CategoryPre-Harvest Pork Safety
Date Full Report Received06/01/2007
Date Abstract Report Received09/09/2008
Funded ByNational Pork Board
The swine industry experiences significant economic loss as a result of Samonella infection (Schwartz, 1990). Treatment of Salmonella enterica var Typhimurium infection in pigs with antibiotics has been reported to be unsuccessful at preventing subsequent shedding and further infection of young pigs (Roesler et al., 2005). The use of low doses of antibiotics for growth promotion in livestock is under continuous scrutiny due to the growing fear of antibiotic resistance (Barton, 2000). The removal of growth promotional antibiotics from livestock diets in Europe has sparked renewed interest into antibiotic alternatives. Probiotics, are usually defined as ‘live microorganisms which when administered in adequate amounts, confer health benefits on the host’ (FAO/WHO, 2001). Direct-fed microbials (DFMs) as they are known in animal nutrition, have been shown to improve growth performance (Simon et al., 2001), beneficially alter intestinal microbial balance (Fuller, 1989) and in general, positively impact gastrointestinal health. Certain DFMs selected based on their anti-Salmonella activity demonstrated the ability to reduce Salmonella shedding following a Salmonella enterica var Typhimurium challenge in pigs (Casey et al., 2007). Also, the addition of organic acids to water or feed seems to be promising for reduction of Salmonella in swine (Wingstrand et al., 1997). The objective of this study was to evaluate the potential of a water delivered Enterococcus/Bacillus combination or organic acid as a substitute for antibiotics following a Salmonella challenge in weanling pigs. Therefore, the objective of this experiment was to determine the effects of water delivered DFMs or organic acids on nursery pig growth performance, gut health and integrity, and immune status prior to and following an oral Salmonella Typhimurium challenge in comparison to responses observed when subtherapeutic levels of antibiotics were included in the diet.
To accomplish this objective, 88 crossbred pigs (equal barrows and gilts) were weaned at an average of 19 d of age and used in a 14 d study to evaluate the potential of direct fed microbials (DFMs) or organic acids to replace antibiotics following a Salmonella enterica var Typhimurium challenge. At weaning, pigs were randomly assigned to 4 treatments:
2) Control + water delivered DFM
3) Control + water delivered organic acid based blend
4) Control + 55 ppm carbadox in the feed
Diets were fed continuously from d 0 – 14. Pigs were allotted based on genetics, sex and initial BW (average = 6.2 kg). There were 4 pigs/pen and 6 pens/trt with the exception of diets 1 and 4 which had 5 pens/trt. All pigs had unlimited access to feed and water through a 5-hole self feeder and a single nipple waterer in each pen. Pigs were housed in an isolated room at the USDA Livestock Behavior Research Unit at Purdue University. Dietary treatments were administered for 14 consecutive days. All diets were formulated to meet or exceed the estimated nutrient requirements for pigs (NRC, 1998). Pigs were individually weighed and feed disappearance was recorded on d 0, 5, 8, 10 and 14 for calculation of growth rate, feed intake, and feed efficiency. Pigs were challenged with Salmonella 6 d post commencement of treatments. Serum samples were taken on d 6, 8, 10, and 14 for determination of TNFα concentration. Fecal samples were taken on d 0, 5, 7, and 11 for detection of Salmonella shedding and enumeration of Enterobacteriace. Pigs (n=22/d) were harvested on d 6, 8, 10, and 14. Intestinal and cecal tissue and contents and mesenteric lymph nodes were taken for Salmonella detection. Jejunum samples were taken for determination of nutrient uptake in modified Ussing Chambers. Duodenal, jejunal and ileal mucosal scrapings and tissue were taken for measurement of mucosal TNFα concentration and intestinal morphology, respectively. All treatments, in particular water administration of DFM improved growth rate from d 2 to 6 post-challenge compared to the negative control (P < 0.05). Duodenal villus height also tended to be improved (P=0.08) by DFM administration on d 4 post-challenge. Salmonella presence was reduced (P=0.001) in mesenteric lymph nodes, feces and ileal and cecal tissue over time. Antibiotic and DFM treatments tended to reduce (P=0.09) Salmonella presence in ileal contents. Serum TNFα tended to increase (P=0.10) up to d 4 post-challenge while TNFα concentrations in the duodenum tended to linearly decrease (P=0.10) post-challenge and TNFα in the ileum decreased (P=0.008) immediately postchallenge. Salmonella infection resulted in a linear decrease in phosphorus (P=0.001) active transport, and an increase (P=0.001) in glutamine uptake up to d 4 post-challenge. Glucose uptake was increased immediately post-challenge by in-feed antibiotics or water delivered DFM (P=0.009). Active ion transport was reduced by Salmonella infection, however water delivered DFM or organic acid treatments were most successful at attenuating this decline (P=0.001). Water acidification and antibiotic treatment tended to reduce carbachol induced chloride secretion (P=0.07).
In conclusion, water delivery of a DFM combination or organic acid appears to be a successful means of administering a potential antibiotic alternative to weanling pigs. Following a Salmonella enterica var Typhimurium challenge, both DFM and organic acid treated drinking water enhanced growth performance and gastrointestinal histology. Salmonella presence in ileal contents was reduced by DFM treatment and active glucose transport increased, while water acidification reduced induced chloride secretion. Current findings suggest that under a disease challenge situation water acidification and DFM treated drinking water performed similar or in some cases superior to in feed antibiotics and therefore must be considered as a viable alternative in weanling pig diets.