|Schroeder, Sasha - TX A&M UNIVERSITY|
|Hallford, D - NEW MEXICO STATE UNIV|
Submitted to: Comparative Endocrinology International Congress Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 4, 2005
Publication Date: May 22, 2005
Citation: Schultz, C.L., Edrington, T.S., Schroeder, S.B., Hallford, D.M., Genovese, K.J., Callaway, T.R., Anderson, R.C., Nisbet, D.J. 2005. Effect of the thyroid on fecal shedding of E. coli O157:H7 and generic E. coli in naturally-infected yearling beef cattle [abstract]. International Congress of Comparative Endocrinology. p. 116. Technical Abstract: Seasonal differences in E. coli O157:H7 (EHEC) shedding in dairy and beef cattle have been well documented, with a greater prevalence of fecal shedding observed during the spring and summer months. The thyroid gland is one of two organs which respond to photoperiod and demonstrates circannual rhythms in hormone synthesis and secretion. To determine if thyroid activity affects fecal shedding of EHEC, eight yearling cattle, previously identified as shedding EHEC, received either 0 (CONT) or 10 mg 6-N-propyl-2-thiouracil (PTU) kg BW**-1 d**-1 for 14 d to reduce serum concentrations of the thyroid hormones, T3 and T4. Animals were monitored daily for changes in fecal shedding of EHEC and generic E. coli (GEC) for the 14-d treatment period and an additional 7 d post-treatment. Body weight was measured weekly and serum concentrations of T3 and T4 were determined every 3 d. No differences in fecal shedding of EHEC were observed during the 14-d treatment period. However, compared to CONT animals, a greater percentage of PTU-treated cattle shed EHEC on d 16 (50 vs 12.8%) and 18 (37.5 vs 0%) of the post-treatment period. Serum T3 was lower in PTU-treated cattle during the 14-d treatment period but was significantly greater (P < 0.01) in PTU-treated cattle on d 18 of the post-treatment period. Although short-term chemical inhibition of thyroid hormones had minimal effects on fecal shedding of EHEC in naturally infected cattle, the simultaneous increase in serum T3 and shedding of EHEC by PTU-treated cattle during the post-treatment period, suggests a direct or indirect effect of thyroid hormones and their potential role in the seasonal shedding patterns of EHEC by ruminant animals.