Immersion Foot Syndrome in 6 Equids Exposed to Hurricane Floodwaters.

Prolonged exposure to water, known as immersion foot syndrome in humans, is a phenomenon first described in soldiers during World War I and characterized by dermal ischemic necrosis. In this report, we describe the pathologic findings of a condition resembling immersion foot syndrome in 5 horses and 1 donkey with prolonged floodwater exposure during Hurricane Harvey. At necropsy, all animals had dermal defects ventral to a sharply demarcated "water line" along the lateral trunk. In 5 animals, histologic examination revealed moderate to severe perivascular dermatitis with vasculitis and coagulative necrosis consistent with ischemia. The severity of the lesions progressed from ventral trunk to distal limbs and became more pronounced in the chronic cases. The pathophysiology of immersion foot syndrome is multifactorial and results from changes in the dermal microvasculature leading to thrombosis and ischemia. Prompt recognition of this disease may lead to appropriate patient management and decreased morbidity.

Nephrectomy via ventral median celiotomy in equids.

OBJECTIVE: To report technique for, and outcome after, nephrectomy through a ventral median celiotomy in equids. STUDY DESIGN: Case series. ANIMALS: Equids with unilateral renal disease (n = 6), aged 2 months to 18 years, weighing 90-434 kg. METHODS: A ventral median celiotomy was used to access the left or right kidney. To facilitate surgical exposure, the small intestine was reflected towards the diaphragm using laparotomy sponges and the ascending colon was exteriorized and in some cases evacuated. The peritoneum over the affected kidney was incised and blunt dissection used to free the kidney from the retroperitoneal fat, then the renal artery, vein, and ureter were isolated and ligated. Abdominal lavage with sterile saline solution was performed before abdominal closure. RESULTS: Four horses, 1 donkey, and 1 mule had unilateral nephrectomy to treat verminous nephritis (1), idiopathic hematuria (1), and ectopic ureter (4). A ventral median approach provided adequate access to the kidney in all 6 cases. Two horses had postoperative complications (peritonitis, chylous abdominal effusion) that resolved with medical therapy. No complications attributable to nephrectomy were reported by the owners upon follow-up 1-8 years after surgery. CONCLUSIONS: A ventral median approach for nephrectomy can be used for unilateral nephrectomy in equids weighing up to 434 kg.

Effects of location for collection of air samples on a farm and time of day of sample collection on airborne concentrations of virulent Rhodococcus equi at two horse breeding farms.

OBJECTIVE: To determine whether airborne concentrations of virulent Rhodococcus equi at 2 horse breeding farms varied on the basis of location, time of day, and month. SAMPLE POPULATION: 2 farms in central Kentucky with recurrent R equi-induced pneumonia in foals. PROCEDURES: From February through July 2008, air samples were collected hourly for a 24-hour period each month from stalls and paddocks used to house mares and their foals. Concentrations of airborne virulent R equi were determined via a modified colony immunoblot technique. Differences were compared by use of zero-inflated negative binomial methods to determine effects of location, time, and month. RESULTS: Whether mares and foals were housed predominantly in stalls or paddocks significantly affected results for location of sample collection (stall vs paddock) by increasing airborne concentrations of virulent R equi at the site where horses were predominantly housed. Airborne concentrations of virulent R equi were significantly higher from 6:00 pm through 11:59 pm than for the period from midnight through 5:59 am. Airborne concentrations of virulent R equi did not differ significantly between farms or among months. CONCLUSIONS AND CLINICAL RELEVANCE: Airborne concentrations of virulent R equi were significantly increased when horses were predominantly housed at the site for collection of air samples (ie, higher in stalls when horses were predominantly housed in stalls and higher in paddocks when horses were predominantly housed in paddocks). Concentrations of virulent R equi among air samples collected between the hours of 6:00 am and midnight appeared similar.

The effects of signalment, diet, geographic location, season, and colitis associated with antimicrobial use or Salmonella infection on the fecal microbiome of horses.

BACKGROUND: The fecal microbiome of healthy horses may be influenced by signalment, diet, environmental factors, and disease. OBJECTIVES: To assess the effects of age, breed, sex, geographic location, season, diet, and colitis caused by antibiotic use (antimicrobial-associated diarrhea [AAD]) and Salmonella infection on fecal microbiota. ANIMALS: Healthy horses (n = 80) were sampled from nonhospital environments across multiple geographical locations in the United States. Horses with AAD (n = 14) were defined as those that developed diarrhea secondary to antimicrobial use. Horses with Salmonella infection (n = 12) were presented with spontaneous onset of colitis and subsequently tested positive on Salmonella quantitative polymerase chain reaction. All horses were >1 year of age and stratified by a dietary scale that included forages (pasture and hay) and concentrates grouped by percentage of fiber and amount. METHODS: Illumina sequencing of 16S rRNA genes was performed on fecal DNA. RESULTS: Healthy horses fed higher amounts of grain clustered separately from those fed lower amounts of grain (analysis of similarities [ANOSIM], R = 0.356-0.385, Q = 0.002). Horses with AAD and Salmonella had decreased richness and evenness compared to healthy horses (P < .05). Univariable analysis of the 3 groups identified increases in Bacteroidetes (Q = 0.002) and Protebacteria (Q = 0.001) and decreases in Verrucomicrobia (Q = 0.001) in AAD horses whereas Salmonella horses had less Firmicutes (Q = 0.001) when compared to healthy horses. CONCLUSIONS AND CLINICAL IMPORTANCE: Although the amount of grain in the diet had some impact on the fecal microbiome, colitis had a significantly larger influence. Horses with ADD have a more severe dysbiosis than do horses with Salmonella.

Pharmacokinetics of gallium maltolate after intragastric administration in adult horses.

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.

Phosphine intoxication following oral exposure of horses to aluminum phosphide-treated feed.

CASE DESCRIPTION: 66 horses were potentially exposed to phosphine (a gas) 14 hours after being fed a pelleted ration treated with aluminum phosphide. CLINICAL FINDINGS: 28 horses had clinical signs of profuse sweating, tachycardia, tachypnea, pyrexia, ataxia, seizures, and widespread muscle tremors. Clinically relevant laboratory findings included hypoglycemia and high plasma concentrations of lactate and ammonia and activities of gamma-glutamyl transpeptidase, aspartate aminotransferase, and alkaline phosphatase. At least 4 horses had signs consistent with hepatic encephalopathy. Necropsy findings included petechial and ecchymotic hemorrhages in multiple organs, widespread vascular congestion, hepatic lipidosis, and neuronal necrosis in the brain. Phosphine was detected in the stomachs of the 3 horses tested. TREATMENT AND OUTCOME: On the farm, horses were treated with gastric lavage followed by administration of di-tri-octahedral smectite, atropine, fluids, and sedatives. Six horses were hospitalized, and lactated Ringer's solution and flunixin meglumine were administered IV. Additionally, 10% dextrose, corn syrup, and di-tri-octahedral smectite were administered PO. Twenty-seven horses died within 2 days after exposure. Two survivors (1 without clinical signs of toxicosis) made a complete recovery. CLINICAL RELEVANCE: Progression of clinical signs in affected horses in this report was rapid, with few treatment options available, leading to a high case fatality rate. Fumigation with aluminum phosphide is commonly performed to eliminate weevils and other insects from stored grains. When appropriate precautions are used during fumigation, risk to livestock is typically minimal.

Determination of the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and treatment outcome in foals infected with antimicrobial-resistant isolates of R equi.

OBJECTIVE: To determine the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and to describe treatment outcome in foals infected with antimicrobial-resistant isolates of R equi. DESIGN: Cross-sectional study. SAMPLE POPULATION: 38 isolates classified as resistant to macrolide antimicrobials or rifampin received from 9 veterinary diagnostic laboratories between January 1997 and December 2008. PROCEDURES: For each isolate, the minimum inhibitory concentration of macrolide antimicrobials (ie, azithromycin, erythromycin, and clarithromycin) and rifampin was determined by use of a concentration-gradient test. Prevalence of R equi isolates from Florida and Texas resistant to macrolide antimicrobials or rifampin was determined. Outcome of antimicrobial treatment in foals infected with antimicrobial-resistant isolates of R equi was determined. RESULTS: Only 24 of 38 (63.2%) isolates were resistant to >or= 1 antimicrobial. Two isolates were resistant only to rifampin, whereas 22 isolates were resistant to azithromycin, erythromycin, clarithromycin, and rifampin. The overall prevalence of antimicrobial-resistant isolates in submissions received from Florida and Texas was 3.7% (12/328). The survival proportion of foals infected with resistant R equi isolates (2/8 [25.0%]) was significantly less, compared with the survival proportion in foals that received the same antimicrobial treatment from which antimicrobial-susceptible isolates were cultured (55/79 [69.6%]). Odds of nonsurvival for foals infected with resistant R equi isolates were 6.9 (95% confidence interval, 1.3 to 37) times the odds for foals infected with susceptible isolates. CONCLUSIONS AND CLINICAL RELEVANCE: Interpretation of the results emphasized the importance of microbiological culture and antimicrobial susceptibility testing in foals with pneumonia caused by R equi.

Ivermectin toxicosis in three adult horses.

CASE DESCRIPTION: 3 adult Quarter Horses were evaluated for acute, progressive neurologic signs 18 hours after oral administration of 1 dose of 1.87% ivermectin paste. CLINICAL FINDINGS: Clinical signs included depression, forelimb and hind limb ataxia, drooping of the superior and inferior lips, and muscle fasciculations. Bilateral mydriasis, decreased pupillary light reflexes, and absent menace reflexes were evident. Clinical signs progressed in severity for 36 hours after administration of the ivermectin. TREATMENT AND OUTCOME: All horses were treated supportively with IV administration of fluids and anti-inflammatory medications. Two horses survived with no apparent long-term sequelae. One horse was euthanized, and a high concentration of ivermectin was detected in its brain tissue at postmortem examination. Analysis of the ivermectin concentration in the paste product revealed that the concentration was approximately that indicated on the packaging. CLINICAL RELEVANCE: Ivermectin toxicosis is an uncommonly reported condition in equids that should be considered when acute neurologic impairment develops after ivermectin administration. Recovery is possible with supportive care and time.

Extrapulmonary disorders associated with Rhodococcus equi infection in foals: 150 cases (1987-2007).

OBJECTIVE: To describe frequency, types, and clinical outcomes of extrapulmonary disorders (EPDs) in foals in which Rhodococcus equi infection was diagnosed, and to identify factors determined at the time of admission that differentiated foals that developed EPDs from foals with R equi infection identified only in the lungs. DESIGN: Retrospective case series. ANIMALS: 150 foals aged 3 weeks to 6 months with a diagnosis of R equi infection. PROCEDURES: Medical records were reviewed for information on date of admission, signalment, history, clinical signs, diagnostic testing, treatment, duration of hospitalization, invoice, and outcome. For each EPD identified, further information was collected on the identification, location, treatment, and outcome of the lesion. RESULTS: Of 150 foals with R equi infections, 111 (74%) had at least 1 of 39 EPDs. Survival was significantly higher among foals without EPDs (32/39 [82%]) than among foals with EPDs (48/111 [43%]), but many EPDs were only recognized after death. Risk factors significantly associated with EPDs included referral status, duration of clinical signs prior to admission, leukocytosis, and neutrophilia. Foals with EPDs also had a higher heart rate and BUN concentration than foals without. CONCLUSIONS AND CLINICAL RELEVANCE: Practitioners should recognize that extrapulmonary manifestations of R equi occur with high prevalence affecting diverse organ systems, that multiple systems are generally affected when EPDs occur, and that suspicion of R equi infection should prompt evaluation and monitoring of extrapulmonary sites. Improved recognition of the presence of these disorders will help practitioners to better advise their clients in the treatment and outcome of foals with R equi infections.

Tendinitis of the proximal aspect of the superficial digital flexor tendon in horses: 12 cases (2000-2006).

OBJECTIVE: To determine clinical signs, ultrasonographic findings, and outcome of horses with tendinitis of the proximal portion of the superficial digital flexor tendon (SDFT; group A horses) and to compare signalment, horse use, and outcome in these horses with that of horses with tendinitis of the midmetacarpal region of the SDFT (group B horses). DESIGN: Retrospective case series. ANIMALS: 12 group A horses and 22 group B horses. PROCEDURES: Medical records were reviewed for signalment, horse use, and outcome information; data for group A horses also included severity of lameness, diagnostic results, and treatment. RESULTS: Most group A horses were aged (mean, 18 years; median, 17 years; range, 11 to 23 years) Quarter Horses (9/12 horses) and had a grade 3 or 4 (on a scale from 1 to 5) forelimb lameness. Most group A horses (8/12 horses) had positive reactions to carpal flexion and were (9/12 horses) sound following ulnar nerve blocks. Ultrasonographic evaluation revealed hypoechoic SDFT lesions (median echogenicity score, 3/4; median fiber alignment score, 3/3; and mean length, 9.75 cm). Group A horses were significantly older and had a poorer outcome for return to previous use (2/12 horses), compared with group B horses (median age, 5 years; 10/22 horses returned to previous use). Thirteen of 22 group B horses were Thoroughbreds. CONCLUSIONS AND CLINICAL RELEVANCE: Tendinitis of the proximal portion of the SDFT was a cause of lameness in aged performance horses; prognosis for return to previous use was poor.

Association of soil concentrations of Rhodococcus equi and incidence of pneumonia attributable to Rhodococcus equi in foals on farms in central Kentucky.

OBJECTIVE: To determine whether soil concentrations of total or virulent Rhodococcus equi differed among breeding farms with and without foals with pneumonia caused by R equi. SAMPLE POPULATION: 37 farms in central Kentucky. Procedures-During January, March, and July 2006, the total concentration of R equi and concentration of virulent R equi were determined by use of quantitative bacteriologic culture and a colony immunoblot technique, respectively, in soil specimens obtained from farms. Differences in concentrations and proportion of virulent isolates within and among time points were compared among farms. RESULTS: Soil concentrations of total or virulent R equi did not vary among farms at any time point. Virulent R equi were identified in soil samples from all farms. Greater density of mares and foals was significantly associated with farms having foals with pneumonia attributable to R equi. Among farms with affected foals, there was a significant association of increased incidence of pneumonia attributable to R equi with an increase in the proportion of virulent bacteria between samples collected in March and July. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that virulent R equi were commonly recovered from soil of horse breeding farms in central Kentucky, regardless of the status of foals with pneumonia attributable to R equi on each farm. The incidence of foals with pneumonia attributable to R equi can be expected to be higher at farms with a greater density of mares and foals.

Chemoprophylactic effects of azithromycin against Rhodococcus equi-induced pneumonia among foals at equine breeding farms with endemic infections.

OBJECTIVE: To determine the effect of azithromycin chemoprophylaxis on the cumulative incidence of pneumonia caused by Rhodococcus equi, age at onset of pneumonia, and minimum inhibitory concentration (MIC) of azithromycin for R equi isolates cultured from fecal and clinical samples. DESIGN: Controlled, randomized clinical trial. ANIMALS: 338 foals born and raised at 10 equine breeding farms; each farm had a history of endemic R equi infections. PROCEDURES: Group 1 foals were control foals, and group 2 foals were treated with azithromycin (10 mg/kg [4.5 mg/lb], PO, q 48 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 azithromycin. Isolates of R equi were tested for susceptibility to azithromycin. RESULTS: The proportion of R equi-affected foals was significantly higher for control foals (20.8%) than for azithromycin-treated foals (5.3%). Adverse effects of azithromycin treatment were not detected, and there were no significant differences between groups for the MICs of azithromycin for R equi isolates cultured from fecal or clinical samples. CONCLUSIONS AND CLINICAL RELEVANCE: Azithromycin chemoprophylaxis effectively reduced the cumulative incidence of pneumonia attributable to R equi among foals at breeding farms with endemic R equi infections. There was no evidence of resistance to azithromycin. Nonetheless, caution must be used because it is possible that resistance could develop with widespread use of azithromycin as a preventative treatment. Further investigation is needed before azithromycin chemoprophylaxis can be recommended for control of R equi infections.

Pharmacokinetics of gallium maltolate after intragastric administration in neonatal foals.

OBJECTIVE: To determine the pharmacokinetics of gallium maltolate (GaM) after intragastric administration in healthy foals. ANIMALS: 6 healthy neonatal foals. PROCEDURES: Each foal received GaM (20 mg/kg) by intragastric administration. Blood samples were obtained before (time 0) and at 0.25, 0.5, 1, 2, 4, 8, 12, 24, 36, and 48 hours after GaM administration for determination of serum gallium concentrations by use of inductively coupled plasma mass spectroscopy. RESULTS: Mean +/- SD pharmacokinetic variables were as follows: peak serum gallium concentration, 1,079 +/- 311 ng/mL; time to peak serum concentration, 4.3 +/- 2.0 hours; area under the serum concentration versus time curve, 40,215 +/- 8,420 ng/mL/h; mean residence time, 39.5 +/- 17.2 hours; area under the moment curve, 1,636,554 +/- 931,458 ng([h](2)/mL); and terminal half-life, 26.6 +/- 11.6 hours. The mean serum concentration of gallium at 12 hours was 756 +/- 195 ng/mL. CONCLUSIONS AND CLINICAL RELEVANCE: Gallium maltolate administered via nasogastric tube at a dose of 20 mg/kg to neonatal foals resulted in gallium serum concentrations considered sufficient to suppress growth or kill Rhodococcus equi in macrophages and other infected tissues.

Effect of hyperimmune plasma on the severity of pneumonia caused by Rhodococcus equi in experimentally infected foals.

This study evaluated the prophylactic effectiveness of hyperimmune plasma (HIP) as an aid in the prevention of pneumonia caused by experimental infection with Rhodococcus equi. Thirty neonatal foals were administered R. equi HIP or saline at 2 days of age and were infected with virulent R. equi at 7 days. All foals developed signs or symptoms of respiratory disease. Radiographic scores on day 28 and neutrophil concentrations on day 49 were significantly greater in control foals, and time to respiratory effort score of 2 or higher was significantly shorter for control foals. Three foals, all in the principal group, died or were euthanized before the end of the study, but there was no significant difference in mortality between groups. VapA titers were significantly greater in principal foals. Administration of R. equi HIP decreased the severity of radiographic lesions and prolonged time to increased respiratory effort due to R. equi-induced pneumonia.

Signalment, clinical features, and outcome for male horses with urethral rents following perineal urethrotomy or corpus spongiotomy: 33 cases (1989-2013).

OBJECTIVE To describe the signalment, clinical features, and outcome for male horses with urethral rents following perineal urethrotomy (PU) or corpus spongiotomy (CS). DESIGN Retrospective case series. ANIMALS 33 horses. PROCEDURES Medical records of male horses examined because of hematuria or hemospermia caused by urethral rents that underwent PU or CS at a referral hospital between 1989 and 2013 were reviewed. Data regarding signalment, clinical features, urethroscopic findings, surgical treatment, and outcome were recorded. Long-term follow-up information was obtained by telephone interviews. RESULTS Age of the study population ranged from 3 to 18 years. Nineteen geldings and 1 stallion were examined because of hematuria, of which 13 and 7 underwent PU and CS, respectively, at a mean of 56 days after onset of clinical signs. Thirteen stallions were examined because of hemospermia, of which 7 and 6 underwent PU and CS, respectively, at a mean of 193 days after onset of clinical signs. Hematuria resolved following 1 surgical procedure in all 17 horses for which long-term information was available. Of the 12 stallions for which long-term information was available, 7 had resolution of hemospermia after 1 PU or CS and 5 developed recurrent hemospermia that required additional PUs or CSs (n = 3) or primary closure of the urethral rent (2). CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that PU and CS were reliable treatments for resolution of hematuria in male horses with urethral rents; stallions with urethral rents may require multiple PUs or CSs or primary closure of the rent for resolution of hemospermia.

Hematuria associated with cystic hematomas in three neonatal foals.

Cystic hematomas were diagnosed in 3 neonatal foals. In all 3 foals, cystic hematomas resulted from umbilical trauma or thrombocytopenia. Findings in these foals suggest that cystic hematoma should be included in the differential diagnosis of hematuria in neonatal foals. Management of cystic hematomas includes both medical and surgical options.

Farm characteristics and management practices associated with development of Rhodococcus equi pneumonia in foals.

OBJECTIVE: To identify farm characteristics and management practices associated with development of Rhodococcus equi pneumonia in foals. DESIGN: Prospective case-control study. ANIMALS: 5230 foals on 138 breeding farms with 9136 horses. PROCEDURE: During 2003, participating veterinarians provided data from 1 or 2 farms with > or =1 foal with R equi pneumonia and unaffected farms. Data from affected and unaffected farms were compared by use of logistic regression analysis. RESULTS: A number of variables relating to farm size and desirable management practices were significantly associated with increased odds of farms being affected with R equi pneumonia. By use of multivariate logistic regression, affected farms were determined significantly more likely to have raised Thoroughbreds, housed > or =15 foals, used concrete floors in foaling stalls, and tested foals for passive transfer of immunity than unaffected farms. These results remained significant even after accounting for exposure of foals to other breeding farms during the first month of life. Conclusions and Clinical Relevance-Breeding farms with large acreage and a large number of mares and foals have greater odds of being affected by R equi pneumonia. Clinical relevance of associations with Thoroughbred breed and concrete flooring in foaling stalls remains uncertain. Desirable management factors commonly used on farms were not effective for controlling or preventing development of R equi pneumonia. This finding indicates a need to focus on host factors that influence disease development.

Intravascular hemolysis associated with severe cutaneous burn injuries in five horses.

Five horses were evaluated because of severe cutaneous burn injuries following a barn fire. Gross hemolysis and morphologic changes in RBCs consistent with oxidative damage were detected in all of the horses. Of these horses, 4 became azotemic. The overall goals of treatment included wound care, correction of dehydration and provision of diuresis, control of inflammation, pain management, and prophylaxis against sepsis. After treatment, 2 horses survived and were discharged from the hospital. Red blood cell damage and hemolysis following cutaneous burn injury have been investigated in other species and appear to be a result of the release of oxygen radicals from complement-activated neutrophils. Early intervention with aggressive fluid therapy is recommended in the treatment of human burn patients and is likely to be of benefit in horses with burn injuries; a beneficial role of free radical scavengers and xanthine oxidase inhibitors has also been suggested.

Gallium maltolate as an alternative to macrolides for treatment of presumed Rhodococcus equi pneumonia in foals.

BACKGROUND: Macrolide-resistant isolates of Rhodococcus equi are emerging, prompting the search for clinically effective alternative antimicrobials. HYPOTHESIS: The proportion of foals with ultrasonographic evidence of pneumonia presumed to be caused by R. equi that had a successful outcome when administered gallium maltolate (GaM) PO would not be more than 10% inferior (ie, lower) than that of foals receiving standard treatment. ANIMALS: Fifty-four foals with subclinical pulmonary abscesses among 509 foals at 6 breeding farms in Kentucky. METHODS: Controlled, randomized, prospective noninferiority study. Foals with ultrasonographic lesions >1 cm in diameter (n = 54) were randomly allocated to receive per os either clarithromycin combined with rifampin (CLR+R) or GaM, and followed up for 28 days by daily physical inspections and weekly (n = 1 farm) or biweekly (n = 4 farms) thoracic ultrasound examinations by individuals unaware of treatment-group assignments. Treatment success was defined as resolution of ultrasonographically identified pulmonary abscesses within 28 days of initiating treatment. Noninferiority was defined as a 90% confidence interval for the observed difference in CLR+R minus GaM that was ≤10%. RESULTS: The proportion of GaM-treated foals that resolved (70%; 14/20) was similar to that of foals treated with CLR+R (74%; 25/34), but we failed to demonstrate noninferiority for GaM relative to CLR+R; however, GaM was noninferior to CLR+R treatment when results from a noncompliant farm were excluded. CONCLUSIONS AND CLINICAL IMPORTANCE: Gallium maltolate is not inferior to macrolides for treating foals with subclinical pneumonia. Use of GaM might reduce pressure for macrolide-resistance in R. equi.

Composition and Diversity of the Fecal Microbiome and Inferred Fecal Metagenome Does Not Predict Subsequent Pneumonia Caused by Rhodococcus equi in Foals.

In equids, susceptibility to disease caused by Rhodococcus equi occurs almost exclusively in foals. This distribution might be attributable to the age-dependent maturation of immunity following birth undergone by mammalian neonates that renders them especially susceptible to infectious diseases. Expansion and diversification of the neonatal microbiome contribute to development of immunity in the gut. Moreover, diminished diversity of the gastrointestinal microbiome has been associated with risk of infections and immune dysregulation. We thus hypothesized that varying composition or reduced diversity of the intestinal microbiome of neonatal foals would contribute to increased susceptibility of their developing R. equi pneumonia. The composition and diversity indices of the fecal microbiota at 3 and 5 weeks of age were compared among 3 groups of foals: 1) foals that subsequently developed R. equi pneumonia after sampling; 2) foals that subsequently developed ultrasonographic evidence of pulmonary abscess formation or consolidation but not clinical signs (subclinical group); and, 3) foals that developed neither clinical signs nor ultrasonographic evidence of pulmonary abscess formation or consolidation. No significant differences were found among groups at either sampling time, indicating absence of evidence of an influence of composition or diversity of the fecal microbiome, or predicted fecal metagenome, on susceptibility to subsequent R. equi pneumonia. A marked and significant difference identified between a relatively short interval of time appeared to reflect ongoing adaptation to transition from a milk diet to a diet including available forage (including hay) and access to concentrate fed to the mare.