Objective—To evaluate the effects of using retentionpond
water for dust abatement on performance of
feedlot steers and carriage of Escherichia coli O157
and Salmonella spp.
Design—Matched cohort studies.
Animals—2 groups of feedlot steers comprising
3,510 (pathogen carriage) and 3,737 (performance)
animals housed in a large commercial feedlot in the
Procedure—Steers were systematically allocated to
treatment pens approximately 60 days after arrival
(pathogen carriage) or at arrival (performance). For
evaluation of pathogen carriage, feces and hide swab
specimens were collected from 25 animals in each
pen within 10 days of slaughter. Samples were submitted
for bacterial culture for E coli O157 and were
tested with a polymerase chain reaction-based assay
for Salmonella spp. For evaluation of performance,
pen weights of animals were obtained at arrival and
slaughter and feed delivered to each pen was recorded.
The exposure of interest for both studies was
application of retention-pond water through fixed
Results—Carriage of E coli O157 and Salmonella spp
and animal performance were not adversely affected
by exposure to retention-pond water. Prevalences of
E coli O157 in feces, on hides, and either in feces or
on hides for those exposed to retention-pond water
were 8.3%, 8.9%, and 15.4%, respectively; prevalences
for those unexposed to retention-pond water
were 11.4%, 15.4%, and 22.6%, respectively.
Conclusions and Clinical Relevance—Results suggest
that use of retention-pond water for dust abatement in
feedlot pens does not adversely affect pathogen carriage
or animal performance. (J Am Vet Med Assoc 2005;226:
Objective—To evaluate site-to-site variation within
fecal pats from cattle with regard to detection of
Escherichia coli O157 and determine the effect on the
accuracy of prevalence estimates of assay of multiple
samples collected from the same fecal pat.
Sample Population—120 freshly voided fecal pats
collected from 2 beef feedlots.
Procedures—5 samples were systematically collected
from each fecal pat and analyzed for E coli O157 via
selective preenrichment techniques, immunomagnetic
separation, and biochemical tests. Presumptive isolates
were definitively identified via agglutination
assays and polymerase chain reaction techniques. Best
estimators of prevalence were calculated from the distribution
of E coli O157–positive samples per pat.
Results—Of the 120 fecal pats, 96, 13, 4, 2, 3, and 2
fecal pats had 0, 1, 2, 3, 4, and 5 E coli O157–positive
samples, respectively. The greatest estimate of E coli
O157 prevalence (20%) was achieved when all 5 samples
were assessed; this estimate represented a 2.4-
fold increase in prevalence, compared with that provided
via analysis of 1 sample/pat (8.2%). Compared
with assessment of 5 sites/pat, the relative sensitivity
of detecting an E coli O157–positive fecal pat via
analysis of 1 site/pat was 40.1%.
Conclusions and Clinical Relevance—Results suggest
that estimates of E coli O157 prevalence derived
from sampling of 1 location/pat are likely underestimates
of the true prevalence of this pathogen in fecal
pats (and by extension, cattle). Additional research is
warranted to confirm these results in situations of
high and low prevalence and across different feedlots.
(Am J Vet Res 2005;66:2023–2027)
Objective—To evaluate trends in feedlot cattle mortality
ratios over time, by primary body system affected,
and by type of animal.
Design—Retrospective cohort study.
Animals—Approximately 21.8 million cattle entering
121 feedlots in the United States during 1994 through
Procedures—Yearly and monthly mortality ratios
were calculated. Numbers of deaths were modeled
by use of Poisson regression methods for repeated
measures. Relative risks of death over time and by
animal type were estimated.
Results—Averaged over time, the mortality ratio
was 12.6 deaths/1,000 cattle entering the feedlots.
The mortality ratio increased from 10.3
deaths/1,000 cattle in 1994 to 14.2 deaths/1,000
cattle in 1999, but this difference was not statistically
significant (P = 0.09). Cattle entering the feedlots
during 1999 had a significantly increased risk
(relative risk, 1.46) of dying of respiratory tract disorders,
compared with cattle that entered during
1994, and respiratory tract disorders accounted for
57.1% of all deaths. Dairy cattle had a significantly
increased risk of death of any cause, compared with
beef steers. Beef heifers had a significantly
increased risk of dying of respiratory tract disorders,
compared with beef steers.
Conclusions and Clinical Relevance—Results suggested
that although overall yearly mortality ratio did
not significantly increase during the study, the risk of
death attributable to respiratory tract disorders was
increased during most years, compared with risk of
death during 1994. The increased rates of fatal respiratory
tract disorders may also reflect increased rates
of non-fatal respiratory tract disorders, which would
be expected to have adverse production effects in
surviving animals. (J Am Vet Med Assoc 2001;219:1122–1127)
Objective—To estimate prevalence of cattle persistently
infected (PI) with bovine viral diarrhea virus
(BVDV) at arrival at a feedlot, prevalence of chronically
ill and dead PI cattle, and the magnitude of excess
disease attributable to a PI animal.
Design—Cross-sectional and cohort studies.
Animals—2,000 cattle at the time they arrived at a
feedlot, 1,383 chronically ill cattle from 7 feedlots, and
1,585 dead cattle from a single feedlot.
Procedure—Skin biopsy specimens were collected
and evaluated via immunohistochemistry. Cattle were
characterized as either PI or not PI with BVDV on the
basis of characteristic immunostaining. Follow-up was
obtained for the 2,000 cattle from which samples
were collected at arrival, and health outcomes were
determined for cattle exposed and not exposed to a
Results—Prevalence of PI cattle was 0.3% at arrival,
2.6% in chronically ill cattle, and 2.5% in dead cattle.
Risk of initial treatment for respiratory tract disease
was 43% greater in cattle exposed to a PI animal,
compared with those not exposed to a PI animal.
Overall, 15.9% of initial respiratory tract disease
events were attributable to exposure to a PI animal.
Conclusions and Clinical Relevance—Relatively few
PI cattle arrive at feedlots. However, those cattle are
more likely to require treatment for respiratory tract
disease and either become chronically ill or die than
cattle that are not PI. In addition, they are associated
with an increase in the incidence of respiratory tract
disease of in-contact cattle. (J Am Vet Med Assoc
Ensuring appropriate animal welfare is a high priority for the beef industry, and poorly defined abnormalities in the mobility of cattle at abattoirs have gained considerable attention recently. During the summer of 2013, abattoirs throughout the United States reported concerns about nonambulatory or slow and difficult to move cattle and cattle that sloughed hoof walls. This report describes various cattle that developed these mobility problems soon after arrival at an abattoir. Affected cattle had various clinical signs including tachypnea with an abdominal component to breathing, lameness, and reluctance to move. Some cattle sloughed 1 or more hoof walls while in lairage pens and were euthanized. Other cattle recovered after being rested overnight. Affected cattle had serum lactate concentration and creatine kinase activity increased from reference ranges. Histologic findings included diffuse necrosis of the epidermal laminae with degenerate collagen and perivascular infiltration of neutrophils in the underlying deep dermis, and were similar for digits that had and had not sloughed the hoof wall. With the exception of the sloughed hoof walls, the clinical signs and serum biochemical abnormalities observed in affected cattle were similar to those observed in pigs with fatigued pig syndrome, and we propose that fatigued cattle syndrome be used to describe such cattle. Although anecdotal evidence generated concern that cattle fed the β-adrenergic receptor agonist zilpaterol hydrochloride were at greater risk of developing mobility problems, compared with cattle not fed zilpaterol, this condition is likely multifactorial. Strategies to prevent this condition are needed to protect the welfare of cattle.
Objective—To determine effects of vaccination with siderophore receptor and porin (SRP) proteins derived from Salmonella enterica serotype Newport on milk production, somatic cell count, and shedding of Salmonella organisms in female dairy cattle.
Animals—180 female Holsteins.
Procedures—Cattle were randomly assigned to receive Salmonella Newport SRP vaccine or control solution. Vaccine or control solution was injected 45 to 60 days before parturition, and cattle received a second dose 14 to 21 days before parturition. Milk production was monitored for the first 90 days of lactation. Feces for isolation of Salmonella and blood samples for detection of antibodies against Salmonella Newport were collected at day of first injection and at days 7 to 14 and 28 to 35 of lactation.
Results—Cattle inoculated with Salmonella Newport vaccine produced significantly more milk (1.14 kg/d), compared with cattle injected with the control solution. Cattle administered the vaccine had significantly higher concentrations of circulating antibody against Salmonella Newport SRP proteins at 7 to 14 days and 28 to 35 days of lactation. Salmonella Newport was not recovered; however, Salmonella enterica serotype Agona was recovered from 31 (20.3%) cattle, but likelihood of recovery did not differ significantly between vaccinates and control cattle.
Conclusions and Clinical Relevance—Administration of a vaccine against Salmonella Newport SRP proteins to healthy dairy cattle prior to parturition increased milk production, even in cattle without detectable shedding of Salmonella Newport or clinical signs of salmonellosis. Additional research is needed to clarify the mechanisms by which productivity was improved.
Objective—To determine effects of administration of ceftiofur crystalline-free acid (CCFA) on antimicrobial susceptibility of Escherichia coli in feedlot cattle.
Animals—61 feedlot steers.
Procedures—A cohort study was conducted. Steers were housed in pens (5 pens with 10 steers and 1 pen with 11 steers). Five steers in each pen were administered CCFA, and 5 served as control steers (1 pen had 6 control steers). The CCFA administration included a single-dose regimen (6.6 mg/kg, SC, on day 0), two-thirds–dose regimen (4.4 mg/kg, SC, on day 0), and 3-dose regimen (6.6 mg/kg, SC, on days 0, 6, and 13). Fecal samples were collected on days 0, 2, 6, 9, 13, 16, 20, and 28. Fecal samples were collected immediately before CCFA administration. Minimum inhibitory concentrations of 15 antimicrobials were determined for 3 E coli isolates/fecal sample. Escherichia coli were enumerated by use of direct-plating techniques.
Results—Resistance to 1 or more antimicrobials was detected in 986 of 1,441 (68.4%) isolates recovered. Administration of CCFA was associated with a transient increase in the population of ceftiofur-resistant isolates. Susceptibility returned to day 0 values (ie, samples collected immediately before CCFA administration) approximately 2 weeks after completion of CCFA administration. Agreement between ceftiofur resistance and coresistance to ampicillin, chloramphenicol, streptomycin, sulfisoxazole, and tetracycline was almost perfect (κ 0.97). We did not detect variation in susceptibility of E coli recovered from commingled control steers.
Conclusions and Clinical Relevance—Administration of CCFA provided selection pressure that favored transient expansion of multiple-resistant variants.
Objective—To evaluate administration of chlortetracycline in feed of cattle as a method to select for tetracycline resistance among enteric bacteria in feedlot settings.
Procedures—Steers were randomly assigned to an exposed cohort (n = 10) or an unexposed cohort (control cohort; 10). Chlortetracycline (22 mg/kg) in cottonseed meal was administered to the exposed cohort on days 0 through 4, 6 through 10, and 12 through 16. The control cohort was administered only cottonseed meal. Fecal samples were collected from 16 steers on days −7, 0, 2, 6, 8, 12, 14, 19, 22, 26, and 33, and Escherichia coli and Enterococcus spp were isolated. Minimum inhibitory concentration (MIC) of selected antimicrobials was estimated.
Results—Overall, 56.0% and 31.4% of E coli and Enterococcus isolates, respectively, were resistant to tetracycline. Exposure to chlortetracycline was associated with a significant temporary increase in log2 MIC for both genera but returned to preexposure values by day 33. Averaged across time, the proportion of tetracycline-resistant E coli and Enterococcus isolates was significantly greater in exposed than in unexposed steers. Although all ceftiofur-resistant E coli isolates were coresistant to tetracycline, exposure to chlortetracycline led to a significant decrease in the proportion of E coli resistant to ceftiofur during exposure.
Conclusions and Clinical Relevance—Exposure to chlortetracycline was associated with a temporary increase in the likelihood of recovering resistant bacteria. Exposure to chlortetracycline decreased the likelihood of recovering ceftiofur-resistant E coli isolates, even though isolates were coresistant to tetracycline. These findings warrant further investigation.
Objective—To evaluate viral and bacterial respiratory
pathogens and Mycoplasma spp isolated from lung
tissues of cattle with acute interstitial pneumonia (AIP)
and cattle that had died as a result of other causes.
Sample Population—186 samples of lung tissues
collected from cattle housed in 14 feedlots in the
western United States.
Procedure—Lung tissues were collected during routine
postmortem examination and submitted for histologic,
microbiologic, and toxicologic examinations.
Histologic diagnoses were categorized for AIP, bronchopneumonia
(BP), control samples (no evidence of
disease), and other disorders.
Results—Cattle affected with AIP had been in feedlots
for a mean of 127.2 days before death, which was
longer than cattle with BP and control cattle.
Detection of a viral respiratory pathogen (eg, bovine
respiratory syncytial virus [BRSV], bovine viral diarrhea
virus, bovine herpesvirus 1, or parainfluenza
virus 3) was not associated with histologic category
of lung tissues. Bovine respiratory syncytial virus was
detected in 8.3% of AIP samples and 24.0% of control
samples. Histologic category was associated with
isolation of an aerobic bacterial agent and
Mycoplasma spp. Cattle with BP were at greatest risk
for isolation of an aerobic bacterial agent and
Conclusion and Clinical Relevance—Analysis of
these results suggests that AIP in feedlot cattle is not
a consequence of infection with BRSV. The increased
risk of isolation of an aerobic bacterial agent from cattle
with AIP, compared with control cattle, may indicate
a causal role or an opportunistic infection that follows
development of AIP. (Am J Vet Res 2001;
OBJECTIVE To investigate the effects of dietary supplementation with the β-adrenoceptor agonists ractopamine hydrochloride and zilpaterol hydrochloride on ECG and clinicopathologic variables of finishing beef steers.
DESIGN Randomized controlled trial.
ANIMALS 30 Angus steers.
PROCEDURES Steers were grouped by body weight and randomly assigned to receive 1 of 3 diets for 23 days: a diet containing no additive (control diet) or a diet containing ractopamine hydrochloride (300 mg/steer/d) or zilpaterol hydrochloride (8.3 mg/kg [3.8 mg/lb] of feed on a dry-matter basis), beginning on day 0. Steers were instrumented with an ambulatory ECG monitor on days −2, 6, 13, and 23, and continuous recordings were obtained for 72, 24, 24, and 96 hours, respectively. At the time of instrumentation, blood samples were obtained for CBC and serum biochemical and blood lactate analysis. Electrocardiographic recordings were evaluated for mean heart rate and arrhythmia rates.
RESULTS Steers fed zilpaterol or ractopamine had greater mean heart rates than those fed the control diet. Mean heart rates were within reference limits for all steers, with the exception of those in the ractopamine group on day 14, in which mean heart rate was high. No differences in arrhythmia rates were identified among the groups, nor were any differences identified when arrhythmias were classified as single, paired, or multiple (> 2) beats.
CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that dietary supplementation of cattle with ractopamine or zilpaterol at FDA-approved doses had no effect on arrhythmia rates but caused an increase in heart rate that remained within reference limits.