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Description:
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Due to the seasonal nature of E . coli O157 :H7 shedding and of hormone
production by the thyroid gland , two studies were initiated to determine whether
chemical inhibition of the thyroid gland influences fecal shedding of Escherichia coli
O157 :H7 . Twenty -four crossbred sheep (68 .6 kg BW ) were randomly assigned to pen
and either 0 .0 mg /kg BW PTU or 20 mg /kg BW PTU for 5 , 11 , or 14 days . Sheep were
experimentally infected (d 0 ) with E . coli O157 :H7 11 days prior to PTU treatment .
Fecal and serum samples were collected for bacterial enumeration and for analysis of T3
and T4 , respectively . Sheep were humanely euthanized and tissue and content samples
were collected from the rumen , ileum , colon and rectum . Detection of E . coli O157 :H7
increased toward the terminal end of the GI tract . In the treatment group , serum T3
levels decreased to an overall lower level than the control group . A correlation was seen
between T3 levels and daily O157 :H7 bacterial shedding (P=0 .003 ; r=0 .37 ) . In
experiment 2 , 12 growing lambs (41 .04 kg BW ) were exposed to either 0 .0 mg /kg BW
PTU or 40 mg /kg BW PTU for 21 days . Fecal samples were collected for analysis of
generic E . coli and body weights were recorded on days 0 , 7 , 14 , and 21 . Feed intake
was recorded throughout the experiment . Animals were experimentally infected with E .
coli O157 :H7 on day 15 . Sheep were humanely euthanized on day 21 and GI tract tissue and content was collected from the rumen , ilium , colon and rectum . A date by treatment
interaction was observed for T4 (P=0 .0016 ) and hormone levels decreased in treated
animals . Thyroxine and E . coli O157 :H7 display a multivariate treatment (P=0 .0005 )
and date effect (P=0 .0174 ) but no significant interaction . Triiodothyronine and E . coli
O157 :H7 shedding have a slight date trend (P=0 .065 ) but no significant treatment or
treatment by date interaction . Generally , the treatment group shed genreric E . coli at
higher levels throughout the study period with slightly more than a log count difference
between groups at the last collection point (control = 3 .8 CFU /gram of feces (log10 ) ;
treatment = 4 .9 CFU /gram of feces (log10 ) ) . Results from these experiments suggest that
correlations exist between both E . coli O157 :H7 and generic E . coli shedding in sheep . |