Elsevier

Preventive Veterinary Medicine

Volume 131, 1 September 2016, Pages 79-86
Preventive Veterinary Medicine

Effect of feeding sodium butyrate in the late finishing period on Salmonella carriage, seroprevalence, and growth of finishing pigs

https://doi.org/10.1016/j.prevetmed.2016.07.009Get rights and content

Abstract

Pork is an important source of human salmonellosis and low-cost on-farm control measures may provide a useful element in reducing the prevalence of this pathogen in food. This study investigated the effectiveness of dietary supplementation with sodium butyrate administered to finisher pigs for ∼4-weeks prior to slaughter to control Salmonella shedding on highly contaminated farms.

Two trials (A and B) were conducted on two commercial pig farms, which had a history of high Salmonella seroprevalence. In both trials, pens (14 pens of 12 pigs/pen in Trial A and 12 pens of 12–17 pigs/pen in Trial B) were randomly assigned to a control (finisher feed without additive) or a treatment group (the same feed with 3 kg sodium butyrate/t) for 24–28 days, depending on the trial. Faeces were collected from each pig on days 0, 12 and 24/28, and blood, caecal digesta and ileocaecal/mesenteric lymph nodes were collected from the slaughterhouse. Pigs were weighed at the start and end of the trials, feed intake was recorded, and carcass quality parameters were recorded at slaughter.

In Trial A, Salmonella shedding was reduced in the treatment compared to the control group at the end of the trial (30% versus 57% probability of detecting Salmonella in faeces, respectively; p < 0.001). This reflected the serology results, with detection of a lower seroprevalence in the treatment compared to the control group using the 20% optical density cut-off (69.5% versus 89%; p = 0.001). However, no effect on faecal shedding or seroprevalance was observed in Trial B, which may be explained by the detection of a concomitant infection with Lawsonia intracellularis. No significant differences in Salmonella recovery rates were observed in the caecal digesta or lymph nodes in either trial. Furthermore, feed intake, weight gain, and feed conversion efficiency (FCE) did not differ between groups (p > 0.05) in either trial. Numerical improvements in weight gain and FCE were found with sodium butyrate treatment, which gave a cost benefit of €0.04/kg of live-weight gain.

Overall, results suggest that strategic feeding of sodium butyrate, at 3 kg/t of feed, to finishing pigs for 24–28 days prior to slaughter was effective in reducing Salmonella shedding and seroprevalance but perhaps only in the absence of co-infection with other pathogens. However, sodium butyrate supplementation at this rate did not influence intestinal carriage, nor did it reduce seroprevalence to below the cut-off used for the high Salmonella risk category in Ireland (50%), or significantly improve growth performance.

Introduction

Asymptomatic intestinal carriage of Salmonella in pigs presented for slaughter can result in pork carcass contamination. An EU baseline survey conducted in 2006–2007, showed that Ireland had a high prevalence of Salmonella contamination on pork carcasses (20%) (EFSA, 2008). This can be linked to the relatively high prevalence of Salmonella in some Irish pig herds (McCarthy et al., 2013, Burns et al., 2015). In an attempt to reduce this prevalence, the National Pig Salmonella Control Program (NPSCP) was updated in 2010 (Department of Agriculture Food and the Marine (DAFM), 2010). Despite this, Salmonella herd prevalence has not declined (DAFM personal communication). This highlights a need to find low-cost control measures to reduce Salmonella shedding in pigs at primary production, especially finishing pigs (35–100 kg), as carriage rates are high during this stage of production (Burns et al., 2015) and finishers are a significant source of Salmonella in the abattoir (Duggan et al., 2010, Argüello et al., 2013a).

Dietary supplementation with organic acids or their salts is a potential strategy for the control of Salmonella in finishing pigs (Creus et al., 2007, Wales et al., 2010). Organic acids can decrease gastrointestinal pH, thus creating an environment, which is hostile to Salmonella while favouring the growth of beneficial bacteria such as lactobacilli. The un-dissociated form of various acids can also freely cross the bacterial cell membrane and enter the bacterial cell, causing cell death (Van Immerseel et al., 2006). In addition, some organic acids (e.g., butyric acid and propionic acid) also down regulate the expression of invasion genes (e.g., hilA) in Salmonella, thereby suppressing its ability to invade intestinal epithelial cells (Boyen et al., 2008).

Dietary supplementation with sodium butyrate has previously been shown to reduce Salmonella shedding and intestinal colonization in weaner pigs which were deliberately infected with Salmonella (Boyen et al., 2008). However, to our knowledge, no field trial has evaluated the effectiveness of sodium butyrate as a Salmonella control measure in finishing pigs on farms with historically high levels of the pathogen. In addition, despite the number of field trials that have evaluated organic acids for the control of Salmonella in pigs, few have investigated their use for a short targeted period prior to slaughter and the cost-benefit associated with their use (Gálfi and Bokori, 1990, Creus et al., 2007). Therefore, the objectives of the present study were to conduct a field study on two selected farms with a high Salmonella seroprevalence, to investigate the ability of dietary supplementation with sodium butyrate during the last month of growth pre-slaughter to: (1) reduce faecal shedding and intestinal carriage of Salmonella, and (2) impact growth performance in finisher pigs. Based on the findings, a cost-benefit analysis was also conducted.

Section snippets

Animal ethics and experimental licensing

Two separate feeding trials (Trial A and Trial B) were performed on two commercial pig farms in the last quarter of 2014 and the first quarter of 2015. Ethical approval was obtained from the Waterford Institute of Technology ethics committee and an experimental license was obtained from the Irish Department of Health and Children (number B100/2982). All animals were handled in a humane manner and were slaughtered in a regulated abattoir.

Trial A farm

Trial A was conducted on a 90 sow farrow-to-finish farm.

Faecal shedding of Salmonella

For Trial A, one female pig was removed from the treatment group following the administration of penicillin. The probability of detecting Salmonella was similar in control and treatment groups on day 12. By the end of the trial (day 28), the administration of sodium butyrate to finishing pigs had resulted in a decline in the probability of detecting Salmonella compared to the control group (30% versus 57%, respectively; p < 0.05; Table 1). Table 2 details the number of Salmonella-positive faecal

Discussion

Decreasing Salmonella at farm-level can be considered an initial step in any overall control strategy to limit its spread throughout the pig production cycle (Goldbach and Alban, 2006, Ojha and Kostrzynska, 2007). Control strategies at farm-level not only decrease the infection pressure during production but the resultant reduction in Salmonella carriage can also lessen cross contamination in transport vehicles and lairage – two points at which pigs are prone to acquiring Salmonella (Berends et

Conclusions

Overall, strategic feeding of sodium butyrate to finishing pigs for a relatively short period of time (< 30 days) immediately prior to slaughter was effective in reducing Salmonella shedding and seroprevalance in one of two trials. Lack of efficacy in the second trial may be explained by a concomitant infection with L. intracellularis. Sodium butyrate supplementation did not reduce intestinal carriage, nor did it reduce seroprevalence to below the cut-off used for the high Salmonella risk

Acknowledgments

This work was funded by the Irish Government under the National Development Plan 2007–2013, through the Food Institutional Research Measure (FIRM) administered by the Department of Agriculture, Food and the Marine (DAFM), Ireland. The sodium butyrate feed additive was provided by Nutriad, Kasterlee, Belgium. The authors also gratefully acknowledge the participating farmers, Vincent Rafter and his staff at Dawn Pork and Bacon, Grannagh, Waterford and Stephen Finn and his staff at Finns Abbatoir,

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