Abstract A total of 45 weanling pigs (241 × 600 DNA; initially 7.0 ± 0.21 kg) were used in a 14-d study to evaluate the effect of Enterotoxigenic Escherichia coli (ETEC) F18 inoculum concentration on growth performance and fecal characteristics of nursery pigs. Pigs were group-housed for a 7-d acclimation period (-7) before being individually housed for inoculation (d 0 of the study). From d -7 to 14, pigs were fed a common nursery diet without pharmacological levels of Zn or Cu. Pigs were randomly allotted to one of three inoculum concentrations (109, 108, or 107 cfu/mL) in a completely randomized design with 15 replications per treatment. Inoculum was administered via orogastric gavage using a 10 Fr feeding tube and each pig received 6 mL of the respective inoculum concentration followed by 6 mL of sterile phosphate buffered saline. The isolate used was an F18 fimbrial type, with genes for heat labile enterotoxin (LT), heat stable toxin A (STa), heat stable toxin B (STb), and shiga toxin type 2e (Stx2e) as determined via PCR and was derived from a field clinical case submission. Pig weights were measured on d -7, 0, 7, and 14 to determine ADG, ADFI, and G:F, and fecal samples were collected on d 0, 3, 7, 10, and 14 to measure fecal dry matter (DM) by drying at 55 °C for 48 h. All animals were euthanized on d 14 post-challenge at the conclusion of the experiment. Bodyweight at inoculation was used as a covariate for all statistical analysis. No differences (P 0.10) were observed for growth performance during period 1 (d 0 to 7), period 2 (d 7 to 14), or overall (d 0 to 14). Growth rates were very low for d 0 to 7 for all treatment groups and improved from d 7 to 14 for the pigs remaining. A total of 5 pigs died or were euthanized for welfare reasons during the experiment (P = 0.888), with 2, 0, and 3 animals resulting in mortality from treatments 109, 108, and 107 cfu/mL, respectively. For fecal DM, there was no evidence of a treatment × day interaction (P = 0.488), although a significant time effect (P 0.0001) and marginally significant treatment effect (P = 0.066) were observed. Mean fecal DM was 15.7, 11.4, 12.5, 19.3, and 15.8%, for d 0, 3, 7, 10, and 14, respectively. Averaged across all sample collection days, fecal DM was 15.8, 15.8, and 13.3% for treatments 109, 108, 107 cfu/mL, respectively, although no significant means separation was observed. In conclusion, the ETEC F18 inoculum concentrations used in this study resulted in similar growth performance and clinical outcome.
Smallfield et al. (Wed,) studied this question.
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