M Keith Chaffin

Texas A&M University, College Station, TX, United States

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Publications (89)130.5 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Objective-To ascertain the frequency of ultrasonographic identification of liver at sites recommended for blind percutaneous liver biopsy in middle-aged horses and to determine whether the liver is obscured by other organs or too thin for safe sample collection at recommended locations. Design-Prospective case series. Animals-36 healthy middle-aged (between 6 and 18 years old) Quarter Horses or Quarter Horse crosses. Procedures-Blood samples were collected from each horse and submitted for evaluation of liver function. Horses with any indication of liver dysfunction on serum biochemical analysis were excluded. The region just below a line drawn between the dorsal aspect of the tuber coxae and the point of the elbow joint in the right 11th, 12th, 13th, and 14th intercostal spaces (ICSs) was imaged by ultrasonography for the presence of liver. In each ICS, liver thickness and whether there was partial obstruction in viewing the liver caused by other abdominal or thoracic organs were recorded. Results-39% (14/36) of horses had liver imaged on ultrasonographic examination in all of the 11th to 14th ICSs. None of the 36 horses had liver of adequate thickness (ie, liver thickness ≥ 3.5 cm) for biopsy in all of the imaged ICSs. For 22 horses in which the liver was not visible on ultrasonographic examination of an ICS, lung was imaged instead in 12 (55%) horses, intestine in 8 (36%), and both intestine and lung in 2 (9%). Conclusions and Clinical Relevance-On the basis of the results of this study, the practice of blind percutaneous liver biopsy in horses is not recommended because of the risk of serious complications.
    Journal of the American Veterinary Medical Association 10/2014; 245(8):939-943. · 1.72 Impact Factor
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    ABSTRACT: Pneumonia caused by Rhodococcus equi is a common cause of disease and death in foals. Although agent and environmental factors contribute to the incidence of this disease, the genetic factors influencing the clinical outcomes of R. equi pneumonia are ill-defined. Here, we performed independent single nucleotide polymorphism (SNP)- and copy number variant (CNV)-based genome-wide association studies to identify genomic loci associated with R. equi pneumonia in foals. Foals at a large Quarter Horse breeding farm were categorized into 3 groups: 1) foals with R. equi pneumonia (clinical group [N = 43]); 2) foals with ultrasonographic evidence of pulmonary lesions that never developed clinical signs of pneumonia (subclinical group [N = 156]); and, 3) foals without clinical signs or ultrasonographic evidence of pneumonia (unaffected group [N = 49]). From each group, 24 foals were randomly selected and used for independent SNP- and CNV-based genome-wide association studies (GWAS). The SNP-based GWAS identified a region on chromosome 26 that had moderate evidence of association with R. equi pneumonia when comparing clinical and subclinical foals. A joint analysis including all study foals revealed a 3- to 4-fold increase in odds of disease for a homozygous SNP within the associated region when comparing the clinical group with either of the other 2 groups of foals or their combination. The region contains the transient receptor potential cation channel, subfamily M, member 2 (TRPM2) gene, which is involved in neutrophil function. No associations were identified in the CNV-based GWAS. Collectively, these data identify a region on chromosome 26 associated with R. equi pneumonia in foals, providing evidence that genetic factors may indeed contribute to this important disease of foals.
    PLoS ONE 01/2014; 9(6):e98710. · 3.53 Impact Factor
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    ABSTRACT: Objective-To determine risk factors associated with the development of nasopharyngeal cicatrix syndrome (NCS) in horses. Design-Retrospective case-control study. Animals-242 horses referred for endoscopic evaluation of the upper portion of the respiratory tract (121 horses with NCS and 121 control horses). Procedures-Medical records of horses that had an endoscopic evaluation of the upper airway performed between January 2003 and December 2008 were reviewed. Signalment, housing management, and season of evaluation were recorded and reviewed for each horse. The associations between clinical signs and endoscopic findings were evaluated by the use of a prospective logistic model that included a Bayesian method for inference. Results-Breed and sex had no significant effect on the risk of having NCS. The risk that a horse had NCS increased significantly with age. Exclusive housing in a stall was protective against the development of NCS. In addition, the amount of pasture turnout had a dose-related effect, with exclusive pasture turnout positively correlated with increased risk of developing NCS, compared with a mixture of pasture turnout and stall confinement. Horses were significantly more likely to be evaluated because of clinical signs of the syndrome during the warm months of the year. Conclusions and Clinical Relevance-The risk factors for NCS identified in this study may support chronic environmental exposure to an irritant or infectious agent as the cause of NCS. Information gained from this study should be useful for investigating the cause of NCS.
    Journal of the American Veterinary Medical Association 05/2013; 242(9):1267-70. · 1.72 Impact Factor
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    ABSTRACT: Case Description-4 horses with enthesopathy and desmitis of the medial collateral ligament of the cubital joint were examined. Clinical Findings-All 4 horses had a history of acute, severe, unilateral forelimb lameness and had signs of pain during manipulation of the affected upper forelimb; 2 also had swelling in the axillary region. There was no improvement in lameness after diagnostic local analgesia below the carpal region, and 1 of 4 horses had mild improvement after cubital joint analgesia. Radiography revealed enthesophyte formation on the radial tuberosity and linear mineralization of the medial collateral ligament in 2 horses and periosteal reaction on the humeral condyle in all 4 horses. One horse had mild osteoarthritis of the cubital joint, and 3 had osteophytosis of the cranial aspect of the radius. Although all horses were initially examined because of an acute onset of lameness, all had chronic abnormalities visible on imaging. Ultrasonography revealed an irregular boney contour and enthesopathy at the insertion of the short medial collateral ligament to the radial tuberosity and desmitis of the short medial collateral ligament. Two horses had radiographic evidence of similar but less severe lesions of the contralateral cubital joint. Treatment and Outcome-All horses received phenylbutazone and rest. All horses were free of lameness after a median of 3 months (range, 2 to 4 months) and returned to previous use after a median of 6 months (range, 3 to 8 months). Conclusions and Clinical Relevance-The results of the present report suggested that performance horses with enthesopathy and desmitis of the medial collateral ligament of the cubital joint may have a good prognosis for return to previous use following appropriate treatment.
    Journal of the American Veterinary Medical Association 04/2013; 242(8):1152-8. · 1.72 Impact Factor
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    ABSTRACT: 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.
    Veterinary Surgery 02/2013; · 1.24 Impact Factor
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    ABSTRACT: 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.
    American Journal of Veterinary Research 01/2013; 74(1):102-9. · 1.35 Impact Factor
  • Carolyn E Arnold, M Keith Chaffin
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    ABSTRACT: Objective-To determine clinical signs, diagnostic methods, treatment, and outcome for a series of adult horses with abdominal abscesses. Design-Retrospective case series. Animals-61 adult horses. Procedures-Medical records of adult horses with abdominal abscesses treated at Texas A&M Veterinary Medical Teaching Hospital (1993 to 2008) were reviewed. Information was recorded regarding signalment, history, clinical signs, diagnosis, treatment, and short- and long-term outcomes. Risk factors for survival were determined. Results-61 horses met the criteria for inclusion. Clinical signs included colic (67%), fever (46%), anorexia (51%), signs of depression (57%), tachycardia (46%), and weight loss (30%). The diagnosis was made on the basis of abdominal ultrasonography, exploratory celiotomy, palpation per rectum, and necropsy. Abscesses were variable in size, location, and number. Only 15 (24.6%) horses survived to discharge. Multiple bacterial isolates were identified from aspirates of abscesses, and subsequent abdominal adhesion formation limited survival, affecting outcome. Risk factors for survival included age and heart rate at admission. Conclusions and Clinical Relevance-Adult horses with abdominal abscesses often have severe adhesion formation. Multiple bacterial isolates are frequently identified from the abscess. Prognosis for survival is guarded.
    Journal of the American Veterinary Medical Association 12/2012; 241(12):1659-1665. · 1.72 Impact Factor
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    ABSTRACT: Objective-To determine whether the concentration of airborne virulent Rhodococcus equi varied by location (stall vs paddock) and month on horse farms. Sample-Air samples from stalls and paddocks used to house mares and foals on 30 horse breeding farms in central Kentucky. Procedures-Air samples from 1 stall and 1 paddock were obtained monthly from each farm from January through June 2009. Concentrations of airborne virulent R equi were determined via a modified colony immunoblot assay. Random-effects logistic regression was used to determine the association of the presence of airborne virulent R equi with location from which air samples were obtained and month during which samples were collected. Results-Of 180 air samples, virulent R equi was identified in 49 (27%) and 13 (7%) obtained from stalls and paddocks, respectively. The OR of detecting virulent R equi in air samples from stalls versus paddocks was 5.2 (95% confidence interval, 2.1 to 13.1). Of 60 air samples, virulent R equi was identified in 25 (42%), 18 (30%), and 6 (10%) obtained from stalls during January and February, March and April, and May and June, respectively. The OR of detecting virulent R equi from stall air samples collected during May and June versus January and February was 0.22 (95% confidence interval, 0.08 to 0.63). Conclusions and Clinical Relevance-Foals were more likely to be exposed to airborne virulent R equi when housed in stalls versus paddocks and earlier (January and February) versus later (May and June) during the foaling season.
    American Journal of Veterinary Research 10/2012; 73(10):1603-9. · 1.35 Impact Factor
  • Journal of Equine Veterinary Science 10/2012; 32(10):S20. · 0.62 Impact Factor
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    ABSTRACT: BACKGROUND: Representatives from a herd of horses with acute onset of neurologic signs after administration of ivermectin presented for evaluation and treatment. OBJECTIVES: Describe clinical signs of horses intoxicated by ingestion of Solanum sp. and administered ivermectin. ANIMALS: Six of 11 affected unrelated horses presented for evaluation and treatment. The remaining 5 affected horses were treated at the farm. Four additional horses, housed separately, were unaffected. METHODS: Case series is presented. Serum ivermectin concentrations were evaluated in the 6 hospitalized horses. The remnants of the tubes of ivermectin paste were analyzed for ivermectin concentration. The hay fed to the affected horses was analyzed for the presence of toxic plants. RESULTS: Serum ivermectin concentrations were higher than expected, given the dosage of ivermectin administered. The ivermectin concentration remaining in the administration tubes did not exceed specifications. The hay was heavily contaminated by 2 Solanum species. All horses returned to normal neurologic function with supportive care. CONCLUSIONS AND CLINICAL IMPORTANCE: Horses might exhibit signs of ivermectin toxicity after appropriate dosing of the drug if they concurrently consume toxic plants of the Solanum family.
    Journal of Veterinary Internal Medicine 09/2012; · 2.06 Impact Factor
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    ABSTRACT: To characterize the associations between clinical signs of nasopharyngeal cicatrix syndrome (NCS) and endoscopic findings in horses. Retrospective, case-control study. 239 horses (118 case horses and 121 control horses). Medical records of horses that had an endoscopic evaluation of the upper airway performed between January 2003 and December 2008 were reviewed. Clinical signs and the appearance and anatomic locations of lesions identified during endoscopic evaluation were reviewed and recorded for each horse. The associations between clinical signs and endoscopic findings were evaluated by the use of a prospective logistic model that used a Bayesian method for inference and was implemented by a Markov chain Monte Carlo method. Nasal discharge was associated with acute inflammation of the pharynx and larynx. Exercise intolerance was associated with circumferential pharyngeal lesions. Respiratory noise was associated with chronic scarring of the pharynx, a combination of pharyngeal and laryngeal scarring, and circumferential scarring of the pharynx. Respiratory distress was associated with acute inflammation of all portions of the airway, especially when there was preexisting scarring and narrowing of the airway by ≥ 50%. Cough did not have any significant association with NCS, compared with results in control horses. Associations between the endoscopic appearance of NCS lesions and relevant clinical signs will help practitioners identify horses with NCS and allow them to select appropriate treatment.
    Journal of the American Veterinary Medical Association 03/2012; 240(6):734-9. · 1.72 Impact Factor
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    ABSTRACT: The schistosome Heterobilharzia americana infects dogs, raccoons, and other mammals in the southeastern United States. Migration of eggs into the liver results in parasitic granulomas with varying degrees of fibrosis and inflammation. Recently, hepatic parasitic granulomas in horses were shown to be caused by H. americana infection. In the present study, samples of liver from 11 of 12 horses with hepatic granulomas identified at necropsy (n = 11) or surgical biopsy (n = 1) were used for DNA extraction, polymerase chain reaction amplification and sequencing using primers specific for a portion of the H. americana small subunit ribosomal RNA gene. A polymerase chain reaction amplicon of the correct size was produced from the extracted DNA in 8 of the 11 horses. Amplicons from 5 of the 8 positive horses were sequenced and had 100% identity with H. americana. In all but 2 of the 12 horses, Heterobilharzia was not responsible for the primary clinical disease, and the hepatic granulomas were considered an incidental finding.
    Veterinary Pathology 01/2012; 49(3):552-6. · 1.93 Impact Factor
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    ABSTRACT: This report describes a 4-month-old Quarter Horse filly with an ectopic ureter. The filly presented with signs of urinary incontinence, which had been present since birth. Computed tomography (CT) examination and cystoscopy confirmed a diagnosis of a unilateral ectopic ureter. A nephrectomy of the left kidney was performed and renal function was closely monitored post operatively. The filly was treated for abdominal chylous effusion as a post operative complication. The filly survived to discharge from the hospital, and maintained normal urinary function at 12 months post operatively.
    Equine Veterinary Education. 12/2011; 23(12).
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    ABSTRACT: A 1.5-year-old Quarter Horse gelding with a history of chronic nasal discharge and leukocytosis presented with signs of increased lethargy and muscular pain. The horse quickly became recumbent and unable to rise and was euthanized due to a poor prognosis. At necropsy, severe bilateral guttural pouch empyema was observed, as well as numerous well-demarcated areas of pallor within the skeletal muscles of all major muscle groups. Polymerase chain reaction testing of the guttural pouch exudate confirmed an infection with Streptococcus equi subsp. equi, and an S. equi–associated immune-mediated rhabdomyolysis was initially considered to be the most likely diagnosis. This report briefly discusses the various etiologies that should be considered in cases of equine myopathy, and it demonstrates the complexity of these poorly understood muscular disorders.
    Veterinary Pathology 11/2011; 48(6):E52-E59. · 1.93 Impact Factor
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    ABSTRACT: Rhodococcus equi, a gram-positive facultative intracellular pathogen, is one of the most common causes of pneumonia in foals. Although R. equi can be cultured from the environment of virtually all horse farms, the clinical disease in foals is endemic at some farms, sporadic at others, and unrecognized at many. On farms where the disease is endemic, costs associated with morbidity and mortality attributable to R. equi may be very high. The purpose of this consensus statement is to provide recommendations regarding the diagnosis, treatment, control, and prevention of infections caused by R. equi in foals.
    Journal of Veterinary Internal Medicine 11/2011; 25(6):1209-20. · 2.06 Impact Factor
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    ABSTRACT: CASE DESCRIPTION-A 22-year-old American Paint Horse gelding from the Gulf Coast region of Texas was evaluated for regrowth of a perirectal squamous cell carcinoma that had been surgically removed 11 months previously. CLINICAL FINDINGS-A necrotic and ulcerated mass was present below the anus. The horse had paraphimosis and was having difficulty with urination. Histologic examination of the mass revealed that it was squamous cell carcinoma, and the horse was euthanized because of the unlikelihood that the mass could be adequately resected and its close proximity to the urethra. OUTCOME-At necropsy, in addition to the squamous cell carcinoma, hundreds of round, white to pale yellow nodules were disseminated throughout the liver, resulting in a so-called starry-sky appearance. Similar granulomas were seen in the right caudal lung lobe and small intestinal serosa. A single granuloma in the liver, which differed from the others by its larger size, contained a pair of adult schistosomes. Several hepatic granuloma specimens were used for PCR amplification and sequencing. Use of primers specific for a portion of the Heterobilharzia americana small subunit rRNA gene resulted in amplification of a 487-base pair product that had 100% sequence identity with H americana. CLINICAL RELEVANCE-Severe cases of disseminated granulomas in the liver of horses may result in a liver with a grossly abnormal starry-sky pattern. To our knowledge, this is the first report documenting the association of granulomas with H americana infection along with adult schistosomes in the liver of a horse.
    Journal of the American Veterinary Medical Association 10/2011; 239(8):1117-22. · 1.72 Impact Factor
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    ABSTRACT: Pneumonia is a major cause of disease and death in foals. Rhodococcus equi, a Gram-positive facultative intracellular pathogen, is a common cause of pneumonia in foals. This article reviews the clinical manifestations of infection caused by R. equi in foals and summarizes current knowledge regarding mechanisms of virulence of, and immunity to, R. equi. A complementary consensus statement providing recommendations for the diagnosis, treatment, control, and prevention of infections caused by R. equi in foals can be found in the same issue of the Journal.
    Journal of Veterinary Internal Medicine 10/2011; 25(6):1221 - 1230. · 2.06 Impact Factor
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    ABSTRACT: The starry sky hepatic pattern is an unusual ultrasonographic appearance of equine liver characterized by numerous small, hyperechoic foci, some of which cast an acoustic shadow, distributed randomly throughout the hepatic parenchyma. Our objectives were to describe the signalment, clinical signs, clinicopathological findings, primary disease process, and ultrasonographic findings of horses with this ultrasonographic pattern, as well as determine the associated gross and histologic changes. The starry sky pattern was identified in 18 adult horses of mixed gender and breed. The horses had various clinical signs, with weight loss and anorexia reported most commonly. Liver size and parenchymal echogenicity were normal in most horses. The hyperechoic foci frequently caused acoustic shadowing. Biliary dilation was noted rarely. The ultrasonographic pattern was the result of numerous fibrosing hepatic granulomas in all horses evaluated histologically. γ-Glutamyltransferase was the most commonly elevated hepatic enzyme, though it was increased in fewer than half the horses. Fifteen horses had an additional disease that was identified as the apparent cause of clinical signs. Three horses had primary hepatic disease while 12 had diseases of other body systems. Therefore, the starry sky ultrasonographic pattern is likely incidental in most horses and not clinically significant. Improved recognition of this pattern and further investigation of affected horses may help refine the etiology and clinical significance of the granulomas.
    Veterinary Radiology &amp Ultrasound 07/2011; 52(5):568-72. · 1.41 Impact Factor
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    ABSTRACT: To determine the chemoprophylactic effect of gallium maltolate on the cumulative incidence of pneumonia caused by Rhodococcus equi infection in foals. 483 foals born and raised on 12 equine breeding farms with a history of endemic R equi infections. 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. There were no significant differences in the cumulative incidence of R equi pneumonia among the 2 groups. 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.
    American Journal of Veterinary Research 07/2011; 72(7):945-57. · 1.35 Impact Factor
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    ABSTRACT: The sonographic characteristics of intraabdominal abscesses in 11 foals and intraabdominal lymphadenitis in five foals with Rhodococcus equi infections are presented. Intraabdominal abscesses were usually present in the ventral abdomen adjacent to the ventral body wall, well-marginated, and contained a mixed or complex echo pattern. Lymphadenitis appeared as singular or multiple clusters of lymph nodes of mixed echogenicity adjacent to any portion of the gastrointestinal tract or body wall. Sonographic findings were supported by necropsy examinations, but sonographic measurements consistently underestimated the size of abscess.
    Veterinary Radiology &amp Ultrasound 03/2011; 52(4):462-5. · 1.41 Impact Factor

Publication Stats

723 Citations
130.50 Total Impact Points

Institutions

  • 1990–2012
    • Texas A&M University
      • • Department of Veterinary Pathobiology
      • • Department of Large Animal Clinical Sciences
      • • Department of Veterinary Physiology & Pharmacology
      College Station, TX, United States
  • 2006
    • Iowa State University
      • Department of Veterinary Clinical Sciences
      Ames, IA, United States
  • 2001
    • Kitasato University
      • Graduate School of Veterinary Medicine and Animal Sciences
      Edo, Tōkyō, Japan