Infectious risk factors and clinical indicators for tracheal mucus in British National Hunt racehorses.
Authors: Cardwell J M, Smith K C, Wood J L N, Newton J R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Tracheal Mucus and Infectious Risk Factors in National Hunt Racehorses Previous respiratory research in racehorses has typically examined tracheal mucus and airway neutrophilia together, obscuring the specific aetiologies of each; Cardwell and colleagues addressed this by conducting a two-year prospective study in National Hunt horses with monthly tracheal washes and viral serology to isolate the infectious drivers of endoscopically visible tracheal mucus. The presence of *Streptococcus zooepidemicus* alone or with nonhaemolytic streptococci (NHS) significantly increased odds of tracheal mucus, with combined isolation producing a 12.5-fold increase in the odds of substantial mucus accumulation (score ≥2/3). Notably, NHS demonstrated an independent pathogenic effect not previously documented—isolation of NHS alone carried a 3.7-fold increased odds of increased mucus—suggesting that this heterogeneous bacterial group warrants species-level identification rather than blanket classification. The study also revealed that the first 3–6 months in training represented a critical risk period, with six-fold increased odds of even small mucus accumulation during the initial three months. For practitioners, these findings underline the importance of targeted bacteriological identification (particularly differentiating NHS species), heightened respiratory surveillance during the early training phase, and caution in relying on clinical signs alone—coughing and nasal discharge, whilst specific indicators, proved too insensitive to reliably predict significant tracheal mucus.
Read the full abstract on PubMed
Practical Takeaways
- •Young National Hunt racehorses entering training for the first time warrant closer respiratory monitoring, particularly in the first 3-6 months, as they show significantly elevated risk of tracheal mucus development
- •Detection of both S. zooepidemicus and nonhaemolytic streptococci in tracheal samples indicates considerably higher risk of significant airway mucus compared to either organism alone
- •Clinical signs of coughing at exercise and nasal discharge alone are unreliable indicators of tracheal mucus; endoscopic examination may be needed for accurate assessment
Key Findings
- •Combined isolation of S. zooepidemicus and nonhaemolytic streptococci increased odds of small amounts of mucus (OR 2.6) and substantially increased odds of increased mucus (OR 12.5)
- •First 3 months in training associated with 6.3-fold increased odds of small amounts of mucus; first 6 months with 2.9-fold increased odds of increased mucus
- •Coughing at exercise and increased serous nasal discharge were specific but insensitive clinical indicators of increased tracheal mucus
- •Nonhaemolytic streptococci showed an independent effect on tracheal mucus that had not been previously reported