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Feedlot calves (n = 3784) were systematically randomized and allocated in a 2 × 2 factorial study to receive metaphylactic oxytetracycline (OTC) on arrival or no antimicrobial, as well as florfenicol once subcutaneously or twice intramuscularly (48 h apart) if diagnosed with bovine respiratory disease (BRD). Calves of different treatment groups were comingled and followed from placement to re-implantation (~100 days). Animals receiving OTC had a reduced risk of BRD, an increased risk of arthritis, and no significant differences in average daily gain, BRD relapse, overall mortality, or BRD mortality. There were no significant differences between treatment protocols. Deep nasal swabs (n = 233) taken at arrival (n = 122), treatment (n = 77), and swabs from lungs and joints at postmortem (n = 34) were cultured for Mycoplasma bovis from 61 animals ill or dying of chronic pneumonia and arthritis and from 61 healthy calves. There was significant variation in diversity among isolates (n = 51) between study years and different cattle. Metaphylaxis or antimicrobial treatment did not affect the diversity of isolates. Except for tilmicosin, isolates were largely susceptible to tested antimicrobials.

Effet du traitement antimicrobien et des stratégies préventives sur le complexe respiratoire bovin ainsi que la relation génétique et l'antibiorésistance des isolats deMycoplasma bovisdans un parc d'engraissement de l'Ouest canadien. Les veaux d'un parc d'engraissement (n = 3784) ont été systématiquement randomisés et répartis dans une étude factorielle 2 × 2 pour recevoir de l'oxytétracycline métaphylactique (OTC) à l'arrivée ou pas d'antimicrobien, ainsi qu'une injection sous-cutanée ou deux injections intramusculaires (à intervalle de 48 h) de florfénicol s'ils étaient diagnostiqués avec le complexe respiratoire bovin (CRB). Les veaux de différents groupes de traitement ont été regroupés pêle-mêle et suivis du placement à la réimplantation (~100 jours). Les animaux recevant l'OTC avaient un risque réduit de CRB, un risque accru d'arthrite et ne présentaient pas de différences significatives pour le gain de poids quotidien moyen, la rechute du CRB, la mortalité globale ou la mortalité associée au CRB. Il n'y avait aucune différence significative entre les protocoles de traitement. Des écouvillonnages nasaux profonds (n = 233) prélevés à l'arrivée (n = 122), au traitement (n = 77) et des écouvillonnages des poumons et des articulations post mortem (n = 34) ont été cultivés pour Mycoplasma bovis à partir de 61 animaux malades ou mourants de pneumonie chronique et d'arthrite et de 61 veaux en santé. Il n'y avait aucune variation significative dans la diversité des isolats (n = 51) entre les années d'étude et les différents bovins. La métaphylaxie ou le traitement antimicrobien n'a pas affecté la diversité des isolats. Sauf pour la tilmicosine, les isolats étaient largement sensibles aux antimicrobiens testés.(Traduit par Isabelle Vallières).

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A manpower survey of veterinary practices in western Canada found that there were potentially 314 full-time equivalent veterinary vacancies. However, only 8% of the respondents were in urgent need of another veterinarian. The results underscore that hiring intentions are best viewed as a continuum and not as a simple dichotomous variable: "Looking to hire? (Yes/No)".

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Production losses from abortions, stillbirths, and early calf mortality were described for the 2002 calf crop in 203 beef herds in western Canada. A total of 1689 calves were examined. A summary diagnosis was reported for 64% of aborted calves, 78% of stillborn calves, 88% of neonatal calves, and 94% of the calves > 3 d of age. Diagnoses for aborted calves included: thyroid gland lesions, pneumonia, developmental anomalies, placentitis, and myocardial necrosis or myopathy. For stillborn calves, diagnostic findings included: dystocia, thyroid gland lesions, myocardial necrosis or myopathy, developmental anomalies, and skeletal myopathy or necrosis. The most common diagnoses for neonatal calves (≤ 3 d) were: pneumonia, skeletal myopathy or necrosis, myocardial necrosis or myopathy, accident or trauma, and septicemia. For older calves (3 d to 3 mo), the most common diagnoses included: starvation, abomasal ulcer or perforation, enteritis or colitis, pneumonia, and intestinal volvulus, obstruction, or perforation.

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Inadequate consumption of colostrum can negatively affect calf health and survival. The serum immunoglobulin G (IgG) concentrations of 935 beef calves from 152 herds in Alberta and Saskatchewan have been described, using radial immunodiffusion. The determinants and health effects of serum IgG concentrations were studied in 601 calves sampled between 2 and 8 days of age. Of these calves, 6% had failure of passive transfer and an additional 10% had marginal passive transfer. Serum IgG concentrations were lower in calves born to a heifer, as a twin, or experiencing dystocia. The odds of both calf death and treatment were increased in calves with serum IgG concentrations below 24 g/L; a threshold notably higher than the 16 g/L usually considered as providing adequate passive transfer. The finding of 1/3 of calves with serum IgG concentrations less than 24 g/L suggests that calfhood treatments and mortality could be decreased by ensuring that high risk calves consume colostrum.

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Campylobacter spp. (n = 405), isolated from the feces of apparently healthy grow-finish pigs in 20 herds, were tested for susceptibility to 10 antimicrobials representing seven classes. Twelve percent of the isolates were susceptible to all drugs, while 64% were resistant to two or more antimicrobial classes. Resistance was most common to clindamycin, azithromycin, and erythromycin (71% each), and 10% of the isolates were resistant to ciprofloxacin. An antimicrobial use risk-factor analysis and a variance analysis explored the connection between antimicrobial resistance and the herd. The antimicrobial exposure of each production phase of each herd, through feed and water, was evaluated as a potential risk factor for resistance to macrolides and quinolones. Every 100,000 pig days of macrolide exposure in nursery pigs increased the odds of resistance to macrolides by a factor of 1.3. In contrast, the odds of resistance to a quinolone were nine times higher in Campylobacter from herds without beta-lactam exposure in grow-finish pigs compared with those with exposure. The variance analysis identified remarkably high clustering between isolates within herds; the intraclass correlations for resistances ranged from 0.52 to 0.82. Such extreme clustering demonstrates the potential for herd-level interventions to influence antimicrobial resistance in Campylobacter. The three key findings of this study, i.e., the prevalent resistance to macrolides, the association between macrolide exposure and Campylobacter resistance to macrolides, and the high clustering of resistance within herds, illustrate the need for continued study of antimicrobial-resistant Campylobacter on pig farms and the importance of judicious antimicrobial use in pork production.

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Escherichia coli often carries linked antimicrobial resistance genes on transmissible genetic elements. Through coselection, antimicrobial use may select for unrelated but linked resistance or virulence genes. This study used unconditional statistical associations to investigate the relationships between antimicrobial resistance phenotypes and antimicrobial resistance genes in 151 E. coli isolates from healthy pigs. Phenotypic resistance to each drug was significantly associated with phenotypic resistance to at least one other drug, and every association found that the probability of observing the outcome resistance was increased by the presence of the predictor resistance. With one exception, each statistical association that was identified between a pair of resistance genes had a corresponding significant association identified between the phenotypes mediated by those genes. This suggests that associations between resistance phenotypes might predict coselection. If this hypothesis is confirmed, evaluation of the associations between resistance phenotypes could improve our knowledge of coselection dynamics and provide a cost-effective way to evaluate existing data until large-scale genotypic data collection becomes feasible. This could enable policy makers and users of antimicrobials to consider coselection in antimicrobial use decisions. This study also considered the unconditional relationships between resistance and virulence genes in E. coli from healthy pigs (aidA-1, eae, elt, estA, estB, fedA1, stx1, and stx2). Positive statistical associations would suggest that antimicrobial use may select for virulence in bacteria that may contaminate food or cause diarrhea in pigs. Fortunately, the odds of detecting a virulence gene were rarely increased by the presence of an antimicrobial resistance gene. This suggests that on-farm antimicrobial use did not select for the examined virulence factors in E. coli carried by this population of healthy pigs.

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Antimicrobial resistance (AMR) is an emerging animal welfare and public health issue linked to antimicrobial use (AMU) in livestock. This study was conducted in 2004 on 20 swine farms in Alberta and Saskatchewan. On-farm records and questionnaires were used to retrospectively describe the antimicrobial exposures of pigs through feed, water, and injection. Antimicrobial use in all production categories was described over 12 months. On-farm records and questionnaires provided sufficient data to describe antimicrobial exposure rates through feed and water. In contrast, on-farm records did not supply sufficient data to describe parenteral antimicrobial exposure rates. Records lacked data on the number of exposures per treatment, therefore parenteral AMU was described as an exposure incidence. Parenteral exposure records were often unavailable for pigs less than 22 kg, in which case questionnaires were used. The incidence of parenteral AMU was significantly higher in herds reporting exposure by questionnaire compared with existing records, suggesting that on-farm records did not reliably describe parenteral AMU. However, because antimicrobial exposures in feed and water were markedly more common than through injection, it was concluded that existing on-farm data would be a valuable resource for investigating AMU and AMR in pigs.

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Salmonella spp. (n = 468), isolated from the feces of sows, nursery, and grow-finish pigs in 20 farrow-to-finish herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. No resistance was identified to amikacin, amoxicillin-clavulanic acid, ceftiofur, ceftriaxone, ciprofloxacin or nalidixic acid, and less than 1% of the isolates were resistant to cefoxitin and gentamicin. Isolates were most commonly resistant to tetracycline (35%) and sulfamethoxazole (27%). Overall, 59% of the Salmonella were susceptible to all 16 drugs (pansusceptible). Isolates from sows were more likely to be pansusceptible than isolates from nursery or grow-finish pigs. Resistance to 2 or more drugs occurred in 29% of the isolates and was significantly more likely to occur in Salmonella from nursery pigs than from sows. The odds of resistance to 4 of the drugs, streptomycin, ampicillin, kanamycin and cephalothin, were significantly higher in isolates from nursery pigs than grow-finish pigs, while the odds of resistance to 2 drugs, tetracycline and streptomycin, were higher in Salmonella from nursery pigs than from sows. More age-specific risk factor studies are needed to investigate these differences between production phases.

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Escherichia coli (n = 1439), isolated from the feces of apparently healthy grow-finish pigs in 20 herds in Alberta and Saskatchewan, were tested for susceptibility to 16 antimicrobials. All isolates were susceptible to amikacin, ceftriaxone, and ciprofloxacin and less than 1% was resistant to amoxicillin-clavulanic acid, cefoxitin, ceftiofur, gentamicin, and nalidixic acid. Resistance was most common to tetracycline (66.8%), sulfamethoxazole (46.0%) and streptomycin (33.4%). Twenty-one percent of the isolates were susceptible to all drugs, while 57% were resistant to 2 or more antimicrobials. Unconditional associations between resistances provided insight into the potential for co-selection. Every resistance-outcome was associated with at least 2 other drug-resistances. These associations illustrate the propensity for resistance phenotypes to occur together and the importance of considering co-selection in antimicrobial use decisions. A 2nd analysis explored the associations between resistance phenotypes in E. coli and Salmonella spp. from the same herd. Only 2 resistances in Salmonella were associated with herd-level E. coli resistance, indicating that E. coli is a poor sentinel for Salmonella AMR within herds. Herd-level management, including antimicrobial use, could affect antimicrobial resistance. The intra-class correlation between isolates within herds ranged from 0.1 to 0.46, which confirmed resistance clustered within herds. This suggests herd-level interventions might mitigate antimicrobial resistance. Overall, these results reflect the on-farm selection pressure for resistance and the potential food-safety risk from near-market animals. These data provide a baseline for comparisons with future on-farm monitoring of antimicrobial resistance in E. coli.

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Escherichia coli (n = 1439), isolated from the feces of apparently healthy grow-finish pigs in 20 herds, were tested for susceptibility to 16 antimicrobials. Logistic regression models were developed for each resistance that was observed in more than 5% of the isolates. Each production phase's (suckling, nursery, grow-finish pigs or sows) antimicrobial exposure rate, through feed or water, was considered as a risk factor. Management variables were evaluated as potential confounders. Six resistance outcomes were associated with an antimicrobial use risk factor and four included exposures of pigs outside the grow-finish phase. In the case of sulfamethoxazole, the odds of resistance increased 2.3 times for every 100,000 pig-days of nursery pig exposure to sulfonamides. Thus, swine producers and veterinarians must be aware that antimicrobial use in pigs distant from market could have food safety repercussions. Five resistance outcomes were associated with exposure to an unrelated antimicrobial class. Most notably, the odds of sulfamethoxazole and chloramphenicol resistance were each six times higher in herds reporting high (more than 500/1,000 pig-days) grow-finish pig, macrolide exposure compared to herds with no macrolide use in grow-finish pigs. Therefore, the potential for co-selection should be considered in antimicrobial use decisions. This study emphasizes the importance of judicious antimicrobial use in pork production.

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