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Title: The effects of dexamethasone administration and E. bovis challenge on fecal oocyst count and immune function in weaned beef calves

Author
item Lucas, Aaron - VIRGINIA-MARYLAND REGIONAL COLLEGE OF VETERINARY MEDICINE (VMRCVM)
item Swecker, William - VIRGINIA-MARYLAND REGIONAL COLLEGE OF VETERINARY MEDICINE (VMRCVM)
item Neel, James - Jim
item Lindsay, David - VIRGINIA-MARYLAND REGIONAL COLLEGE OF VETERINARY MEDICINE (VMRCVM)
item Elvinger, Francois - VIRGINIA-MARYLAND REGIONAL COLLEGE OF VETERINARY MEDICINE (VMRCVM)
item Witonsky, Sharon - VIRGINIA-MARYLAND REGIONAL COLLEGE OF VETERINARY MEDICINE (VMRCVM)
item Zajac, Anne - VIRGINIA-MARYLAND REGIONAL COLLEGE OF VETERINARY MEDICINE (VMRCVM)

Submitted to: American Association of Veterinary Parasitologists Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/12/2011
Publication Date: 7/16/2011
Citation: Lucas, A.S., Swecker, W.S., Neel, J.P., Lindsay, D.S., Elvinger, F., Witonsky, S.G., Zajac, A.M. 2011. The effects of dexamethasone administration and E. bovis challenge on fecal oocyst count and immune function in weaned beef calves. In: Proceedings of the 56th Annual American Association of Veterinary Parasitologists Proceedings, July 16-19, 2011, St. Louis, Missouri. p. 40.

Interpretive Summary:

Technical Abstract: Stressful events are believed to predispose beef calves to clinical coccidiosis. Previous studies aimed at reproducing stress-induced coccidiosis have been unsuccessful. No study has simultaneously subjected calves to stress and Eimeria challenge. Our initial goal was to develop a model of stress and E. bovis challenge that would increase fecal oocyst count (FOC). We found that a single dose of 500,000 E. bovis oocysts and dexamethasone injection (0.35 mg/kg IM) 7 days post challenge (PC) increased FOC above baseline. This model was then employed to investigate the immune response to E. bovis challenge during times of stress. Thirty-two Angus-cross calves (6-7 mo.) were blocked by FOC and randomly assigned within blocks to one of 4 treatment groups: non-stressed non-challenged (NSNC), non-stressed challenged (NSC), stressed non-challenged (SNC), and stressed challenged (SC). Challenged calves were gavaged with 1.5 million oocysts on day 0 and stressed calves were given dexamethasone (0.35 mg/kg) on day 7 PC. Blood was collected from 4 calves per treatment on days -1, 8, 21 PC. Feces were collected from all calves on day 8 and daily 15-28 PC. Complete blood counts and lymphocyte separations were carried out on blood samples. Lymphocytes were stained for cell surface markers for flow cytometric analysis, and stimulated with E. bovis antigen and mitogen for lymphocyte proliferation, IFN-gamma and IL-4 production. Modified McMaster tests and fecal dry matter analysis were conducted on all fecal samples. Stressed calves had increased neutrophil:lymphocyte ratios and IL-4 production on day 8 PC while lymphocyte proliferation, CD4+, CD8+, WC1+, and CD21+ lymphocytes, and IFN-gamma production were decreased. The FOC increased in the SC group (day 22-26), but remained unchanged in other groups. In conclusion, dexamethasone effectively suppressed the cellular immune response and both stress and E. bovis challenge may be required to increase FOC.