PhD Candidate Université de Montréal Sainte-Madeleine, Quebec, Canada
Abstract:
Background: Dry hay can trigger severe equine asthma exacerbations. Propionic acid is sometimes used as a preservative to inhibit microbial growth.
Hypothesis/
Objectives: To assess the effects of propionic acid on fungal growth in hay, and of propionic acid–treated hay (PAH) on airway limitation and inflammation.
Animals: Nine research horses with severe asthma.
Methods: Prospective crossover study. Hay was harvested from a single field the previous year and baled at high moisture content (>15%), with or without propionic acid. Fungal culture was performed on 20 samples (10 PAH, 10 untreated hay (UH), Welch t test). Horses were maintained on a low-antigen diet before receiving PAH or UH for 4 weeks, with a 4-week washout period. Pulmonary resistance and bronchoalveolar lavage fluid (BALF) cytology were assessed before and after each period (two-way repeated-measures ANOVA with post hoc comparisons).
Results: Mold counts were significantly lower in PAH compared to UH (mean [SD], 4.41 [1.02] vs 5.26 [0.44] log10 CFU/g; p = 0.03). Pulmonary resistance increased after UH (median [IQR], 0.90 [0.95] to 1.50 [1.04] cm H₂O/L/s; p = 0.02) but not after PAH (0.75 [0.87] to 0.84 [1.04] cm H₂O/L/s; p = 0.58). BALF neutrophil percentage increased after UH (6.50 [6.50] to 11.50 [6.63] %; p < 0.01) but not after PAH (4.75 [5.13] to 7.25 [6.38] %; p = 0.16).
Conclusion and Clinical Importance: Propionic acid reduced molds in hay baled at high moisture content. Feeding PAH may attenuate, but not completely prevent, exacerbations of severe equine asthma.
