|Chitko Mckown, Carol|
Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: October 3, 2003
Publication Date: November 9, 2003
Citation: KEEN, J.E., LAEGREID, W.W., CHITKO MCKOWN, C.G., BONO, J.L., FOX, J.M., CLAWSON, M.L., HEATON, M.P. EFFECT OF EXOGENOUS GLUCOCORTICOIDS AND DIETARY CHANGE ON WINTER AND SUMMER STEC O157 FECAL SHEDDING IN NATURALLY-INFECTED BEEF CATTLE. RESEARCH WORKERS IN ANIMAL DISEASES CONFERENCE PROCEEDINGS. 2003. ABSTRACT NO. 83. Technical Abstract: Undefined "stress" is often invoked as an initiator or enhancer of livestock fecal shedding of zoonotic pathogens such as Salmonella and shiga-toxigenic E coli (STEC) O157. However, the influence of stressors or of host stress responses on initiation, duration, recrudescence, or cessation of STEC O157 fecal shedding has not been directly studied. Cattle STEC O157 shedding is seasonal with summer peaks and winter troughs in prevalence. The interaction of season with stress on bovine STEC O157 occurrence is also unknown. Study objectives were to measure the effects of (1) brief dietary change: from grain concentrate to alfalfa hay for 3 days (dietary stress), and (2) short-term exogenous glucocorticoid (single therapeutic IM dose of dexamethasone) on fecal STEC O157 shedding in naturally-infected fed beef cattle in winter and summer. In each season in 2003, 120 finished steers were randomized into 3 treatment groups (control, alfalfa, and dexamethasone). Each group consisted of 8 pens of 5 cattle each (parallel group-randomized design). Cattle were cultured for STEC O157 on days 0, 3, 6, and 9. In the winter trial, day 0-9 pooled prevalence was 23/160, 28/160, and 8/160 in the control, alfalfa, and dexamethasone cattle, respectively; in the summer trial, day 0-9 prevalence was 44/160, 97/160, and 89/160 in these same groups. There was no winter alfalfa or dexamethasone effect, but both treatments resulted in significantly higher STEC O157 fecal shedding in summer versus controls. Transition state analysis suggested that both "stresses" caused already infected steers to shed STEC O157 longer than in control animals. These findings may have pre-harvest STEC O157 control implications for feedlot cattle.