Individual and group antimicrobial usage rates on 34 farrow-to-finish swine farms in Ontario, Canada.

Antimicrobial drug-use was assessed on 34 farrow-to-finish operations that marketed at least 500 hogs/yr. These operations either did not use any antimicrobials or used narrow-spectrum or broad-spectrum antimicrobials in rations of post-weaning pigs. Total antimicrobial use was measured for two months after obtaining inventories and records of all antimicrobials used. The collection of empty medication bottles and inventories of drugs on hand was convenient for producers and useful for estimating or validating recorded treatment rates, particularly for antimicrobials that were used only in one class of pig. Treatment records, however, underestimated by approximately 35% the amounts used for 27/29 farm-antimicrobial combinations. Rates of individual-pig treatment varied from 0-24.1 pigs treated/1000 pig-days, with a median of 5.29. Most individual animal treatments were given to piglets and sows at parturition and penicillin was the most commonly used antimicrobial. Gentamicin was administered to suckling piglets on 19 of the farms.

Prevalences of resistance to seven antimicrobials among fecal Escherichia coli of swine on thirty-four farrow-to-finish farms in Ontario, Canada.

Fecal specimens were composited and a hydrophobic-grid membrane-filter method was used to measure antimicrobial resistance to ampicillin 16 micrograms/ml, carbadox 30 micrograms/ml, gentamicin 4 mu/ml, nitrofurantoin 32 micrograms/ml, spectinomycin 16 micrograms/ml, sulfisoxazole 32 micrograms/ml and tetracycline 8 micrograms/ml among 8119 Escherichia coli isolates from 68 fecal samples collected on 34 farrow-to-finish swine farms marketing over 500 hogs/yr. The overall prevalences of resistance to antimicrobials among these isolates were: ampicillin 29%, carbadox 3.5%, gentamicin 0.6%, nitrofurantoin 27%, spectinomycin 28%, sulfasoxizole 38% and tetracycline 71%. Thirty to seventy-six per cent of the variations in prevalences were explained by between-farm differences.

Associations among antimicrobial drug treatments and antimicrobial resistance of fecal Escherichia coli of swine on 34 farrow-to-finish farms in Ontario, Canada.

Logistic regression was used to model associations between antimicrobial treatment and resistance among fecal Escherichia coli of finisher pigs at the farm level. Four sets of potential risk factors representing different levels of refinement of antimicrobial use on farms were modelled on resistance to antimicrobials. Final models for each antimicrobial were constructed from treatment and management variables significant on initial screening, and corrections for overdispersion were made. In general, in-feed antimicrobial treatment of pigs was more consistently associated with an increased risk of resistance than individual-animal treatment. Antimicrobial treatment in starter rations was significant in final models of resistance to ampicillin, carbadox, nitrofurantoin, sulfisoxizole, and tetracycline. Treatment in grower-finisher rations was significantly associated with resistance to ampicillin, spectinomycin, sulfisoxizole, and tetracycline. There was little evidence that in-feed antimicrobials increased the risk of resistance to gentamicin, which is a drug used only for individual-pig treatment in this study population. These results suggest that antimicrobial medication of rations of post-weaning pigs selects for and maintains antimicrobial resistance among E. coli of finisher pigs. Although resistance was common on farms that did not medicate rations of post-weaning pigs, the results indicate that antimicrobial use does increase the risk of resistance to the antimicrobials studied.

Impact of stocking density, breed, and feathering on the prevalence of abdominal skin scratches in broiler chickens.

Associations between abdominal skin scratches and stocking density, strain of birds, and degree of feathering were investigated in a clinical trial. Four hundred eighty 1-day-old male broiler chicks from two different strains (A and B) were assigned to four groups: 1) high density (0.07 m2/bird) and strain A, 2) high density and strain B, 3) normal density (0.14 m2/bird) and strain A, and 4) normal density and strain B. Birds were examined for scratches and feathering at 28, 35, and 42 days of age. Two outcomes were considered for scratches: presence (yes/no) and severity (severe [if a deep cut or at least three superficial cuts were present]/not severe). Only the examination at 35 days of age was blind. The outcome "scratches" was significantly associated with stocking density at all ages (P < or = 0.0001), strain A at 28 days of age (P = 0.0480), and poor feathering at 35 days of age (P < or = 0.0001). The outcome "severe scratches" was significantly associated with stocking density at 35 (P = 0.0003) and 42 days of age (P = 0.0021), strain A at 35 (P = 0.0089) and 42 days of age (P = 0.0306), and poor feathering at 35 days of age (P = 0.0018). Stocking density, strain of birds, and degree of feathering could be considered as potential risk factors for abdominal scratches in broiler chickens.

Farm management risk factors associated with cellulitis in broiler chickens in southern Ontario.

A mail survey of 171 farms with broiler chicken flocks processed in a single processing plant in southern Ontario was conducted during the period July-August 1993 as part of a retrospective study. The population farm prevalence of cellulitis was 31/10,000 birds. The survey provided information about the management of broiler chickens in southern Ontario and allowed investigation of the association between cellulitis and management risk factors. Univariate and multivariate analyses were performed to examine the relationship between a binary outcome (high/low prevalence) and management risk factors using logistic regression. Cellulitis was positively associated (P < or = 0.05) with male and mixed (males and females) flocks, use of straw as litter, certain feed companies, use of zinc bacitracin as a growth promoter, and other diseases diagnosed at the processing plant. Total down time was negatively associated with cellulitis.

Description of cellulitis lesions and associations between cellulitis and other categories of condemnation.

A total of 110 broiler flocks processed in a single processing plant in southern Ontario were studied for purposes of describing the cellulitis lesions and investigating possible associations between cellulitis and other categories of condemnation at the processing plant. Two hundred and ninety-five carcasses condemned for cellulitis were examined. They came from 65 of the 110 flocks. The lesions tended to be unilateral with most carcasses (87%) having one lesion. The majority of the lesions (92%) were located on the abdomen. Almost 65% of the lesions were large (> or = 8.1 cm2), and 27% were medium (2.1-8.0 cm2). On the basis of gross appearance, 69% of the lesions were classified as severe, 26% moderate, and 5% mild. Of 149 lesions examined histologically, 74% were classified as chronic, 21% ongoing, and 5% mild-acute. Condemnation data from the 110 broiler flocks were analyzed using Poisson regression. Simple relationships were examined between a count outcome (number of cellulitis-condemned carcasses per flock) and other categories of condemnation and average bird weight. Cellulitis was significantly associated with average bird weight (P = 0.0018), Escherichia coli-related conditions (SEROSITIS; P < or = 0.0001), ascites (P = 0.0004), cyanosis (P < or = 0.0001), valgus varus deformity (P < or = 0.0001), REJECT (combined carcass condemnations for bruising, mutilation, and contamination; P = 0.0003), and the interaction terms "average bird weight and ascites" (AVWT*ASCIT; P < or = 0.0001) and "average bird weight and cyanosis" (AVWT*CYAN; P < or = 0.0001). Average bird weight, SEROSITIS, ascites, cyanosis, valgus varus deformity, and AVWT*ASCIT were the only significant factors after adjusting for clustering. No association was observed between cellulitis and emaciation and dead on arrival. Variables significantly associated with cellulitis in the multivariate analysis could be considered as potential predictors. These predictors may share common risk factors predisposing broiler chickens to cellulitis.

A prospective study of cellulitis in broiler chickens in southern Ontario.

This study investigated the associations among cellulitis and hatchery, farm, and abattoir factors. Forty-four broiler flocks from 24 farms located in southern Ontario were followed from hatching to processing. Poisson regression was used to analyze the data. Cellulitis as a count outcome (CELLCOUNT) was significantly associated (P < or = 0.05) with the hatchery of origin, strain of birds, farm size, type of litter, lighting system, total down time, prevalence of abdominal scratches, Escherichia coli-related conditions (SEROSITIS), ascites, and valgus varus deformity. However, only farm size, abdominal scratches, SEROSITIS, ascites, and valgus varus deformity were significant (P < or = 0.05) after adjusting for clustering. No significant associations were found between cellulitis and source of eggs, sex, average bird weight, feed company, growth promoter, or stocking density. Factors significantly associated with cellulitis in this study could be considered as potential risk factors for cellulitis in broiler chickens in southern Ontario.

A path model of factors influencing morbidity and mortality in Ontario feedlot calves.

The principles of path analysis and causal modelling are discussed. Path analysis was applied to three data sets to assess the relationship between group characteristics (number per group and "mixing" subgroups of cattle, feeding-management of the group and processing factors (vaccination and prophylactic antimicrobials) and subsequent morbidity and mortality in feedlot cattle. The major findings agree with previously reported results but the timing and pathways of the effects are elaborated. In general, morbidity in week 1 was correlated with morbidity in week 2, which was correlated with morbidity in weeks 3-5. The same was generally true for mortality. In general, morbidity was not strongly correlated with mortality. Lots (unmixed groups) did not arrive in better condition, but experienced fewer subsequent health problems than mixed groups. (Silage-fed lots appeared to do poorly, however this was apparently due to the positive association between lots and vaccination, the latter being detrimental to mortality rates.) The more cattle per group, the greater the health problems in weeks 3-5 postarrival. Prophylactic antimicrobials in the water supply on arrival lead to increased health problems in the three to five week postarrival period. Antibiotic containing starter rations had a beneficial effect on health status in this period. This effect appeared to be partly due to delaying making silage the major ration component in silage-fed cattle receiving antimicrobial containing starter rations. Vaccination against respiratory disease in either of the first two weeks postarrival had detrimental direct and indirect effects on subsequent health status. Vaccination during weeks 3-5 postarrival was not significantly related to health status in that period.

Epidemiology of Haemophilus somnus in young rams.

The prevalence of Haemophilus somnus in the prepuce of young rams was examined. Of 473 rams entering Record of Performance (ROP) stations at 50 days of age, 43 (9.1%) were positive. Average daily gain was not affected by Haemophilus status, but was influenced by breed of ram. Suffolks were predicted to gain 0.515 kg daily compared to 0.427 kg for a group combining all other breeds. Using logistic regression to identify risk factors for individual H. somnus infection, rams in 1989 were 0.382 times as likely to be infected as rams in 1988, and Suffolks were 0.314 times as likely to be infected as the other breeds group, but these factors were not significant at the flock level. Of 80 eligible flocks of origin, 22 (27.5%) were classified as infected with H. somnus, based on rams submitted to the ROP station. Infected flocks contributed 133 rams, 43 (32.3%) of which were positive. There was no association between H. somnus status and lambing percent of the percent of abortions and stillbirths, but there was a statistically significant association with the percent of ewes which failed to lamb. In the model developed, 6% of the bred ewes in noninfected flocks failed to lamb, compared to a rate of 12% in infected flocks. These results suggest H. somnus may influence ewe fertility earlier, rather than later in gestation. Purchasing replacement animals and having cattle on the farm were risk factors for Haemophilus infection in the flock. Where replacements had been purchased within the previous year, the risk of flock infection rose 8.5 times, and on farms having cattle as well as sheep, the risk rose 13.2 times.(ABSTRACT TRUNCATED AT 250 WORDS)

An epidemiological study of selected calf pathogens on Holstein dairy farms in southwestern Ontario.

Fecal samples from calves on 78 randomly selected Holstein dairy farms in southwestern Ontario were screened for Salmonella, Campylobacter jejuni/coli, enteropathogenic Escherichia coli, rotavirus and coronavirus. Based on the observed prevalence, 22% of farms had calves infected with Salmonella, 13% with Campylobacter jejuni/coli, 41% with enteropathogenic E. coli, 19% with rotavirus and 5% with coronavirus. These estimates can be modified, using a method developed by Mullen and Prost (1983) for the World Health Organization, to account for the nature of the laboratory test used. If the test is assumed to have no false positives (that is, if an organism is detected it must be there), then the observed prevalence estimates seen on this study may greatly underestimate the true prevalence of infected premises. The use of nipple feeders for calves was associated with an increased probability of farms having calves shedding detectable fecal levels of Salmonella, E. coli, or one of the two viruses. The use of group pens was associated with an increased odds of finding C. jejuni. Calves with diarrhea on these farms tended to have increased odds of shedding rotavirus, and E. coli with the K99 antigen. However, at the farm level, none of the organisms was associated with above median levels of morbidity. Farms positive for one or other of the viruses had increased odds of experiencing calf mortality relative to virus-negative farms, and farms positive for C. jejuni/coli had decreased odds of mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

An assessment of condemnations of broiler chicken carcasses.

An epidemiological study was conducted to assess the rates of condemnation and the diagnoses made on condemned broiler chicken carcasses in a federally-inspected abattoir. The first objective was to determine the predictive value of a positive test: the proportion of birds that were truly unfit for human consumption among condemned carcasses. The second objective was to assess the degree of agreement between diagnoses made in the abattoir and diagnoses determined by a detailed gross postmortem examination on the same condemned carcasses. A two-stage convenience sampling technique was used to obtain the birds needed. Fifteen lots of birds were selected and within each of these, approximately 45 condemned carcasses were selected for a total of 680. All the diagnoses made on these birds at the abattoir were recorded and the carcasses individually identified. The sampled carcasses were transported to the Ontario Veterinary College where a panel of three federal veterinarians independently judged whether the birds were fit for human consumption. In addition, a detailed gross postmortem examination was conducted on each carcass. An overall predictive value of a positive test of approximately 70% was found. The degree of agreement among members of the panel of examiners was also tested. The overall agreement was good (Kappa = 0.62 between examiners 1 and 2 and 0.51 between examiners 1 and 3). However, carcasses condemned for specific conditions at the abattoir, namely valgus varus deformity, mutilation, cellulitis and hepatitis showed no agreement beyond chance, while other carcasses condemned for conditions such as cyanosis and bruising showed poor agreement concerning their disposition for at least one pair of examiners.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of bovine parvovirus infection in Ontario dairy cattle.

Studies were conducted to determine prevalence and dynamics of bovine parvovirus (BPV) infection. Dairy cows from 29 randomly selected herds in southwestern Ontario were tested twice, one year apart, for the presence of hemagglutination inhibition (HI) antibodies against BPV. Fifty-one percent of 1141 cows tested had BPV-HI titers > 1:32. One year later, the seroprevalence was 83% in 1131 cows from the same farms. The herd mean seroprevalence was 49% and 86% for the year-1 and year-2 samples, respectively. Evidence of BPV infection was found in 96% (27/28) of herds in year-1 and 100% of herds in year-2. A comparison of titers from 716 cows tested twice showed evidence of frequent BPV infection. Sixty-two percent of 326 animals selected in a systematic manner from 40 Guelph area dairy farms had BPV-HI titers > 1:32. The herd mean seroprevalence was 64% Two herds had no animals with titers above the critical titer (1:32) while in one-quarter of the herds all animals exceeded the critical titer.

Factors associated with productivity in Canadian sheep flocks.

A mail survey of Canadian sheep flocks registered on the Record of Performance program was conducted, and the association of management practices and diseases with productivity was studied using multiple regression techniques. The relationships between management practices and diseases of lambs which were associated with production were also investigated using discriminant analysis. Flocks in the maritimes had a lower average flock productivity than those in Ontario-Quebec and the western provinces. In purebred flocks, the average adjusted weight at 100 days of age was higher than in other types of flocks, and the prevalence of scours was lower. At the herd level, the rates of pregnancy toxemia and vaginal prolapse were associated with heavier lambs, while the average daily weight gain between 50 and 100 days of age was lower in herds affected by scours and starvation. Using pasture and bush as winter housing was also detrimental to lamb productivity. No management practices discriminated between case and control flocks for scours and starvation in lambs. It was concluded that the reasons for the geographic differences should be investigated as should the management differences between purebred and other producers. Prevention of scours and starvation in lambs should be given priority in order to increase productivity.

The effect of early calfhood health status on survivorship and age at first calving.

Survival to maturity and age at first calving were studied in heifer calves from 34 randomly selected Holstein dairy farms in southwestern Ontario. Calves were divided into cohorts on the basis of treatment for pneumonia, scours, other diseases, or no treatments, during the first 90 days of life. An effect of pneumonia and scours together, over and above the effects of each disease alone, was assessed by means on an interaction term in the statistical analyses. Heifers which had been treated for pneumonia during the first three months of life were 2.5 times more likely to die after 90 days of age than heifers which had not been treated for pneumonia, after controlling for the farm effect. Heifers with a calfhood history of being treated for scours were 2.5 times more likely to be sold for dairy purposes than other calves. Heifers which had been treated for scours were 2.9 times more likely to calve after 900 days of age than other heifers, after controlling for the farm effect.

Selenium content in the hair of newborn dairy heifer calves and its association with preweaning morbidity and mortality.

Hair samples from newborn heifer calves on Holstein dairy farms in southwestern Ontario were analyzed for selenium content by means of instrumental neutron activation analysis. The mean selenium level in the hair of calves which subsequently died at less than six weeks of age did not differ from selenium levels in the hair of calves matched by farm and birthday (overall mean 0.28 ppm). The mean selenium level in the hair of calves which were not treated for disease during the first four weeks of life was 0.42 ppm, while that from appropriately matched treated calves was 0.36 ppm; the difference between the means was significant at p = 0.054. Based on the above associations, it is suggested that higher selenium levels in newborn calves may have some protective effect against morbidity.

The prevalence of verocytotoxin-producing Escherichia coli and antimicrobial resistance patterns of nonverocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens.

The prevalence of verocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens was determined by culturing cloacal samples from 500 individual birds selected from 50 poultry farms. Resistance to antimicrobials was determined for each of the isolates. In addition, abattoir and farm-level management data were obtained to evaluate variables that may be considered risk factors for infection. The variables selected included: Percentage of birds condemned at slaughter, percentage of birds dead-on-arrival, bird weight, truck number, farm size, hatchery source, litter source and type, feed source, mortality levels, type of water drinker, water sanitization, down time, barn clean out and history of antibiotic treatment. None of the cloacal samples revealed the presence of verocytotoxin-producing E. coli, though 19/500 (3.8%) contained Salmonella organisms. Nine different Salmonella serotypes were isolated; the most common being S. hadar, S. heidelberg and S. mbandaka. Resistance to tetracycline and streptomycin was common among Salmonella (63%) and E. coli (25.2%) isolates. Resistance to two or more antimicrobials occurred in 420/500 (84%) of the E. coli isolates. No statistically significant associations between abattoir or farm-level management variables and the Salmonella-status of farms were demonstrated.

Associations between dairy production indices and lipoarabinomannan enzyme-immunoassay results for paratuberculosis.

Data from an epidemiological study in Ontario, involving 304 dairy herds, were used to identify associations between selected production indices and lipoarabinomannan antigen serological test results for paratuberculosis (LAM-ELISA). Analyses were conducted at both the herd and individual cow levels of organization. After analytically controlling for management and cow factors in the respective regression models, positive serological paratuberculosis status (as defined by the LAM-ELISA test), was associated with higher milk somatic cell counts at both the herd average (p less than 0.01), and individual cow levels of organization (p less than 0.0001). In contrast, LAM-ELISA test results were consistently not associated with calving intervals in either the herd average or individual cow level analyses. Associations between LAM-ELISA results and milk production were inconsistent. No associations were found at the herd level of organization, and LAM-ELISA results were not associated with a change in breed class average (BCA) for milk, between the previous and the most recent lactations of individual cattle. However, at the individual cow level, LAM-ELISA results were positively associated with higher milk production as measured by the current BCA (p less than 0.05), and individual cow average kg of milk produced per year of life since two years of age (p less than 0.0001).

An epidemiological study of paratuberculosis in dairy cattle in Ontario: study design and prevalence estimates.

An observational study involving 304 dairy herds and three abattoirs was conducted between 1986 and 1989 to investigate the epidemiology of paratuberculosis in dairy cattle in Ontario. The objectives of this paper were to describe the method of data collection for the study, to present descriptive production statistics and to present estimates of the prevalence of paratuberculosis among dairy cattle in Ontario. Mycobacterium paratuberculosis was isolated from the distal ileum and/or the ileocecal lymph node of 5.5% of 400 cull cows. Based on a lipoarabinomannan antigen enzyme-linked immunosorbent assay (LAM-ELISA) on sera, the predicted true prevalence of paratuberculosis among 14,923 dairy cattle from 304 herds, was 6.1%. Nineteen percent of 2,943 fecal cultures were uninterpretable because of overgrowth with contaminating bacteria or fungi. It was concluded that the true prevalence of paratuberculosis among dairy cattle in Ontario was no greater, and may be less than the true prevalence among dairy cattle from various regions of the United States. However, at a practical level, for the purposes of trade policy, the present study suggests that the functional prevalence is very similar in the two countries.

Effect of time of year, weather, and the pattern of auction market sales on fatal fibrinous pneumonia (shipping fever) in calves in a large feedlot in Alberta (1985-1988).

A total of 58,885 spring-born calves entering a large commercial feedlot in southwestern Alberta were studied to examine the associations between shipping fever mortality and the pattern of calf sales at the auction markets, time of year, and weather. The observational study followed calves purchased from 42 auction markets in the 4 western provinces between September 1 and December 31 in each of the years from 1985 to 1988. Calf sales at the auction markets consistently peaked during the last week of October and the first week of November. Calves entering the feedlot in November had a risk of fatal shipping fever 2 to 8 times greater than calves entering in September or December. The pattern was the same for all 4 years, with maximum risk occurring 2 to 4 weeks after the peak time for calf sales at the markets. A number of factors could have contributed to this pattern, including changes in transport truck availability, changes in the density of calves at the markets, changes in population dynamics at the feedlot that affected feedlot crew efficiency, and weather. The finding that the risk of fatal shipping fever appears to increase significantly as the feedlot fills with calves in the fall deserves the attention of feedlot owners, so they can design their treatment strategies appropriately, and of researchers, who may gain useful knowledge about the natural history of the disease by investigating why this change in risk occurs.

The prevalence of leptospirosis and its association with multifocal interstitial nephritis in swine at slaughter.

An abattoir survey was undertaken to determine the prevalence of leptospirosis and its association with lesions of multifocal interstitial nephritis (so-called "white spotted kidneys") in swine at slaughter. Both cross-sectional and case-control study designs were used. Of 197 kidneys from hogs randomly selected at slaughter, 11 (5.6%) had generalized grey-white foci typical of multifocal interstitial nephritis (MFIN). Antibody titers greater than or equal to 1:80 against Leptospira pomona were detected in nine (4.6%) hogs and against L. bratislava in 63 (32%) of these hogs. Leptospira pomona (kennewicki) was detected by immunofluorescence in 5/197 (2.5%) of randomly selected hogs. Leptospires identified as genotype kennewicki were isolated from six (9.8%) of 61 kidneys cultured. Leptospira bratislava was not detected by immunofluorescence or culture. There was a highly significant (p = 0.00) and strong association (odds ratio (OR) = 195) between high L. pomona titer (greater than or equal to 1:80) and the presence of leptospires in the kidneys, as detected by culture. There was also a significant (p = 0.046) and strong (OR = 8.10) association between multifocal interstitial nephritis and the presence of renal leptospires as detected by culture. The association between leptospiral titer and MFIN lesions in the prevalence survey group of animals was statistically significant (p = 0.031), but this association was not significant in the case-control study group (p = 0.071) The failure to identify L. bratislava despite serological evidence of infection suggests that some of these seropositive animals may have been transiently infected at an early age, that serological findings were falsely positive, or that immunofluorescence and isolation attempts failed to detect L. bratislava if they were indeed present in the kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)