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Ammonia in Commercial Layer Houses

by 5m Editor
10 March 2004, at 12:00am

By A. Bruce Webster, Extension Poultry Scientist, University of Georgia, Athens, Georgia. Published by Poultry Science - This study compares two types of layer houses, the manure belt house and the high rise house, to try to learn the NH3 production rates typical of different types of commercial layer houses.

Ammonia in Commercial Layer Houses - By A. Bruce Webster, Extension Poultry Scientist, University of Georgia, Athens, Georgia. Published by Poultry Science - This study compares two types of layer houses, the manure belt house and the high rise house, to try to learn the NH3 production rates typical of different types of commercial layer houses.

Poultry manure is high in nitrogen, some of which is released as ammonia, NH3, when manure moisture and temperature are high enough to support NH3 production. High concentrations of NH3 can have an adverse impact on hens. For this reason, the 2003 United Egg Producers Animal Husbandry Guidelines specify that commercial flocks should be exposed to less than 25 parts per million (ppm) NH3 and not more than 50 ppm.

It is also possible that large layer houses emit significant quantities of NH3 into the atmosphere, creating the risk that commercial egg farms will be identified as point sources for emission of NH3 as an air pollutant. If this were to happen, large egg production facilities could become subject to regulation of NH3 emission under the Clean Air Act.

Egg producers have had difficulty coming to grips with NH3 because there is no reliable technology available to continuously measure NH3 levels in commercial housing environments. Without this technology, it is not possible to establish how serious a problem NH3 is inside a layer house, nor to accurately estimate how much NH3 a house actually emits.

Researchers have used portable monitoring units to try to learn the NH3 production rates typical of different types of commercial layer houses. Some results have recently been published for houses located in Iowa (Liang, et al. 2003. Ammonia emissions from layer houses in Iowa. Pages 1-9 in: Proceedings of the International Symposium on Gaseous and Odour Emissions from Animal Production Facilities. Horsens, Jutland, Denmark, June 1-4).

Two types of houses were studied. The manure belt house had exhaust fans located on each end of the house and two continuous slot air inlets in the ceiling running the length of the house. Manure was removed daily. The high-rise house had all exhaust fans installed in the side walls of the bottom level, where the manure was stored. Continuous slot ceiling inlets were located over each cage row.

Several months accumulation of manure was in place at the start and no manure was removed during the study. Flock size was more than 100,000 hens in each house. The ventilation rate was based on house temperature. NH3 levels were recorded in the living space of the hens and at the exhaust fans at intervals of about 2 weeks from February to October. During each sampling period, recordings of NH3 were taken every 30 minutes for at least 48 hours.

In the manure belt house, daily average NH3 concentrations were low in all seasons, ranging from 1 to 7 ppm. This reflects the fact that there was little manure in the house to produce NH3. The high-rise house had daily average concentrations of NH3 in the living space of the birds ranging from 3 to 61 ppm. In this house, NH3 levels were highest in the winter, exceeding a daily average of 50 ppm on one of the five days monitored in February and March. From April to late October, daily average NH3 levels were below 20 ppm.

Calculated NH3 emission rates were lowest in winter (February-March) and highest in summer (June-August) from both types of house. The amount of NH3 released from each house, however, differed considerably. For the manure belt and high-rise house, respectively, average NH3 emission rates in winter were 0.09 lbs/1000 hens/day and 1.64 lbs/1000 hens/day, and in summer were 0.82 lbs/1000 hens/day and 2.90 lbs/1000 hens/day. When projected to an annual basis, the average daily NH3 emission rate was calculated to be 0.38 lb/1000 hens/day for the manure belt house, and 2.27 lb/1000 hens/day for the high-rise house.

The data clearly favor the manure belt house with daily manure removal for control of NH3. There is no reason to believe that NH3 levels would differ greatly from those seen in this study in any similar house with the same manure management. Hens in the manure belt house were never observed to be exposed to stressful concentrations of NH3. NH3 emissions from the house were low, making it possible to argue that any size of house of this type should not be classified as a point source for air pollution. Of course, the manure removed from such a the house would have the potential to produce as much NH3 as that produced in a highrise house, unless managed in a way that curtails NH3 release.

The high-rise type of house can have problems with NH3. In winter, when ventilation rates were low, it was not unusual for hens in the high-rise house to be exposed to aversive levels of NH3, i.e., more than 25 ppm and evidently on occasion, even more than 50 ppm. Moreover, if the EPA non-agricultural industry standard for point source pollution of 100 lb NH3/day were to be applied, almost all high-rise layer houses would be classified as point sources for NH3 emission, if the emission rates observed in this study are typical.

High-rise houses in southern regions of the U.S. are usually bi-directionally tunnel ventilated, as opposed to the drop-down ventilation design evaluated in the study. Since most of the fans in tunnel-ventilated layer houses are mounted on the upper (living space) level, air drawn from the lower level to be exhausted from the house may expose hens at the ends of the cage rows to higher concentrations of NH3.

Although tunnel houses generally keep manure quite dry, it seems unlikely that NH3 production from a tunnel house would be much less than that seen in the high-rise house studied, based on differences in manure dryness. The manure moisture in this house was reported to be only 15% in June, a time when NH3 emission rates from the house were highest. These conjectures, of course, would need to be verified.

For animal welfare and environmental reasons, NH3 control in layer houses may become a critical issue for the egg industry. It appears that if the high-rise house is to remain a viable design for the commercial layer husbandry, manure management strategies will need to be employed at critical times of the year to reduce interior NH3 concentrations or NH3 emission rates. This will require research and development because at present such strategies have not been well defined.

The study is published in the University of Georgia's Poultry Science - Poultry Tips for the Year 2004

Source: University of Georgia - Poultry Science - January 2004