Soaking Hay Can Lower Dust Concentrations

For horses that are sensitive to inhaled irritants, eating hay can be a problem. Even the cleanest, highest-quality hay is likely to contain a moderate amount of fine material. When a horse plunges his head into a pile of hay or pulls mouthfuls out of a haynet, he inhales countless small particles of dust, mold spores, and fibrous plant material. Collectively known as the respirable dust concentration (RDC) these fine particles can cause severe airway irritation in sensitive horses. Heaves, broken wind, and recurrent airway obstruction are terms for the condition that can manifest as mild coughing or severe bronchial spasms that preclude any sort of training or exercise.

Management steps--wetting or soaking hay, selecting alternative bedding materials, and removing horses from stalls during periods of peak stall and barn cleaning activity--have been taken to determine how to minimize RDC impact. A study conducted at the University of Edinburgh in Scotland examined the effect of soaking hay on RDC in the horse's breathing zone--a two foot sphere around the end of his nose. The study was designed to determine the usefulness of brief hay immersion as opposed to longer soaking periods and to investigate how management of one stall influences the RDC in a neighboring stall.

The hay-soaking trial involved three hay treatments: dry hay, hay immersed in a bucket of water and then fed immediately, and hay immersed for 16 hours prior to feeding. For each treatment, a haynet with 5 kg of hay was placed in the same location in the stall. Wood shavings were used for bedding. The stall was prepared an hour before the horse (a 15-year-old mare familiar with the site and the sampling equipment) was brought in. The haynet was placed in the stall ten minutes later, and RDC monitoring began 10 minutes after the hay was presented. For each treatment, mean and maximum RDC readings were recorded in the horse's breathing zone during a two-hour sampling period. Six repetitions were performed for each protocol.

There was a significant difference in RDC readings in the horse's breathing zone for the three treatments. Compared to feeding of dry hay, feeding of immersed hay resulted in a 60% reduction in mean RDC, and feeding of soaked hay resulted in a 71% reduction. Maximum RDC readings showed that feeding immersed hay resulted in a 53% reduction compared with dry hay, while feeding soaked hay resulted in a 34% reduction.

The common air space tests were conducted in a stable with two side-by-side stalls. The stalls were separated by gates, sharing a common entrance and common air space above the divider. Two treatments were used: haylage, wood shavings, and an open window; or hay, straw bedding, and a closed window. The same mare was brought into the stall by 6:00 p.m. and was left undisturbed until she was taken out to pasture at 8:30 a.m. Manure and dirty/soaked bedding were removed immediately after the horse left the stall. Fresh bedding, if needed, was added daily, and hay or haylage was provided in a net suspended in the corner of the stall. The second stall contained no feed or bedding, and these materials were not stored in the vicinity of the building. Air sampling was conducted in both stalls. Eight days of sampling were done for each treatment. Mean and maximum RDC readings between the stalls were compared to determine the effect of treatment type and activity in one stall on air quality in an adjoining stall.

Changing the setup in the first stall from hay, straw bedding, and a closed window to haylage, wood shavings, and an open window resulted in a significant reduction in background mean RDC in both stalls. Making this management change reduced the median RDC value in the stall containing the horse by 73%, and in the second stall by 68%. RDC levels were higher during periods of greater stable activity. There was a 19-fold increase in RDC in the first stall while it was being mucked out. There was also a 9-fold increase in RDC in the adjoining empty stall when the first stall was being cleaned.

This research enables horse owners to limit their horses' exposure to RDC by following a few simple guidelines:

Wetting hay before it is offered to horses can significantly reduce the dust concentration in the horse's breathing zone. Prolonged hay soaking removes some soluble nutrients, so immersing hay seems the most sensible course of action. Hay should be fed as soon as possible after wetting, as allowing hay to dry could allow RDC to increase.

Additionally, this study confirmed that optimizing the management system in one stall resulted in a significant reduction in RDC in an adjoining stall. Peak RDC levels tended to coincide with times of high stable activity, such as mucking out stalls or moving horses in and out of the stall, so consider removing sensitive horses from the stable during these times.

Article reprinted with the permission of copyright holder Kentucky Equine Research (KER). Visit for more horse health and nutrition information.

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