How to get rid of ammonia smell in a horse barn (without masking it)
Barn ammonia comes from bacteria breaking down urine and manure. Here is what it does to a horse's lungs and how to fix it with cleaning, ventilation and a stall deodorizer.
Short answer: ammonia comes from bacteria breaking down urine and manure, so you get rid of it by taking away what feeds it and keeping the air moving: pull wet bedding, let the floor dry, ventilate, and if you want extra help, put a mineral stall deodorizer under the bedding. In a University of Kentucky trial, ammonia near the floor of untreated stalls passed 200 ppm within seven days even with daily cleaning, and an ammonia-absorbing stall product brought floor levels about 25% lower after two weeks. A scent that does not absorb or bind ammonia changes what you smell, not what the horse breathes.
We run horses on our own place outside Sherwood Park. Here is where the smell comes from, what it does to a horse, and the three fixes that work together.
Where the ammonia comes from
Ammonia is a gas released by bacteria as they break down organic material in urine and manure (EQUUS). In animal buildings it is highest near the floor, the University of Kentucky notes. In its trial, in dirt-floored stalls bedded with straw, ammonia stayed low for the first few days and then climbed fast, especially at floor level. Diet plays a part too: Karen Waite, an equine extension specialist at Michigan State University, points out that high-protein diets produce more ammonia in urine.
What it does to a horse’s lungs
The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) says gases such as ammonia form acids that burn respiratory tissue. The University of Kentucky says high concentrations irritate the mucous membranes of the eyes, nose and mouth and may make animals more susceptible to respiratory infections. EQUUS adds that ammonia inhibits the cilia that sweep particles out of the airway, weakening a horse’s natural defences.
Nobody has pinned down a safe level for horses. Kentucky says the unhealthy level is not known, but the 200 ppm it measured near the floor is higher than levels found to harm other animals, and it says foals or sick horses that spend long hours lying down might face a respiratory challenge. For horses with heaves, the Merck Veterinary Manual says managing the environment is the single most important treatment. The dust side of the same problem is in Arena dust and your horse’s lungs.
Step 1: clean to the floor and let it dry
EQUUS puts it simply: remove all manure and wet bedding, and leave the floor or mats exposed until they are dry. Daily cleaning alone was not enough in the Kentucky trial, so pull wet bedding down to the floor in the urine corner, and keep enough bedding in the stall to absorb urine before it reaches the floor. If the smell persists on a dry floor, EQUUS says a dirt floor saturated with urine may need to be dug out and replaced, or the drainage under your mats may need work.
Step 2: move air
A stall that never dries is not getting enough ventilation. EQUUS suggests opening doors or windows until the cross breeze dries a stall within half a day, or placing a large fan to draw out stagnant air. OMAFRA gives numbers: in winter, 25 to 40 CFM (12 to 19 L/s) of fresh air per horse is ideal, and in summer up to 300 CFM. It wants at least two air changes an hour, notes many barns manage one to save on heating, and puts relative humidity at 60% to 70%. If a barn gets too cold, OMAFRA’s answer is heat, not less ventilation. A smoke pencil shows how air moves, and gas detection tubes measure ammonia.
Step 3: add a mineral deodorizer under the bedding
Sirocco Stall Fresh is a natural mineral stall deodorizer. Its product page says it absorbs moisture and neutralizes ammonia at the stall floor, contains no artificial perfumes, and is safe for horses, livestock, poultry and other barn animals. Use it like this, per the page:
- Remove all wet and soiled bedding.
- Sprinkle it evenly over the floor, with extra where your horse urinates.
- Add fresh bedding on top.
- Reapply at each full cleanout, or spot-apply mid-week in high-use areas.
It works with shavings, pellets, straw and most other bedding, and the page says you can apply it straight onto rubber or polyethylene stall mats. It comes in 4 kg ($39.95 CAD) and 25 kg ($78.95 CAD). The page is straight about its limits: it is not a replacement for good stall management.
The Kentucky trial tested a different commercial product, so it supports the category, not Stall Fresh in particular. In that trial the product did not eliminate ammonia: floor levels were about 25% lower after two weeks, and ammonia over fresh urine spots fell by 60% or more within 15 minutes of application. Think of a stall deodorizer as one of three tools, not a replacement for the other two. We covered how Stall Fresh works in our earlier piece on neutralizing ammonia naturally.
Lime or a mineral product?
- Agricultural lime (barn lime or garden lime) is mostly calcium carbonate, which is non-toxic. Waite could find no scientific evidence that it harms horses, but it is a fine powder: apply it with the horses out and wear a mask. Pelleted lime can reduce the irritation risk.
- Quicklime and hydrated lime are caustic and can burn skin. Waite says to avoid them in barns, and EQUUS notes hydrated lime can be extremely caustic.
- Mineral stall deodorizers go under the bedding. The Stall Fresh page says it is formulated for active stalls and safe when horses return after cleanout, and EQUUS says many horsekeepers choose commercial stall products to get similar results without lime’s downsides.
Uncle Jeeter says: “Don’t wait until your eyes are watering when you walk in the barn to do something about ammonia. By the time you can smell it that strong, it’s been sitting in your horse’s lungs for a while already. Put this down at every cleanout, focus it on the wet corners, and stay ahead of it. A little effort at cleanout time saves a lot of misery in between.”
Questions people ask
Why is the ammonia worse in winter?
Closed-up barns hold moisture and gas. OMAFRA’s ideal winter ventilation is 25 to 40 CFM (12 to 19 L/s) per horse, and a barn that cannot keep to that will hold more ammonia. Check how air moves with a smoke pencil and fix ventilation before you add product.
Does a stall deodorizer replace mucking out?
No. In the University of Kentucky trial an ammonia-absorbing product lowered ammonia but did not eliminate it, and the Stall Fresh page says it is not a replacement for good stall management.
Is lime safe to use in horse stalls?
Agricultural lime is mostly calcium carbonate, and Michigan State University’s Karen Waite found no scientific evidence that it harms horses. It is a fine powder, so apply it with the horses out and wear a mask. Quicklime and hydrated lime are caustic and best avoided.
How much deodorizer do I use per stall?
The Stall Fresh page says a standard 12 by 12 ft (3.7 by 3.7 m) stall needs a light, even layer across the floor with a bit extra in the wet spots. The guide on the packaging gives a more precise rate.
What ammonia level is safe for horses?
No one has set one. The University of Kentucky says the level that is unhealthy for horses is not known, so aim to keep it as low as you can. Gas detection tubes (OMAFRA) will give you a number for your barn.
Sources: University of Kentucky Ag Equine Programs, “Controlling Ammonia in Horse Stalls” (2009, on Pratt et al., Journal of Equine Veterinary Science, 2000); OMAFRA, “Horse barn ventilation” (2023, updated 2026); EQUUS, “What ammonia smells mean” and “Is agricultural lime safe for horse stalls?” (Karen Waite, Michigan State University); Merck Veterinary Manual, “Recurrent Airway Obstruction (Heaves) in Horses”; Sirocco Stall Fresh product page at farmandbarn.com.
Next step: try Sirocco Stall Fresh on your wettest stall for a week, with the cleaning and ventilation fixes above. Not sure which size? Message the barn with your stall count.
