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gentamicin (1 .1 %), amoxicillin/clavulanic acid (0.7 %), and cefoxitin (0.7 %). Higher frequencies of resistance were observed for tetracycline (78 .9%), sulfisoxazole (49.9%), streptomycin (49.6 %), ampicillin (30 .6%), chloramphenicol (17 .62%), kanamycin (10%), and trimethoprim/sulfamethoxazole (6 .4 %). Most of the aforementioned antimicrobials are members of drug classes frequently used in veterinary medicine. Therefore, both judicious antimicrobial selection and use is needed when treating animals to preserve the ir efficacy. The most common multidrug-resistant patterns (resistance to ~ 2 antimicrobials} were streptomycin-tetracycline (9.38% ), streptomycin-sulfisoxazole-tetracycline (6.20% ), and ampicillin-streptomycin-sulfisoxazole-tetracycline (6.15% ). More clustering (less variation) in AMR was observed at the farm visit than the farm level indicating that sampling more farms with longer periods of time between farm visits might be required for better understanding of shifts in AMR over time. Risk factor analysis on the potential associations between certain on -farm AMU practices and observed AMR has been initiated and the results will be presented at the Symposium.

The prevalence of Salmonella contamination was assessed at five points in a Canadian pork slaughter plant. In the cooler only 0.5% (2/429) carcasses were positive, even though Salmonella were detected in 51.3% of all cecal samples and in the cecum of at least one pig in 91.5% (43/47) lots tested. Hogs held overnight in lairage were significantly more likely to have positive cecal samples. Salmonella was isolated at least once from the truck, holding pen or cecum of hogs from all 31 producers. Four serotypes comprised 70.3% of 299 isolates: Bovismorbificans, Derby, Brandenburg and Agona. PFGE showed several Salmonella strains were identical between fecal samples and carcass swabs. Many strains were different, suggesting resident bacteria or cross contamination during processing may be important in this plant. Processing interventions appear to be successfully minimizing carcass contamination in this plant. Introduction Salmonella is considered the most important food-borne pathogen from pork. Markets are requiring evidence of Salmonella control both during the production of hogs as well as pork processing. The epidemiology of Salmonella contamination is complex and not well understood. Determining the baseline prevalence of Salmonella at several steps in the pork production chain is a first step in developing a control program. Rates of Salmonella contamination on pork carcasses have been shown to vary widely between individual plants in Canada (Quessy et al., 2004). Differences in infection status of incoming hogs and different procedures in each plant play a role in carcass contamination rates. It has been reported that essentially all Salmonella spp. on pork carcasses leaving the kill floor in a slaughter plant arrive in or on the pig (Berends et al., 1997). Hogs from some farms may be chronically infected with high levels of Salmonella spp, while others may rarely be infected (Rajic et al., 2001, Berends et al., 1996). There is a reported positive correlation between the number of animals that carry Salmonella spp. in their feces and the number of contaminated carcasses (Morgan et al., 1987). Cross contamination and infection of animals can occur during lairage, making the relationship between on-farm infection status and carcass contamination less clear. Negative hogs can become infected with Salmonella within a few hours in a contaminated lairage pen. Increasing lairage time has been reported to increase infection and carcass contamination rates (Hurd et al., 2001, Morgan et al., 1997) Lairage and transport have been identified as interventionpoints where carcass contamination rates can be easily reduced (Hurd et al., 2002, Berends et al., 1996). Some authors indicate that the most cost effective place to intervene may be during processing (Berends et al., 1996). Onfarm controls have also been suggested as effective. In order to identify effective intervention points, the sources of contamination must be identified. Pulsed-field gel electrophoresis (PFGE) is one method that may be used to determine genetic relatedness of strains and sources of contamination. The objectives of this study were to determine the prevalence of Salmonella at five steps in the production chain (truck, lairage pen, cecum, carcass before evisceration, carcass in cooler); to describe Salmonella serovar diversity and relatedness at each step; and to identify risk factors for contamination. This processor would like to determine which steps are the most effective in controlling carcass contamination, and whether to focus control efforts on the farm or at the plant. Materials and Methods Hogs were purposively selected to represent the entire slaughter population based on farm of origin, duration of lairage (length of time the hog is rested before slaughter), lot size, and time of slaughter. A lot was defined as a group of hogs from one farm that were shipped together. Nine hogs were systematically selected from each targeted lot. Lots were not mixed during transport, lairage or processing. Sampling was done over three different seasons. Samples consisted of fecal samples from the truck (TF) and holding pens after lairage (HP), cecal contents (CS); and carcass swabs before O R A L P R E S E N T A T IO N S 39 SafePork 2005 evisceration (BE) and in the chilling cooler (CL). TF and HP samples consisted of 5 individual droppings combined into one 25 g sample. The side of the carcass swabbed was alternated between animals. Carcasses were swabbed following the USDA protocol (USDA, 1996) with one modification; the order of swabbing was belly, jowls then ham. Samples were transported in coolers and tested the following day. The entire swab or 10 g fecal/cecal material was enriched in buffered peptone water for 24 hours. 1 mL of this broth was transferred to tetrathionate broth (TB) and 0.1 mL to Rappaport-Vassiliadis (RVB) broth. The TB was incubated at 35 °C and RV at 42 °C for 24 hours. 150 μL of TB and RVB were combined and screened for Salmonella with real-time PCR (R-PCR). R-PCR positive samples were culturally confirmed and three isolates per sample were frozen. One isolate from each CS sample and all three isolates from CL, BE, TF and HP samples were analyzed by pulsed-field gel electrophoresis (PFGE). PFGE was performed using the PulseNet method (CDC, Atlanta, GA). Representative strains from each PFGE profile were sent to the Public Health Agency of Canada laboratory for serotyping. Results Samples were taken from 47 different lots representing 31 different farms. Salmonella was isolated at least once from the truck, holding pen or cecum of hogs from all 31 producers. Thirty-four of the 47 lots tested were held overnight in lairage before slaughter, which is representative of the typical kill at this plant where 75% of hogs are held overnight. There were significantly more positive fecal samples from the pen floor after lairage (82.9%) than from the truck floor upon arrival (40.5%) (p

The study objectives were to describe antimicrobial use (AMU) and Salmonella resistance on 90 Alberta swine farms. The vast majority of antimicrobials were used in-feed. In weaners, in-feed use did not vary among farms, suggesting heavy reliance on in-feed antimicrobials. For grow-to-finish production phases, most farms reported heavy reliance on in-feed antimicrobials, but 6 and 14 farms did not report any in-feed AMU in growers and finishers, respectively. The tetracycline-sulphametazinepenicillin combination and carbadox were the most common antimicrobials added to the weaner rations, while tylosin and lincomycin were the most common antimicrobials added to grower and finisher rations. No resistance was observed to nalidixic acid, ciprofloxacin, amikacin and ceftriaxone. A low frequency of resistance (