Infectious risk factors and clinical indicators for tracheal mucus in British National Hunt racehorses.

The research article explores the infection risk factors that contribute to visible tracheal mucus in National Hunt racehorses, and the correlation between the presence of certain bacteria (namely Streptococcus zooepidemicus and non-haemolytic streptococci) and increased mucus production.

Study Methodology and Objectives

• The study was undertaken over two years and was prospective and longitudinal in nature.
• It sought to provide further understanding of the respiratory disease in racehorses, particularly focusing on tracheal mucus and airway neutrophilia by examining them independently.
• The researchers conducted monthly quantitative bacteriological examinations of tracheal wash samples taken from the racehorses and viral serological examinations to clear the presence of any pathogens.
• The specific objective was to identify risk factors for two levels of tracheal mucus – ‘small amounts of mucus’ and ‘increased mucus’ – using a scoring system.

Key Findings

• The research found that the odds of having small amounts of mucus were increased when both Streptococcus zooepidemicus and nonhaemolytic streptococci (NHS) were isolated in a horse’s system, but not when either species was present independently.
• Increased mucus production was associated with the presence of either S. zooepidemicus or NHS, with an increased effect when both were isolated together.
• The study also found that the odds of finding small amounts of mucus were about six times higher within the first three months of a horse’s training. A threefold increase in odds was noted for increased mucus within the first six months of training.
• Interestingly, coughing at exercise and increased serous nasal discharge were found to be specific, but not very sensitive, indicators of increased mucus.

Conclusions and Further Research

• The study managed to confirm previous research findings associating S. zooepidemicus with respiratory disease in racehorses, but an independent effect of NHS had not been previously reported.
• The researchers recommend considering the possibility that there are individual pathogenic species within the NHS group.
• They also suggest conducting further research to identify subtypes of the S. zooepidemicus species and the NHS species that are associated with disease.
• Lastly, the research concludes that closely monitoring the respiratory health of horses entering training for the first time could prove valuable.