Soaking or steaming hay either in an attempt to reduce the sugar content or prevent respiratory irritation is common practice amongst horse owners. But which of these ‘treatments’ is most effective and could they in fact increase the bacterial content of your forage? A study carried by Jean Scott Moore-Coyler et al (2014) in collaboration with WALTHAM® investigated these very questions.


Method (what they did)

Five different UK hays were each subjected to the following treatments

  • Dry (no treatment)
  • 50 minutes steaming (Haygain- 600 steamer)
  • Soaked for 9 hours (water temperature 16°C)
  • Steamed for 50 minutes then soaked for 9 hours
  • Soaked for 9 hours then steamed for 50 minutes


All hays were then tested for water soluble carbohydrate (WSC = the sum of sugar plus fructan, the storage form of sugar in grass and other forages), bacteria and mould contents. Crude protein and ash levels were also tested.



  • Soaking, soaking then steaming and steaming then soaking were all equally effective at reducing WSC to a level currently considered suitable for laminitics
  • Steaming alone did not significantly reduce the WSC content
  • Both steaming and soaking then steaming reduced bacteria and mould counts
  • Soaking alone significantly increased the amount of bacteria compared to dry hay
  • Protein and ash levels were not affected by any treatment


What does this mean?

  • In this study soaking and then steaming was shown to be the most effective method for reducing WSC whilst also improving the hygienic quality of hay
  • Steaming alone improves the hygienic quality of hay but is not effective at reducing WSC
  • Soaking and steaming then soaking reduces the hygienic quality and therefore the potential effect this may have on the horse’s health needs further investigation



  • Whilst the soaking for 9 hours reduced WSC to a level currently regarded as suitable for laminitics in this study, results are variable (Longland et al 2011 and Longland et al 2014) and therefore soaking or soaking and steaming cannot guarantee safety/ suitability for laminitics
  • Reduce soaking to a maximum of 6 hours in hot weather
  • If your aim is to reduce the microbial contamination of your hay steaming is an effective choice