Characterising viable bacteria on hat fed to horses when left dry, after soaking in water or after high temperature steaming.

Conserved forages can pose problems with equid respiratory health, thus pre-feeding wetting treatments are employed, including soaking (W) and high temperature steaming (HTS) to reduce respiratory disease symptoms. The effect of these treatments on bacterial viability and community profile on the hay is unknown. The aim of this study was to characterise the viable bacterial community profile of four hays; two Meadow (M) and two Italian Ryegrass (IRG) from two different locations in UK. Three 2.5kg haynets for each hay were subjected to dry (D), W or HTS. HTS was conducted in a HG600 for 60 minutes (manufacturer's instructions), W by submergence in 45L tap water at 16°C for 12 hours. Three grab samples (100g) from each post-treated hay were chopped and half (n=36) were treated with Propidiam monoazide (PMA) dye, to assess the bacterial viability. Bacterial DNA were extracted for bacterial community profiling of the 16S rRNA gene from all 72 samples, sequencing was conducted on the Ilumina MiSeq platform. Bioinformatics using the QIIME pipeline (v1.9.1) to create an OTU table and PICRUSt to predict metabolic pathways. LEfSe was used to identify differences in OTUs and KEGG orthologs between hays and treatments. HTS reduced proportions of viable bacteria compared to W and D hay. Soaking reduced the bacterial diversity within samples (p<0.001) compared to D and HTS. Core bacterial communities differed between hays and treatments. W and HTS reduced (P<0.05) viable bacteria known to cause respiratory disease, and HTS dental disease with the greatest reductions overall from HTS. We conclude that the bacterial community profile of hays appears to be influenced most significantly by different wetting treatments to hays with some influence from hay type and location. HTS reduced respiratory pathogens and those associated with dental disease while keeping the bacterial diversity closer to that of dry hay.