Effects of feed particle size at dietary presence of added organic acids on caecal parameters and the prevalence of Salmonella in fattening pigs on farm and at slaughter

In a field study with fattening pigs, effects of feed particle size at the dietary presence of organic acids on Salmonella prevalence were measured. On two farms (f1/f2), each holding ～800 pigs, diets based on finely ground (control) or coarsely ground ingredients (experiment) were fed as crumbs. On f1 both control and experimental grower and finisher diets contained identical concentrations of formic and propionic acid (0.4% and 0.2% respectively). On f2 only finisher diet of the experimental group contained 1.2% potassium diformate. At the start of the fattening period no statistical differences were measured between Salmonella prevalence in animals fed control and experimental diets on both farms. At slaughter Salmonella prevalence in caecal contents was lower (p < 0.05) on f1 in animals fed the experimental diet. Furthermore, the number of seronegative meat juice samples taken from these animals [optical density (OD) <10] was higher (p < 0.001); seropositive as well as distinct seropositive samples (OD ≥20 and ≥40 respectively) were less frequent (p < 0.01) compared to samples from animals fed the control diet. Feeding the experimental diet on f2 resulted in a lower Salmonella detection rate in faeces before slaughter (p < 0.01). Salmonella prevalence was lower in caecal content at slaughter for pigs fed the experimental diet compared to those fed control diet (p < 0.0001). The number of distinct seropositive meat juice samples (OD ≥40) was lower (p < 0.01) for pigs fed the experimental than for those fed the control diet. In comparison to pigs in the control group, starch concentrations in the caecal content from pigs in the experimental groups on both farms were higher (p < 0.05) and the pH values lower (p < 0.05). Propionate (p < 0.0001) and butyrate (p < 0.01) concentrations were higher in the caecal content taken from pigs in the experimental group on f2.     

Impact of the Salmonella status of market-age pigs and the pre-slaughter process on Salmonella caecal contamination at slaughter

The aim of this study was to evaluate the impact of the pre-slaughter process on Salmonella caecal contamination of pigs at slaughter. An observational study was carried out in 2001 on 101 conventional farrow-to-finish pig farms. On each farm, one batch of contemporary pigs was followed from the end of the fattening period until slaughter. The Salmonella bacteriological status of the batches was assessed by environmental samples of faecal material. The serological Salmonella status was obtained on 30 individually identified market-age pigs using an indirect ELISA test. At the slaughterhouse, 25 g of caecal contents were taken from 10 of the identified pigs. Faecal and caecal material were analysed according to a classical bacteriological method. A questionnaire was designed to obtain information about the type of feeding during the fattening period (dry versus wet), the duration of fasting on the farm before leaving for the slaughterhouse, the duration of transport between the farm and the slaughterhouse, the holding time in lairage at the slaughterhouse and loading and unloading conditions on the farm and at the slaughterhouse. To assess the relationships between these factors and the Salmonella caecal status of the pigs and the batches, two logistic models were fitted at the individual and at the batch level, respectively. The first analysis was performed using a random effects logistic regression model. The second analysis was based on a cumulative logit model with a positive caecal rate classified into three classes as the outcome variable. The results showed that the Salmonella status of market-age pigs assessed on the farm either by serological or bacteriological examinations and the time spent in lairage before slaughtering played a crucial role on caecal contamination. In the light of these results, actions should be considered both on the farm and at the slaughterhouse to decrease the risk of Salmonella contamination of the caecal contents.     

Effect of organic acids in drinking water during the last 2 weeks prior to slaughter on Salmonella shedding by slaughter pigs and contamination of carcasses

In this study, we investigated the effect of adding organic acids to the drinking water of finishing pigs 2 weeks prior to slaughter on the shedding and prevalence rate of Salmonella at slaughter. Approximately 600 animals from four Belgian pig herds infected with Salmonella were included. At two herds, the study was conducted twice. Before the start of the study, overshoes were taken at the different herds. Two weeks prior to the expected slaughter date, the pigs were randomly divided into two groups (treatment and control group) each containing on average 50 animals within each herd. The treatment group received from this day onwards acidified drinking water (pH = 3.6-4.0), the control group received non-treated water (pH = 7.8-8.5). All other housing, feeding and management factors were identical in both groups. At the slaughterhouse, 10 pigs of each group (20 pigs for each group of study group 6) were randomly selected and sampled (blood, contents of ileum and rectum, mesenteric lymph nodes and carcass swabs). All samples were immediately transported to the laboratory and submitted to Salmonella isolation. Salmonella was isolated out of 11.9% (66/554) of the samples taken at the slaughterhouse, with the highest frequency found in the content of the ileum (18.7%), followed by 17.8% in the lymph nodes, 7.2% in the content of the rectum and 3.6% in the carcass swabs. The results did not reveal a significant difference between the treatment and control groups for the different slaughterhouse samples. The study documented that the investigated control strategy namely, the strategic application of organic acids during the last 2 weeks prior to slaughter was insufficient to decrease Salmonella shedding and contamination shortly before and during slaughter.     

Evaluation of protective immunity in pigs following oral administration of an avirulent live vaccine of Lawsonia intracellularis

OBJECTIVE: To evaluate the efficacy of an orally administered avirulent live vaccine to protect pigs against challenge exposure with virulent Lawsonia intracellularis. ANIMALS: 108 weaned 3-week-old pigs (35 in experiment 1 and 73 in experiment 2). PROCEDURE: 2 experiments were conducted. On day 0, vaccinates were orally administered vaccine via drench or in drinking water, whereas challenge-control pigs were administered cultured medium. On day 21, pigs were challenge exposed with a virulent heterologous isolate of L. intracellularis. Clinical observations, weights, seroconversion, and fecal excretion of L. intracellularis were measured until day 42. At study termination, pigs were euthanatized and examined for L. intracellularis-specific lesion development of the ileum and colon. RESULTS: Pigs receiving a single dose of vaccine were protected when challenge exposed with virulent L. intracellularis (at least 10(77) TCID50/dose). In experiment 1, vaccinates had significantly less fecal excretion (47% and 40% for days 35 and 42, respectively), compared with challenge-control pigs. In experiment 2, vaccinates had significantly less fecal excretion (50% and 58% for days 35 and 42, respectively), compared with challenge-control pigs. Significant reductions in lesion development were evident in the ileum of vaccinated pigs (70% and 56% at day 42 for experiments 1 and 2, respectively), compared with challenge-control pigs. CONCLUSIONS AND CLINICAL RELEVANCE: Oral administration by drench or via drinking water of an avirulent live vaccine against L. intracellularis resulted in substantial protection against proliferative enteropathy among vaccinates and offers a better way to reduce stress of pigs during vaccine administration.     

Pharmacokinetics of amoxicillin administered in drinking water to recently weaned 3- to 4-week-old pigs with diarrhea experimentally induced by Escherichia coli O149:F4

OBJECTIVE: To measure effects of Escherichia coli O149:F4-induced diarrhea on water consumption and pharmacokinetics of amoxicillin after administration in drinking water. ANIMALS: 24 recently weaned 24- to 28-day-old crossbred pigs. PROCEDURE: 10 pigs were inoculated with E. coli O149:F4; all 10 pigs subsequently developed diarrhea. Pigs were medicated by administration of amoxicillin in the drinking water (0.75 mg/mL) for a 4-hour period on 2 consecutive days. Fourteen age-matched noninfected healthy pigs (control group) were medicated in a similar manner. Blood samples were obtained from both groups daily, and plasma concentrations of amoxicillin were analyzed by use of high-performance liquid chromatography. RESULTS: Diarrhea reduced the area under the plasma concentration-versus-time curve (AUC) and maximum plasma concentration (C(max)) of amoxicillin on the first day of medication by 56% and 63%, respectively. The AUC of amoxicillin on the second day of medication for diarrheic pigs did not differ significantly from that of control pigs on the first day of medication. CONCLUSIONS AND CLINICAL RELEVANCE: E. coli-induced diarrhea reduced the AUC of amoxicillin and time that plasma concentration of amoxicillin was > 0.025 microg/mL and, hence, less likely to have a therapeutic effect on the first day of administration in drinking water. On the assumption that plasma concentrations may indirectly reflect concentrations at the site of infection, analysis of our results suggests that higher doses of amoxicillin may be appropriate for administration in drinking water during a 4-hour period on the first day that pigs have diarrhea attributable to E. coli O149:F4.     

Decreased mortality of weaned pigs with Streptococcus suis with the use of in-water potassium penicillin G

This study evaluated the efficacy of potassium penicillin G in drinking water of weaned pigs to reduce mortality and spread of infection caused by Streptococcus suis. A total of 896 18-day-old weaned pigs were randomly assigned to either treatment with potassium penicillin G in-water (Treated), or no treatment (Control). The outcomes analyzed were total mortality, mortality due to S. suis, and overall counts of S. suis colonies. The risk of mortality due to S. suis and total mortality were significantly increased in the Control group compared with Treated pigs (P < 0.05). Bacterial culture of posterior pharyngeal swabs indicated that Control pigs were significantly more likely to have ≥ 1000 colonies of S. suis per plate than were Treated pigs (P < 0.05). This study demonstrates that potassium penicillin G administered in drinking water is effective in reducing mortality associated with S. suis infection and reducing tonsillar carriage of S. suis.     

Estimation of the diagnostic accuracy of the invA-gene-based PCR technique and a bacteriological culture for the detection of Salmonella spp. in caecal content from slaughtered pigs using Bayesian analysis

The goal of this study was to estimate the accuracy of the invA-gene-based polymerase chain reaction (PCR) and a culture technique based on pre-enrichment with buffered peptone water, three selective enrichment media (selenite, tetrathionate and Rappaport-Vassiliadis broths) and four selective, solid media (Xylose-Lysine-Tergitol-4, Salmonella/Shigella, Hekton-Enteric and MacConkey), for the detection of Salmonella organisms from caecal samples from slaughter pigs. For this purpose a latent-class (Bayesian) approach was used. Two hundred and three slaughtered pigs were used after grouping them into two groups of 96 and 107 animals. Sensitivity (Se) was estimated to be 56% (95% probability interval 40, 76) for culture and 91% (81, 97) for PCR. The specificity (Sp) of the PCR was 88% (80, 95) while the Sp of the culture had been considered 100% in the statistical analysis as all culture-positive samples were confirmed by serotyping. PCR Se was not affected by the Salmonella serotypes present in the samples analysed. Accordingly, a minimum of 25.5% of the pigs was estimated to harbour Salmonella organisms in their faeces. It was concluded that bacteriology on caecal samples alone was a poor diagnostic method, and that the PCR method could be considered a cost-effective alternative to culture in Salmonella monitoring programmes. However, given the moderate Sp of this molecular technique, PCR-positive samples should be further confirmed through bacteriology.     

THE ISOLATION OF SALMONELLA FROM JEJUNAL AND CAECAL LYMPH NODES OF SLAUGHTERED ANIMALS

One jejunal and one caecal lymph node were sampled from each of 50 cows, 40 yearling cattle, 25 sheep, 20 lambs and 45 pigs after slaughter. Salmonella, Clostridium perfringens and Staphylococcus aureus , all organisms which cause food poisoning in man, were sought by direct plating methods. The samples were also enriched and cultured for Salmonella. Organisms were cultured from 208 (58%) of the 360 lymph nodes; aerobic plate counts yielded up to 25,000 organisms per gram of tissue, although from most infected samples less than 1000 organisms per gram were cultured. Salmonella was isolated directly from 5% of samples, with counts up to 1,500 per gram. After enrichment Salmonella was isolated from nodes taken from 15 cows, 2 yearling cattle, one sheep and 8 pigs. Cl. perfringens was isolated from the caecal nodes of 2 yearling cattle and 2 pigs; S. aureus was not isolated from any sample. It was concluded that mesenteric lymph nodes may be a significant reservoir of Salmonella for transfer to meat and meat products.     

Controlling Salmonella infection in weanling pigs through water delivery of direct-fed microbials or organic acids: Part II. Effects on intestinal histology and active nutrient transport

The objective of this study was to evaluate the effects of water-delivered, direct-fed microbials (DFM) or organic acids on intestinal morphology and active nutrient absorption in weanling pigs after deliberate Salmonella infection. Pigs (n = 88) were weaned at 19 ± 2 d of age and assigned to 1 of the following treatments, which were administered for 14 d: 1) control diet; 2) control diet + DFM (Enterococcus faecium, Bacillus subtilis, and Bacillus licheniformis) in drinking water at 10(9) cfu/L for each strain of bacteria; 3) control diet + organic acid-based blend (predominantly propionic, acetic, and benzoic acids) in drinking water at 2.58 mL/L; and 4) control diet + 55 mg/kg carbadox. Pigs were challenged with 10(10) cfu Salmonella enterica var Typhimurium 6 d after commencement of treatments. Pigs (n = 22/d) were harvested before Salmonella challenge and on d 2, 4, and 8 after challenge. Duodenal, jejunal, and ileal mucosal tissues were sampled for measurement of villus height and crypt depth. Jejunal tissue was sampled for determination of active nutrient absorption in modified Ussing chambers. Duodenal villus height was greater in pigs fed in-feed antibiotic before infection (P < 0.05). Jejunal crypts were deeper in DFM- and acid-treated pigs on d 4 after infection compared with all other treatments (P < 0.05). Salmonella infection resulted in a linear decrease in phosphorus (P < 0.001) and glucose (P < 0.05) active transport, and an increase (P < 0.001) in glutamine uptake immediately after challenge. Salmonella infection reduced basal short-circuit current (I(sc)); however, water-delivered DFM or organic acid treatments caused greater basal I(sc) on d 2 after challenge than did carbadox. Carbachol-induced chloride ion secretion was greatest in negative control pigs before infection (P < 0.01) and DFM-treated pigs (P < 0.05) after infection. In conclusion, both the DFM and acidification treatments induced increases in basal active ion movement and jejunal crypt depth, which could be interpreted as responses consistent with increased Salmonella pathology, but none of the additives markedly affected intestinal absorptive and secretory function in response to Salmonella challenge.     

Prevalence of Salmonella serotypes on pig carcasses from high- and low-risk herds slaughtered in three abattoirs

The aim of this study was to compare the prevalence of Salmonella serotypes at two different sites on pig carcasses from herds classified as high-risk or low-risk and to elucidate the relationship between carcass contamination levels and serological status. Caecal samples and carcass surface swabs were cultured for Salmonella from a total of 210 pigs from low risk herds (< 19% of pigs in herd Salmonella seropositive) and 209 pigs from high risk herds (> 32% of pigs in herd Salmonella seropositive) in three abattoirs. Meat juice samples were collected for analysis by ELISA. The prevalence of Salmonella in the caecal contents of "low-risk" pigs was 10%, which was significantly lower than the 19% prevalence in "high-risk" pigs (p < 0.01). The corresponding figures for skin samples collected immediately post-evisceration were 2% and 12%. The predominant Salmonella serotype in the caecal contents of both the low-risk and high-risk pigs was Salmonella Typhimurium. Salmonella Kentucky and Salmonella Derby were the most frequent isolates from the carcass surface swabs of low- and high-risk pigs respectively. There was a positive association between seropositivity of pigs from high-risk herds and caecal carriage (p < 0.05). Results showed that herd categorisation based on serological results was useful in predicting Salmonella isolation rates from caecal samples and surface swabs of slaughtered pigs.     

Effect of transportation and feed withdrawal on shedding of Salmonella typhimurium among experimentally infected pigs.

OBJECTIVE: To determine whether stress associated with transportation or feed withdrawal increased fecal shedding of Salmonella Typhimurium among pigs experimentally infected with the organism. ANIMALS: 86 healthy pigs. PROCEDURE: Pigs were challenge exposed with Salmonella Typhimurium at 4 weeks old and reared conventionally. When pigs reached market weight, they were assigned to groups and subjected to various combinations of transportation and feed withdrawal. Ileocecal contents were collected after slaughter and tested for Salmonella Typhimurium. RESULTS: Salmonella Typhimurium was not detected in feces collected from pigs just prior to slaughter. When feed was withheld for 24 hours prior to slaughter, the proportion of transported pigs with Salmonella Typhimurium in ileocecal contents at the time of slaughter was not significantly different from the proportion of nontransported pigs. However, when feed was not withheld prior to slaughter, the proportion of transported pigs with Salmonella Typhimurium in ileocecal contents at the time of slaughter was significantly higher than the proportion of nontransported pigs. CONCLUSIONS AND CLINICAL RELEVANCE: When carrier pigs remained on feed, transportation stress increased the proportion positive for Salmonella sp. On the basis of results reported here, it is suggested that producers withhold feed from pigs for 24 hours prior to transportation to a slaughter plant.     

Coated fatty acids alter virulence properties of Salmonella Typhimurium and decrease intestinal colonization of pigs

Salmonella Typhimurium infections in pigs are a major source of human foodborne salmonellosis. To reduce the number of infected pigs, acidification of feed or drinking water is a common practice. The aim of the present study was to determine whether some frequently used short- (SCFA) and medium-chain fatty acids (MCFA) are able to alter virulence gene expression and to decrease Salmonella Typhimurium colonization and shedding in pigs using well established and controlled in vitro and in vivo assays. Minimal inhibitory concentrations (MIC) of 4 SCFA (formic acid, acetic acid, propionic acid and butyric acid) and 2 MCFA (caproic and caprylic acid) were determined using 54 porcine Salmonella Typhimurium field strains. MIC values increased at increasing pH-values and were two to eight times lower for MCFA than for SCFA. Expression of virulence gene fimA was significantly lower when bacteria were grown in LB-broth supplemented with sub-MIC concentrations of caproic or caprylic acid (2 mM). Expression of hilA and invasion in porcine intestinal epithelial cells was significantly lower when bacteria were grown in LB-broth containing sub-MIC concentrations of butyric acid or propionic acid (10 mM) and caproic or caprylic acid (2 mM). When given as feed supplement to pigs experimentally infected with Salmonella Typhimurium, coated butyric acid decreased the levels of faecal shedding and intestinal colonization, but had no influence on the colonization of tonsils, spleen and liver. Uncoated fatty acids, however, did not influence fecal shedding, intestinal or tonsillar colonization in pigs. In conclusion, supplementing feed with certain coated fatty acids, such as butyric acid, may help to reduce the Salmonella load in pigs.     

Different feed withdrawal times before slaughter influence caecal fermentation and faecal Salmonella shedding in pigs

The effects of different pre-slaughter feed withdrawal times (FWT) on the gastrointestinal tract (GIT) weight and the gut environment of pigs and Salmonella shedding were investigated. Trial 1 evaluated the effects under experimental conditions (feed withdrawal for 18, 30 and 36 h) and trial 2 under commercial conditions (15 and 30 h). In trial 1, the GIT weight tended to decrease (P=0.07), the caecal pH increased (P<0.0001), short-chain fatty acids (SCFA) decreased (P<0.001) and percentage of branched-chain fatty acids (BCFA) increased as FWT increased. Similar results were observed in trial 2, but Enterobacteriaceae numbers and Salmonella positive pigs tended to increase whereas lactobacilli decreased (P<0.0005) as FWT increased. The increase in FWT involved changes in the gut microbial ecosystem that could be associated with the trend of increased caecal Enterobacteriaceae and Salmonella in faeces, and may represent a higher risk of carcass contamination in cases of laceration of viscera.     

屠宰猪肠道沙门氏菌的分离鉴定、耐药性分析及致病性试验

为了解广西南宁市猪源沙门氏菌的污染状况、耐药状况及致病力情况,在南宁市某生猪屠宰场随机直接从131头屠宰猪的肠道采集样品,采用鉴别培养基分离,生化鉴定的方法对样品中的沙门氏菌进行分离鉴定,并采用标准K-B纸片法对分离菌株进行25种抗生素敏感试验,最后对分离株进行小白鼠致病性试验。结果从131份屠宰猪的肠道中共分离到沙门氏菌45株,检出率为34.35%;其中鼠伤寒沙门氏菌14株,甲型副伤寒杆菌2株,肠炎沙门氏菌3株。45株分离菌株全部耐药,耐药率高达100%,其中44株为多重耐药菌株,占97.78%。45株沙门氏菌中有40株对小白鼠具有致病性,致病率达88.89%。这表明南宁市的屠宰猪存在一定程度的沙门氏菌污染,并且分离菌株存在较严重的耐药现象以及具有较强的致病性。应采取有效措施控制沙门氏菌在猪群中的污染和限制抗生素在养猪过程中的使用并严格遵守休药期,以减少细菌耐药性的产生,保障猪肉及猪肉制品的食品安全。     

Controlling Salmonella infection in weanling pigs through water delivery of direct-fed microbials or organic acids. Part I: effects on growth performance, microbial populations, and immune status

Pigs (n = 88) weaned at 19 ± 2 d of age were used in a 14-d study to evaluate the effects of water-delivered direct-fed microbials (DFM) or organic acids on growth, immune status, Salmonella infection and shedding, and intestinal microbial populations after intranasal inoculation of Salmonella Typhimurium (10(10) cfu/pig). Pigs were challenged with Salmonella 6 d after commencement of water treatments. Treatments were 1) control diet; 2) control diet + DFM (Enterococcus faecium, Bacillus subtilis, and Bacillus licheniformis) in drinking water at 10(9) cfu/L for each strain of bacteria; 3) control diet + an organic acid-based blend (predominantly propionic, acetic, and benzoic acid) in drinking water at 2.58 mL/L; and 4) control diet + 55 mg/kg of carbadox. Serum samples were taken on d 6, 8, 10, and 14 for determination of tumor necrosis factor α (TNFα) concentrations. Fecal samples were taken on d 0, 5, 7, and 11 for determination of Salmonella shedding and enumeration of coliforms. Pigs were euthanized on d 6, 8, 10, and 14. Intestinal and cecal tissue and digesta and mesenteric lymph nodes were sampled and analyzed for Salmonella. Duodenal, jejunal, and ileal mucosal scrapings were sampled for measurement of mucosal TNFα concentrations. Water delivery of DFM prevented a decline in ADG on d 2 to 6 postchallenge compared with the negative control (P < 0.05). Coliform counts tended to be greater (P = 0.09) in the cecum of the DFM treatment group on d 2 postinfection compared with the negative control and acid treatment groups. However, Salmonella prevalence in the feces, gastrointestinal tract, or lymph nodes was not affected by water delivery of acids or DFM. Serum and mucosal TNFα concentrations were not affected by treatment throughout the study with the exception of ileal concentrations on d 4 postchallenge, which were greater in the negative control group compared with all other treatments (P < 0.05). The in-feed antibiotic was the only treatment that reduced Salmonella prevalence and this was localized to the cecum on d 8 postinfection. In conclusion, the DFM and organic acid treatments used in this study offered little or no benefits to pigs infected with Salmonella and should not be considered under the constraints of this study as viable alternatives to in-feed antibiotics in a pathogen challenge situation.     

Effect of separate transport, lairage, and slaughter on occurrence of Salmonella typhimurium on slaughter carcasses

The study aimed to reduce cross-contamination between finishers from Salmonella-positive and Salmonella-negative herds during transport, lairage, and slaughter, thereby reducing the prevalence of Salmonella Typhimurium on slaughter carcasses. In Phase 1 of the study, pigs from Salmonella-negative herds were kept in lairage for 2-4 hours either in clean pens (intervention group) or pens contaminated with Salmonella-infected faeces (control group). All pigs were slaughtered on the same slaughterline, and carcass swabs 24 hours after slaughter revealed a low degree of cross-contamination in the pens: there was no difference in Salmonella-positive carcasses between intervention (1.7%) and control groups (0.8%). In Phase 2, control pigs from Salmonella-negative herds were mixed with pigs from Salmonella-positive herds during lairage for 2-4 hours, while the intervention group still consisted of pigs from Salmonella-negative herds. All pigs were slaughtered on the same line: first intervention, then control. Carcass swabs taken 24 hours after slaughter failed to show a reduction in Salmonella-positive carcasses in the intervention group (4.5%) compared with the originally Salmonella-negative pigs in the control group (3.6%). In pigs from Salmonella-positive herds the occurrence of Salmonella was substantially higher at 10.4%. When the results were corrected for 6 carcass samples found positive with S. Heidelberg on the same day, which was attributed to a transient hygiene failure, only 2.2% of the carcasses in the intervention group were Salmonella-positive. We conclude that even though cross-contamination occurs in the abattoir pens, its importance on the slaughter line may be greater. However, the final results of this study should be awaited to conclude whether separate slaughter of pigs from Salmonella-positive and Salmonella-negative herds should be recommended.     

Effect of withdrawing feed from swine on meat quality and prevalence of Salmonella colonization at slaughter

OBJECTIVE: To determine whether withholding feed from pigs prior to slaughter had any effects on meat quality, percentage of pigs with Salmonella spp in cecal contents during slaughter, or percentage of pigs with lacerations of the gastrointestinal tract during slaughter. DESIGN: Split-plot design. ANIMALS: 873 pigs. PROCEDURES: At the finishing barn, pigs were assigned to 30 pens. Feed withdrawal times were assigned to pens at random, and pigs in each pen were marketed in 3 groups. The first marketing group consisted of the 10 heaviest pigs in each pen, the second consisted of the next 10 heaviest pigs, and the third consisted of all remaining pigs. RESULTS: Withdrawing feed improved the redness score assigned to the meat but did not have any other significant effects on carcass composition or meat quality. The percentage of pigs with Salmonella spp in the cecal contents decreased from the first (73%) to the second (64%) to the third (52%) marketing group. However, isolation of Salmonella spp from cecal contents was not associated with feed withdrawal time or with pen prevalence of Salmonella shedding during the 2 months prior to slaughter. Feed withdrawal time and marketing group did not have any significant effects on overall prevalence of gastrointestinal tract lacerations. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that withdrawal of feed from pigs prior to slaughter does not increase the prevalence of Salmonella colonization or the risk of carcass contamination associated with gastrointestinal tract lacerations during slaughter but only slightly enhances meat quality.     

Effects of microcin 24-producing Escherichia coli on shedding and multiple-antimicrobial resistance of Salmonella enterica serotype typhimurium in pigs

OBJECTIVE: To investigate the effect of an Escherichia that produced microcin 24 (Mcc24) on shedding of of Salmonella enterica serotypeTyphimurium in swine and evaluate evidence of in vivo activation of the Mcc24-mediated, multiple-antibiotic resistance (mar) operon. ANIMALS: 36 crossbred weaned pigs. PROCEDURE: 24 pigs were allocated to 2 groups (12 pigs/group). Pigs in 1 group received daily oral administration of an Mcc24-producing E coli, whereas the other group received a non-Mcc24-producing E coli. All pigs were challenge exposed with Salmonella Typhimurium chi4232. A third group of 6 pigs received Mcc24-producing E coli and was challenge exposed with an Mcc24-sensitive, marA-deleted strain of Salmonella Typhimurium 4232. After challenge exposure, fecal samples from all pigs were cultured to detect shedding of Salmonella Typhimurium and Salmonella Typhimurium isolates were screened for resistance to ciprofloxacin. Fecal samples were collected throughout the study, and tissue samples were collected during necropsy. RESULTS: Differences in shedding of Salmonella Typhimurium were not detected between groups receiving Mcc24-producing or non-Mcc24-producing E coli. No significant differences were found in quantitative analysis between groups receiving Mcc24-producing and non-Mcc24-producing E coli. Evidence of mar activation was not detected. CONCLUSIONS AND CLINICAL RELEVANCE: Microcin-producing E coli did not exert an effect on shedding of SalmonellaTyphimurium or mar activation in pigs. It may be difficult or impractical to create the conditions required for Mcc24 to be an effective part of a food safety intervention to reduce shedding of Salmonella Typhimurium.     

Assessment of various treatments to reduce carriage of Salmonella in swine.

In this study, different strategies to reduce carriage of Salmonella spp. in pigs were evaluated. Probiotics, prebiotics, vaccination, and acidification of drinking water were assessed as means of reducing Salmonella. Acidification of water, use of egg yolk-specific immunoglobulins, and vaccination with an endotoxin vaccine did not reduce Salmonella excretion in experimentally infected pigs. A reduction of Salmonella in the colonization of mesenteric lymph nodes was observed with the use of bambermycins and a live attenuated vaccine. A reduction in the shedding of S. Typhimurium was also observed after supplementation with fructooligosaccharides in drinking water. The use of probiotics and prebiotics appeared to change the pig fecal bacterial flora as indicated by Gram staining of smears from rectal swabs.     

Effects of a "step-up" ractopamine feeding program, sex, and social rank on growth performance, hoof lesions, and Enterobacteriaceae shedding in finishing pigs

Increasing concern for animal well-being and food safety has stimulated the investigation of feed additives such as ractopamine (RAC), a beta-agonist widely used to improve production performance of finishing pigs. The objective of this study was to determine effects of RAC feeding, delivered as a "step-up" program (5 mg/kg for 2 wk followed by 10 mg/kg for 2 wk), on growth performance, Enterobacteriaceae shedding, including Salmonella, and hoof lesions, also taking into account sex and social rank of pigs. A total of 64 barrows and gilts (balanced by treatment and sex) were assigned to pens of 4 (by sex) as either control (CTL) or RAC treatment. Social ranks (dominant, intermediate, and subordinate) of pigs in each pen were determined by behavioral observation during 48 h post-mixing. Fecal samples were collected once per week for 5 wk. At slaughter, the 32 dominant and subordinate barrows and gilts (16/sex) were examined for hoof lesions, and luminal contents from ileum, cecum, and rectum were collected. Pigs fed RAC had increased growth performance (P < 0.05) with social rank of animals affecting overall ADG (P < 0.05). Gilts gained more backfat than barrows when comparing to baseline values at both 10th and last ribs (P < 0.05), whereas loin eye area increased at a similar rate for both barrows and gilts (P > 0.10). No significant effect of RAC feeding was found on backfat or loin eye area (P > 0.10). At slaughter, RAC-fed pigs had greater BW (P < 0.05). Despite the positive effects of RAC feeding on growth performance, pigs fed the compound had a greater frequency of front and rear hoof lesions as did barrows and dominant individuals (P < 0.05). Detectable concentrations of Salmonella shedding were not identified at any time during the experiment. Enterobacteriaceae shedding concentrations from RAC-fed pigs peaked at the first week of feeding and progressively decreased until slaughter. At slaughter, rectal and cecal Enterobacteriaceae concentrations were less in RAC-fed pigs than in CTL pigs (P < 0.05). Social rank tended to affect gut Enterobacteriaceae populations of barrows more than in gilts (P < 0.10). The effects of RAC feeding on hoof soundness and Enterobacteriaceae populations in the gastrointestinal tract of finishing pigs warrant further investigation. It is also proposed that the integration of the social rank status of the individual into future studies should be considered, because it may affect treatment responses.