Determining relevant risk factors associated with mid- and late-feeding-stage bovine respiratory disease morbidity in cohorts of beef feedlot cattle

Abstract

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 characteristics 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 classification were used. In the veterinarian classification method, hierarchical clustering created 20 temporal patterns, which were categorized by veterinary consultants as early-feeding-stage, mid-feeding-stage, or late-feeding-stage morbidity 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 different stages of the feeding phase. Ordinal regression was used to determine associations between cohort characteristics 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-level 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 evaluated 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.