Journal of the American Veterinary Medical Association2003; 223(12); 1791-1799; doi: 10.2460/javma.2003.223.1791

Foal-related risk factors associated with development of Rhodococcus equi pneumonia on farms with endemic infection.

Abstract: To identify foal-related risk factors associated with development of Rhodococcus equi pneumonia among foals on farms with endemic R. equi infection. Methods: Prospective case-control study. Methods: 220 foals at 2 equine breeding farms in Texas during a 2-year period. Methods: Information collected for each dam included age, time housed on the farm prior to parturition, whether there were any peripartum illnesses, parity, and health of previous foals. Information collected for each foal included breed, sex, gestational age, month and year of birth, location of birth, type of flooring and bedding in stall, postpartum management and preventive health care, passive immunity status, supplementation of immunoglobulins, exposure to other farms or foals affected with R. equi pneumonia, stall and pasture exposure, commingling with other mare-foal pairs, age at weaning, and whether the foal developed R. equi pneumonia. Results: 32 of the 220 (15%) foals developed R. equi pneumonia, of which 4 (13%) died. Foals at 1 of the 2 farms and foals born during the second year of the study were more likely to develop R. equi pneumonia. Foal-related factors that were examined were not significantly associated with risk of R. equi pneumonia in multivariate analyses. Conclusions: Results suggest that there are farm- and year-related effects on the risk that foals will develop R. equi pneumonia. Other foal-related factors significantly associated with R. equi pneumonia were not identified.
Publication Date: 2003-12-24 PubMed ID: 14690209DOI: 10.2460/javma.2003.223.1791Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't
  • Research Support
  • U.S. Gov't
  • Non-P.H.S.


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This research study looked into the possible foal-related risk factors that could lead to the development of Rhodococcus equi pneumonia in foals on farms, specifically those with endemic R. equi infection. The study discovered that it’s primarily the farm’s environment and the specific time period rather than the foal-specific factors that influence the likelihood of developing this disease.


  • The study was conducted as a prospective case-control study on 220 foals located at two different horse breeding farms in Texas over a two year period.
  • Detailed information was gathered pertaining to both the dams (female parent) and foals, including age, duration of stay on the farm prior to giving birth, health of previous foals, feed, illness around birthing time, breed, sex, gestational age, birth location, and postpartum care.
  • Additional data such as type of stall flooring, passive immunity status, exposure to other foals with R. equi pneumonia, and the foal’s age at weaning was also collected to ensure thorough analysis.


  • Out of the 220 foals included in the study, 32 (or 15%) developed R. equi pneumonia, and out of these, 4 (or 13%) did not survive.
  • Foals at one of the farms and those born in the second year of the study were found to be more likely to develop the pneumonia proving that environmental and time factors play a crucial role.
  • Despite the comprehensive list of foal-related factors examined, none showed a significant correlation with the risk of contracting the R. equi pneumonia when run through multivariate analyses.


  • Based on the findings, the researchers concluded the biggest influences on the development of R. equi pneumonia in foals were related to the farm environment and the specific year, rather than specific foal-related factors.
  • The study could not identify any other foal-specific factors that showed a significant association with the incidence of R. equi pneumonia.

Cite This Article

Chaffin MK, Cohen ND, Martens RJ, Edwards RF, Nevill M. (2003). Foal-related risk factors associated with development of Rhodococcus equi pneumonia on farms with endemic infection. J Am Vet Med Assoc, 223(12), 1791-1799.


ISSN: 0003-1488
NlmUniqueID: 7503067
Country: United States
Language: English
Volume: 223
Issue: 12
Pages: 1791-1799

Researcher Affiliations

Chaffin, M Keith
  • Department of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843-4475, USA.
Cohen, Noah D
    Martens, Ronald J
      Edwards, Ronnie F
        Nevill, Mark

          MeSH Terms

          • Actinomycetales Infections / epidemiology
          • Actinomycetales Infections / etiology
          • Actinomycetales Infections / veterinary
          • Animal Husbandry / methods
          • Animals
          • Animals, Newborn
          • Case-Control Studies
          • Female
          • Horse Diseases / epidemiology
          • Horse Diseases / etiology
          • Horses
          • Logistic Models
          • Male
          • Multivariate Analysis
          • Pneumonia, Bacterial / epidemiology
          • Pneumonia, Bacterial / etiology
          • Pneumonia, Bacterial / veterinary
          • Prospective Studies
          • Rhodococcus equi / isolation & purification
          • Rhodococcus equi / pathogenicity
          • Risk Factors
          • Texas / epidemiology


          This article has been cited 11 times.
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          2. Hassanpour A, Moghaddam S. Evaluation of serum concentration of acute-phase proteins (haptoglobin and serum amyloid A) in the affected Arabian foals with rhodococcosis.. Vet Med Sci 2023 Jan;9(1):144-149.
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          3. Cohen ND, Kahn SK, Bordin AI, Gonzales GM, da Silveira BP, Bray JM, Legere RM, Ramirez-Cortez SC. Association of pneumonia with concentrations of virulent Rhodococcus equi in fecal swabs of foals before and after intrabronchial infection with virulent R. equi.. J Vet Intern Med 2022 May;36(3):1139-1145.
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          5. u00c1lvarez-Narvu00e1ez S, Berghaus LJ, Morris ERA, Willingham-Lane JM, Slovis NM, Giguere S, Cohen ND. A Common Practice of Widespread Antimicrobial Use in Horse Production Promotes Multi-Drug Resistance.. Sci Rep 2020 Jan 22;10(1):911.
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          9. Kuskie KR, Smith JL, Wang N, Carter CN, Chaffin MK, Slovis NM, Stepusin RS, Cattoi AE, Takai S, Cohen ND. 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.. Am J Vet Res 2011 Jan;72(1):73-9.
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