Objective—To evaluate a real-time quantitative polymerase
chain reaction (QPCR) assay in the detection
and quantitation of virulent Rhodococcus equi.
Sample Population—1 virulent, 2 intermediately virulent,
and 2 avirulent strains of R equi and 16 isolates
of bacteria genetically related to R equi.
Procedure—The QPCR assay was evaluated for
detection and quantitation of the virulence-associated
gene (vapA) of R equi in pure culture and in samples
of tracheobronchial fluid, which were inoculated with
known numbers of virulent R equi. Results were compared
with those derived via quantitative microbial
culture and standard polymerase chain reaction
Results—The QPCR assay detected the vapAgene in
pure culture of R equi and in tracheobronchial fluid
samples that contained as few as 20 CFUs of virulent
R equi/mL and accurately quantitated virulent R equi
to 103 CFUs/mL of fluid. The assay was highly specific
for detection of the vapA gene of virulent R equi
and was more sensitive than standard polymerase
chain reaction for detection of R equi in tracheobronchial
Conclusions and Clinical Relevance—The QPCR
assay appears to be a rapid and reliable method for
detecting and quantitating virulent R equi. The accuracy
of the QPCR assay is comparable to that of
quantitative microbial culture. The increased sensitivity
of the QPCR method in detection of virulent
R equi should facilitate rapid and accurate diagnosis
of R equi pneumonia in foals. (Am J Vet Res
Objective—To characterize the temporality of dates
of breeding and abortion classified as mare reproductive
loss syndrome (MRLS) among mares with abortions
during early gestation.
Animals—2,314 mares confirmed pregnant at
approximately 28 days after breeding from 36 farms in
central Kentucky, including 515 mares that had earlyterm
Procedure—Farm veterinarians and managers were
interviewed to obtain data for each mare that was
known to be pregnant to determine pregnancy status,
breeding date, last date known to be pregnant, and
date of abortion.
Results—Mares bred prior to April 1, 2001,
appeared to be at greatest risk of early-term abortion,
both among and within individual farms.
Mares bred in mid-February appeared to be at
greatest risk of abortion, with an estimated weekly
incidence rate of abortion of 66% (95% CI, 52% to
Conclusions and Clinical Relevance—Mares in
central Kentucky bred between mid-February and
early March were observed to be at greatest risk of
early-term abortion, and risk gradually decreased to
a background incidence of abortion of approximately
11%. Mares bred after April 1, 2001, appeared to
be at markedly less risk, indicating that exposure to
the cause of MRLS likely occurred prior to this
date. (Am J Vet Res 2005;66:1792–1797)
Objective—To estimate spatial risks associated with
mare reproductive loss syndrome (MRLS) during
2001 among horses in a specific study population and
partition the herd effects into those attributable to
herd location and those that were spatially random
and likely attributable to herd management.
Animals—Pregnant broodmares from 62 farms in 7
counties in central Kentucky.
Procedure—Veterinarians provided the 2001 abortion
incidence proportions for each farm included in the
study. Farms were georeferenced and data were analyzed
by use of a fully Bayesian risk-mapping technique.
Results—Large farm-to-farm variation in MRLS incidence
proportions was identified. The farm-to-farm
variation was largely attributed to spatial location
rather than to spatially random herd effects
Conclusions and Clinical Relevance—Results indicate
that there are considerable data to support an
ecologic cause and potential ecologic risk factors for
MRLS. Veterinary practitioners with more detailed
knowledge of the ecology in the 7 counties in
Kentucky that were investigated may provide additional
data that would assist in the deduction of the
causal factor of MRLS via informal geographic information
systems analyses and suggest factors for
inclusion in further investigations. (Am J Vet Res 2005;66:17–20)
Objective—To evaluate the correlation between halftime
of liquid-phase gastric emptying (T50), determined
with nuclear scintigraphy using technetium
Tc 99m pentetate, and absorption variables of orally
Animals—6 mature horses.
Procedure—Technetium Tc 99m pentetate (10 mCi)
and acetaminophen (20 mg/kg of body weight) were
administered simultaneously in 200 ml of water. Serial
left and right lateral images of the stomach region
were obtained with a gamma camera, and T50 determined
separately for counts obtained from the left
side, the right side and the geometric mean. Power
exponential curves were used for estimation of T50
and modified R2 values for estimation of goodness of
fit of the data. Serial serum samples were taken, and
acetaminophen concentration was determined, using
fluorescence polarization immunoassay. Maximum
serum concentration (Cmax), time to reach maximum
serum concentration (Tmax), area under the curve for
240 minutes and the absorption constant (Ka) were
determined, using a parameter estimation program.
Correlations were calculated, using the Spearman
rank correlation coefficient.
Results—Correlations between T50 and Tmax and
between T50 and Ka were significant.
Conclusions and Clinical Relevance—Tmax and Ka
are valuable variables in the assessment of liquidphase
gastric emptying using acetaminophen absorption.
Acetaminophen absorption may be a valuable
alternative to nuclear scintigraphy in the determination
of gastric emptying rates in equine patients with
normally functioning small intestine. (Am J Vet Res
Objective—To evaluate the effect of erythromycin on
motility of the ileum, cecum, and pelvic flexure of horses
during the postoperative and post-recovery periods.
Animals—8 healthy adult horses.
Procedure—Horses were anesthetized and bipolar
electrodes were implanted in smooth muscle of the
ileum, cecum, and pelvic flexure. Approximately 4, 16,
and 24 hours (postoperative recording sessions) and
at least 8 days (post-recovery recording session) after
surgery, myoelectric activity was recorded before and
after administration of erythromycin (0.5 mg/kg).
Results—Following erythromycin administration,
myoelectric activity was increased in the ileum during
all postoperative recording sessions but not during
the post-recovery recording session. Myoelectric
activity was increased in the cecum following erythromycin
administration only during the post-recovery
recording session. Myoelectric activity was
increased in the pelvic flexure following erythromycin
administration during all recording sessions. During
several recording sessions, there were short periods
during which myoelectric activity was significantly
decreased following erythromycin administration.
Conclusions and Clinical Relevance—Results suggest
that erythromycin has an effect on myoelectric
activity of the ileum, cecum, and pelvic flexure in
horses; however, prokinetic effects of erythromycin
administered during the postoperative period were
not always the same as effects obtained when the
drug was administered after horses had recovered
from the effects of surgical implantation of recording
devices. Therefore, caution must be exercised when
extrapolating results of prokinetic studies in healthy
animals to animals with abnormal gastrointestinal
tract motility. (Am J Vet Res 2000;61:420–424)
Objective—To evaluate effects of IV administration of
penicillin G potassium (KPEN) or potassium chloride
(KCl) on defecation and myoelectric activity of the
cecum and pelvic flexure of horses.
Animals—5 healthy horses.
Procedure—Horses with 12 bipolar electrodes on the
cecum and pelvic flexure received KPEN or KCl solution
by IV bolus 4 hours apart. Each horse received
the following: 2 × 107 U of KPEN (high-dose KPEN) followed
by 34 mEq of KCl (high-dose KCl), 1 × 107 U of
KPEN (low-dose KPEN) followed by 17 mEq of KCl
(low-dose KCl), high-dose KCl followed by high-dose
KPEN, and low-dose KCl followed by low-dose KPEN.
Number of defecations and myoelectric activity were
recorded for 60 minutes. The first three 5-minute segments
and first four 15-minute segments of myoelectric
activity were analyzed.
Results—Number of defecations during the first 15-
minute segment was greater after high-dose KPEN
treatment than after high-dose or low-dose KCl treatment.
Compared with reference indexes, myoelectric
activity was greater in the pelvic flexure for the first 5-
minute segment after high-dose KCl treatment, in the
cecum and pelvic flexure for the first 5-minute segment
and in the pelvic flexure for the first 15-minute
segment after low-dose KPEN treatment, and in the
pelvic flexure for the first and second 5-minute segments
and the first three 15-minute segments after
high-dose KPEN treatment.
Conclusions and Clinical Relevance—IV administration
of KPEN stimulates defecation and myoelectric
activity of the cecum and pelvic flexure in horses.
Effects of KPEN may be beneficial during episodes of
ileus. (Am J Vet Res 2003;64:1360–1363)
Objective—To determine the chemoprophylactic effect of gallium maltolate on the cumulative incidence of pneumonia caused by Rhodococcus equi infection in foals.
Animals—483 foals born and raised on 12 equine breeding farms with a history of endemic R equi infections.
Procedures—Group 1 foals were treated with a placebo and group 2 foals were treated with gallium maltolate (approx 30 mg/kg, PO, q 24 h) during the first 2 weeks after birth. Foals were monitored for development of pneumonia attributable to R equi infection and for adverse effects of gallium maltolate.
Results—There were no significant differences in the cumulative incidence of R equi pneumonia among the 2 groups.
Conclusions and Clinical Relevance—Chemoprophylaxis via gallium maltolate administered orally at approximately 30 mg/kg daily for the first 2 weeks after birth failed to reduce the cumulative incidence of pneumonia attributable to R equi infection among foals on breeding farms with endemic R equi infections. Further investigation is needed to identify strategies for control of R equi infections.
Objective—To determine the pharmacokinetics of gallium maltolate (GaM) after intragastric administration in adult horses.
Animals—6 adult horses.
Procedures—Feed was withheld for 12 hours prior to intragastric administration of GaM (20 mg/kg). A single dose of GaM was administered to each horse via a nasogastric tube (time 0). Blood samples were collected at various time points from 0 to 120 hours. Serum was used to determine gallium concentrations by use of inductively coupled plasma-mass spectroscopy. Noncompartmental and compartmental analyses of serum gallium concentrations were performed. Pharmacokinetic models were selected on the basis of the Akaike information criterion and visual analysis of plots of residuals.
Results—Serum concentration data for 1 horse were such that this horse was considered an outlier and excluded from noncompartmental and compartmental analyses. Noncompartmental analysis was used to determine individual pharmacokinetic parameters. A 1-compartment model with first-order input and output and lag time was selected as the best-fit model for the data and used to determine mean — SD values for maximum observed serum concentration (0.28 — 0.09 μg/mL), time of maximum concentration (3.09 — 0.43 hours), time to the first measurable concentration (0.26 — 0.11 hours), apparent elimination half-life (48.82 — 5.63 hours), area under the time-concentration curve (20.68 — 757 h—μg/mL), and apparent volume of distribution (73,493 — 18,899 mL/kg).
Conclusion and Clinical Relevance—Further studies are necessary to determine the bioavailability of GaM after intragastric administration in adult horses.
Objective—To determine whether the concentrations of airborne virulent Rhodococcus equi in stalls housing foals during the first 2 weeks after birth are associated with subsequent development of R equi pneumonia in those foals.
Sample—Air samples collected from foaling stalls and holding pens in which foals were housed during the first 2 weeks after birth.
Procedures—At a breeding farm in Texas, air samples (500 L each) were collected (January through May 2011) from stalls and pens in which 121 foals were housed on day 1 and on days 4, 7, and 14 after birth. For each sample, the concentration of airborne virulent R equi was determined with an immunoblot technique. The association between development of pneumonia and airborne R equi concentration was evaluated via random-effects Poisson regression analysis.
Results—Some air samples were not available for analysis. Of the 471 air samples collected from stalls that housed 121 foals, 90 (19%) contained virulent R equi. Twenty-four of 121 (20%) foals developed R equi pneumonia. Concentrations of virulent R equi in air samples from stalls housing foals that developed R equi pneumonia were significantly higher than those in samples from stalls housing foals that did not develop pneumonia. Accounting for disease effects, air sample concentrations of virulent R equi did not differ significantly by day after birth or by month of birth.
Conclusions and Clinical Relevance—Exposure of foals to airborne virulent R equi during the first 2 weeks after birth was significantly (and likely causally) associated with development of R equi pneumonia.
OBJECTIVE To determine the effects of oral omeprazole administration on the fecal and gastric microbiota of healthy adult horses.
ANIMALS 12 healthy adult research horses.
PROCEDURES Horses were randomly assigned to receive omeprazole paste (4 mg/kg, PO, q 24 h) or a sham (control) treatment (tap water [20 mL, PO, q 24 h]) for 28 days. Fecal and gastric fluid samples were collected prior to the first treatment (day 0), and on days 7, 28, 35, and 56. Sample DNA was extracted, and bacterial 16S rRNA gene sequences were amplified and sequenced to characterize α and β diversity and differential expression of the fecal and gastric microbiota. Data were analyzed by visual examination and by statistical methods.
RESULTS Composition and diversity of the fecal microbiota did not differ significantly between treatment groups or over time. Substantial variation in gastric fluid results within groups and over time precluded meaningful interpretation of the microbiota in those samples.
CONCLUSIONS AND CLINICAL RELEVANCE Results supported that omeprazole administration had no effect on fecal microbiota composition and diversity in this group of healthy adult horses. Small sample size limited power to detect a difference if one existed; however, qualitative graphic examination supported that any difference would likely have been small and of limited clinical importance. Adequate data to evaluate potential effects on the gastric microbiota were not obtained. Investigations are needed to determine the effects of omeprazole in horses with systemic disease or horses receiving other medical treatments.