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March 2021 issue is now available!


The Winter Ammonia Blues


Compiled By Nancy Brannon, Ph.D.

During the cold winter months, horse owners tend to keep their horses in barns for longer period of times, usually with doors and windows closed to keep their horses warmer. But these tightly closed barns may be presenting a respiratory hazard for horses.

When you open the barn or stall door, pitchfork in hand, are you hit with an acrid smell? That characteristic pungent and unpleasant odor is ammonia, which comes from urea. Horses excrete urea to eliminate excess nitrogen from their bodies, and that urea is quickly converted to ammonia once excreted. Ammonia is a colorless gas that is made up of one part nitrogen (N) and three parts hydrogen (H3). Ammonia can be extremely irritating to the mucous membranes that line the mouth, eyes, and respiratory tract.

Equine Wellness Magazinestated that ammonia is the second-leading cause of respiratory disease in horses—second only to dust. The article explained the dangers of ammonia, rated bedding products, and recommended ways to reduce ammonia, including with stall amendments.

Research published in the Journal of Animal Science (2009) and the Journal of Equine Veterinary Science (2000) found that ammonia levels are highest near barn and stall floors. Since horses frequently eat off the floor, have their heads down, and lie down when stabled for long periods of time, they can be exposed to high levels of ammonia. Ammonia levels in an average horse stall can exceed 200 ppm. For humans, the U.S. Occupational Safety and Health Administration (OSHA) has set a 15-minute exposure limit for gaseous ammonia levels of 35 ppm. This means that both horses and humans can be exposed to very unhealthy levels of ammonia in barns. Ammonia inhalation on a daily basis can result in inflammation and constriction of the airways and mucus accumulation (Equine Veterinary Journal, 2006).

Experts advise that environmental management is the best way to reduce ammonia within the stable. Remove manure and wet bedding often, and then apply an ammonia-eliminating or ammonia-absorbing compound to neutralize the ammonia and decrease the levels reaching the horse’s airways.

Pratt, et al., (2000) measured ammonia concentrations in horse stalls treated with ammonia-absorbing compounds (AAC). Over a 14-day period, they measured stalls treated with AAC vs. non-treated control stalls. The horses remained in the stalls at all times, except for a 30-minute daily turnout. They measured the ammonia levels at the stall floor and through diffusion tubes attached to the horses’ halters to determine the level of ammonia exposed to the horse. On day 14, they found that ammonia concentrations near the stall floor were 25% lower in treated stalls than in control stalls. They also found that concentrations measured at the halter were much lower and that horses in treated stalls had lower ammonia exposure than horses in control stalls.

Types of ammonia-absorbing compounds include: (1) lime-based products. For many years people have used hydrated lime to help rid stables of ammonia. However, research at North Carolina State University found that lime products “increase the litter alkalinity and convert more of the ammonium into ammonia gas, which must be vented to the outdoors and can become an environmental problem.” (2) Natural minerals such as diatomaceous earth, clay, and zeolites. These products are nontoxic and noncaustic, moisture-absorbing, and they trap ammonia.

Sweet PDZ is a product made with zeolites, which were formed from ancient volcanic activity. The clinoptilolite that comprises Sweet PDZ is one of the best at ammonia absorption and odor neutralization. When Sweet PDZ is applied on the floor of the stall or barn environment, it quickly begins to work at adsorbing the ammonia, which is the action of the ammonia gas particle sticking to the surface of the Sweet PDZ granules.  The ammonia gas then hydrolyzes and is locked up within the mineral structure through a positive/negative ionic bond known as cation exchange. 

Sweet PDZ can also be used for neutralizing odors in every type of livestock pen or pet habitat, including dog runs, cat boxes, small critter cages, rabbit hutches, chicken coops and goat/sheep pens.  

Sweet PDZ is OMRI Listed as an organic material.  It is described as a full-circle/green-earth mineral.  It is harvested from the earth, then loaded up with noxious ammonia and other odors, and then returned to the earth (compost, gardens, fields) where it benefits the soil as an organic slow-release nitrogen soil conditioner.

 (3) Microbe-containing products: microscopic organisms break down the ammonia-forming molecules in urine and feces. These microbes decrease the amount of ammonia and are noncaustic.

The bottom line for protecting equine respiratory health is good ventilation in the barn. EquiMed reminds readers of the importance of good ventilation in horse barns. “A poorly ventilated barn is unnaturally damp and dusty, which can lead to respiratory problems. Some contaminants in barns may compromise respiratory health and produce performance-limiting problems: chronic obstructive pulmonary disease (COPD) or recurrent airway obstruction (RAO). …Proper ventilation is extremely crucial to respiratory health.”

ATSDR – Public Health Statement: Ammonia
Clark, Terri. 2020. “Ammonia in your barh – what you need to know.” Equine Wellness Magazine. March 17.
Oke, Stacey, DVM. 2010. “Ammonia & Respiratory Health.” The Horse. Sept. 22.
“The Dangers of Hydrated Lime.”
Paulick Report. 2020.  “Addressing Ammonia and Respiratory Disease in Horses.” March 22.
“Poultry Litter Amendments”
Pratt, S.E., L.M. Lawrence, T. Barnes, D. Powell, and L.K. Warren. 2000. “Measurement of ammonia concentrations in horse stalls.” Journal of Equine Veterinary Science. Vol. 20, No. 3. March.
Sweet PDZ:
Thomas, Heather Smith. 2019. “Importance of Good Ventilation in Horse Barns.” EquiMed. July 14.
Additional resource: “How Bad is Stable Ammonia for Your Horse’s Health?” Horse and Rider.

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