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J APPL POULT RES 2008. 17:34-46. doi:10.3382/japr.2006-00125
© 2008 Poultry Science Association
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Research Reports

Determining the Nitrogen Budget and Total Ammoniacal Nitrogen Emissions from Commercial Broilers Grown in Environmental Chambers

L. Mitran*, J. M. Harter-Dennis*,1 and J. J. Meisinger{dagger}

* University of Maryland Eastern Shore, Department of Agriculture, Princess Anne 21853; and {dagger} USDA-ARS, Beltsville, MD 20705

1 Corresponding author: jmharterdennis{at}umes.edu


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
One of the undesirable by-products of raising commercial broilers in confinement is the production and release of NH3 into the environment. Ammonia negatively affects flock performance, reduces air quality, increases N deposition into neighboring ecosystems, and reduces plant-available litter N. Animal agriculture is currently under pressure to reduce NH3 emissions. Understanding the fate of N inputs and outputs from commercial broiler operations is important for increasing flock N efficiency and reducing gaseous N emissions. A total direct-measurement N balance trial was conducted on broilers from 0 to 42 d of age with all N inputs and outputs measured. The N inputs included feed and chick N, whereas outputs included broiler N retention, total ammoniacal N (TAN) emissions, mortality N, and litter N accumulation. The major N input was feed N, accounting for 99% of total inputs. After 42 d, the percentage of N input recovered was as follows: 67 ±2% in live broilers, 26 ±2% accumulated in the litter, and 13 ±0.4% in TAN emissions. The average difference between the measured N inputs and outputs was 5 ±3%, indicating a good N balance. The period from 0 to 21 d of age accounted for 23% of the flock total TAN emissions. The remaining 77% of TAN loss occurred from 22 to 42 d of age, most likely due to greater N excretions in the feces and a rise in litter pH and moisture resulting in greater NH3 production. Daily TAN emissions ranged from 0.13 to 0.78 g of TAN per bird, with a 0 to 42 d mean of 0.37 g of TAN per bird. Total TAN emissions over 42 d averaged 15.3 ±0.5 g of TAN per bird, which is consistent with other literature values and the high N recovery in the broilers. The TAN emission from a complete broiler cycle, including the emissions for a week interval between flocks, was 17.5 ±0.5 g of TAN per bird. These results support the view that management practices leading to high broiler N recovery are consistent with lower TAN emissions.

Key Words: ammonia emission • nitrogen budget • broiler • ammoniacal nitrogen


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Agricultural animal production has become increasingly concentrated in recent years, leading to large operations that have resulted in more localized and concentrated production of waste products, liquid, solid, and airborne. As public scrutiny of the environment has increased, the poultry industry has faced pressure to reduce harmful impacts to the environment. One of the major environmental concerns in the poultry industry is NH3 volatilization [1]. Ammonia is produced in broiler houses by the conversion of uric acid, spilled feed, and undigested protein N in the manure, into NH3 through microbial decomposition in the litter. The NH3 gas thus produced is removed from the broiler house by the ventilation systems and released into the atmosphere. Sims and Wolf [2] suggested that over 50% of poultry manure N might be volatilized in the form of NH3. Later, Patterson and coworkers [3, 4] used an N-balance difference method to estimate that the proportion of feed N lost to the atmosphere as NH3 was about 18% for commercial broilers, 32% for pullets, and 40% for laying hens.

Ammonia reacts in the atmosphere with different compounds and contributes to the formation of the air pollutant known as particulate matter (PM). Particulate matter refers to small airborne solid particles or liquid droplets: PM with an aerodynamic equivalent diameter of 2.5 µm or less is referred to as PM2.5. The PM2.5 particles can contribute to respiratory diseases in humans (e.g., aggravated asthma, chronic bronchitis) and to the formation of haze-associated reductions in visibility [5, 6].

Ammonia emissions can also increase N deposition into neighboring ecosystems as gaseous NH3 or as ammonium salts formed after the reaction of NH3 with acidic compounds in the atmosphere (oxides of S and N). These depositions can cause acidification of soils, due to the production of acids during the conversion of ammonium to nitrate in the soil. The additional atmospheric N input can also reduce species diversity in native ecosystems [6], and if the NH3 deposition results in excess N inputs, it can contribute to pollution of ground and surface waters with nitrates [7]. The atmospheric aerosols of ammonium salts can be transported over long distances before being deposited [7].

Exposure of poultry to NH3 within the production facility has long been known to have direct negative effects on production. These production impacts include a lowered resistance to infection with Newcastle disease virus [8], decreased growth rate and egg production [9], reduced feed efficiency [10], damage to the respiratory tract [11], and increased incidence of airsacculitis [12].

Loss of NH3 also lowers the fertilizer value of poultry litter. Ammonia emissions not only reduce the N content of the litter but also increase the P to N ratio in litter, causing P to accumulate faster than potential crop uptake in soils where litter is applied at a rate to meet crop N requirements [1, 2, 13].

Another problem with NH3 in the production facility is its effect on animal caretakers. Exposure of workers to NH3 can irritate the respiratory tract and eyes, even at low levels. Donham et al. [14] reported that a significant decrease in pulmonary function of poultry workers can result from exposure to levels of NH3 as low as 12 ppm over a work shift. Because of the many problems associated with NH3, Carlile [15] suggested that 25 ppm NH3 should not be exceeded in poultry houses.

The EPA is currently considering regulations that would restrict the amount and nature of the emissions from animal feeding operations (AFO). Agricultural scientists from the public and private sectors are evaluating air emissions and modifications to animal production techniques that would mitigate the effects of air emissions. Acting jointly, the USDA and EPA appointed a Committee on Air Emissions from AFO to review, evaluate, and make recommendations on methods and future research needed to reduce emissions from AFO. This committee recommended that "Scientifically sound and practical protocols for measuring air concentrations, emission rates, and fates are needed for the various elements (nitrogen, carbon, sulfur), compounds (e.g., ammonia, NH3, CH4, H2S), and particulate matter" [16]. They also recommended that "reliable and accurate calibration standards should be developed, particularly for ammonia" and that NH3 emission measurements be accompanied by traditional N budget measurements [16]. Thus, accurately quantifying NH3 emissions from broilers should ideally include direct NH3 measurements plus an N budget that would include N inputs and N outputs from representative broiler production facilities. Currently, there are inadequate data available on ammoniacal N emissions from broilers. Improved estimates of NH3 emissions would expand our understanding and management of NH3 losses from AFO.

Therefore, the purpose of this research was to prepare the total N budget and measure the total ammoniacal N (TAN =NH3-N +ammonium-N) emissions of commercial broilers raised from 0 to 42 d of age in large negative-pressure ventilated, environmentally controlled chambers on used litter. Results of this study will provide the poultry industry and agricultural scientists with information on the fate and distribution of N during the production of commercial broilers.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Bird Husbandry and Chamber Description
Five hundred (250 females, 250 males) 1-d-old commercial broiler chicks (Ross xRoss), obtained from a commercial hatchery, were placed in each of 5 environmentally controlled chambers located at the Poultry Research Center at the University of Maryland Eastern Shore. The chambers were designed to mimic common negative-pressure ventilated broiler production facilities with each chamber being about 6 m on a side with a 2.6-m-high ceiling [17]. Each chamber was equipped with a commercial-type pancake brooder heating system, a commercial pan feeding system, and 2 nipple watering lines. Each chamber had 2 ventilation fans, a 25.4-cm squirrel cage unit with a manually adjusted intake port, and a 61-cm diameter fan activated by chamber temperature primarily for summer temperature control. In this study, only the smaller fan was used, because it provided sufficient ventilation for the autumn flock. The 500 chicks placed in each chamber gave a bird density of 0.075 m2 per bird, a common density for broiler production in this region. The birds were raised for 42 d, from October 27 to December 8, 2003, using continuous lighting. Temperature and ventilation rates were similar to those in commercial broiler production in the region; actual ventilation rates were determined with balometer readings as described below. The temperature in each chamber was measured every 30 min with thermocouples and recorded on data loggers over the entire 42-d grow-out. The chamber ventilation rate was periodically increased over the grow-out by manually adjusting the size of the intake port of the small fan.

Throughout the 42-d experimental period, feed and water were offered ad libitum. A 4-phase feeding program was used: the birds were fed a commercial starter, grower 1, grower 2, and withdrawal diet from 0 to 19, 20 to 27, 28 to 35, and 36 to 42 d of age, respectively. Feed was analyzed for CP using AOAC procedures as described below and were found to contain 19.8, 19.7, 18.7, and 17.8% CP, respectively.

Litter Preparation
The litter within each chamber consisted of a wood shavings-sawdust base plus the manure from 5 previous flocks. A regular practice in the poultry industry is to reuse litter for several flocks; however, to determine an N budget, an accurate estimate of litter N content is required. To accurately estimate litter N accumulation, the litter from all 5 chambers was combined into 1 large quantity, thoroughly mixed using a total mix ratio wagon used in dairy cattle feeding, weighed, and sampled for N and moisture content. After this homogenization, equal amounts of 1,410 kg were placed back into each chamber and leveled to obtain an approximate depth of 10 cm. At the end of the trial, the litter from each chamber was totally removed, individually homogenized, weighed, and sampled for N and moisture content to estimate the N content of the litter after the 42-d grow-out period.

N Budget Data and Sample Collection
Estimating the N budget for broilers requires estimating the major N inputs and outputs of each chamber. This requires documenting the N entering in the chicks, the feed, and the makeup air, N leaving in the fully grown broilers, the TAN emissions, plus the N accumulation in the litter. The N budget is as follows:


Formula


Formula

The total amount of N contained in the litter at the time of bird placement was estimated from the N content of the homogenized litter placed into each chamber minus the TAN emitted between the time of litter and chick placement. The litter samples collected at the beginning and the end of the trial were analyzed for moisture, pH, and N content as described below. In addition, litter samples were also collected twice a week during the 42-d grow-out and were analyzed for pH and moisture content.

The feed N input for each chamber was determined from the weighed quantities of all feed entering each chamber and the N content of the feed as determined by direct chemical analysis. The N content of the feed was determined from feed samples collected on d 0, 20, 28, and 36 when feed types were changed. On d 42, feed was withdrawn approximately 5 h before removing the birds for processing, with all unconsumed feed weighed.

On d 0, six chicks from each chamber were randomly selected, weighed, euthanized by CO2 asphyxiation, and frozen for later N analysis. The initial chamber broiler N content was determined by bulk-weighing the 500 chicks within each chamber and multiplying this weight by the average N content.

On d 42, before collecting the birds for processing, 10 representative males and 10 females per chamber were individually wing-banded, humanely killed using CO2 asphyxiation, weighed, and frozen for N analysis.

The N removed in broiler mortalities during the 42 d was determined by weighing the mortalities from each chamber and multiplying by the average carcass total N concentration of the chicks and the fully grown birds.

Sample Preparation and Chemical Analysis
The frozen carcasses of the chicks and final broilers were thawed, defeathered, weighed, ground, and analyzed for N and moisture content. The 6 chicks/chamber taken at d 0 were pooled, ground, and 4 subsamples (about 200 g) were autoclaved for 3 h and then homogenized for 30 s in a food homogenizer. The samples were then freeze-dried using a VirTis freeze-dryer [18]. The N content of the carcasses, feed, and litter was determined by Dumas dry-combustion method using a Leco FP-528 Nitrogen/Protein Determinator [19], with determination made in accordance with official method 990.03 of AOAC [20]. The N contained in the feathers was estimated by multiplying the mass of feathers obtained from defeathering by 82%, the protein percentage in feather meal as determined by Ewing [21], and then multiplying by 16%, which is the commonly accepted N concentration in protein.

The moisture content of litter from each chamber was determined in triplicate by drying for 24 h at 105°C in a convection oven. The pH of the litter samples was determined in duplicate samples immediately after collection, by adding 40 mL of distilled water to 10 g of fresh litter, stirring, and measuring pH with an electronic Basic pH meter [22].

The ammonium-N concentration trapped in the acid scrubber solutions was determined by the colorimetric Bertholet reaction using a model 8000 Quick Chem Automated Ion Analyzer, according to standard method number 10-107-06-2-J [23].

Sampling Exhaust Air for TAN and Chamber Air for NH3
The TAN emission rate was calculated as the product of TAN concentration in the exhaust air (mass/vol) and the chamber ventilation rate and was expressed on a daily basis of grams of TAN per bird.

The exhaust fans in each chamber were mounted on the opposite wall of the air intake vent, with make-up air entering from a shared central hallway. The exhaust fan had a sheet metal exhaust duct that contained a cross-section proportional-flow grid sampler spanning the entire inside dimensions of the duct (Figure 1Go). The grid sampler contained 5 rows of small diameter polyvinyl chloride pipe each containing 5 inlet holes. The holes were drilled in 1 of 9 sizes varying between 1.6 mm (1/16 in.) to 4.8 mm (3/16 in.) using increments of 0.4 mm (1/64 in.). The hole size was based on the flow-velocity pattern within the duct, which was previously measured with a small thermal anemometer (Alnor CompuFlow model 8575 [24]). The grid sampler was connected to a vacuum system (Figure 1Go), which drew air into the grid sampler and then into a large 4-L container of a dilute acid (10 mM H3PO4). A second 4-L scrubber was connected in series behind the first scrubber to ensure quantitative trapping of all TAN (Figure 1Go).


Figure 1
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  		Figure 1. Schematic diagram (plan front-view) of exhaust air sampling system for measuring total ammoniacal N (TAN) concentrations in exhaust air from environmental chambers showing the following: grid sampler, vacuum line to acid scrubbers passing in front of fan, acid scrubbers for trapping TAN, airflow control apparatus, and vacuum pump (not to scale).

 
The airflow rate through the gas scrubbers was regulated by adjusting the valve on a calibrated rotameter-type flow meter set at a flow rate corresponding to 4 L/min. The rotameter was calibrated in place under normal working conditions with fully charged scrubbers by inserting a thermal flow meter, designed for measuring airflow through a pipe (Aalborg model GFM171 mass flow meter [25]), into the vacuum line leading to the first scrubber so that it captured the total airflow into the scrubber. The rotameter was then adjusted across its total range of operation, and the rotameter values and corresponding thermal flow meter airflow rates were recorded, producing a rotameter calibration curve under actual operating conditions. The vacuum source for the gas scrubbers was a dual-chamber diaphragm pump [26] that ran continuously, allowing continuous sampling of the exhaust air, 24 h/d, over the entire grow-out period. The acid scrubber samples were typically collected after a 3- or 4-d exposure period, by recording the time and the corresponding flow meter values, draining the acid solutions and measuring their volume, mixing, and then sub-sampling for laboratory ammonium-N analysis. New acid solution was then placed in the scrubbers, and the cycle was repeated. The TAN concentration of the exhaust air (TAN mass/vol) was calculated from the mass of ammonium-N trapped in the acid scrubbers (laboratory ammonium-N concentration xvolume of acid) divided by the total volume of air that passed through the scrubbers (flow meter readings xduration time). The TAN emission from each chamber was calculated by multiplying the TAN concentration in the exhausted air by the total volume of air exhausted from each chamber, as determined from calibrated balometer measurements (ALNOR model APM150) [27] of the entire air stream from the exhaust duct. This air sampling technique provided estimates of total TAN emissions from each chamber over a 3- or 4-d period with cumulative emissions over the entire flock determined by summation. Volumetric NH3 concentrations (vol/vol) were estimated from the acid scrubber concentrations (mass/vol, ppm) by converting the TAN to a molar basis (assuming a negligible NH4-N component in TAN, see below) and applying ideal gas laws to adjust to 1 atmospheric standard pressure and to the average temperature within each chamber over the respective sampling interval.

The TAN concentrations of the make-up air entering the chambers were determined by continuous sampling of the hallway air with a small acid-scrubbing system described by Meisinger et al. [28] that used 150 mL of 10 mM H3PO4 in gas scrubbing bottles, a calibrated flow meter, and vacuum pump.

The N species trapped in the acid scrubbers are NH3-N gas, NH4-N associated with airborne solid particulates (such as dust), or liquid droplets. These species are trapped in 10 mM phosphoric acid (pH 2.5) and converted to dilute ammonium phosphate by simple acid neutralization. The NH4-N content is then determined by Bertholet reaction (see description above) with the final result representing the TAN in the sample.

Further evaluation of the acid scrubbers involved assessing the likely impact of dust on scrubber TAN (see below). This was accomplished by collecting dust from the exhaust ducts and analyzing it for total N and adsorbed NH4-N as described above.

Measurement of TAN emissions began immediately after the distribution of well-mixed litter back into each chamber before bird placement, with monitoring continuing for 3 d. The acid scrubbers were then changed, the birds placed into each chamber, and monitoring continued over the entire 42-d grow-out. After the birds were removed at the end of grow-out, the scrubbers were changed, and TAN emissions were monitored for another 7 d before removing the litter from each chamber for postflock mixing, weighing, and total N analysis. Thus, TAN emissions were measured for the litter alone for 3 d preflock, for the entire 42-d grow-out period, and for the litter alone during a 1-wk postflock period, for a total of 52 d.

Statistical Analysis
Data from 5 identical replicate chambers were summarized using descriptive statistics and analyzed using the GLM procedure of STAT-ISTIX [29]. Data means and SEM are presented using the mean value followed by a ±value. A 2-segment linear regression model was applied using the nonlinear regression procedure of GraphPad Prism 4.0 for Windows [30] to determine the influence of bird age on TAN emissions.


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
N Budget
Weight gain, feed efficiency, and livability data from birds in this experiment are summarized in Table 1Go and are consistent with average broiler performance values on the Delmarva Peninsula [31]. Results from the broiler N budget are summarized in Table 2Go and show that feed N accounted for 99% of the N inputs over the 0- to 42-d grow-out period. The incoming air commonly had concentrations of about 800 µg of TAN/m3, compared with the exhaust air that averaged about 16,000 µg of TAN/m3.


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  		Table 1. Performance of commercial broilers raised from 0 to 42 d of age1
 

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  		Table 2. Nitrogen balance for commercial broilers raised from 0 to 42 d of age1
 
The largest N output was in the broilers, amounting to 67 ±2% of total N inputs with secondary outputs of N accumulations in the litter, 26 ±2%, and TAN emissions amounting to 13 ±0.4% of the total N inputs. The average difference between the total N inputs and measured N outputs was only about 5 ±3% of the N inputs, indicating a good N balance.

The variations in the N budget components across chambers illustrate some of the strengths and difficulties of constructing N budgets for broilers. The variations in documenting feed N and chick N were small, as shown by their low CV. The variations in estimating the final broiler N and TAN emissions were modest, being 5 and 7% of the means, respectively. Upon first inspection, the variation in bird mortalities appears to be large, but the high CV results from a low mean from this small N output. The most variable component was the N accumulation in the litter, which amounted to 17% of the mean. The 17% CV should be viewed as a minimum estimate, because considerable effort was made to thoroughly mix and analyze the litter before the flock was placed and to measure postflock litter N in each chamber by total removal, mixing, and multiple analyses. Thus, any N budget for broilers would benefit from careful and thorough analysis of the litter. The variability in the difference component was over 100% of the mean, because the final N budget difference was small (i.e., the N budget balanced). The statistical analysis of the average difference component across chambers and the test of the hypothesis that the mean difference equals zero produced a nonsignificant t-value of 1.74 (P =0.16). Thus, the N inputs were statistically accounted for in the measured N outputs, with other potential inputs or losses (e.g., denitrification, dust, etc.) being statistically nonsignificant and of minor importance.

The N budget in Table 2Go compares favorably with other budgets reported in the literature. Patterson et al. [3] used an N budget approach on broilers by documenting feed N, broiler carcass N, and N accumulation in the litter at several commercial broiler facilities and found that the broiler carcasses accounted for 51% of the feed N, whereas 31% was in the litter with the remaining 18% attributed to NH3-N emissions. In another study, Coufal et al. [32] estimated the N mass balance for 18 flocks grown at 1 location over 3 yr; the dietary N was distributed as follows: 57% in broiler carcass, 22% in litter, and 21% as NH3-N loss, which was measured indirectly (by difference). In this study, there was a higher N recovery in the broilers (67% compared with 51 or 57%), lower N losses to TAN emissions (13% compared with 18 or 21%), but similar accumulations in the litter (26% compared with 31 or 22%). The higher recoveries by the broilers and corresponding lower TAN losses are likely due to improved efficiencies over time due to genetic selection in commercial broilers and better formulation of diets such as phase feeding and better balancing of amino acids.

Estimated NH3 Emissions During Grow-Out
Ammonia emission estimates from broilers vary widely, as shown by the range in losses cited above, because many factors affect NH3 volatilization in a given study. For example, loss estimates can be affected by the following: the method of measurement, protein content of the diet, strain of bird, temperature and ventilation regimen in the facility, season of the year, and litter management practices that affect pH and moisture.

The average estimated NH3 concentrations within the entire chamber over the 42-d grow-out are summarized in Figure 2Go, along with the within-chamber contributing factors of litter pH, ventilation rate, chamber temperature, and litter moisture content. Figure 2aGo shows 2 distinct trends over time: a low concentration period over the first 3 wk and a higher concentration period from 3 to 6 wk. The estimated NH3 concentrations declined from about 26 ppm at the start of the study to about 16 ppm on d 18 and then followed an increasing trend for the remainder of the study. The elevated concentrations in the first week probably resulted from NH3 emissions from the litter that were associated with handling and mixing the litter before the study began. During the first 14 d, litter moisture levels were relatively low (13 to 16%, Figure 2dGo) due to moisture loss during mixing and the low respiratory and fecal moisture losses from the young chicks, which is consistent with data published by Elliot and Collins [33]. The estimated NH3 levels declined between d 0 and 20, despite a stable pH of about 7.7 (Figure 2cGo) and a steady increase in litter moisture (Figure 2dGo). Apparently, the NH3 emissions generated from the young flock were counterbalanced by a larger decline in NH3 losses from the litter.


Figure 2
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  		Figure 2. a) Estimated NH3 concentration (Conc.) within environmental chambers [ppm (vol/vol)] throughout the 42-d grow-out period of 500 broilers, b) chamber ventilation (Vent.) rate [air exchanges (exch.) per hour], c) litter pH, and d) litter moisture content (%) and chamber temperature (°C).

 
Between 3 and 6 wk, the estimated NH3 concentrations increased due to the increased N excretions by the growing flock, a rise in pH, and a rise in litter moisture. Temperatures in the chamber were about 32°C at the start of the study and steadily declined to about 22°C (Figure 2dGo). The rise in estimated NH3 concentrations from 3 to 6 wk occurred along with an increase in pH, which reached a maximum of 8.6 (Figure 2cGo). During the same time, the litter moisture increased to a stable value of 25 to 28% (Figure 2dGo) due to increased water consumption and fecal excretion by the flock. The 2 brief declines in estimated NH3 concentrations between wk 3 and 7 were associated with increases in chamber ventilation rates (see Figure 2bGo). The data summarized in Figure 2Go clearly illustrates the dynamic trends in litter pH, litter moisture, ventilation rate, and temperature, plus their interactions, on estimated NH3 concentrations over the growth of a typical broiler flock. Litter pH and moisture have generally been considered to be the major factors controlling NH3 concentrations [33, 34]. However, when the individual estimated NH3 concentrations from each chamber were pooled (65 observations) and related to the corresponding variables in Figure 2Go, no clear-cut causative variable could be identified, due to the strong interactions among pH, moisture, temperature, and ventilation rate, although pH had the largest single-variable correlation (r =0.76) with estimated NH3 concentrations.

The estimated NH3 concentrations in this study are consistent with other reports. For example, Wathes et al. [35] monitored NH3 concentrations in perchery, cages, and broiler houses and reported NH3 concentrations ranging from 12 to 24 ppm, with maximum hourly values exceeding 40 ppm. Paul et al. [36] determined NH3 concentrations in 4 independent broiler chambers, each with a capacity of 200 birds, and found that NH3 concentrations increased from less than 1 ppm in the first week to 40 ppm when the birds approached 6 wk of age.

Estimated NH3 Emissions After Grow-Out
Because it was impossible to do total litter collections from the chambers immediately after bird movement, it was necessary to measure the NH3 emissions from the time of bird movement until chamber clean-out. The acid scrubbers and chamber ventilation system were operated for 1 wk after the flock was removed. Chamber ventilation rates during this time were 40% of the rate on d 42, averaging 3.1 exchanges/h (compare with Figure 2bGo). The litter was not disturbed after the flocks were removed, so litter conditions were the same as those at the end of the flock, namely, a pH of 8.3 with 25% moisture.

Total Ammoniacal N Emission Rates
The TAN emission rates (Figure 3cGo) show the expected dependence on the within-chamber estimated NH3 concentrations and chamber ventilation rates (Figure 3dGo), with the daily emissions ranging from 0.13 to 0.78 g of TAN/bird and an average daily emission rate of 0.37 ±0.01 g of TAN/bird over the 42-d period. Daily TAN emissions were steady (about 0.18 g of TAN per bird) during the early growth period (0 to 21 d) followed by a slow increase from 21 to 42 d of age (Figure 3cGo). The majority of TAN, specifically 77%, was emitted during the last half of the grow-out from 21 to 42 d. The total TAN emission over the 42 d averaged 15.3 ±0.5 g of TAN/bird or 15.3 kg of TAN/1,000 birds as shown in Figure 3aGo. The cumulative TAN emission curve (Figure 3aGo) also bears a strong resemblance to the cumulative feed N input data for the chambers over the 42-d grow-out (Figure 3bGo). Of course, this resemblance is due to the fact that feed N input is highly correlated with excreted N, because a certain proportion of the dietary N (about one-third in this study) was excreted and available to be lost as NH3. Results of the nonlinear breakpoint analysis used to regress TAN emissions on bird age revealed an r2 of 0.91, indicating that 91% of the variation in emissions was explained by bird age. For similar experiments [36, 37], a strong correlation between emission rate and bird age (r2 =0.8 and 0.92, respectively) was also observed.


Figure 3
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  		Figure 3. a) Total ammoniacal N (TAN) emissions (kg of N/1,000 birds) from environmental chambers throughout the 42-d grow-out period of 500 broilers, b) cumulative (Cum.) feed N input (kg of N), c) daily TAN emission(Emiss.) rate (daily grams of TAN/bird), and d) within-chamber estimated NH3 concentration (Conc., mass/volume) and chamber ventilation rate [air exchanges (Exch.) per hour].

 
The TAN emission data obtained in this study are consistent with literature values of 15 to 20 g of N/bird over a 42-d production cycle [37, 38]. For example, Wheeler et al [38] reported mean daily NH3-N emissions ranging from 0 to 1.28 g of NH3-N/bird for birds from 0 to 44 d of age. The Wheeler et al. [38] study was conducted during cold weather in Pennsylvania, and the overall mean daily emission was 0.49 g of NH3-N/bird, with a CV of 13.3%. In addition, an earlier study by Wheeler at al [39] evaluated the effect of different litters and found that average daily NH3-N emission rates were much lower with new litter, averaging 0.36 g of NH3-N/bird (with a CV of 11%), than from reused litter that averaged 0.61 g of NH3-N/bird (with a CV of 14%). The results from this study agree well with those obtained from houses with new litter, but they are somewhat lower than those obtained in houses with reused litter. However, the somewhat lower TAN emissions observed in this study are due to the higher-than-average N recovery by the broilers, suggesting that newer poultry management practices that result in high N recovery by the broilers will also lead to lower TAN emissions.

Other recent work monitoring commercial production facilities has been reported by Casey et al. [40], who found daily NH3-N emissions ranging from 0.10 to 0.98 g of NH3-N/bird during cold weather when the bird age ranged from 11 to 56 d old. Data from experiments conducted in 4 European countries [13], using direct monitoring of building exhaust, reported average emission rates of 0.21, 0.27, 0.44, or 0.48 g of NH3-N/bird per day for broilers raised on fresh litter from Germany, the Netherlands, England, and Denmark, respectively. Measurements of NH3 emissions from a commercial chicken houses on the Delmarva Peninsula have been reported by Siefert et al. [41] and Roadman et al [42]. Siefert et al [41] monitored the NH3 plume emanating from 2 commercial broiler houses during 2 summer flocks with 7 deployments of passive samplers using exposure durations of 6 to 12 h each. The NH3 plume measurements were then back-calculated to whole-house NH3 emissions based on a Gaussian plume dispersion model. Their study estimated daily NH3 emissions of 0.27 to 2.17 g of NH3-N/bird with a weighted mean value of 0.74 g of NH3-N/bird per day, after adjusting for the nonlinear increase in NH3 during the grow-out cycle. The weighted mean produced a total NH3-N emission of 31 g of NH3-N/bird over the 6-wk grow-out, which is about 50% higher than the common value of 15 to 20 g of NH3-N/bird over 6 wk [37, 38, 40, 42]. Other monitoring data on Delmarva by Roadman et al [42] measured NH3 concentrations in the house and in the exhaust air, using short deployments of passive samplers. The NH3 concentrations and house ventilation rates were then used to estimate total NH3-N emissions over a flock, which produced a final estimate of 19± 3 g of NH3-N/bird. Thus, the total 42-d TAN emission of 15.3 ±0.5 g of TAN/bird in this study is in agreement with other estimates in the literature and is consistent with the N budget constructed for each chamber.

Total Ammoniacal N Emissions over a Complete Broiler Cycle
The above TAN emissions apply to the 42-d broiler grow-out period; however, a commercial grower will also lose NH3 from the litter between flocks. The estimated NH3 concentrations during the week after flock removal averaged 23 mg of NH3-N/m3, and the exhaust TAN coupled with the ventilation rate produced an average daily TAN emission of 0.16 kg of NH3-N from each chamber, which is equivalent to a daily rate of 0.32 g of TAN/bird based on the fact that each chamber had housed about 500 birds. Over the 7-d postflock period, the TAN emissions amounted to the equivalent of an additional 2.2 g of TAN/bird. Thus, if a producer averages a 1-wk interval between flocks, the TAN emission for the complete broiler cycle would be 17.5 ±0.5 g of TAN/bird. It should be noted that this value is probably a high estimate of the TAN emissions over an entire flock cycle, because under commercial conditions, the caked litter would be removed from the house within days of flock movement.

Results of this research indicate that although broiler N recovery was high, a considerable amount of the feed N is still excreted and deposited in the litter or is emitted as NH3 gas. The commercial broiler industry currently uses litter acidifiers to reduce NH3 emissions, but new technologies may also help to improve environmental quality as well as improve human and bird health.


   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 

  1. A N budget was successfully constructed for commercial broilers grown in 500-bird flocks in each of 5 identical environmental chambers. The N budget successfully balanced the N inputs in feed and chicks with the N outputs in mature broilers, directly measured TAN emissions, and the N accumulation in the litter.
  2. The dominant N input was through the feed.
  3. For a 0- to 42-d growing period, N inputs were accounted for as follows: 67 ±2% in the broilers, 26 ±2% accumulated in the litter, and 13 ±0.4% in TAN emissions.
  4. The average daily TAN emissions ranging from 0.13 to 0.78 g of TAN/bird over the 42-d grow-out, with an average daily emission rate of 0.37 ±0.01 g of TAN/bird across the 42 d. The total TAN emissions over 42 d averaged 15.3 ±0.5 g of TAN/bird.
  5. The TAN emissions were greatest during the last 4 wk of the 42-d grow-out when 77% of the total NH3-N loss occurred. The larger losses during the final 4 wk were attributed to greater N excretion rates as the birds matured and to increases in litter pH and moisture.
  6. The TAN emission from a complete broiler cycle, including the emissions for a 1-wk interval between flocks, was 17.5 ±0.5 g of TAN/bird.
  7. These results support the view that management practices leading to high broiler N recovery and minimizing litter N loses are consistent with lower ammoniacal N emissions.


   ACKNOWLEDGMENTS
 
We wish to acknowledge the valuable assistance of Gary Seibel and the late Lew Carr of the University of Maryland for fabrication and installation of the exhaust ducts and acid scrubber system. We also thank Bruce Foster, Steve Bishop, and Joe Hartman (University of Maryland Eastern Shore) for their excellent assistance in animal caretaking, record-keeping, and data collection from the flocks and the analytical laboratory.


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

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