Large pen feedlot studies (n = 7) with heifers and steers (n = 17,571) were conducted in North America to determine the effects of orally administered Megasphaera elsdenii NCIMB 41125 (Lactipro; Axiota Animal Health, Fort Collins, CO, USA) on late feeding period mortality and growth performance. Study designs were randomized complete blocks, and treatments included no administration of Megasphaera elsdenii NCIMB 41125 (CON) and administration of a commercial dose of Megasphaera elsdenii NCIMB 41125 (LP). Treatments were administered 51 to 147 d on feed to coincide with terminal implant administration and/or sorting into marketing cohorts, on subsequent mortality and growth performance. Data were analyzed with linear mixed models to account for the hierarchical design structure and fitted for mortality and performance outcomes. Mortality incidence was reduced (P = 0.005) when dosing Megasphaera elsdenii NCIMB 41125 [0.011 vs. 0.007 (per 100 head days) ± 0.002 for CON versus LP cattle, respectively]. Thus, the death rate during the risk period was 1.57 times greater in cattle not administered LP. No treatment × sex interaction (P ≥ 0.53) was observed for any growth performance measures. A significant effect of sex (P < 0.01) was observed for dry matter intake (DMI), average daily gain (ADG), and gain:feed (G:F), with steers exhibiting increased performance across all outcomes. No difference (P ≥ 0.18) between treatments was noted for DMI, ADG, or G:F. Orally administering Megasphaera elsdenii NCIMB 41125 to steers and heifers at terminal implant processing can be a management strategy to decrease mortality following terminal processing and during the late finishing phase.

Bovine respiratory disease (BRD) is an important disease of fed cattle and knowledge gaps exist regarding factors predict­ing treatment success. The study objective was to identify po­tential relationships between risk factors known at the time of initial BRD treatment with 3 post-treatment outcomes: first treatment success (FTS), non-cause specific case fatal­ity risk (CFRALL), and cause-specific case fatality risk (CFRBRD). This retrospective analysis used generalized linear mixed models to evaluate relationships between covariates of interest with each outcome. Analysis included 132,521 individual-animal initial BRD treatment re­cords from 14 central U.S. feedyards (May 2017 to Dec 2020) with overall FTS of 67.8%, CFRALL of 10.0%, and CFRBRD of 6.3%. The FTS was associated (P < 0.05) with all covariates ex­cept sex, CFRALL was associated with all covariates, and CFR­BRD was associated with all covariates except day-of-week treated. Treatments early in the feeding phase (DOF 0-10, 11- 20) resulted in lower (P < 0.05) FTS (49.2% ± 0.8; 55.3% ± 0.8), higher (P < 0.05) CFRALL (12.5% ± 1.3; 12.6% ± 1.4) and higher (P < 0.05) CFRBRD (6.3% ± 1.1; 6.1% ± 1.0) compared to cattle treated on days 21-70. Rectal temperature in the 103.1-104.0 (39.4-40.0 °C) category had higher (P < 0.05) CFRALL (15.3% ± 1.5) and CFRBRD (9.2% ± 1.5) compared to other rectal tempera­ture categories. Specific risk factors including days on feed at treatment, sex and weight at the time of treatment were associ­ated with treatment outcomes. Results can be useful for defin­ing expectations following first treatment for BRD.

OBJECTIVE:To evaluate the risk and timing of right heart failure (RHF) in feedlot cattle.ANIMALS:Study population consisted of 1,717,356 cattle (5,527 cohorts) in 13 US and Canadian feedlots. There were 1,336 RHF diagnosed at necropsy.PROCEDURES:Multivariable models were utilized to evaluate risk and timing of RHF death.RESULTS:Arrival year was associated with RHF and was influenced by arrival quarter on the magnitude of risk of RHF (P < .01), but no linear increase over years was identified. The impact of feedlot elevation on RHF was modified by breed (beef, dairy, or dairy-cross; P < .01) with beef cattle in the highest elevation category having 0.54 times the risk of RHF as dairy cattle in the same elevation category (LCL = 0.31; UCL = 0.962). Cattle that died due to RHF and were treated for bovine respiratory disease died 11 days (LCL = 1.33, UCL = 20.2 days) sooner than cattle never treated for bovine respiratory disease (P = .03). Cattle breed was associated with RHF timing (P = .01), and dairy-cross cattle RHF cases died approximately 37 days earlier (SE = 13.0 days; P = .01) compared to beef cattle.CLINICAL RELEVANCE:This research showed demographic factors associated with RHF and their respective influence on risk and timing of RHF. Risk rates of RHF were similar to previous research. This could allow for comparisons across different feedlot populations, using different diagnoses at necropsy and RHF risk/rates do not appear to be increasing.

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.

OBJECTIVE:Determine bovine leukemia virus (BLV) seroprevalence of adult female cattle in Eastern Kansas beef herds and the proviral load (PVL) of those cattle found to be ELISA positive.ANIMALS:Convenience sample of 2,845 cows from 44 beef herds.PROCEDURES:BLV serostatus was determined using an ELISA antibody test (gp-51; IDEXX). BLV quantitative PCR (qPCR) status and PVL were determined utilizing a qPCR test (SS1 qPCR test; CentralStar Laboratories). The association of age, herd size, and body condition score (BCS) category on the probability of being BLV positive was evaluated with a multiple variable logistic regression analysis that used BLV status as a binary outcome, herd nested within ranch as a random effect, and BCS, herd size, and age category as fixed effects.RESULTS:Forty-two of 44 herds had at least 1 BLV ELISA-positive cow (95.5% herd seroprevalence). Overall, 1,564 of the 2,845 cows were BLV ELISA positive (55.0% individual animal prevalence). No association between BLV ELISA status and herd size or BCS was identified. When evaluated by age, the model-adjusted probability of being BLV ELISA positive was lowest for heifers (1 year of age, first parity) and increased until 5 to 6 years of age. Of the 1,564 ELISA-positive animals, 838 were qPCR positive (53.6%). The model-adjusted probability of being qPCR positive was not associated with age, herd size, or BCS category.CLINICAL RELEVANCE:This study indicated that BLV-seropositive status both as a herd classification and individual animal classification was very common in this population. Because the percentage of BLV-seropositive cows varied between herds and by age, this study provides evidence that it is essential for investigators to control for herd and age in any analysis of the association of BLV serostatus and health and production outcomes of interest. Some BLV ELSIA-seropositive cows were classified as BLV negative by qPCR, and risk factors may differ between classification status by ELISA and qPCR.

OBJECTIVE Determine the association between bovine leukemia virus (BLV) status and fertility in beef cows. BLV-status was defined using 3 different testing strategies (ELISA-, quantitative polymerase chain reaction- [qPCR], and high proviral load [PVL]-status). Fertility was defined as the overall probability of pregnancy as well as the probability of becoming pregnant in the first 21 days of the breeding season. ANIMALS Convenience sample of 2,820 cows from 43 beef herds. PROCEDURES The association of BLV-status with the probability of becoming pregnant was evaluated with a multivariable logistic regression analysis that used pregnancy status as a binary outcome, herd nested within ranch as a random effect, and BLV-status (ELISA-, qPCR-, and PVL-status as separate models) and potential covariates (eg, age, Body Condition Score [BCS] category, and interactions) as fixed effects. RESULTS Raw data revealed that 55% (1,552/2,820) of cows were classified as BLV-positive by ELISA, and 95.3% (41/43) of herds had a least 1 ELISA-positive cow. Classification as BLV ELISA-positive was positively associated with the probability of being pregnant; however, when qPCR or PVL were used to classify BLV-status, there was no association with the probability of being pregnant. None of the methods of classifying BLV-status were associated with the probability of becoming pregnant in the first 21 days of the breeding season. CLINICAL RELEVANCE This study did not find evidence that testing beef cows for BLV-status using ELISA, qPCR, or a cut-off of 0.9 PVL and removing test-positive cows will improve cowherd fertility as described by the probability of becoming pregnant during the breeding season or becoming pregnant during the first 21 days of the breeding season.

The objective of this study was to report antimicrobial use in a convenience sample of U.S. beef feedyards for the years 2018 and 2019. In addition to antimicrobial use metrics, also reported are the indications for antimicrobial use and outcomes related to these indications. Antimicrobial use is characterized at the study and feedyard levels for a total of 1,141,846 head of cattle in 20 U.S. feedyards. Antimicrobial use is reported as milligrams of active antimicrobial ingredient per kilogram of liveweight sold (mg/kg-LW) and regimens of antimicrobials per animal year (Reg/AY). Regimens are described by antimicrobial class within use category as characterized by mg of active antimicrobial product per regimen (mg/Reg) and calendar days of administration per regimen (CDoA/Reg). A total of 1,128,515 regimens of medically important antimicrobials were captured from records. The number of regimens/100 head-in (Reg/100 head-in) are described in a subset of 10 feedyards with adequate data granularity to directly determine indications for antimicrobial administration. For the indications of bovine respiratory disease (BRD), Lameness (Lame), Liver Abscess Control (LAC), and Other (e.g., central nervous system disease, cellulitis) the Reg/100 head-in study-level values are 37.1, 0.8, 98.4, and 0.7, respectively, for 2018, with similar values for 2019. The regimens for BRD are further categorized in these 10 feedyards by the use categories in-feed, control of BRD, and individual animal therapy, yielding study level values of 4.6, 19.6, and 12.9 Reg/100 head-in, respectively, for 2018, with similar values for 2019. Outcomes of therapy for individual animal treatment of BRD, Lame, and Other are reported as treatment success, retreatment, or mortality by 30 days after the initial therapy of an animal for a disease. Treatment success rates (no treatment or mortality in the next 30 days) for 2018 in the 10 feedyards with sufficient data granularity are 76.5, 86.5, and 83.0% for BRD, Lame, and Other, respectively. The comparison of these results with other reports of antimicrobial use in North American feedyards highlights how differing approaches in calculating metric values may result in substantially different conclusions regarding antimicrobial use, especially in relation to long-duration uses.

OBJECTIVE To evaluate predictive model ability to determine whether an animal finished the feeding period using data known at first treatment for bovine respiratory disease (BRD). Additional comparisons evaluated the potential benefits of predictions by adding weather data, utilizing balancing techniques, and creating models for individual feedyards. ANIMALS This retrospective study included animal, pen, and feedyard data from 12 US feedyards from 2016 to 2021. The final dataset consisted of 96,382 BRD cases of which 14.2% did not finish the feeding phase. PROCEDURES Five predictive models were trained and underwent threshold probability adjustment to maximize F1 score. Model performance was evaluated using accuracy, sensitivity specificity, positive and negative predictive values, and area under the receiver operating characteristics curve (AUC). RESULTS Overall, model performance was low with a median AUC value of 0.675. The addition of weather data had little effect on AUC but resulted in more variation in sensitivity and specificity. Resampling the dataset had a limited effect on performance. Individual feedlot models had higher AUC values than others with the decision tree typically performing best in most feedyards. CLINICAL RELEVANCE Results indicated some utility of predictive models evaluating BRD cases to predict cattle that did not finish the feeding phase. These models could be valuable in assisting health providers making decisions on individual cases.

In order to accurately portray antimicrobial use in food animals, the need for standardized metrics, and an understanding of the characteristics of different metrics, has long been recognized. Fourteen U.S. feedyards were used to evaluate the effects of using centralized constants such as defined daily dose (DDD) and defined course dose (DCD) applied to the weight of medically important antimicrobials by class (mg) as opposed to using electronic individual animal treatment records and lot level in-feed antimicrobial records obtained from the same population. Three numerators were calculated directly from recorded data for each drug product: the number of antimicrobial regimens associated with indication (Reg), milligrams of drug administered per regimen (mg), and calendar days of administration for each regimen (CDoA). There were four use indications to which numerators were assigned: liver abscess control (LAC), bovine respiratory disease (BRD), lameness (lame), or all other indications combined (other). Three denominators were also calculated directly from the data, these being the number of days animals were present (head days), number of cattle received (head in), and kilograms of live weight sold (kg-LW). Numerators and denominators were calculated at the lot level. The use of DDD or DCD was explored to determine how their use would affect interpretation of comparisons between lots or feedyards. At the lot level across both study years, the lot estimate of nDDD differed from the CDoA value by >25% in 49.2% of the lots. The number of Defined Course Doses (nDCD) was then compared to the number of Regimens (Reg). Comparing nDCD to Reg at the lot level across both study years, the lot estimate of nDCD differed from the Reg value by >25% in 46.4% of lots. Both year and metric were also shown to affect numerical feedyard ranking by antimicrobial use according to seven different metrics. The analysis reported here adds to the body of literature reporting substantial effects of metric choice on the conclusions drawn from comparing antimicrobial use across multiple production sites.

The last U.S. national beef BLV herd prevalence study occurred in 1997 by the USDA and found an AGID/ELISA herd prevalence of 36.4% and an individual animal prevalence of 7.73% of ani­mals tested in the northcentral U.S. which included the state of Kansas. Kansas State University and Michigan State University, in a collaborative effort, performed a BLV herd and with-in-herd prevalence study of beef cattle in eastern Kansas in the fall of 2021.

Bovine respiratory disease (BRD) is a frequent disease in feedlot cattle, but little is known on the role of pen housing conditions. The objective of this research is to use a retrospective analysis with data from 10 U.S. feedlots to determine potential associations between BRD risk during the first 45 days after arrival with pen-level management factors including the number of water sources, shared water sources, and shared fence lines. Generalized linear mixed models were used to evaluate associations between management factors, cattle demographics, and BRD incidence. The effect of shared water sources on BRD risk was modified by arrival weight and cohort size (p < 0.05). Cattle with two water sources had lower BRD morbidity (5.55% ± 0.98) compared to cattle with one water source (8.80% ± 1.50) when arrival weight was 227 kg to 272 kg, while there were few differences in heavier weight cattle. Cattle with two water sources had lower BRD morbidity (3.11% ± 0.56) compared to one water (5.50% ± 0.10) when cohort size was 100–175 head, but there were no BRD morbidity differences when bigger or smaller cohorts were evaluated. Shared fence lines and water sources were associated with BRD risk; however, no biologically meaningful results were identified. The number of water sources was associated with BRD risk, and effects were modified by cohort size and arrival weight.

Feedlot mortality negatively affects animal welfare and profitability. To the best of our knowledge, there are no publications on predictive models for weekly all-cause mortality in feedlot cattle. In this study, random forest models to predict weekly mortality for cattle purchase groups (n = 14,217 purchase groups; 860,545 animals) from arrival at the feeding location (Day 1) to Day 42 and cumulative mortality from Day 43 until slaughter were built using records, weather, and transport data available at the time of purchase. Models were evaluated by calculating the root mean squared error (RMSE) and accuracy (as defined as the percent of purchase groups that had predictions within 0.25% and 0.50% of actual mortality). The models had high accuracy (>90%), but the RMSE estimates were high (range = 1.0% to 4.1%). The best predictors were maximum temperature and purchase weight, although this varied by week. The models performed well among purchase groups with low weekly mortality but performed poorly in high mortality purchase groups. Although high mortality purchase groups were not accurately predicted utilizing the models in this study, the models may potentially have utility as a screening tool for very low mortality purchase groups after arrival. Future studies should consider building iterative models that utilize the strongest predictors identified in this study.

The purpose of this study was to utilize retrospective commer­cial feedlot data to evaluate the potential associations between pen housing management factors and first treatment BRD inci­dence during the first 45 days on feed (DOF). Our study popula­tion included 1,733 cohorts of feedlot cattle representing 188,188 total animals from 2018 to 2020. Our explanatory variables of interest in this study were pen area per animal and bunk space per animal. These variables were categorized as either having below, adequate, or above recommended pen area/bunk space per animal-based guidelines from the central United States. Our data were analyzed with a generalized linear mixed model utilizing a binomial link function. Results demonstrated that pen housing management factors were significantly (P < 0.05) associated with BRD incidence in the first 45 DOF, but their ef­fects were modified by relevant cattle demographic factors (co­hort size at arrival, average arrival weight, sex, and quarter of arrival). For example, cohorts with an average arrival weight between 900 to 1,000 lb. (409 to 453 kg) had a higher probability of BRD incidence in the first 45 DOF when provided below rec­ommended pen area per head compared to similar weighted co­horts that had adequate, or above, recommended pen area per head. Our results from this study identify potential situations where pen housing management factors, combined with cattle demographics, may impact the risk of BRD in feedlot cattle. Further defining these situations may allow feedlot managers to utilize these estimates to manage feedlot cattle health more effectively.

Data from 14 U.S. feedlots from January 1, 2017, through De­cember 31, 2020, were evaluated for disease treatment on the probability of being terminally diagnosed with heart disease (HD). The study objective was two-fold: 1) determine the as­sociation between the number of bovine respiratory disease (BRD) treatments (0,1,2,3+) and HD, and 2) determine the as­sociation of common feedlot disease treatment (AIP, BRD, Complex Disease, GI+Bloat, Other), and cohort demographics with HD. Data were analyzed using generalized mixed-effects models to evaluate the probability of terminal HD. Covariates of interest include: BRD treatments, feedlot disease category, average cohort arrival weight, arrival year, arrival quarter, feedlot elevation and sex. The number of BRD treatments was associated with HD (P < 0.01). Cattle requiring additional BRD treatments increased their probability of not finishing the feeding period due to HD. The magnitude of this association was influenced by average cohort arrival weight, feedlot eleva­tion, sex and arrival quarter (P < 0.01). Feedlot disease catego­ries were associated with the probability of not finishing the feeding phase due to a HD diagnosis (P < 0.01). The magnitude of this association was influenced by average cohort arrival weight, and feedlot elevation (P < 0.01). Sex was influenced by feedlot elevation on the probability of not finishing due to HD diagnosis (P < 0.01) with higher elevations having a greater probability of HD. The majority of HD cattle were railed prior to death at the feedlot (9 of the 15 per 10,000 cattle received).

This manuscript explores a method of benchmarking antimicrobial use within the context of farm level therapeutic incidence (a proxy for disease incidence), and the outcome of that therapy. This is reported both within the same farm over time (2016-2019), as well as evaluated across participating farms. Reporting antimicrobial use in this format addresses multiple primary questions necessary for evaluating on farm antimicrobial stewardship: How much disease is recorded? How much antimicrobial use is recorded? How often are antimicrobials included in therapy for each disease? What is the outcome of therapy? The three primary metrics reported are: therapeutic events per 100 cow years (TE/100CY), antimicrobial regimens per 100 cow years (REG/100CY), and the percent therapeutic success (% Success). Success was defined as: the cow remained in the herd and had no further TE recorded within 30 days of the end of the TE being evaluated. These measures identify opportunities for change on an individual farm, such as improvement in disease prevention, or a change in choices about when to include an antimicrobial in the treatment protocol. Therapeutic outcomes provide additional context, in some instances demonstrating differences in recording practices and case definitions, while in other cases serving to safeguard animal welfare as efforts are made to decrease antimicrobial use in the future. Although developed for farm level reporting, the metrics may also be more broadly summarized to meet future reporting requirements for marketing chain or national level antimicrobial use reports. The process outlined here serves as a prototype to be considered when developing antimicrobial use reporting systems where farm level antimicrobial stewardship is the primary objective.

Bovine respiratory disease (BRD) dramatically affects young calves, especially in fattening facilities, and is difficult to understand, anticipate and control due to the multiplicity of factors involved in the onset and impact of this disease. In this study we aimed to compare the impact of farming practices on BRD severity and on antimicrobial usage. We designed a stochastic individual-based mechanistic BRD model which incorporates not only the infectious process, but also clinical signs, detection methods and treatment protocols. We investigated twelve contrasted scenarios which reflect farming practices in various fattening systems, based on pen sizes, risk level, and individual treatment vs. collective treatment (metaphylaxis) before or during fattening. We calibrated model parameters from existing observation data or literature and compared scenario outputs regarding disease dynamics, severity and mortality. The comparison of the trade-off between cumulative BRD duration and number of antimicrobial doses highlighted the added value of risk reduction at pen formation even in small pens, and acknowledges the interest of collective treatments for high-risk pens, with a better efficacy of treatments triggered during fattening based on the number of detected cases.

Previous literature reported a rise in risk of right heart failure (RHF). The objective of the current study was to use a validated case definition of RHF to determine the risk and timing of RHF. Data were analyzed using mixed effects models to evaluate the risk of RHF and timing of RHF in 13 US and Canadian feedlots from January 2016 through December 2020. Cohort-level covariates of interest include breed (beef, dairy, dairy-cross), type (yearlings, calves), bovine respiratory disease (BRD) risk (high, medium, low), BRD morbidity category (0 to 5%, 6 to 12%, 12.1 to 27% and > 27%), elevation category, sex, arrival quarter, and arrival year. The non-adjusted risk over the study population was 7.8 in 10,000 cattle received and mean and median unadjusted timing to RHF death was 179 and 174 DOF respectively. Arrival year was associated with RHF and was influenced by arrival quarter on the magnitude of risk of RHF (P < 0.01). Bovine respiratory disease risk category’s association with risk of RHF, was influenced by placement year and by feedlot elevation (P < 0.01). Elevation category association with risk of RHF was influenced by breed (beef, dairy, or dairy-cross) (P < 0.01). Heifers had a risk ratio of 1.23 compared to steers (LCL = 1.06, UCL = 1.43) (P < 0.01). BRD risk category association with timing of RHF was influenced by average cohort arrival weight (P < 0.01). Cattle that died due to RHF and were treated for BRD died 11 days (LCL = 1.33, UCL = 20.2 days) sooner than cattle never treated for BRD (P = 0.03). Cattle breed was also found to be associated the timing of RHF (P = 0.01). Dairy-cross cattle that died due to RHF died approximately 37 days earlier in the feeding period (SE = 13.0 days, P = 0.01) compared to beef cattle. Overall, many factors affected the risk and timing of RHF in feedlot cattle.

Objective: Previous bovine respiratory disease (BRD) research has focused on events early in the feeding phase, but the objective of this study was to determine charac-teristics and risk factors associated with cohort-level BRD morbidity in the middle and late portions of the feeding phase.Materials and Methods: The analysis was performed on records from 13 commercial feedlots in the United States from 2017 through 2020. Cohorts were analyzed over their first 100 d on feed. Two methods of classifica-tion were used. In the veterinarian classification method, hierarchical clustering created 20 temporal patterns, which were categorized by veterinary consultants as early -feed-ing-stage, mid-feeding-stage, or late-feeding-stage morbid-ity curves. In the days classification method, cohorts were categorized based on which portion of the feeding period (0 to 42 d, 43 to 71 d, or 72 to 100 d) had the greatest percentage of treatments for BRD. An events/trials model was used to determine morbidity and mortality across dif-ferent stages of the feeding phase. Ordinal regression was used to determine associations between cohort character-istics and BRD timing. Year and feedlot were included as random effects to account for the hierarchical structure of the data. Results and Discussion: Combined classification yielded 2,429 early-feeding-stage cohorts, 108 mid-feeding -stage cohorts, and 61 late-feeding-stage cohorts. The only factor significantly (P < 0.05) associated with cohort -lev-el BRD morbidity timing was quarter of arrival. Cattle arriving in the second quarter (Q) were more likely to be mid-feeding stage or late-feeding stage (5.5%, 10.2%, respectively) compared with cattle arriving in the other quarters of the calendar year (Q1: 2.7%, 4.5%; Q3: 1.4%, 2.2%, or Q4: 1.4%, 2.3%).Implications and Applications: This study evaluat-ed risk factor relationships with cohort-level BRD timing. No cattle characteristics were significantly associated with BRD timing; however, cattle arriving in Q2 were at higher risk for cohort-level mid-or late-feeding-stage BRD.

Objective: Previously published research on bovine re-spiratory disease (BRD) has emphasized the initial por-tion of the feeding phase; yet, little work has investigated risk factors associated with BRD incidence later in the feeding period. Our study objective was to identify risk factors associated with BRD morbidity and mortality tim-ing within the feeding phase.Materials and Methods: Individual animal records for first BRD treatment (n = 188,437) or BRD mortality (n = 13,991) were classified as early stage, middle stage, or late stage based on the percentage of their cohorts' feeding phase that was complete at day of event (event days on feed/cohort total days on feed). Results and Discussion: There were 141,097 early stage, 33,871 middle stage, and 13,469 late stage at first treatments for BRD and 7,821 early stage, 3,625 middle stage, and 2,545 late stage at death. Two ordinal logis-tic regression models (morbidity, mortality) were used to evaluate the association of cattle demographic factors (ar-rival weight, arrival lot size, sex, metaphylaxis, quarter of arrival) and the probability of an individual animal first treatment for BRD or mortality from BRD being early, middle, or late stage. All 2-way interactions of cattle de-mographics for morbidity were significant (P < 0.05), whereas for mortality, main effects of arrival weight and metaphylaxis were significant (P < 0.05) and only the 2-way interactions of sex by quarter of arrival and sex by lot size were significant (P < 0.05).Implications and Applications: In general, heifers, heavier animals at arrival, and cattle that arrived at the yard in the first and second quarter were the most like - ly demographic categories to have an initial diagnosis of BRD in the mid or late stage of the feeding phase. ly demographic categories to have an initial diagnosis of BRD in the mid or late stage of the feeding phase.