Chapter 14 - Introduction
Chapter 14 - Introduction
The most prevalent noxious gas in poultry housing is ammonia (NH3). Exposure to high concentrations of ammonia for extended periods has serious consequences on human and poultry respiratory health. Ammonia is a colorless gas generated from the volatilization(vaporization) of decomposed uric acid in chicken manure. Microbial decomposition of uric acid to ammonia and carbon dioxide is a function of the litter moisture content, temperature, and pH, all of which influence the number and type of microorganisms (bacteria and fungi) present in the litter. The moisture content of air and floor litter impacts particle generation. If floor litter is excessively dry, air and broiler movement tend to increase the amount of particles in the air. Misting systems may be used to moisten dry, dusty litter.
To limit ammonia production, the litter pH should be below 7.0; litter moisture below 30%; and temperature at the level of the broiler’s comfort demands. Chemicals may be added to the litter/manure pack to either reduce microbial growth and action, thereby slowing the decomposition of uric acid. The use of products that limit microbial growth is often discouraged, however, because the litter then loses it composting microbes. Other chemical treatments attempt to lower litter pH below 7, thus keeping nitrogen in the form of ammonium (NH4) rather than ammonia (NH3). Aluminum sulfate (alum), ferrous sulfate, ferric chloride, and phosphoric acid are chemicals that have been shown to reduce ammonia volatilization. Alum and phosphoric acid have been shown to reduce ammonia volatilization by over 90% in broiler houses. Alum would at first appear to be more desirable than phosphoric acid because it does not contribute to soil phosphorus loads when litter is spread to fields. However, there is insufficient evident to predict the long-term effects on soil of accumulated alum.
The scarcity and expense of bedding material and the problem of litter disposal in some regions have dictated its reuse. When a mixture of manure and bedding material is reused, the flocks are often exposed to extremely high ammonia concentrations during brooding as warm air temperatures increase volatilization of ammonia from waste in the litter.
Methods for reducing ammonia or other noxious gas generation or concentration include lowering the broiler stocking density, litter pH, or litter moisture content; and increasing the ventilation rate will reduce gas concentrations. While these recommendations help by providing more fresh airflow per broiler, they may be economically impractical in many cases. Better litter and manure management is also recommended through more frequent cleanout and/or litter treatment.
As ventilation rates increase, ammonia concentrations are lowered and litter is dried. The interaction between ventilation rates, moisture content of manure or litter, and the resulting ammonia concentrations is difficult to predict, however. Limiting litter or manure moisture content to below 30% can control ammonia generation; however, ammonia release can be boosted by increased air movement over litter. Although increasing ventilation may sometimes encourage a short-term ammonia release, the air exchange provided by ventilation replaces contaminated air with fresh air and is therefore useful in lowering ammonia concentrations.
