Temporal distributions of respiratory disease events within cohorts of feedlot cattle and associations with cattle health and performance indices

Bovine respiratory disease complex (BRDC) the most common cause of post-weaning disease in North American beef cattle is a multifaceted process involving pathogen host environment and management factors Although the importance of describing and evaluating the timing of BRDC cases has been recognized a formal analysis of the temporal patterns of BRDC has not been described in the literature Our objectives were to classify within-cohort temporal patterns of BRDC cases during the first 100 days at risk using operational data from commercial feedlots and then to evaluate associations among temporal patterns and common cohort-level measures of feedlot performance and health while controlling for common potential confounders We used retrospective cohort-level and individual animal health data (2000-2008) from 10 U S feedlots We defined cumulative distributions representing the timing of cases within cohorts using the daily percentage of cases relative to the total number of cases within a cohort Ward s hierarchical clustering method was used to group cohorts exhibiting similar cumulative distributions of BRDC cases Linear mixed models and generalized estimating equations then were used to determine associations between temporal patterns and economically important measures of cattle performance (mean daily weight gain total days on feed and carcass measures) and health (mortality risk and retreatment risk) outcomes while accounting for possible confounding variables (gender arrival month arrival year arrival weight arrival risk classification cumulative morbidity and the feedlot Itself) Cluster analysis identified seven different cohort-level temporal patterns of BRDC cases Our independent variable of interest (temporal pattern) was associated with mean daily weight gain total days on feed and carcass weight and the estimated effects were modified by arrival weight category and risk classification Temporal patterns also were associated with USDA measures of carcass yield and quality that largely affect carcass price We also found associations among temporal patterns and health outcomes (cumulative mortality and retreatment risk) and these effects were significantly modified by arrival weight and cumulative morbidity Our results are the first to demonstrate that there are several temporal patterns of BRDC repeatedly observed among cohorts of feedlot cattle and that these BRDC patterns may differentially affect cattle health and performance (C) 2010 Elsevier B V All rights reserved