In-feed organic acids as a strategy to combat Salmonella in growing pigs

Salmonella carriage in pigs is a significant food safety issue. Dietary supplementation with organic acids has previously been shown to reduce shedding and transmission of Salmonella and favourably modulate the intestinal microbiota, however, the literature shows variability. The success in reducing Salmonella seroprevalence, excretion rate and the length of the Salmonella shedding period is linked to the choice of acid(s), concentration used, treatment duration and concomitant on-farm factors. Therefore, this study aimed to examine the effect of three commercially available organic acid-based products on Salmonella levels in grower pigs, using a novel protocol for evaluating Salmonella control measures based on exposure to an artificially contaminated environment that closely mimics natural exposure to the organism. Seven week old trial pigs (n = 40) with a mean weight of 14.7 kg were placed in one of four pens with 10 pigs/pen. Pens had previously been contaminated with Salmonella pigs. Trial pigs received one of four diets for 28 days: 1, control diet; 2, sodium butyrate supplemented diet; 3, benzoic acid supplemented diet and 4, formic-citric acid supplemented diet. A further 10 pigs were placed in a Salmonella-free pen receiving the control diet. Pigs were weighed and blood sampled on days 0 and 28. Faeces was collected on day 0, 2, 3, 5, 7, 14, 21 and 28 and examined for Salmonella. On day 28, 5 pigs/group were euthanised and ileocaecal lymph nodes (ILN) and caecal contents sampled for culture. The remaining 5 pigs/pen were then fed the control diet and faeces were collected on days 35 and 42. On day 42 pigs were euthanised and ILN and caecal contents tested for Salmonella levels. The trial was repeated once.

Within the first two days of exposure to the contaminated environment, 96% (77/80) of pigs became infected. Most pigs shed Salmonella at levels of between 100–10³ CFU/g faeces for at least 7 days post-exposure. A significant reduction in Salmonella faecal concentration was observed after supplementation with sodium butyrate and a formic citric acid blend. Average daily weight gain (ADWG) was significantly increased in all groups fed the supplemented feed when compared to the positive control group. The use of sodium butyrate or a blend of formic and citric acid in feed could be considered a cost-effective control measure to reduce Salmonella faecal shedding and improve ADWG in Salmonella infected herds.

H. Lynch, F.C. Leonard, K. Walia, P.G. Lawlor, G. Duffy, S. Fanning, B.K. Markey, C. Brady, G.E. Gardiner, H. Argüello. (2017). Investigation of in-feed organic acids as a low cost strategy to combat Salmonella in grower pigs. Preventive Veterinary Medicine, 139, 50-57. http://dx.doi.org/10.1016/j.prevetmed.2017.02.008