Associations between weather conditions during the first 45 days after feedlot arrival and daily respiratory disease risks in autumn-placed feeder cattle in the United States1

Abstract

Data on associations between weather conditions and bovine respiratory disease (BRD) morbidity in autumn-placed feedlot cattle are sparse. The goal of our study was to quantify how different weather variables during corresponding lag periods (considering up to 7 d before the day of disease measure) were associated with daily BRD incidence during the first 45 d of the feeding period based on a post hoc analysis of existing feedlot operational data. Our study population included 1,904 cohorts of feeder cattle (representing 288,388 total cattle) that arrived to 9 US commercial feedlots during September to November in 2005 to 2007. There were 24,947 total cases of initial respiratory disease (animals diagnosed by the feedlots with BRD and subsequently treated with an antimicrobial). The mean number of BRD cases during the study period (the first 45 d after arrival) was 0.3 cases per day per cohort (range = 0 to 53.0), and cumulative BRD incidence risks ranged from 0 to 36% within cattle cohorts. Data were analyzed with a multivariable mixed-effects binomial regression model. Results indicate that several weather factors (maximum wind speed, mean wind chill temperature, and temperature change in different lag periods) were significantly (P < 0.05) associated with increased daily BRD incidence, but their effects depended on several cattle demographic factors (month of arrival, BRD risk code, BW class, and cohort size). In addition, month and year of arrival, sex of the cohort, days on feed, mean BW of the cohort at entry, predicted BRD risk designation of the cohort (high or low risk), cohort size, and the interaction between BRD risk code and arrival year were significantly (P < 0.05) associated with daily BRD incidence. Our results demonstrate that weather conditions are significantly associated with BRD risk in populations of feedlot cattle. Defining these conditions for specific cattle populations may enable cattle health managers to predict and potentially manage these effects more effectively; further, estimates of effects may contribute to the development of quantitative predictive models for this important disease syndrome.

Associations between animal characteristic and environmental risk factors and bovine respiratory disease in Australian feedlot cattle

“…Nonetheless, the fitted models indicated that induction weight was important after controlling for breed, sex, source region and other covariates. Although previous studies have reported increased risk with reduced mean cohort weight (Cernicchiaro et al, 2012a;Cernicchiaro et al, 2012b, c), these studies used group-or cohort-level analyses and did not adjust for animal-level weight. By fitting both animal level and mean cohort-level induction weight in the same model, we have assessed the contextual effect of induction weight.…”

“…Because peak BRD incidence typically occurs between 2 and 4 weeks after induction and weather variables are thought to have a lagged effect (Cernicchiaro et al, 2012a), the weather variables analysed in the current study were estimated for the first week from day 0 (i.e. including day 0 to day 6).…”

“…Source region and feedlot region have been linked to BRD incidence (Cernicchiaro et al, 2012b). Variation in BRD incidence with the year and season of feedlot entry have been described in several studies (Cernicchiaro et al, 2012a;Cernicchiaro et al, 2012b;Martin et al, 1988;Snowder et al, 2006b). Increased risk of BRD in the autumn and summer has been reported in large North American studies (Cernicchiaro et al, 2012b, c), but univariable associations between arrival quarter and cohort-level BRD incidence did not persist in multivariable models in another study (Sanderson et al, 2008).…”

“…In one Australian study, a moderate correlation between minimum daily temperature and occurrence of BRD was noted after accounting for serial correlation of temperature between days (Cusack et al, 2007). In a large North American study, the lagged effects of several weather variables were significantly associated with BRD risk and a number of interactions between weather variables and between weather variables and demographic variables were reported (Cernicchiaro et al, 2012a).…”

“…Several animal characteristics have been associated with increased risk of BRD, including breed, with the Hereford breed consistently associated with increased risk (Cusack et al, 2007;Hägglund et al, 2007;Snowder et al, 2006a), sex, typically with higher risk in steers (Alexander et al, 1989;Cernicchiaro et al, 2012a;Cernicchiaro et al, 2012b;Sanderson et al, 2008;Snowder et al, 2006b), and bodyweight, with lighter animals being at higher risk (Cernicchiaro et al, 2012a;Reinhardt et al, 2009;Sanderson et al, 2008;Snowder et al, 2006b). The influence of age was assessed in a bull testing facility population; younger age at arrival was associated with fever (used as a proxy for BRD) after adjusting for weight (Townsend et al, 1989).…”