Is Steamed Hay Beneficial for Horses With Severe Equine Asthma?

Steaming hay reduces respirable particles and is often recommended for horses with asthma. However, clinical studies examining the benefits of steamed hay have shown inconsistent results. A new crossover in vivo experiment aimed to assess the effects of steamed hay on lung function and airway inflammation in horses with severe equine asthma (SEA) in remission and compare those effects with a dry hay diet. 

Researchers fed horses steamed and dry hay for four weeks with a four-week washout period. Lung function, bronchoalveolar lavage (BALF) cytology, and a 23-point weighted clinical score (WCS) were recorded before and after four weeks of hay feeding. The researchers used a mixed linear model with post hoc tests. 

Resistance at 5 Hz (R5) increased over the four-week period (time effect and post hoc end vs. baseline: p < 0.001), with no difference between treatments (mean [SD], kPa/L/s) (baseline dry: 0.065 [0.014]; end dry: 0.079 [0.019]; baseline steamed: 0.063 [0.009]; end steamed: 0.078 [0.014]). There was a significant increase in BALF neutrophil percentages over time (end vs. baseline: p < 0.001) (baseline dry: 6.7 [5.4]; end dry: 13.1 [6.0]; baseline steamed: 5.6 [2.6]; end steamed: 10.5 [4.3]). WCS did not change significantly (baseline dry: 2.6 [1.5]; end dry: 2.2 [1.2]; baseline steamed: 2.9 [1.5]; end steamed: 1.9 [1.3]). 

Bottom Line 

Both dry and steamed hay induced a mild but significant deterioration of lung function and inflammation in horses with SEA, with no notable difference between dry and steamed hay. The lack of differences with dry hay could be due to the unexpectedly mild exacerbation during this study, meaning a difference might have been harder to detect.  

https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.70089

Related Reading

• Research Spotlight: Managing Equine Asthma
• Disease Du Jour: Equine Asthma and EIPH
• Impact of Steamed Hay and Alfalfa Pellets on Severe Equine Asthma

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