Influence of exogenous triiodothyronine (T3) on fecal shedding of Escherichia coli O157 in cattle.

摘要: Fecal prevalence of Escherichia coli O157 in ruminants is highest the summer months and decreases to low or undetectable levels winter. We hypothesize that seasonal variation this pathogen a result physiological responses within host animal changing day length. The thyroid an endocrine gland known respond Two experiments were conducted determine if hyperthyroid status would initiate fecal shedding E. cattle during winter when virtually nonexistent (winter experiment) influence actively (summer experiment). Yearling group-penned under dry-lot conditions, adjusted high concentrate ration, randomly assigned treatment: control (1 mL corn oil injected s.c. daily) triiodothyronine (T3; 1.5 mg suspended s.c daily). Cattle individually processed daily for collection blood samples. Treatment with exogenous T3 produced significant change serum hormone concentrations indicative both experiments. No differences (P>0.10) observed experiment. In experiment, was decreased (P=0.05) by administration treatment period (days 1–10), tended be lower (P=0.08) following 7-day no treatment, (P=0.01) examined across entire experimental period. Results research indicate its hormones may involved patterns cattle.