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