Experimental model of enterotoxigenic Escherichia coli infection in pigs: potential for an early recognition of colibacillosis by monitoring of behavior

The hypothesis that altered behavior is a sign for an early recognition of disease was tested. The experiment was conducted to evaluate the behavioral patterns of pigs in a model of postweaning colibacillosis. Twenty-five weaned pigs (from a herd that was previously found to be highly susceptible to F4 super(+) Escherichia coli strains) were randomly assigned into 5 groups, kept in isolated pens under the controlled ambiental conditions. One day after weaning, the pigs from three groups were intragastrically inoculated (via orogastric tube) with either F4ac super(+) (1466 or 2407) or F4 super(-) (1467) nonenterotoxigenic E. coli (non-ETEC) strains, respectively. The pigs from the fourth group were inoculated with F4ac super(+) ETEC strain M1823 and the remaining 5 pigs that received broth containing 1.2% sodium bicarbonate were kept as noninoculated controls. The pigs were examined daily and the frequency and duration of their behavioral patterns, such as eating, drinking, lying, standing, urinating, defecating, rooting and playing were monitored for 300 h during a period of 10 days. In this model, three conditions were also observed in F4-susceptible pigs: (1) acute fatal diarrheal disease; (2) moderate diarrhea and weight loss and (3) no diarrhea and weight loss. The incidence (both frequency and duration) of defecating was significantly higher (P < 0.05) in pigs inoculated with F4ac super(+) ETEC strain M1823 as compared to that of noninoculated (control) pigs. Pigs inoculated with F4ac super(+) non-ETEC strain 1466 had a significantly lower frequency of eating (P < 0.05) and frequency/duration of drinking (P < 0.05) than did the controls. The 1466-inoculated pigs, had an increased diarrhea score, but frequency/duration of defecating was not significantly different. Pigs inoculated with F4ac super(+) non-ETEC strain 2407 spent more time in lying (P < 0.05) than did noninoculated pigs. Conversely, the pigs that received F4 super(-) non-ETEC strain 1467 laid shorter (P < 0.05) and ate/drank less frequently (P < 0.05) than the controls. It was concluded that the changed occurrence of defecating and eating in pigs that were inoculated with either F4ac super(+) ETEC (M1823) or non-ETEC (1466) strain, respectively, was consistent with the pending clinical disease, i.e. postweaning colibacillosis.