Development of a Salmonella Typhimurium challenge model in weaned pigs to evaluate effects of water and feed interventions on fecal shedding and growth performance

The aim of this study was to develop a Typhimurium (ST) challenge model in weaned pigs suitable to evaluate effects of water and feed interventions on fecal shedding and growth performance. Two studies were performed. In Exp. 1 weaned pigs were fed either a standard diet (CON) or a diet with a high buffer capacity (HB) and challenged for either 3 or 7 consecutive days in a Latin square design with 4 × 8 individually housed pigs. In Exp. 2, the CON 7-d challenge method was chosen for further model development and validation. Thirty-two individually housed weaned pigs were divided over 4 treatments: a nonchallenged control group (NCON), a challenged positive control group (PCON), a challenged intervention group with acidified water (WATER), and a challenged intervention group with acidified feed (FEED). Pigs were orally challenged once daily on d 7 to 9 or d 7 to 13 after weaning (d 0) with 1 ×10 cfu ST. From d 0 to 28, rectal temperature and occurrence of diarrhea were recorded daily, and BW and feed intake were measured weekly. Fecal samples were collected on d 0, 2, 7, 9, 13, 16, 20, 23, and 27 in Exp. 1 and d 0, 2, 7, 8, 9, 13, 15, and 27 in Exp. 2 for quantification. The results of both experiments showed quantifiable fecal shedding (average peak shedding of approximately 3.5 log and 5.5 log cfu/g, respectively), accompanied by a transient 0.5°C increase in rectal temperature and an increase in occurrence of diarrhea. In Exp. 2 during the week of challenge (i.e., d 7 to 14), a reduction in growth performance (ADG: -157 to 200 g/d and G:F: -0.22 to 0.25 g/d; < 0.01) in PCON and FEED was observed compared to NCON, with WATER showing an intermediate response. The WATER treatment also showed a numerically lower peak shedding (difference of -1.3 to 1.4 log cfu/g) compared to PCON and FEED. To conclude, we repeatedly infected weaned pigs successfully with 1 × 10 cfu of ST for 7 consecutive days, resulting in detectable and quantifiable fecal shedding. This ST challenge model may be suitable for evaluation of effects of water and feed interventions on peak fecal shedding and growth performance.