Right-Sided Congestive Heart Failure in North American Feedlot Cattle.

BACKGROUND: Anecdotal reports suggest the incidence of right-sided congestive heart failure (RHF) in feedlot cattle is increasing; however, the rate of occurrence and risk factors are largely unknown. OBJECTIVE: The purposes of this study were to evaluate the risk of RHF over time and among feedlots, to characterize some of the risk factors for RHF, and to investigate how risk factors may affect the timing of RHF occurrence. ANIMALS: The population at risk consisted of 1.56 million cattle that were placed in 10 Canadian feedlots during the years 2000, 2004, 2008, and 2012, and 5 US feedlots during the year 2012. METHODS: A retrospective observational study was conducted. Variables, including year of feedlot entry, were evaluated for association with RHF using zero-inflated negative binomial and logistic regression models. Factors affecting time to RHF were evaluated using Cox proportional hazard regression analyzes. Death from digestive disorders (DD) served as a control. RESULTS: The risk of RHF in Canadian feedlots doubled from the year 2000 to the year 2012 (P = .003). For every 10,000 cattle entering US feedlots in 2012, 11 cattle died from RHF and 45 cattle died from DD. The median time to RHF was 19 weeks. Cattle treated for bovine respiratory disease were 3 times more likely to die from RHF, and they died earlier in the feeding period. CONCLUSIONS: A doubling of the incidence of RHF over a short time period is concerning, particularly for US feedlots situated at moderate altitudes in the High Plains.

Modelling considerations in the analysis of associations between antimicrobial use and resistance in beef feedlot cattle.

A number of sophisticated modelling approaches are available to investigate potential associations between antimicrobial use (AMU) and resistance (AMR) in animal health settings. All have their advantages and disadvantages, making it unclear as to which model is most appropriate. We used advanced regression modelling to investigate AMU-AMR associations in faecal non-type-specific Escherichia coli (NTSEC) isolates recovered from 275 pens of feedlot cattle. Ten modelling strategies were employed to investigate AMU associations with resistance to chloramphenicol, ampicillin, sulfisoxazole, tetracycline and streptomycin. Goodness-of-fit statistics did not show a consistent advantage for any one model type. Three AMU-AMR associations were significant in all models. Recent parenteral tetracycline use increased the odds of finding tetracycline-resistant NTSEC [odds ratios (OR) 1·1-3·2]; recent parenteral sulfonamide use increased the odds of finding sulfisoxazole-resistant NTSEC (OR 1·4-2·5); and recent parenteral macrolide use decreased the odds of recovering ampicillin-resistant NTSEC (OR 0·03-0·2). Other results varied markedly depending on the modelling approach, emphasizing the importance of exploring and reporting multiple modelling methods based on a balanced consideration of important factors such as study design, mathematical appropriateness, research question and target audience.

Evaluation of a Computer-aided Lung Auscultation System for Diagnosis of Bovine Respiratory Disease in Feedlot Cattle.

BACKGROUND: A computer-aided lung auscultation (CALA) system was recently developed to diagnose bovine respiratory disease (BRD) in feedlot cattle. OBJECTIVES: To determine, in a case-control study, the level of agreement between CALA and veterinary lung auscultation and to evaluate the sensitivity (Se) and specificity (Sp) of CALA to diagnose BRD in feedlot cattle. ANIMALS: A total of 561 Angus cross-steers (initial body weight = 246 ± 45 kg) were observed during the first 50 day after entry to a feedlot. METHODS: Case-control study. Steers with visual signs of BRD identified by pen checkers were examined by a veterinarian, including lung auscultation using a conventional stethoscope and CALA that produced a lung score from 1 (normal) to 5 (chronic). For each steer examined for BRD, 1 apparently healthy steer was selected as control and similarly examined. Agreement between CALA and veterinary auscultation was assessed by kappa statistic. CALA's Se and Sp were estimated using Bayesian latent class analysis. RESULTS: Of the 561 steers, 35 were identified with visual signs of BRD and 35 were selected as controls. Comparison of veterinary auscultation and CALA (using a CALA score ≥2 as a cut off) revealed a substantial agreement (kappa = 0.77). Using latent class analysis, CALA had a relatively high Se (92.9%; 95% credible interval [CI] = 0.71-0.99) and Sp (89.6%; 95% CI = 0.64-0.99) for diagnosing BRD compared with pen checking. CONCLUSIONS: CALA had good diagnostic accuracy (albeit with a relatively wide CI). Its use in feedlots could increase the proportion of cattle accurately diagnosed with BRD.

Mannheimia haemolytica in feedlot cattle: prevalence of recovery and associations with antimicrobial use, resistance, and health outcomes.

BACKGROUND: Mannheimia haemolytica is an important etiological agent in bovine respiratory disease. OBJECTIVES: Explore risk factors for recovery of susceptible and resistant M. haemolytica in feedlot cattle and explore associations with health outcomes. ANIMALS: Cattle (n = 5,498) from 4 feedlots sampled at arrival and later in feeding period. METHODS: Susceptibility of M. haemolytica isolates tested for 21 antimicrobials. Records of antimicrobial use and health events analyzed using multivariable regression. RESULTS: M. haemolytica recovered from 29% of cattle (1,596/5,498), 13.1% at arrival (95% CI, 12.3-14.1%), and 19.8% at second sampling (95% CI, 18.7-20.9%). Nearly half of study cattle received antimicrobial drugs (AMDs) parenterally, mostly as metaphylactic treatment at arrival. Individual parenteral AMD exposures were associated with decreased recovery of M. haemolytica (OR, 0.2; 95% CI, 0.02-1.2), whereas exposure in penmates was associated with increased recovery (OR, 1.5; 95% CI, 1.05-2.2). Most isolates were pan-susceptible (87.8%; 95% CI, 87.0-89.4%). AMD exposures were not associated with resistance to any single drug. Multiply-resistant isolates were rare (5.9%; 95% CI, 5.1-6.9%), but AMD exposures in pen mates were associated with increased odds of recovering multiply-resistant M. haemolytica (OR, 23.9; 95% CI, 8.4-68.3). Cattle positive for M. haemolytica on arrival were more likely to become ill within 10 days (OR, 1.7; 95% CI, 1.1-2.4). CONCLUSIONS AND CLINICAL IMPORTANCE: Resistance generally was rare in M. haemolytica. Antimicrobial drug exposures in penmates increased the risk of isolating susceptible and multiply-resistant M. haemolytica, a finding that could be explained by contagious spread.

Latent class comparison of test accuracy when evaluating antimicrobial susceptibility using disk diffusion and broth microdilution to test Escherichia coli and Mannheimia haemolytica isolates recovered from beef feedlot cattle.

The study objective was to use Bayesian latent class analysis to evaluate the accuracy of susceptibility test results obtained from disk diffusion and broth microdilution using bacteria recovered from beef feedlot cattle. Isolates of Escherichia coli and Mannheimia haemolytica were tested for susceptibility to ampicillin, ceftiofur, streptomycin, sulfisoxazole, tetracycline, and trimethoprim-sulfamethoxazole. Results showed that neither testing method was always or even generally superior to the other. Specificity (ability to correctly classify non-resistant isolates) was extremely high for both testing methods, but sensitivity (ability to correctly classify resistant isolates) was lower, variable in the drugs evaluated, and variable between the two bacterial species. Predictive values estimated using Bayesian Markov chain Monte Carlo models showed that the ability to predict true susceptibility status was equivalent for test results obtained with the two testing methods for some drugs, but for others there were marked differences between results obtained from disk diffusion and broth microdilution tests.

Effects of wheat or corn distillers dried grains with solubles on feedlot performance, fecal shedding, and persistence of Escherichia coli O157:H7.

Distillers dried grains with solubles (DDGS) are a coproduct of the ethanol industry and are often used as a replacement for grain in livestock production. Feeding corn DDGS to cattle has been linked to increased fecal shedding of Escherichia coli O157:H7, although in Canada, DDGS are often produced from wheat. This study assessed the effects of including 22.5% wheat or corn DDGS (DM basis) into barley-based diets on performance, carcass characteristics, animal health, and fecal E. coli O157:H7 shedding of commercial feedlot cattle. Cattle (n = 6,817) were randomly allocated to 10 pens per treatment group: WDDGS (diets including 22.5% wheat DDGS), CDDGS (diets including 22.5% corn DDGS), or CTRL (barley substituted for DDGS). Freshly voided fecal pats (n = 588) were collected and pooled monthly for fecal pH measurement and screened for naturally occurring E. coli O157:H7 by immunomagnetic separation (IMS) and direct plating (DP). Hide swabs (n = 367) were collected from randomly selected cattle from each pen before slaughter. Pen-floor fecal samples (n = 18) were collected from treatment groups at entry to the feedlot (<14 d on the finishing diet) and after adapting to the finishing diet for ≥ 14 d, inoculated (10(9) cfu of a 5 strain naldixic acid-resistant E. coli O157:H7 mixture), incubated (20°C) and evaluated weekly (IMS and DP) to assess fecal E. coli O157:H7 persistence. The WDDGS group had 3.0% poorer ADG (P = 0.007), 5.3% poorer G:F (P < 0.001), and a decreased proportion of Canada Quality Grade AAA carcasses (P = 0.022) compared with CTRL cattle. The CDDGS group had a similar ADG (P = 0.06), a decreased proportion of Canada Yield Grade (YG) 1 (P < 0.001), and greater proportions of Canada YG 2 (P = 0.003) and YG 3 (P < 0.001) carcasses compared with the CTRL group. There were no differences among groups in any of the animal health parameters assessed. Inclusion of DDGS in cattle finishing diets had no effect on fecal shedding (P = 0.650) or persistence (P = 0.953) of E. coli O157:H7. However, feces from cattle on starter diets <14 d had longer persistence of E. coli O157:H7 (week) than cattle on finishing diets ≥ 14 d (P < 0.003). Inclusion of DDGS in feedlot diets depends on commodity pricing relative to that of barley and for WDDGS must also include the risk of feedlot performance and carcass grading disadvantages. Feeding cattle barley based-diets with 22.5% corn or wheat DDGS did not affect fecal shedding of E. coli O157:H7.

The prevalence of methicillin-resistant Staphylococcus aureus colonization in feedlot cattle.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen and recent evidence has implicated food animals in the epidemiology of human infections in some regions. While the role of food in MRSA transmission and human health relevance are unclear, MRSA can be found in retail meat products internationally, including beef, yet there has been minimal investigation of MRSA in beef cattle. This study involved screening feedlot cattle for nasal and gastrointestinal colonization with MRSA shortly before the time of slaughter. Methicillin-resistant S. aureus was not isolated from any of 491 nasal swabs and 488 faecal samples. This finding is in contrast to studies that have isolated MRSA from retail beef in Canada, performed in the same laboratory using comparable culture techniques. The reason for this discrepancy is unclear but it demonstrates that further study of MRSA in livestock as well as slaughter, processing and retail environments is needed to elucidate the epidemiology of MRSA contamination of meat.

Genetic characterization and antimicrobial susceptibility of Mannheimia haemolytica isolated from the nasopharynx of feedlot cattle.

A surveillance study was undertaken to examine the population dynamics and antimicrobial resistance of Mannheimia haemolytica isolated from feedlot cattle. A total of 416 isolates were collected from the nasopharynx either upon entry or exit from two feedlots in southern Alberta, Canada. Isolates were serotyped, characterized by pulsed-field gel electrophoresis and tested for susceptibility to ten antimicrobial agents via disk diffusion. Resistant isolates were screened by PCR for select antimicrobial-resistance gene determinants. Isolates were highly diverse, with 335 unique pulsed-field profiles identified among 147 strongly related clusters (similarity ≥ 85%). Clonal spread of isolates throughout the feedlots was limited and no clear association was found between genetic relatedness of M. haemolytica and sampling event (entry or exit). Pulsed-field profiles sharing a common serotype and resistance phenotype tended to cluster together. The majority of isolates were identified as serotype 2 (74.5%) although both serotype 1 (11.9%) and 6 (12.7%) were detected. Only 9.54% of isolates exhibited antimicrobial resistance. Resistance to oxytetracycline was most prevalent (n=16), followed by ampicillin (n=10), and amoxicillin/clavulanic acid (n=7). Multi-drug resistance was observed in five isolates. The tetH gene was detected in all but two oxytetracycline resistant isolates. Other detectable resistance determinates included ermX and bla(ROB-1). In the two feedlots examined, M. haemolytica exhibited considerable genetic diversity and limited resistance to common veterinary antibiotics. Garnering further information on the linkage between genotype and phenotype should contribute toward a better understanding of the pathogenesis and dissemination of M. haemolytica in feedlots.

Comparison of repetitive PCR and pulsed-field gel electrophoresis for the genotyping of Mannheimia haemolytica.

Mannheimia haemolytica is an opportunistic pathogen that can cause fibrinonecrotic pneumonia in cattle and is the main bacterial agent implicated in bovine respiratory disease-complex (BRD). Despite its economic importance to the cattle industry, few studies have characterized the genetic nature of M. haemolytica and none have genotyped isolates from feedlots. Identifying and monitoring genetic variants of M. haemolytica is important to understanding the etiology of BRD in cattle. We investigated the capacity of three genotyping techniques (BOX-PCR, (GTG)(5)-PCR and PFGE analysis of SalI-restricted DNA) to discriminate among 24 reference strains from the family Pasteurellaceae and 40 M. haemolytica isolates collected from feedlot cattle. From cluster analysis of the M. haemolytica isolates, PFGE was revealed as most discriminating, followed by BOX-PCR and then (GTG)(5)-PCR (Simpson's diversity index >0.98, 0.82, and 0.72, respectively). Of these methods, PFGE also had the greatest mean repeatability (0.96). The PFGE and BOX-PCR assays grouped all M. haemolytica in a single cluster but only BOX-PCR and (GTG)(5)-PCR grouped the Mannheimia glucosida and Mannheimia ruminalis strains together. Refinement of genotyping procedures for M. haemolytica could offer new insight into the etiology of this pathogen in BRD.

Recovery of antimicrobial-resistant Escherichia coli after storage of bovine feces in Cary-Blair medium.

The effect of storing bovine feces in Cary-Blair medium on the recovery of antimicrobial-resistant Escherichia coli was investigated. Feces from cattle at a research feedlot (n = 50) and at a commercial feedlot (n = 46) were processed immediately or after storage in Cary-Blair medium for 8 days at 5 degrees C. Total, ampicillin-resistant, and tetracycline-resistant E. coli were isolated. The number of total E. coli decreased slightly after storage (0.19 log units; p < 0.001), but storage of feces in Cary-Blair medium did not affect recovery of ampicillin- or tetracycline-resistant E. coli.

Trans fatty acids and cardiovascular health: translation of the evidence base.

BACKGROUND AND AIM: The recent interest in the development of evidence-based nutrition recommendations has resulted in the development of frameworks which enable a more structured evaluation of the link between diet and chronic disease. This paper examines the application of the frameworks produced by the Scottish Intercollegiate Guidelines Network (SIGN) and the World Cancer Research Fund (WCRF), by using as a case study the association between trans unsaturated fatty acids (TFAs) and coronary heart disease. TFAs arise during industrial hydrogenation of vegetable or fish fats and oils and the natural digestion process in ruminant animals. DATA SYNTHESIS: Numerous studies have examined the effects of TFA intake on serum lipids and lipoproteins and the association between TFA consumption and cardiovascular disease. Metabolic studies and meta-analyses show a clear and consistent association between increasing TFA intakes and an adverse lipid profile. Evidence from case-control and prospective cohort studies examining the association between TFA intakes and coronary heart disease is more heterogeneous and there are limitations in several of the studies. CONCLUSION: While the evidence is sufficient to suggest a probable positive association between TFAs and coronary heart disease, and thus to justify a firm recommendation for a reduction in dietary TFA intake, the evaluation of the data underlines the difficulties in extrapolating the principles of evidence-based medicine to evidence-based nutrition. Furthermore, there is a paucity of research into the effects of animal-derived TFAs in amounts typically consumed in a western diet and their association with adverse lipid profiles or cardiovascular outcomes.

Benzo(a)pyrene-induced anemia and splenomegaly in NZB/WF1 mice.

Benzo(a)pyrene (BaP), a polycyclic aromatic hydrocarbon, is a known immunomodulator. At high doses, BaP is immunosuppressive but at low doses it can enhance the immune response. Studies were conducted to determine if BaP would exacerbate the development of autoimmune disease in genetically prone NZB/WF1 mice. Five week old female NZBW/F1 mice were exposed dermally to 5, 20 and 40 mg/kg BaP for 30 days. Vehicle mice were exposed to an acetone:olive oil mixture for 30 days. BaP did not increase total IgG, anti-DNP-HSA or anti-dsDNA antibody levels. However, hematological evaluation revealed a decrease in erythrocyte number, hemoglobin and hematocrit and an increase in mean corpuscular volume and red cell distribution width in the 20 and 40 mg/kg dose groups. Liver and spleen weights were increased in the high dose groups; however, an increase in spleen cell number was not observed. Histopathological evaluation revealed splenic red pulp expansion in a mouse treated with 40 mg/kg BaP. An increase in splenic CFU-e production was observed in mice treated with 20 and 40 mg/kg BaP. A decrease in splenic total B cells, total T cells, CD4(+) and CD8(+) T cells was observed in mice treated with 20 and 40 mg/kg BaP. An increase in splenic null cells (non-T, non-B cells) was also observed in the high dose groups, consistent with extramedullary hematopoiesis. Coombs' tests, flow cytometry and an immune-mediated hemolysis assay indicated that the anemia was not autoimmune-mediated. Although no change was observed in the percentage of reticulocytes in these animals, further bone marrow analysis is needed to determine if the anemia is due to bone marrow suppression, possibly caused by BaP exposure, or chemical-induced hemolysis, perhaps contributed to by erythrocyte fragility inherited from a parent strain, NZB, which spontaneously develops autoimmune hemolytic anemia and subsequent splenomegaly.

Dietary methoxychlor exposure modulates splenic natural killer cell activity, antibody-forming cell response and phenotypic marker expression in F0 and F1 generations of Sprague Dawley rats.

Methoxychlor, a chlorinated hydrocarbon pesticide, is a persistent environmental contaminant that has been identified in human reproductive tissues. Methoxychlor has been shown to be estrogenic in both in vivo and in vitro studies. As an endocrine disrupter, it may have the potential to adversely affect endocrine, reproductive, and immune systems in animals. The present study evaluated methoxychlor's immunotoxic potential in F0 (dams) and F1 generations of Sprague Dawley rats exposed to an isoflavone-free diet containing methoxychlor at concentrations of 10, 100, and 1000 ppm. In dams, exposure to methoxychlor from gestation day 7 to postpartum day 51 (65 days total exposure) produced a significant increase in the NK activity (1000 ppm) and the percentages of T cells (1000 ppm), helper T cells (1000 ppm) and macrophages (100 and 1000 ppm). In contrast, a decrease in the numbers of splenocytes and B cells was observed at the 100 and 1000 ppm concentrations. In F1 males, exposure to methoxychlor gestationally, lactationally and through feed from postnatal day 22-64 (78 days total exposure) produced an increase in the spleen IgM antibody-forming cell response to sheep red blood cells (100 and 1000 ppm) and the activity of NK cells (1000 ppm). However, there was a decrease in the terminal body weight (1000 ppm), spleen weight (1000 ppm), thymus weight (100 and 1000 ppm), and the numbers of splenocytes (1000 ppm), B cells (100 and 1000 ppm), cytotoxic T cells (1000 ppm) and NK cells (100 and 1000 ppm). In F1 females, exposure to methoxychlor produced a decrease in the terminal body weight (1000 ppm) and the percentages of cytotoxic T cells (10, 100 and 1000 ppm). These results demonstrate that developmental and adult dietary exposure to methoxychlor modulates immune responses in Sprague Dawley rats. Immunological changes were more pronounced in the F1 generation male rats that were exposed during gestation and postpartum, when compared to the F0 and F1 generation females. Increases in antibody-forming cell response and NK cell activity, and altered spleen cell subpopulation numbers were observed in the F1 generation male rats, without similar changes to the F1 generation females.

Dissociation of hypertension and fixed interval responding in two separate strains of genetically hypertensive rat.

The behaviour of spontaneously hypertensive rats (SHR) may model attention-deficit hyperactivity disorder. For example, SHR are hyperactive in an open field and show high terminal rates of responding on certain fixed-interval schedules. Open field behaviour has been dissociated from the accompanying spontaneous hypertension but fixed interval responding has not. We compared the fixed interval responding of two unrelated strains of genetically hypertensive rat, the SHR (n = 6) and the New Zealand genetically hypertensive rat (GH, n = 5), with their normotensive control strains, the Wistar Kyoto (WKY, n = 6) and Wistar (n = 5), respectively. Both hypertensive rat strains showed increased terminal lever-pressing rates on a multiple fixed-interval schedule (FI-EXT) compared to controls. In order to investigate the association of hypertension and the behavioural characteristics in question, an F-2 hybrid strain was obtained by cross-breeding GH and Wistar rats. When these F-2 hybrids (n = 33) were tested on the FI-EXT schedule, terminal lever-pressing rate was not correlated with blood pressure. The independent segregation of these phenotypical characteristics in the hybrids suggests independent genetic control. By contrast, other behavioural characteristics, including high lever-pressing rates during the extinction component and a tendency to emit responses in bursts, did cosegregate with terminal lever-pressing rates. Taken together, these findings suggest that the genetic loci for high blood pressure and responding on the FI-EXT schedule in these two unrelated rat strains are close but distinct.

Returning the chronically unemployed with low back pain to employment.

Much of the research into return to work following rehabilitation for low back pain in the literature reflects work done in those employed. Unemployment is a consequence of chronic low back pain which has considerable health and economic consequences for the individual and society. This paper describes an occupationally orientated rehabilitation programme for long-term unemployed people (mean duration of unemployment 38.9 months). The aim of the project was to identify factors which predict return to work and progress towards employment. Eight six subjects underwent a pain management rehabilitation programme incorporating vocational focussing and advice, subjects were followed up at 6 months to determine work status. At follow-up 38.4% of subjects were employed and another 23% were in voluntary work, or education/training. There were no significant differences on presenting characteristics between those who returned to work and those who did not. Subjects were divided into those who made positive progress (work, education/training or voluntary work) and those who did not (remained unemployed, dropped out of the programme or lost to follow up). Those who failed to make positive progress were characterised by longer duration of unemployment and higher scores on somatic anxiety and depression. A predictive model was able to identify 80% of those who failed to make progress but prediction of those achieving a positive outcome was poor (44% correct prediction). The factors predicting return to work in unemployed people with low back pain differs from the employed, the need for employment skills training and a vocational focus to rehabilitation are highlighted.

Prevalence of sucking and chewing lice on cattle entering feedlots in southern Alberta.

Beef calves from 2 sources entering southern Alberta feedlots in the winters of 1997-98 and 1998-99, were surveyed for the presence of lice. A random sample of multiple source (MS), that is, auction market-derived, calves entering commercial feedlots and single source (SS) calves entering a backgrounding feedlot were examined for the presence of lice at entry to the feedlot. A standardized examination, which involved hair-part examination of 8 louse predilection sites, was conducted on each selected calf to determine prevalence and intensity of infestation. The long-nosed sucking louse, Linognathus vituli, was the most commonly encountered species. This species infested from 57.8% to 95.6% of the calves selected from both MS and SS calves during both winters. Louse index values, indicating intensity of infestation, for L. vituli ranged from 1 to 243 lice per animal. The chewing louse, Bovicola bovis, was present on MS and SS calves only in the winter of 1998-99. The louse index values for B. bovis ranged from 1 to 230 lice per animal. Mixed infestations of the L. vituli and B. bovis were common. The little blue cattle louse, Solenopotes capillatus, was present only on the SS calves in the winter of 1997-98. The short-nosed sucking louse, Haematopinus eurysternus, was present at very low intensities, 1-2 lice per animal, on 2.6% to 4.4% of the MS calves during both winters. Comparison of results from the current study with published literature suggests that efforts to determine the economic impact of louse infestations are confounded by the lack of a uniform method to assess louse population levels.

Relative cost-effectiveness of treatment of feedlot calves with ivermectin versus treatment with a combination of fenbendazole, permethrin, and fenthion.

OBJECTIVE: To compare growth performance, animal health characteristics, and carcass characteristics of feedlot calves treated with ivermectin topically with that of feedlot calves treated with a combination of fenbendazole orally and permethrin and fenthion topically. DESIGN: Clinical trial. ANIMALS: 14,184 British crossbred steer calves (mean weight, 286 kg [630 lb]) in 30 pens at a commercial feedlot in Nebraska. PROCEDURE: On arrival at the feedlot, calves were randomly assigned to be treated with ivermectin topically or with a combination of fenbendazole orally and permethrin and fenthion topically (control). At the time of assignment to treatment groups, fecal samples were collected from 5% of the calves. Growth performance, carcass characteristics, and health information were recorded. RESULTS: Geometric mean fecal egg counts at the time of arrival at the feedlot were not significantly different between groups. Final weight, weight gain, average daily gain, and the dry matter intake-to-gain ratio were significantly improved for calves in the ivermectin group. The percentage of carcasses classified as quality grade choice was higher for the ivermectin group than the control group; however, the percentage of carcasses classified as yield grade 1 and the dressing percentage were higher for the control group than for the ivermectin group. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that topical administration of ivermectin to feedlot calves is relatively more cost-effective than administration of a combination of fenbendazole orally and permethrin and fenthion topically.

Comparative cost-effectiveness of ivermectin versus topical organophosphate in feedlot yearlings.

A replicated-pen field trial was performed under commercial feedlot conditions in western Canada to determine the cost-effectiveness of administering ivermectin to yearling beef cattle upon entry to the feedlot after the grazing season, and to establish the level of trichostrongylid gastrointestinal parasite infection in this population, as estimated by fecal egg counts. Six thousand eight hundred and eighty-three, mixed breed, yearling steers were randomly allocated upon arrival at the feedlot to one of 2 experimental groups as follows: Ivermectin, which received topical ivermectin (0.5%) at the rate of 1.0 mL/10 kg body weight; or Fenthion, which received topical fenthion (20%) at the rate of 12 mL/295 kg body weight. There were 15 pens in each experimental group. Final weight, weight gain, average daily gain, and dry matter intake to gain ratio were significantly (P < 0.05) improved in the Ivermectin group as compared with the Fenthion group. There were no significant (P > or = 0.05) differences in initial weight, days on feed, or daily dry matter intake between the experimental groups. The geometric mean fecal egg counts at the time of allocation were 14.7 eggs/5 g and 16.6 eggs/5 g for the Ivermectin and Fenthion groups, respectively (P > or = 0.05). There were no significant (P > or = 0.05) differences in morbidity or mortality between the experimental groups. In the economic analysis, the significant improvements in feedlot performance in the Ivermectin group resulted in a net economic advantage of $4.20 CDN per animal.