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The pungent smell that can burn your nostrils and throat as you muck out is ammonia, a colourless gas produced by degrading urine.

Dr Kieran O’Brien of Penbode Equine Vets in Devon explains that a horse urinates five to eight times a day, producing around 15 litres — the equivalent of a large bucketful. Bacteria present in droppings, in soiled bedding and on the stable floor convert the urea within urine into ammonia gas.

“The trend for using rubber stable matting with minimal bedding means that urine can become trapped underneath the mats, where it stagnates and releases ammonia,” he says. “High ammonia levels can irritate the horse’s respiratory system and cause inflammation and excess mucus production, which can interfere with oxygen uptake as he works.

“Foals are especially at risk as they spend a lot of time asleep with their head at floor level,” he adds. “Ammonia in the bedding is also known to damage horses’ feet, predisposing them to thrush and white line disease.

“The Health and Safety Executive has set the maximum permitted eight-hour workplace exposure ammonia level for people at 25ppm (parts per million), yet the level in stables can be as high as 250ppm or more. If you can clearly smell ammonia in the stable or on your clothes, the level is likely to be at least 100ppm. Some stabled horses are forced to breathe this for up to 23 hours per day.”

The solution is two-fold: to decrease ammonia production and to allow adequate ventilation to dilute the level in stable air. Kieran adds that horses can be taught to urinate on command and the urine caught in a long-handled muck scoop. One way is habituating a horse with a certain sound (for example whistling) every time the horse urinates. Once this command is learnt he can be taken to an area of a paddock where he has urinated before and urination induced.

“They soon learn that is why they have been taken to that place and will often urinate without being asked,” says Kieran.

“Alternatively, use the reluctance to urinate on bare floor to your advantage. Stand your horse on a bare floor for an hour or so, for example when being fed, after bringing him in from the field. Then scatter bedding and catch any urine that is passed.”

 

7 steps to clear the air

To reduce ammonia levels, Kieran recommends:

1 Use more bedding. A thick layer, spread over a wider area, will absorb urine run-off and allow more complete removal. Soft rubber mats are sometimes associated with unacceptably high ammonia levels. A sloping floor with a channel should allow urine to run away, but the low volume passed means this tends not to happen.

2 Use absorbent materials. Finer bedding materials such as sawdust (from pellets) and shavings result in the smallest urine footprint, though sawdust can work into the gaps between the mats and cause them to lift and separate. If you use straw, use a more absorbent alternative underneath. Remove as much soiled bedding as possible at least twice a day.

3 Muck out when the stable is empty. Exposing the wet bedding and floor will raise the ammonia level. Leave the stable empty afterwards, preferably with the door open.

4 Use a stable disinfectant. If the bedding is pushed back every day, sprinkle the urine footprint with powdered (not granular) garden lime, or a powdered stable disinfectant, both of which inhibit the action of the bacteria.

5 Seal between mats. Lifting mats and disinfecting underneath is
an onerous task that’s rarely done often enough; liquid disinfectant such as Virkon can be brushed into the cracks as a stop-gap measure.

6 Reduce protein. Protein fed to excess results in more urea being excreted in the urine and consequently more ammonia production.

7 Improve ventilation. Every stable should have two air inlets/outlets. Removing window glass, opening doors and using a door chain will improve airflow and dilute the ammonia level.

Ref Horse & Hound; 9 March 2017