Objective—To compare prevalence of tetracycline resistance genes in the fecal flora of conventionally raised feedlot steers and feedlot steers raised without antimicrobials.
Sample Population—61 fecal samples from conventionally raised steers and 61 fecal samples from steers raised without antimicrobials at a single feedlot.
Procedures—Total DNA was extracted from each fecal sample and analyzed by means of 4 multiplex PCR assays for 14 tetracycline resistance genes.
Results—At least 3 tetracycline resistance genes were identified in all 122 fecal samples. For 5 of the 14 tetracycline resistance genes, the percentage of samples in which the gene was detected was significantly higher for fecal samples from conventionally raised cattle than for fecal samples from antimicrobial-free cattle, and for 1 gene, the percent-age of samples in which the gene was detected was significantly higher for fecal samples from antimicrobial-free cattle than for fecal samples from conventionally raised cattle. The percentage of samples with r 11 tetracycline resistance genes was significantly higher for fecal samples from conventionally raised cattle (35/61 [57%]) than for fecal samples from antimicrobial-free cattle (16/61 [26%]).
Conclusions and Relevance—Results suggested that the prevalence of tetracycline resistance genes was significantly higher in the fecal flora of conventionally raised feedlot steers than in the fecal flora of feedlot steers raised without antimicrobials and that a metagenomic approach may be useful in understanding the epidemiology of antimicrobial resistance in food animals.
Objective—To assess fecal and nasal shedding patterns
of bovine torovirus (BoTV) in cattle at time of
arrival and periodically throughout the first 21 days
after arrival at a feedlot.
Procedure—Fecal and nasal-swab samples collected
on days 0, 4, 14, and 21 after arrival were tested for
BoTV, using ELISA. A subset of samples from calves
testing positive and negative for BoTV was analyzed,
using reverse transcriptase-polymerase chain reaction
(RT-PCR). Paired serum samples were collected on
days 0 and 21 and tested for BoTV antibodies, using
a hemagglutination inhibition assay.
Results—Overall rate of fecal shedding of BoTV was
21 of 57 (37%) by ELISA and 40 of 42 (95%) by
RT-PCR with peak shedding on day 4. Diarrhea was
more common in calves shedding BoTV than those
not shedding the virus (odds ratio, 1.72). Overall rate
of nasal shedding of BoTV was 15 of 57 (26%) by
ELISA and 42 of 42 (100%) by RT-PCR, with peak
shedding on day 0. Specificity of the RT-PCR product
was confirmed by sequence analysis. Approximately
93% of the calves seroconverted to BoTV (> 4-fold
increase in titer). Differences were not detected
between calves shedding BoTV and nonshedders in
relation to disease and treatments, perhaps because
of the low number of cattle in the study.
Conclusions and Clinical Relevance—This study
confirmed BoTV infections in feedlot cattle, including
BoTV antigen and viral RNA in nasal secretions, and
the shedding pattern during the first 21 days after
arrival in a feedlot. (Am J Vet Res 2002;63:342–348).
Objective—To assess the relationship between shedding
of bovine coronavirus (BCV) via the respiratory
tract and enteric routes and the association with
weight gain in feedlot cattle.
Animals—56 crossbred steers.
Procedures—Paired fecal samples and nasal swab
specimens were obtained and were tested for BCV,
using antigen-capture ELISA. Paired serum samples
obtained were tested for antibodies to BCV, using
antibody-detection ELISA. Information was collected
on weight gain, clinical signs, and treatments for
enteric and respiratory tract disease during the study
Results—Number of samples positive for bovine respiratory
coronavirus (BRCV) or bovine enteric coro
navirus (BECV) was 37/224 (17%) and 48/223 (22%),
respectively. Some cattle (25/46, 45%) shed BECV
and BRCV. There were 25/29 (86%) cattle positive for
BECV that shed BRCV, but only 1/27 (4%) cattle negative
to BECV shed BRCV. Twenty-seven of 48 (56%)
paired nasal swab specimens and fecal samples positive
for BECV were positive for BRCV. In contrast,
only 10/175 (6%) paired nasal swab specimens and
fecal samples negative for BECV were positive for
BRCV. Only shedding of BECV was associated with
significantly reduced weight gain. Seroconversion to
BCV during the 21 days after arrival was detected in
95% of the cattle tested.
Conclusions and Clinical Implications—Feedlot
cattle infected with BCV after transport shed BCV
from the respiratory tract and in the feces. Fecal
shedding of BCV was associated with significantly
reduced weight gain. Developing appropriate control
measures for BCV infections could help reduce the
decreased weight gain observed among infected
feedlot cattle. (Am J Vet Res 2001;62:1436–1441)
Objective—To determine the prevalence, fecal shedding
pattern, and association of bovine torovirus
(BoTV) with diarrhea in veal calves at time of arrival
and periodically throughout the first 35 days after their
arrival on a veal farm.
Animals—62 veal calves.
Procedure—Fecal samples collected on days 0, 4, 14,
and 35 after arrival were tested for BoTV by use of
ELISA and reverse transcriptase-polymerase chain
reaction (RT-PCR) assay. Paired serum samples
obtained from blood collected on days 0 and 35 were
analyzed for BoTV antibodies with a hemagglutination
inhibition assay. Fecal samples were also screened
for other enteric pathogens, including rotavirus, coronavirus,
and Cryptosporidium spp.
Results—Fecal shedding of BoTV was detected in 15
of 62 (24%) calves by use of ELISA and RT-PCR assay,
with peak shedding on day 4. A significant independent
association between BoTV shedding and diarrhea
was observed. In addition, calves shedding ≥ 2
enteric pathogens were more likely to have diarrhea
than calves shedding ≤ 1 pathogen. Calves that were
seronegative or had low antibody titers against BoTV
(≤ 1:10 hemagglutination inhibition units) at arrival
seroconverted to BoTV (> 4-fold increase in titer);
these calves were more likely to shed virus than
calves that were seropositive against BoTV at arrival.
Conclusions and Clinical Relevance—Shedding of
BoTV was strongly associated with diarrhea in neonatal
veal calves during the first week after arrival at the
farm. These data provide evidence that BoTV is an
important pathogen of neonatal veal calves.
(Am J Vet Res 2003;64:485–490)
Objective—To estimate the relationship between therapeutic use of ceftiofur and recovery of Escherichia coli and Salmonella spp with reduced susceptibility to ceftriaxone from feces of dairy cattle.
Animals—3,840 mature dairy cows on 50 dairy herds in Ohio.
Procedures—Fecal samples were obtained from up to 100 mature dairy cows on each farm. Samples were screened for E coli and Salmonella spp with reduced susceptibility to ceftriaxone by use of selective media.
Results—E coli with reduced susceptibility to ceftriaxone was recovered from 92% (46/50) of the herds and 60.9% (2,338/3,840) of cows. Salmonella spp were recovered from 44% (22/50) of the herds and 9.9% (382/3,840) of cows. No association was found between ceftiofur use and recovery of E coli with reduced susceptibility to ceftriaxone at the herd level. However, recovery of E coli with reduced susceptibility to ceftriaxone was more likely from cows in herds in which Salmonella spp were also recovered on the day of collection (odds ratio, 24.96; 95% confidence interval, 3.17 to 196.68) than from herds in which Salmonella spp were not recovered. Odds of recovery of E coli with reduced susceptibility to ceftriaxone from an individual cow increased 62% (odds ratio, 1.62; 95% confidence interval, 1.16 to 2.25) for every 454-kg increase in herd milk production.
Conclusions and Clinical Relevance—No evidence was found that the use of ceftiofur on dairy farms increases the prevalence or dissemination of Salmonella spp or E coli with reduced susceptibility to ceftriaxone.
Objective—To determine frequency of antimicrobial drug (AMD) use in dogs within 12 months prior to admission to a veterinary teaching hospital.
Design—Owner survey and medical records review.
Animals—435 dogs admitted to a veterinary teaching hospital.
Procedures—Demographic characteristics and information regarding AMD use in dogs were obtained from medical records and results of surveys completed by owners of dogs.
Results—242 (55.6%) dogs received at least 1 AMD within 12 months prior to hospital admission; 125 (51.7%) of these dogs had a disease of the integument at the time of admission. β-Lactam AMDs were used more frequently than AMDs of any other class (176/242 [72.7%] dogs). Three hundred sixty-eight dogs had a medical problem at the time of hospital admission; 225 (61.1%) of these dogs had received at least 1 AMD within 12 months prior to hospital admission. Dogs referred by a veterinarian to the hospital were 2.39 times as likely to have received at least 1 AMD within 30 days prior to hospital admission as were dogs admitted without a referral.
Conclusions and Clinical Relevance—Results indicated AMDs were frequently administered to dogs prior to admission to the teaching hospital. Use of AMDs in animals could be a risk factor for coselection and spread of multidrug-resistant pathogens, and colonization or infection of dogs with such pathogens could have a negative impact on the health of other animals and humans.
Objective—To compare shedding patterns and serologic responses to bovine coronavirus (BCV) in feedlot calves shipped from a single ranch in New Mexico (NM calves) versus calves assembled from local sale barns in Arkansas (AR calves) and to evaluate the role of BCV on disease and performance.
Animals—103 feedlot calves from New Mexico and 100 from Arkansas.
Procedures—Calves were studied from before shipping to 35 days after arrival at the feedlot. Nasal swab specimens, fecal samples, and serum samples were obtained before shipping, at arrival, and periodically thereafter. Bovine coronavirus antigen and antibodies were detected by use of an ELISA.
Results—NM calves had a high geometric mean titer for BCV antibody at arrival (GMT, 1,928); only 2% shed BCV in nasal secretions and 1% in feces. In contrast, AR calves had low antibody titers against BCV at arrival (GMT, 102) and 64% shed BCV in nasal secretions and 65% in feces. Detection of BCV in nasal secretions preceded detection in feces before shipping AR calves, but at arrival, 73% of AR calves were shedding BCV in nasal secretions and feces. Bovine coronavirus infection was significantly associated with respiratory tract disease and decreased growth performance in AR calves.
Conclusions and Clinical Relevance—Replication and shedding of BCV may start in the upper respiratory tract and spread to the gastrointestinal tract. Vaccination of calves against BCV before shipping to feedlots may provide protection against BCV infection and its effects with other pathogens in the induction of respiratory tract disease.
Objective—To estimate the efficacy of a commercially available Salmonella enterica subunit vaccine on the subclinical shedding of S enterica in dairy cattle.
Design—Randomized, controlled trial.
Animals—175 mature cows on 2 dairy farms with a history of S enterica infection.
Procedures—25% of the mature cows from each herd were systematically randomized to receive an S enterica subunit vaccine following label guidelines. The remaining 75% of cows in each herd served as nonvaccinated controls. Fecal samples were collected from all cows at the time of initial vaccination (day 0), booster vaccination (day 14), 2 weeks following the booster vaccination (day 28), and 10 weeks following the start of the trial (day 70). All samples were processed on the day of collection and cultured for S enterica.
Results—651 fecal samples were obtained over the entire study period. Salmonella enterica was recovered from 46 (7.1%) of the samples. Shedding of S enterica was similar for vaccinated and nonvaccinated control cows on each of the collection dates.
Conclusions and Clinical Relevance—The study revealed no evidence that extralabel vaccination with a commercial subunit S enterica vaccine reduced shedding of S enterica in subclinically infected dairy cows in these herds.
Objective—To investigate effects of low dietary vitamin A content on antibody responses in feedlot calves inoculated with an inactivated bovine coronavirus (BCoV) vaccine.
Animals—40 feedlot calves.
Procedures—Calves were fed diets containing high (3,300 U/kg) or low (1,100 U/kg) amounts of vitamin A beginning on the day of arrival at a feedlot (day 0) and continuing daily until the end of the study (day 140). Serum retinol concentrations were evaluated in blood samples obtained throughout the study. Calves were inoculated IM with an inactivated BCoV vaccine on days 112 and 126. Blood samples obtained on days 112 and 140 were used for assessment of BCoV-specific serum IgG1, IgG2, IgM, and IgA titers via an ELISA.
Results—The low vitamin A diet reduced serum retinol concentrations between days 112 and 140. After the BCoV inoculation and booster injections, predominantly serum IgG1 antibodies were induced in calves fed the high vitamin A diet; however, IgG1 titers were compromised at day 140 in calves fed the low vitamin A diet. Other isotype antibodies specific for BCoV were not affected by the low vitamin A diet.
Conclusions and Clinical Relevance—Dietary vitamin A restriction increases marbling in feedlot cattle; however, its effect on antibody responses to vaccines is unknown. A low vitamin A diet compromised the serum IgG1 responses against inactivated BCoV vaccine, which suggested suppressed T-helper 2-associated antibody (IgG1) responses. Thus, low vitamin A diets may compromise the effectiveness of viral vaccines and render calves more susceptible to infectious disease.