EM in the stable, cowshed and henhouse: bedding, ammonia and manure

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You open the stable or henhouse door in the morning and a sharp smell hits you: that is ammonia. It is not just unpleasant. It irritates the airways and eyes, both the animals' and yours, and it is a sign of bedding that is breaking down faster than it is drying out.

Effective microorganisms (EM) are often suggested as a way to improve the atmosphere in stables, cowsheds and henhouses. They can have a place there, provided you use them at the right dose and alongside good hygiene, never instead of it. Here is how to go about it, and what is really known about their effect.

Ammonia, a problem for the animals and for you

Mammal urine contains urea, and poultry droppings contain uric acid. On contact with the bedding, very common bacteria turn these compounds into ammonia, a gas that escapes into the air. The reaction speeds up the warmer, wetter and more trampled down the bedding is.

This gas irritates the nose, throat and eyes. Repeated exposure weakens the airways, which matters a great deal for horses, as they are very sensitive to the air quality in their stable. In broiler chicken farming, European regulations actually set a limit of 20 ppm of ammonia, measured at the animals' head height. If the smell stings your eyes, the concentration is already too high.

Did you know?

The air is most heavily loaded with ammonia right at bedding level. A horse lying down, a foal, a pony or a hen therefore breathes air that is considerably more irritating than what you smell standing in the aisle.

The basics first: bedding, mucking out and ventilation

No product can make up for soaked bedding. Before thinking about EM, check these points:

• Remove droppings and wet patches every day, and replace the bedding completely at regular intervals.
• Choose absorbent bedding. In a comparative trial presented in 2019, wood pellets and shavings produced less ammonia than straw, which absorbs less urine. The EM manufacturer, for its part, recommends straw-type bedding, which ferments better than wood: it is up to you to find the right balance for your animals.
• Ventilate: a building that breathes, without draughts on the animals, clears ammonia and moisture.
• Take the animals out while mucking out: this is when ammonia and dust are at their highest.
• Keep an eye on the diet: excess protein ends up in the urine as nitrogen. Talk to your vet if the smell remains strong despite good upkeep.

Key points

EM come after mucking out, absorption and ventilation, not before. They support well-kept bedding; they will not rescue neglected bedding.

Spraying EM on bedding: doses and frequency

The idea is to introduce lactic acid bacteria and yeasts into the bedding to steer decomposition towards acidic fermentation rather than putrefaction. The manufacturer suggests two dosage levels with EM-A Microferm, the ready-to-dilute solution.

Routine maintenance (henhouse, kennel, small stable)

Dilute Microferm to 1%: 10 ml per litre of water, i.e. 100 ml for a 10-litre sprayer. Spray the bedding regularly. The manufacturer does not set a precise frequency: once or twice a week is a good starting point, to be adjusted according to the smell.

Straw-bedded stables or cowsheds

Prepare a 5% solution (5 litres of Microferm per 100 litres of water, or 50 ml per litre). Spray about 1.5 litres of this solution per 9 m² stable, or 2 litres for 12 m², two to three times a week. When completely renewing the bedding, the manufacturer recommends working in layers: spray the floor, spread the bedding, then spray again.

At these volumes, making your own EM-A works out much cheaper: an activation tank such as our EM Activator, from 60 to 220 litres, turns 1 litre of EM-1 into 20 litres of active solution. It is used at the same dilutions, within 1 to 2 months of preparation. The method is in our guide activating EM-1 step by step.

With rock dust on damp areas

The manufacturer often combines EM with Vulkamin powder, a ground volcanic rock that absorbs moisture. Guidelines given for a horse stable: a layer of about 250 g per m² when laying the bedding, then two applications a week, of about 500 to 750 g for a 9 m² stable and 750 g to 1 kg for 12 m², concentrated on wet areas. The instructions for cattle on deep litter go up to 250 g per m² per day. Wear gloves and a dust mask when spreading it.

The rules that make the difference

• Use non-chlorinated water (rainwater or tap water left to stand for 24 hours), as explained in our golden rules for getting started with EM.
• Never apply EM on the same day as a disinfectant or lime: both destroy the microorganisms. If your vet prescribes disinfection, do that first, let it dry, then resume EM a few days later.
• Aim for the bedding, not the feeders, drinkers or the animals.

Emy's tip

Spray while the animals are outside, in large droplets rather than a fine mist, and let the bedding soak it up for around ten minutes before bringing them back in. Poultry in particular have airways that are very sensitive to anything floating in the air.

Manure that ferments rather than rots

The treated bedding continues its journey on the manure heap. The manufacturer suggests fermenting it without air: about 2 litres of Microferm diluted in around ten litres of water per m³ of fresh manure, compacted and covered airtight for 8 to 10 weeks. We explain this method in detail in our guide speeding up your compost with EM.

For slurry, there is a specific programme combining Pro-Mest Total and Microferm: 2 litres of Pro-Mest Total diluted in water per 100 m³ of slurry at the start, then 20 litres of Microferm per 100 m³ one to two weeks later depending on the instructions, and for maintenance about 1 litre of Pro-Mest Total per week for 50 livestock units. Follow the product instructions, which vary according to the type of pit.

What the studies show

Results do exist, but they are still few and inconsistent. Here are the most telling:

• Broiler chickens, Poland (2026). Bedding with added zeolite, then sprayed weekly with EM, produced about 54% less ammonia, drier bedding and fewer foot lesions. But the zeolite (an absorbent rock) and the EM were used together: it is impossible to tell which was responsible for what.
• Broiler chickens, East Africa. A trial measured less ammonia in the bedding, but EM were also given in the drinking water, which clouds the interpretation.
• Laying hens. A favourable effect on ammonia was reported, in a publication that had not been peer-reviewed.
• Pig slurry, Spain. A preliminary trial measured 59% less ammonia in spring, but no difference in autumn. The authors believe the dose was probably too low.
• Manure, Norway. Fermentation with EM was more pronounced, with no difference in the nitrogen or dry matter of the manure.

In short, a reduction in ammonia is plausible, notably thanks to the acidification of the bedding, but it is not guaranteed and depends heavily on conditions. We have found no independent study on the use of Microferm in a horse stable: the doses above are the manufacturer's. For an overview of the evidence, see our guide what science says about EM.

What not to do

• Do not put EM in the drinking water or in the feed without your vet's advice. Spraying products are not feed. For the diet, there are EM-fermented feeds designed for horses and livestock.
• Do not spray on a wound, in the eyes or in the nostrils.
• Do not expect EM to solve a health problem. An animal that is coughing, has runny eyes or is breathing poorly must be seen by a vet.
• Do not rely on a fragrance to mask ammonia: if the smell comes back quickly, it is the bedding or the ventilation that needs looking at.

In summary

Ammonia in stables, cowsheds and henhouses comes from urine and droppings breaking down in damp bedding. The first response is still daily mucking out, absorbent bedding and good ventilation. EM come next: Microferm diluted to 1% for routine maintenance, or a 5% solution sprayed two to three times a week on the straw in a stable, possibly with rock dust on damp areas. Studies show a possible reduction in ammonia, with no guarantee. Use non-chlorinated water, do not combine them with lime or a disinfectant, keep them out of the drinking water, and leave any health questions to your vet.

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