cattle producing regions of Australia. Exposure variables were derived from questionnaire data provided by farmers supplying cattle (N=10,721) that were a subset of the population included in a nationwide prospective study investigating numerous putative risk factors for BRD. Causal diagrams were used to inform model building to allow estimation of effects of interest. Multilevel mixed effects logistic regression models were fitted within the Bayesian framework. Animals that were yard weaned were at reduced risk (OR: 0.7, 95% credible interval: 0.5–1.0) of BRD at the feedlot compared to animals immediately returned to pasture after weaning. Animals that had previously been fed grain (OR: 0.6, 95% credible interval: 0.3–1.1) were probably at reduced risk of BRD at the feedlot compared to animals not previously fed grain. Animals that received prior vaccinations against Bovine viral diarrhoea virus 1 (OR: 0.8, 95% credible interval: 0.5–1.1) or Mannheimia haemolytica (OR: 0.8, 95% credible interval: 0.6–1.0) were also probably at reduced risk compared to non-vaccinated animals. The results of this study confirm that on-farm management before feedlot entry can alter risk of BRD after beef cattle enter feedlots.

Evaluation of a Computer-aided Lung Auscultation System for Diagnosis of Bovine Respiratory Disease in Feedlot Cattle.

BackgroundA computer‐aided lung auscultation (CALA) system was recently developed to diagnose bovine respiratory disease (BRD) in feedlot cattle.ObjectivesTo determine, in a case–control study, the level of agreement between CALA and veterinary lung auscultation and to evaluate the sensitivity (Se) and specificity (Sp) of CALA to diagnose BRD in feedlot cattle.AnimalsA total of 561 Angus cross‐steers (initial body weight = 246 ± 45 kg) were observed during the first 50 day after entry to a feedlot.MethodsCase–control study. Steers with visual signs of BRD identified by pen checkers were examined by a veterinarian, including lung auscultation using a conventional stethoscope and CALA that produced a lung score from 1 (normal) to 5 (chronic). For each steer examined for BRD, 1 apparently healthy steer was selected as control and similarly examined. Agreement between CALA and veterinary auscultation was assessed by kappa statistic. CALA's Se and Sp were estimated using Bayesian latent class analysis.ResultsOf the 561 steers, 35 were identified with visual signs of BRD and 35 were selected as controls. Comparison of veterinary auscultation and CALA (using a CALA score ≥2 as a cut off) revealed a substantial agreement (kappa = 0.77). Using latent class analysis, CALA had a relatively high Se (92.9%; 95% credible interval [CI] = 0.71–0.99) and Sp (89.6%; 95% CI = 0.64–0.99) for diagnosing BRD compared with pen checking.Conclusions CALA had good diagnostic accuracy (albeit with a relatively wide CI). Its use in feedlots could increase the proportion of cattle accurately diagnosed with BRD.

Evaluating the cost implications of a radio frequency identification feeding system for early detection of bovine respiratory disease in feedlot cattle

New technologies to identify diseased feedlot cattle in early stages of illness have been developed to reduce costs and welfare impacts associated with bovine respiratory disease (BRD). However, the economic value of early BRD detection has never been assessed. The objective was to simulate cost differences between two BRD detection methods during the first 61 d on feed (DOF) applied in moderate- to large-sized feedlots using an automated recording system (ARS) for feeding behavior and the current industry standard, pen-checking (visual appraisal confirmed by rectal temperature). Economic impact was assessed with a cost analysis in a simple decision model. Scenarios for Canadian and US feedlots with high- and low-risk cattle were modeled, and uncertainty was estimated using extensive sensitivity analyses. Input costs and probabilities were mainly extracted from publicly accessible market observations and a large-scale US feedlot study. In the baseline scenario, we modeled high-risk cattle with a treatment rate of 20% within the first 61 DOF in a feedlot of >8000 cattle in Canada. Early BRD detection was estimated to result in a relative risk of 0.60 in retreatment and 0.66 in mortality compared to pen-checking (based on previously published estimates). The additional cost of monitoring health with ARS in Canadian dollar (CAD) was 13.68 per steer. Scenario analysis for similar sized US feedlots and low-risk cattle with a treatment rate of 8% were included to account for variability in costs and probabilities in various cattle populations. Considering the cost of monitoring, all relevant treatment costs and sale price, ARS was more costly than visual appraisal during the first 61 DOF by CAD 9.61 and CAD 9.69 per steer in Canada and the US, respectively. This cost difference increased in low-risk cattle in Canada to CAD 12.45. Early BRD detection with ARS became less expensive if the costs for the system decreased to less than CAD 4.06/steer, or if the underlying true BRD incidence (not treatment rate) within the first 61 DOF exceeded 47%. The model was robust to variability in the remaining input variables. Some of the assumptions in the baseline analyses were conservative and may have underestimated the real value of early BRD detection. Systems such as ARS may reduce treatment costs in some scenarios, but the investment costs are currently too high to be cost-effective when used solely for BRD detection compared to pen-checking.

Estimating the comparative clinical and economic consequences of tulathromycin for treatment of present or anticipated outbreaks of bovine respiratory disease in feedlot cattle in the United States1

The goal of this study was to determine the clinical and economic impact of using tulathromycin as first line treatment for bovine respiratory disease (BRD) compared with other commonly used antimicrobials. Two decision trees were developed simulating the consequences of treating cattle at high risk of developing BRD [control model (CM)] or cattle with first clinical BRD episode [treatment model (TM)]. As comparators florfenicol and tilmicosin were considered in both models whereas enrofloxacin was included in the TM because it was only labeled for treatment of BRD at the time of development of the calculators. A total of 5 (CM) and 10 (TM) comparative clinical studies that reported efficacy data for the selected drugs and indications were identified as suitable for model population. The following outcomes were considered: first treatment success, number of subsequent BRD treatments, chronics, and mortalities. Cost parameters were considered from the perspective of the producer and included treatment costs (first treatment and retreatments) and costs of chronics and deaths derived from published sources for 2010 (default). The models allowed the estimation of clinical and economic consequences according to each individual trial outcomes. Treatment with tulathromycin resulted in more first treatment successes and fewer removals (chronics and deaths) in all comparisons. The average total number of antimicrobial treatments required for the management of BRD was also least with tulathromycin as first treatment option. Because of better efficacy, total costs over the entire study periods were always lowest with tulathromycin. Depending on the study selected as the basis for the efficacy evaluation, cost savings with tulathromycin were calculated in the CM between US$21.00 and $47.86 (vs. florfenicol) and $11.37 and $72.64 (vs. tilmicosin); cost savings in the TM ranged between $28.47 and $143.87 (vs. florfenicol) and $7.75 and $84.91 (vs. tilmicosin) as well as between $23.22 and $47.82 (vs. enrofloxacin), with the ranges reflecting a variety of settings in different trials. Thus, the higher drug costs of tulathromycin were more than offset by reduced BRD treatments, chronics, and mortalities in the herd. Fewer BRD episodes in cattle treated with tulathromycin not only contributes to overall savings in BRD management but also reduces the necessity of repeated antibiotic treatment, supporting prudent use of antimicrobials in livestock.

Associations between Weather Conditions and Bovine Respiratory Disease in Feedlot Cattle

Bovine respiratory disease complex (BRD) is the most common cause of disease in weaned cattle. Ambient environmental conditions affect nutritional requirements, metabolism, and BRD risk; however, data on associations between specific weather conditions and BRD morbidity in cattle are sparse. The goal of our study was to quantify associations between daily BRD incidence rates and preceding weather conditions in different lag periods (considering up to seven days from the current day of interest) in feedlot cattle.

Mannheimia haemolyticaand bovine respiratory disease

Mannheimia haemolytica is the principal bacterium isolated from respiratory disease in feedlot cattle and is a significant component of enzootic pneumonia in all neonatal calves. A commensal of the nasopharynx, M. haemolytica is an opportunist, gaining access to the lungs when host defenses are compromised by stress or infection with respiratory viruses or mycoplasma. Although several serotypes act as commensals, A1 and A6 are the most frequent isolates from pneumonic lungs. Potential virulence factors include adhesin, capsular polysaccharide, fimbriae, iron-regulated outer membrane proteins, leukotoxin (Lkt), lipopolysaccharide (LPS), lipoproteins, neuraminidase, sialoglycoprotease and transferrin-binding proteins. Of these, Lkt is pivotal in induction of pneumonia. Lkt-mediated infiltration and destruction of neutrophils and other leukocytes impairs bacterial clearance and contributes to development of fibrinous pneumonia. LPS may act synergistically with Lkt, enhancing its effects and contributing endotoxic activity. Antibiotics are employed extensively in the feedlot industry, both prophylactically and therapeutically, but their efficacy varies because of inconsistencies in diagnosis and treatment regimes and development of antibiotic resistance. Vaccines have been used for many decades, even though traditional bacterins failed to demonstrate protection and their use often enhanced disease in vaccinated animals. Modern vaccines use culture supernatants containing Lkt and other soluble antigens, or bacterial extracts, alone or combined with bacterins. These vaccines have 50-70% efficacy in prevention of M. haemolytica pneumonia. Effective control of M. haemolytica pneumonia is likely to require a combination of more definitive diagnosis, efficacious vaccines, therapeutic intervention and improved management practices.

Bovine respiratory disease in feedlot cattle: Phenotypic, environmental, and genetic correlations with growth, carcass, and longissimus muscle palatability traits1

Bovine respiratory disease (BRD) is the most costly feedlot disease in the United States. Selection for disease resistance is one of several possible interventions to prevent or reduce the economic loss associated with animal disease and to improve animal welfare. Undesirable genetic relationships, however, may exist between production and disease resistance traits. The objectives of this study were to estimate the phenotypic, environmental, and genetic correlations of BRD with growth, carcass, and LM palatability traits. Health records on 18,112 feedlot cattle over a 15-yr period and slaughter data on 1,627 steers over a 4-yr period were analyzed with bivariate animal models. Traits included ADG, adjusted carcass fat thickness at the 12th rib, marbling score, LM area, weight of retail cuts, weight of fat trim, bone weight, Warner-Bratzler shear force, tenderness score, and juiciness score. The estimated heritability of BRD incidence was 0.08 +/- 0.01. Phenotypic, environmental, and genetic correlations of the observed traits with BRD ranged from -0.35 to 0.40, -0.36 to 0.55, and -0.42 to 0.20, respectively. Most correlations were low or negligible. The percentage of carcass bone had moderate genetic, phenotypic, and environmental correlations with BRD (-0.42, -0.35, and -0.36, respectively). Hot carcass weight and weight of retail cuts had moderate, undesirable phenotypic correlations with BRD (0.37 and 0.40, respectively). Correlations of BRD with LM palatability and ADG were not detected. Low or near zero estimates of genetic correlations infer that selection to reduce BRD in feedlot cattle would have negligible correlated responses on growth, carcass, and meat palatability traits or that selection for those traits will have little effect on BRD susceptibility or resistance.

Bovine respiratory disease in feedlot cattle: Environmental, genetic, and economic factors

The objective of this study was to characterize genetic, environmental, and economic factors related to the incidence of bovine respiratory disease (BRD) in feedlot calves. Records from 18,112 calves representing 9 breeds (Angus, Braunvieh, Charolais, Gelbvieh, Hereford, Limousin, Pinzgauer, Red Poll, and Simmental) and 3 composite types (MARC I, MARC II, and MARC III) over a 15-yr period (1987 to 2001) were evaluated. Disease incidence was observed and recorded by station veterinary and technical staff. The incidence of BRD varied across years, with the annual observed incidence ranging from 5 to 44%. From 1987 to 1992, the annual average incidence generally exceeded 20%. However, in later years the annual incidence did not exceed 14%. The epidemiological pattern indicated that BRD infection increased dramatically after 5 d on feed and remained high until approximately 80 d on feed. Previous BRD infection during the preweaning period did not influence subsequent BRD infection in the feedlot. Steers were more likely to become sick with BRD than heifers; castration before entry in the feedlot may be a predisposing cause. Few significant differences among breeds were detected for BRD incidence. Adjusted solutions from mixed model analyses indicated that Herefords were generally more susceptible to BRD infection (P < 0.05) than MARC I and III composite types. Composite breed types had similar susceptibility compared with other purebred breeds. Mortality associated with BRD was greatest in Red Poll calves (9%) compared with the average over all breeds (4%). Estimates of heritability for resistance to BRD ranged from 0.04 to 0.08 +/- 0.01. When the observed heritability was transformed to an underlying continuous scale, the estimate increased to 0.18. Selection for resistance to BRD could be effective if phenotypes for BRD resistance were known. Thus, development of an inexpensive and humane method of challenging animals with BRD to determine resistance would be an important step in reducing the incidence of BRD. This study also demonstrated that producer-collected field data could be used for selection against this disease. The economic loss associated with lower gains and treatment costs for BRD infection in a 1,000-cattle feedlot was estimated as dollar 13.90 per animal, not including labor and associated handling costs.