Effect of oral tiamulin on the development of porcine proliferative enteropathy in a pure-culture challenge model
Kent Schwartz, DVM, MS; Jeff Knittel, MS; Don Walter, DVM;Michael Roof, PhD; Marlin Anderson, PhD
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Objective: To determine the effect of tiamulin-medicatedfeed in pigs infected with pure cultures of Lawsonia intracellularisby monitoring fecal shedding of L. intracellularis by polymerasechain reaction (PCR), antibody response, clinical effects, andlesion development.
Methods: Thirty-two pigs were allocated to two replicationsof four treatments, each replication with four pigs per treatment;1) noninfected and nonmedicated (CONTROL); 2) infected and nonmedicated(I-NM);3) infected and medicated with feed containing tiamulin hydrogenfumarate (thf) at 35 g per ton (I-35); and 4) infected and medicatedwith feed containing thf at 50 g per ton (I-50). These diets werefed for 35 days, starting 7 days prior to inoculation (day -7).Pigs were intragastrically inoculated with either a pure cultureof L. intracellularis or a placebo. All pigs were monitoreddaily until necropsied 28 days post infection (PI). Fecal sheddingof L. intracellularis by PCR, antibody response, clinicalsigns, growth performance, and the extent of gross and microscopiclesions specific for porcine proliferative enteropathy (PPE) weredetermined.
Results: Fecal shedding of L. intracellulariswas first observed 7 days PI, which coincided with increased diarrheaand loss of condition in the I-NM group. Antibody specific forL. intracellularis was first detected at 21 days PI. Medicationin feed prevented the development of gross lesions, significantlyreduced the prevalence and severity of microscopic lesions, andsignificantly reduced fecal shedding and seroconversion to L.intracellularis.
Implications: Seronegative pigs may shed L. intracellularisin their feces early in the course of infection. Medication statusmay affect the results of antemortem diagnostic tests for L.intracellularis infection. Larger sample sizes may be requiredto increase the probability of detecting infection in medicatedpopulations of pigs. Dietary inclusion of tiamulin was effectivein preventing/controlling the development of PPE.