Theresia Lavergne, Carney, Jr., William A.
The poultry industry is the largest animal agricultural industry in Louisiana and is second only to forestry in total income produced by all agricultural commodities. Louisiana poultry growers produce almost 1 billion pounds of broiler meat each year. The size of the poultry industry in Louisiana has raised concerns about the management of large quantities of litter (mixture of poultry manure and bedding material).
Investigations in Midwestern states and more recently in Louisiana have determined that mismanagement and misuse of animal wastes from confined animal feeding operations (CAFOs), such as feedlots, dairy farms or poultry farms, can contribute to water pollution. Thus, the industry is becoming more environmentally conscious about how this poultry litter is used and handled. In fact, most poultry producers re-use poultry litter from the previous production cycle to help defray production costs and reduce the amount of litter produced.
Improved poultry litter management for reduced nutrient and pathogen contamination of water resources is a key issue affecting Louisiana and other poultry-producing states. Increasing the cost effectiveness of poultry production is also an important goal of poultry producers nationwide. Reduction of potential nutrient loss (for example, nitrogen and phosphorus) during water runoff from soils to which litter is applied and reduction of pathogenic organisms in litter, either stored or land-applied, would reduce environmental pressures placed on poultry producers.
Composting has been used successfully for many years to transform raw manures and other forms of organic matter, including poultry litter, to materials suitable for use as soil amendments. Heat generated during composting (self-heating) kills pathogenic microorganisms. The U.S. Environmental Protection Agency has approved a process, which relies on self-heating during composting, to further reduce pathogens (PFRP) in sewage sludge (biosolids) under the 40CFR.503 regulations (503 rule).
The premise of the 503 rule is that biosolids composted at temperatures exceeding 131 degrees F for 72 hours should have significantly reduced pathogenic microorganisms, making the end product safer to the public and suitable for land application. Additionally, heating and high pH levels that occur during the composting of biosolids reduce the odorous nature of the materials by increasing gaseous emissions, such as ammonia and sulfide gasses. Thus, the self-heating of poultry litter can kill Salmonella, Escherechia coli, Clostridium, Campylobacter, Staphylococus aureus and other microorganisms pathogenic to humans and poultry.
Therefore, with invaluable cooperation and assistance from poultry producers in northern Louisiana parishes, LSU AgCenter personnel have evaluated methods of in-house pasteurization (using composting technology) of broiler litter through demonstration trials conducted in commercial poultry houses. The objectives were to determine:
1) the minimal broiler litter moisture content for adequate self-heating for PFRP,
2) the effects of self-heating on pathogen reduction in re-used litter, and
3) the effect of in-house pasteurization on nutrient content of litter.
LSU AgCenter scientists conducted preliminary testing on poultry litter at the W.A. Callegari Environmental Center to determine the minimum moisture required to achieve 131 degrees F before beginning full demonstration trials. This testing was performed by wetting dried poultry litter to specific moisture contents, compacting the litter in well-insulated flasks, inserting a digital thermometer capable of measuring and recording maximum temperatures, and allowing the litter to undergo pasteurization in the flasks until a maximum temperature had been observed.
The litter used in these trials was from the fourth production cycle. It was determined that approximately 31 percent moisture in poultry litter was the minimum moisture required to generate PFRP temperatures in three replicate Dewar flasks. However, higher moisture levels produced temperatures over 131 degrees F and also were considered for use in demonstration trials. However, to minimize the potential effects of excess moisture after the trials ended, a maximum of 35 percent moisture was expected to be used in on-farm trials.
Typical poultry production cycles last from six to eight weeks, with seven to 10 days between cycles. Each demonstration trial was conducted between production cycles (after birds were removed from the houses and before the placement of a new flock). After flocks of broilers were harvested, poultry growers typically removed the compacted, high-moisture sub-layer of litter (cake) before performing demonstration trials. The interiors of the houses were often pressure-washed to remove excessive dust build-up. Using tractors and operators supplied by poultry growers and an extended-width blade, two litter windrows were formed in each poultry house. The windrows ran the full length of the houses (400 to 600 feet) and were approximately 2 feet high and 4 feet wide.
In the first trials the litter remained in the windrows for the full seven to 10 days before being redistributed over the floor of the houses. To achieve the minimum moisture required to generate PFRP temperatures, some litter required the addition of water to windrow surfaces or to the litter before windrowing, while others relied on ambient moisture levels. These trials were designed to determine the effect of moisture on heating necessary for PFRP and to determine if added moisture could be reduced or not used at all. Too much moisture in the bedding could potentially be harmful to young birds placed in the house. During more recent trials, litter was windrowed for a period adequate to achieve PFRP (72 hours) and then redistributed in houses.
Analyses and Monitoring
In the on-farm demonstration trials, samples were taken from the litter immediately after windrowing and after pasteurizing. Several trials were repeated in the same broiler houses to collect information about application of in-house pasteurization over several broiler flocks. Also, the effects of litter accumulation on potential increases in nutrients and pathogenic microorganisms over time were evaluated.
Litter temperatures were obtained at six-inch and 12-inch depths using digital thermometers capable of recording the maximum, minimum and current temperatures in the building and in the litter. These thermometers allowed detection of the day and time when PFRP temperatures were first achieved. Daily litter temperatures were recorded. The maximum and minimum temperatures and the date and the time of occurrence were recorded, too.
Chemical and physical analyses of litter samples were performed at the Callegari center. Nutrient analyses included total and plant available nitrogen (N), potassium (K), phosphorus (P), sodium (Na), calcium (Ca), magnes-ium (Mg) and sulfur (S). Sample pH, electrical conductivity (soluble salts), moisture and the ash content (soil and inherent minerals) of litter were analyzed and used to determine the effects of composting on poultry litter. Microbiological analyses were performed in private environmental laboratories.
Effects of Pasteurization on Plant Nutrients
The accumulation of nutrients in poultry litter pasteurized over successive production cycles has been of interest to scientists and producers alike because of environmental concerns of land application of litter. Results from the analysis of litter from successive production cycles in houses on two farms participating in the pasteurization trials indicated that the average ash content increased 5 percent over the pasteurization period. Although small decreases in total nutrient contents were observed, the increase in plant-available nutrient contents was not great.
Composting of organic matter releases large concentrations of nutrients that may be measured as soluble salts. However, decreased nutrient availability is usually only observed in materials composted for many months. Availability of nutrients was expected to increase during the short periods of in-house pasteurization for these trials. As expected, the average soluble salt concentrations did increase by 25 percent during pasteurization. A large fraction of the total nutrients are in plant-available form. After the short period of pasteurization, the percentage of total N as ammonium (NH3-N), K, Mg, Ca and Na in plant-available forms in poultry litter were reduced. However, plant-available P and S increased.
Effects of Pasteurization on Pathogens
The litter was analyzed for total anaerobic count for pathogens at the beginning and at the end of each demonstration trial to verify that the pathogen content was reduced due to the litter heat. In demonstration trials, the total anaerobic count for pathogens, measured as colony-forming units per gram, was reduced by approximately 90 percent or more.
This method of in-house pasteurization of broiler litter provides an opportunity for poultry producers to confidently re-use litter from previous flocks of broilers. The ultimate result would be a reduction in the number of times litter would need to be removed from the houses (once a year or every two years as opposed to multiple times in one year) as well as a reduction in the quantity of litter produced in Louisiana each year.