|Hallford, D - NEW MEXICO STATE UNIV|
|Schroeder, Sasha - TX A&M UNIVERSITY|
Submitted to: Comparative Endocrinology International Congress Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 8, 2005
Publication Date: May 22, 2005
Citation: Edrington, T.S., Schultz, C.L., Callaway, T.R., Genovese, K.J., Hallford, D.M., Schroeder, S.B., Anderson, R.C., Nisbet, D.J. 2005. Effect of exogenous melatonin on fecal shedding of E. coli O157:H7 in naturally-infected beef cattle [abstract]. International Congress of Comparative Endocrinology. p. 65. Technical Abstract: Seasonal shedding of E. coli O157:H7 (EC) in ruminants is well documented, however reasons for this phenomenon are unknown. We hypothesize that seasonal shedding of EC is a result of physiological responses by the animal to changing daylength. In a series of experiments utilizing naturally-infected beef cattle and experimentally-infected sheep, we examined the effect of exogenous melatonin administration and chemical inhibition of the thyroid, on fecal shedding and gastro-intestinal (GIT) populations of EC. Animals treated daily with a low oral dose of melatonin (mg) had shedding patterns and GIT populations of EC similar to controls. However, when a high dose of melatonin (g) was orally administered to naturally-infected cattle, the number of cattle shedding EC was lower (P = 0.05) compared to control steers. Chemical inhibition of the thyroid, via administration of propyl-thiouraracil (PTU), had no effect on fecal shedding or GIT populations in naturally- or experimentally-infected cattle and sheep. However, following termination of the PTU treatment in the naturally-infected cattle, a greater percentage of PTU treated animals shed EC compared to control steers. Early results indicate that hormones known to respond to changing daylength may play a role in the seasonal shedding of EC in ruminants.