EM in the stable, barn, and chicken coop: bedding, ammonia, and manure

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You open the stall or chicken coop door in the morning and a sharp smell hits you: that's ammonia. It's not just unpleasant. It irritates the airways and eyes, both the animals' and yours, and it's 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 air in stables, barns, and chicken coops. They can have a place there, provided you use them at the right dose and alongside good hygiene, never instead of it. Here's 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 warmer, wetter, and more trampled the bedding, the faster the reaction.

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 stall. 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 manure and wet spots 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's up to you to find the right balance for your animals.
• Ventilate: a building that breathes, without drafts on the animals, clears out ammonia and moisture.
• Move 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 stays strong despite good upkeep.

Key takeaways

EM come after mucking out, absorption, and ventilation, not before. They support well-kept bedding; they won't 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 toward acidic fermentation rather than putrefaction. The manufacturer suggests two dosage levels with EM-A Microferm, the ready-to-dilute solution.

Routine maintenance (chicken coop, kennel, small stall)

Dilute Microferm to 1%: 1.3 fl oz per gallon of water (10 ml per liter), so 3.4 fl oz (100 ml) for a 2.6-gallon (10-liter) sprayer. Spray the bedding regularly. The manufacturer doesn't 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 barns

Prepare a 5% solution (1.3 gallons (5 liters) of Microferm per 26.4 gallons (100 liters) of water, or 6.4 fl oz per gallon (50 ml per liter)). Spray about 1.6 quarts (1.5 liters) of this solution per 97 sq ft (9 m²) stall, or 2.1 quarts (2 liters) for 129 sq ft (12 m²), two to three times a week. When completely replacing 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 16 to 58 gallons (60 to 220 liters), turns about 1 quart (1 liter) of EM-1 into 5.3 gallons (20 liters) of active solution. It's used at the same dilutions, within 1 to 2 months of preparation. You'll find the method 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 stall: a layer of about 0.8 oz per sq ft (250 g per m²) when laying the bedding, then two applications a week, of about 1.1–1.7 lb (500–750 g) for a 97 sq ft (9 m²) stall and 1.7–2.2 lb (750 g–1 kg) for 129 sq ft (12 m²), concentrated on wet areas. The instructions for cattle on deep bedding go up to 0.8 oz per sq ft (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, waterers, 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 about 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 pile. The manufacturer suggests fermenting it without air: about 2.1 quarts (2 liters) of Microferm diluted in about 2.6 gallons (10 liters) of water per 1.3 cubic yards (1 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 liquid manure (slurry), there is a specific program combining Pro-Mest Total and Microferm: 2.1 quarts (2 liters) of Pro-Mest Total diluted in water per 26,400 gallons (100 m³) of slurry at the start, then 5.3 gallons (20 liters) of Microferm per 26,400 gallons (100 m³) one to two weeks later depending on the instructions, and for maintenance about 1 quart (1 liter) 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's 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 muddies the interpretation.
• Laying hens. A favorable effect on ammonia was reported, in a publication that had not been peer-reviewed.
• Hog slurry, Spain. A preliminary trial measured 59% less ammonia in spring, but no difference in fall. 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 isn't guaranteed and depends heavily on conditions. We have found no independent study on the use of Microferm in a horse stall: 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

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

In summary

Ammonia in stables, barns, and chicken coops 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 stall, possibly with rock dust on damp areas. Studies show a possible reduction in ammonia, with no guarantee. Use non-chlorinated water, don't combine EM with lime or a disinfectant, keep them out of the drinking water, and leave any health questions to your vet.

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