The effect of three different treatments on the respirable particle content, total viable count and mould concentrations in hay for horses

Hay, fed to stabled horses can contain high concentrations of respirable particles (RP) (<5 μm), which are the main cause of recurrent airway obstruction (RAO) in horses. This study measured the efficacy of soaking versus steaming at reducing the RP and microbial contamination in hay. Five 30–35 kg bales of barn-stored Lolium perenne hay made June 2011 were treated as follows: for each bale, half was steamed for 40 minutes in a commercial hay steamer, the other half was divided into two 4–6 kg hay nets. One net was kept dry while the other net was soaked in fresh tap water (15 °C) for 10 minutes then drained for 10 minutes. One hundred gram samples from each of the 3 treatments (100 g combined from 5× 20 g sub samples taken in a W shape) were immediately placed into 3 separate pre-labelled (dry, steamed and soaked), sterile plastic bags. The 15 samples (5 dry, 5 steamed and 5 soaked) were prepared as follows: A one gram sub-sample was weighed into a sterile stomacher bag and 79 ml of peptone saline diluent added and the solution processed for 2 minutes to wash particles into the solution. Sequential dilutions were prepared down to 10–4. 1 ml from each dilution was placed onto two 3 M™ petrifilms and incubated for 3–5 days at 20, 24 (mould films) and 32 °C (bacteria), before counting using a standard colony counter. RP were determined by shaking under a cyclone sampler, according to the method of Moore-Colyer. Differences between treatments were determined using ANOVA on log transformed data. RP concentrations for dry, soaked and steamed hay were 1,327, 0 and 1.5 (sed = 1.72) geometric mean numbers/litre air/kg DM, respectively. Mould concentrations were 1,174,897, 316,227 and 1,072 (sed 1.97), respectively. Total bacterial counts (TVC) were 21,877,616, 37,153,522 and 83,176 (sed 2.55), respectively. Steaming was the most effective treatment for reducing RP, mould and TVC concentrations. Soaking reduced RP but increased TVC and thus did not improve the hygienic quality of the hay.