Poor Barn Air Quality Can Put Horse Respiratory Health at Risk

Article by OSU Equine News: I was recently invited to speak to an industry group about issues affecting horses in barns. One factor that many may dismiss or not consider important is air quality. Sure, we have all been in barns with a strong ammonia smell or high humidity, but it is often just shrugged off as part of normal horse barn odor. However, respiratory function is a key component of success for performance horses and ammonia, humidity or dust accumulation should not be taken lightly as it can dramatically affect airway function. One key factor affecting air quality is the amount of ammonia. Ammonia is created by microbes in the environment converting urea that is present both in manure and urine into ammonia, a highly volatile gas. The degree of conversion depends on many factors, such as pH, temperature and humidity. In general, higher temperatures, humidity and pH all increase the conversion rate of urea to ammonia. If the barn has a strong ammonia smell, that indicates a problem. Due to the weight of the gas, there can be a substantial ammonia concentration gradient between where the human nose is detecting ammonia and where the horse's head is during feed consumption. Ammonia concentration over 50 ppm can cause respiratory damage, and the levels of ammonia at the floor of the stall can vary between 80 and 450 ppm, depending on bedding type, frequency of cleaning and other conditions. One specific factor in controlling ammonia concentrations directly under the owner's control is the diet. Horses that are fed diets more than their protein requirements will excrete excess nitrogen as urea. Therefore, matching requirements with the amount of protein fed will contribute to a reduction of ammonia in the barn. Ventilation is also key. The goal is to achieve 4-8 air changes per hour (ACH). However, outlets for ventilation such as windows and doors are often closed to keep barns at temperatures that are more comfortable for people, rather than horses. The practice of shutting barns up at night can greatly increase ammonia, especially as humidity increases from the respiration of horses. This can not only trap ammonia but speed the conversion of urea to ammonia. Bedding type also influences ammonia in horse barns. While not as common in the US, numerous studies indicate peat bedding outperforms other substrates. For bedding typical in the US, wood shavings have less ammonia and dust production than straw. If ventilation systems are installed, air that draws from the floor (typically placed in corner of stalls) is ideal. As ammonia accumulates at the floor of the stall, this is the most effective means of removal. Installation of ventilation systems can have real impacts on horse health, as one study comparing air quality and horse health pre and post ventilation installation significantly reduced CO2, ammonia and allergens, as well as a reduction in airway inflammatory markers in the horses. There are several environmental amendment products, but most have been studied in other commercial livestock species. Biochar and zeolite have been used extensively in manure slurry to reduce ammonia, and to some extent in poultry litter and dairy bedding. Biochar is stable carbon rich material created by heating organic material at high temperatures without oxygen. However, biochar can be highly variable, depending on heating, duration of processing and pH of the final product. Mixing rice hull-based biochar into traditional sawdust bedding reduced ammonia in dairy bedding (the closest analogy) by 27-43%. However, the pH of the product is highly important. If the material is too alkaline, it can increase volatilization of ammonia. All sources of biochar are also not equivalent, as wood-based biochar did not show a decrease in ammonia production in stored manure. Unfortunately, data in other species cannot be directly extrapolated as nitrogen in poultry excrement is present as uric acid, compared to urea in horses. Unfortunately to date, no research on actual horse stalls has taken place. Zeolite is another product that may have potential for use in horse barns. Zeolite has a crystalline structure (made out of silicon, oxygen and aluminum) with micropores which can trap ammonia. The pores help to bind water, decreasing the ability for the urease enzyme to work. Acid activation of zeolite also improves its effectiveness at reducing ammonia, again keeping the pH below the range that urease drives the urea to ammonia reaction. MCDMH-modified clinoptilolite zeolite, a specialized form of zeolite, has been shown to outperform other materials when used in cat litter. It decreased urease activity by >97% and reduced bacterial CFUs by six log values. Unfortunately, no study has tested it in horse stall bedding specifically, and efficacy depends heavily on application rate, zeolite origin, and moisture conditions. There is also limited information available on the price of such products if they were economically feasible for use in equine facilities. So bottom line, feed protein appropriately, utilize ventilation systems in closed buildings and know that there may be some products available in the future that may greatly assist with ammonia removal and respiratory health in horses.