The E. coli infection model was achieved successfully
in both experiments as indicated by diarrhea scores,
frequency of diarrhea, populations of β-hemolytic coliforms,
other measures, or some combination of these
indicators. However, the E. coli infection was less severe
than anticipated in Exp. 1 based on the diarrhea score
and frequency of diarrhea, perhaps because of protective
interventions. Investigation revealed that the pigs
in Exp. 1 were born to sows immunized against F-4
E. coli. Immunity to the F-4 fimbrial antigen should
not be protective against the F-18 challenge strain used
in these experiments, but the vaccine also contained
the heat-labile toxin that is expressed by the challenge
organism used in these experiments, so it may have
offered some protection. Heat-labile toxin is a potent
immunogen. The pigs in Exp. 1 also received antibiotic
injections after birth and antibiotics in their creep feed,
and these factors may have provided some protection.
The sows and pigs used in Exp. 2 did not receive the
vaccines, the antibiotic injections, or the antibiotics in
creep feed.