Airway inflammation in Michigan pleasure horses: prevalence and risk factors.
Authors: Robinson N E, Karmaus W, Holcombe S J, Carr E A, Derksen F J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Airway Inflammation in Michigan Pleasure Horses Subclinical airway inflammation remains poorly characterised in working horses despite its suspected prevalence, prompting Robinson and colleagues to investigate both how common elevated tracheal inflammation is and which management factors drive it. Their endoscopic examination of 266 pleasure horses across 21 Michigan stables—sampled in both winter and summer—revealed that hay feeding, particularly from round bales, consistently elevated neutrophil counts compared to pasture-fed counterparts, whilst female sex and winter turnout were independent risk factors for inflammatory cell accumulation. Over 70% of the population exhibited neutrophil counts exceeding 20%, challenging the use of this threshold as a reliable diagnostic marker; more clinically relevant was the 20% of horses displaying mucus scores >1, with 17% showing both elevated mucus and elevated neutrophils. The practical implications are significant: management decisions such as maintaining hay-fed horses on pasture during winter where feasible, considering stalling during severe cold snaps for non-heaves-affected individuals, and recognising that older age (>15 years) compounds airway inflammation risk, may substantially reduce subclinical airway disease burden and associated cough in pleasure populations. Importantly, the finding that only half of horses with clinically detectable mucus accumulation actually cough underscores how easily subclinical inflammation escapes detection during routine assessment.
Read the full abstract on PubMed
Practical Takeaways
- •Consider offering pasture or alternative forage sources to hay, particularly round bales, to reduce airway inflammation in pleasure horses
- •Older horses (>15 years) and those fed hay should be monitored closely for subclinical airway inflammation even without visible clinical signs
- •In cold Michigan winters, keeping horses indoors may reduce airway inflammation and mucus accumulation, even in horses without diagnosed heaves
Key Findings
- •Over 70% of pleasure horses had >20% neutrophils in tracheal lavage, indicating subclinical airway inflammation is common
- •Hay feeding, especially from round bales, was associated with significantly more neutrophils compared to pasture feeding
- •Being outdoors >80% of time in winter was a significant risk factor for mucus accumulation and increased inflammatory cells
- •Age >15 years and hay feeding were independent risk factors for mucus accumulation >1, though only 50% of affected horses showed clinical cough