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. 2020 Jun 17;99(8):3885–3896. doi: 10.1016/j.psj.2020.05.009

Air temperature, carbon dioxide, and ammonia assessment inside a commercial cage layer barn with manure-drying tunnels

W Zheng ∗,1, Y Xiong †, RS Gates ‡, Y Wang ∗, KW Koelkebeck §
PMCID: PMC7597998  PMID: 32731975

Abstract

Understanding the air temperature distribution, ammonia (NH3) and carbon dioxide (CO2) levels in poultry housing systems are crucial to poultry health, welfare, and productivity. In this study, 4 Intelligent Portable Monitoring Units and 7 temperature sensors were installed inside and between the cages and above 2 minimum ventilation fans of a commercial stacked-deck cage laying hen house in the Midwest United States (425,000 laying hens) to continuously monitor the interior environment over a 6-month period. During cold conditions (March 12th–May 22nd), there was a variation noted, with barn center temperatures consistently being highest in the longitudinal and lateral direction (P < 0.001) and the top floor deck warmer than the bottom floor (P < 0.05). During hotter conditions (May 23rd–July 26th), the interior thermal environment was more uniform than during the winter, resulting in a difference only in the longitudinal direction. The daily CO2 and NH3 concentrations were 400 to 4,981 ppm and 0 to 42.3 ppm among the 4 sampling locations, respectively. Both CO2 and NH3 decreased linearly with increasing outside temperatures. The mean NH3 and CO2 concentrations varied with sampling locations and with the outside temperatures (P < 0.001). For CO2, the minimum ventilation sidewall had lower values than those measured in the barn’s center (P < 0.05) during cold weather, while the barn center and the manure room sidewall consistently measured the highest concentrations during warmer weather (P < 0.05). For NH3, the tunnel ventilation inlet end consistently had the lowest daily concentrations, whereas the in-cage and manure drying tunnel sidewall locations measured the highest concentrations (P < 0.001). Higher NH3 and CO2 concentrations were recorded within the cage than in the cage aisle (P < 0.05). The highest NH3 concentration of 42 ppm was recorded above the minimum exhaust fan adjacent to the manure drying tunnel, which indicated that higher pressure (back pressure) in the manure drying tunnel allowed air leakage back into the production area through nonoperating sidewall fan shutters.

Key words: ammonia, carbon dioxide, air quality, hen level, laying hens

Introduction

Controlling the living space environment, particularly the interior air temperature and air quality, for example, carbon dioxide (CO2) and ammonia (NH3) levels, is crucial to poultry's health, welfare, and productivity (Webster and Czarick, 2000, Dawkins et al., 2004, Naseem and King, 2018). CO2 and NH3 are among the most common gases produced inside layer houses.

Common sources of CO2 are bird respiration, byproducts of feces breakdown, floor litter buildup in some facilities, and use of unvented conventional propane/natural gas-fueled heaters (Jeppsson, 2000, Miles et al., 2006a, Cândido et al., 2018). Interior CO2 levels are important factors for ventilation management in poultry houses and are commonly used to design appropriate minimum winter ventilation rates for maintaining indoor air quality and controlling moisture (Albright, 1990, Barber et al., 1993, Liang et al., 2005, Xin et al., 2009, Ni et al., 2017, Cândido et al., 2018, ASHRAE, 2019). The International Commission of Agricultural and Biosystems Engineering (CIGR, 1984) established the maximum CO2 concentration inside a facility at 3,000 ppm for general production and 2,500 ppm for poultry production. For other industries, a CO2 concentration of 5,000 ppm is suggested as the 8-h time-weighted exposure threshold limit value (ACGIH, 1998). Barber et al. (1993) evaluated the CO2 concentrations in a number of 173 swine buildings and reported that the CO2 concentrations were below 3,000 ppm for the majority of the swine buildings monitored when the ambient temperature was above 0°C; however, such concentration was a challenge to be maintained below for outside temperatures below 0°C (ASHRAE, 2019).

The magnitude of NH3 concentration in poultry facilities varies by housing systems (cage, on litter, alternative systems, or aviaries), bird density (in cage or on unit floor area), feed composition, house management, and ventilation management (Kilic and Yaslioglu, 2014). High NH3 concentrations in poultry houses can adversely affect the health and production performance of birds (Charles and Payne, 1966a, Miles et al., 2004, Miles et al., 2006b) and can cause respiratory diseases (e.g., coughing, upper respiratory tract bleeding, excessive secretions, and lung bleeding or inflammation). The literature is inconsistent regarding a specific NH3 threshold concentration above which respiratory or physiological problems will occur for poultry. For human workers, recommended threshold NH3 concentration is less than 25 ppm (Charles and Payne, 1966b, Al-Mashhadani and Beck, 1985, Kilic and Yaslioglu, 2014, Naseem and King, 2018). The US National Institute of Occupational Safety and Health and the US Occupational Safety and Health Administration have set human exposure limits to 25 and 50 ppm, respectively, for a time-weighted average (NIOSH, 2005). ASHRAE (2019) suggested that the NH3 concentration should be maintained below 26 ppm or, ideally, 10 ppm for general HVAC environments.

Several studies on thermal environment and air quality have been conducted for laying hen facilities, of which were either survey-type investigations or short-duration studies (Green et al., 2009, Dobeic and Pintaric, 2011), with intermittent measurements (Wathes et al., 1997, Shepherd et al., 2015, Zhao et al., 2015). Wathes et al. (1997) surveyed the concentrations and emission rates of aerial NH3, nitrous oxide (N2O), methane (CH4), and CO2 in typical UK broiler, cage and perchery houses over a 24-h period during winter and summer and reported that the overall mean NH3 concentration was 24.2 ppm, 13.5 ppm, and 12.3 ppm in the broiler, cage, and perchery houses, respectively. Kilic and Yaslioglu (2014) measured the NH3 and CO2 concentrations, air temperature, and relative humidity (RH) in a three-tier, neutral pressured laying hen house with 12,000 hens in Turkey. The average NH3 concentration during the summer of 2013 was 8.1 ppm for exhaust and 5.4 ppm for inlet, while the average CO2 concentration was 732 ppm for exhaust and 625 ppm for inlet throughout the summer. The temperature and RH sensors in the layer houses were installed in the middle of the aisle. The overall minimum, average, and maximum values for indoor air temperature and RH were obtained as 16.8°C, 24.7°C, and 34.7°C and 33.6, 63.7, and 86.2%, respectively. These survey-type and intermittent studies usually used periodic measurements, which typically depict a small part of the actual picture and cannot adequately cover diurnal or seasonal variations (Ni et al. 2012). Ni et al. (2017) suggested that long-term (>6 months) and continuous (or high-frequency) monitoring were needed to reveal seasonal and diurnal variations and to obtain in-depth knowledge about thermal environment and air quality characteristics.

Xin et al. (2009) evaluated the ventilation rate in 2 broiler houses in Kentucky, USA, and reported a difference in CO2 concentration range of 200 to 2,566 ppm between house air inlet and exhaust, which was equivalent to an interior CO2 concentration of approximately 600 to 3,000 ppm (assuming a 400 ppm ambient CO2 concentration). Their results agreed with an earlier study for manure belted layer houses in Iowa, USA (Li et al., 2005), which reported a range of 800 to 2,400 ppm CO2 concentration at ventilation fans. Liang et al., 2005, Liang et al., 2006 estimated NH3 emission rates for manure belted and high-rise layer houses. Their results showed that for manure belt houses, the NH3 concentrations at exhaust fans were up to 15 ppm and 2–4 ppm in for Pennsylvania buildings in winter and summer, respectively; they reported concentrations of up to 8 ppm and 2–3 ppm for Iowa buildings in winter and summer, respectively. By contrast, high-rise houses in Iowa with a manure-pit showed a concentration range of 70–120 ppm during winter, and below 20 ppm during winter was noted at the manure pit. Those in Pennsylvania had NH3 concentrations ranging from 40 to 100 ppm for winter and 10 to 40 ppm for summer. Ni et al. (2012) studied the characteristics of air pollutant concentrations of NH3, H2S, CO2, and particulate matter (PM10) in 2 high-rise houses having A-frame cages with 180,000 hens and 2 ten-tier cages houses with manure belts that housed 200,000 hens located in Indiana, USA, over a 2-year period. The results showed that variations in pollutant concentrations were affected by outdoor temperature, ventilation, hen condition, and farm management practices. When compared to the manure-belt houses, gas concentrations in the high-rise houses were higher for NH3 and lower for CO2. However, the scope of this study was limited to reporting pollutant concentrations only at the ventilation outlets of the fans. Zhao et al. (2015) compared the indoor NH3 and CO2 concentrations and thermal environment in three housing systems that included a conventional cage (200,000 hens), an aviary (50,000 hens), and an enriched colony (50,000 hens). Results showed that the average indoor temperatures were 24.6°C, 25.2°C, and 26.7°C, and the average RH were 57, 56, and 54%. The daily mean indoor NH3 concentrations were 4.0 ppm, 6.7 ppm, and 2.8 ppm, and the daily mean indoor CO2 concentrations were 2,083 ppm, 2,475 ppm, and 2,216 ppm for the conventional cage, aviary, and enriched colony house, respectively.

It is noted that large variations exist among results from different studies, which are associated with differences in housing types, management practices, local climatic conditions, and, to some extent, the associated measurement methods (Kaasik and Maasikmets, 2013). It was acknowledged that in previous studies, the sensors measuring the interior thermal environment (temperature, RH) or air quality (NH3, H2S, CO2, PM10, PM2.5) in the manure-belt layer houses were generally installed in the middle of the aisle between cages (Green et al., 2009, Dobeic and Pintaric, 2011, Shepherd et al., 2015, Zhao et al., 2015). In other words, these measurements are more appropriate to demonstrate the thermal environment representing the building environment, rather than that experienced by the laying hens. The thermal environment and air quality at hen level can directly and negatively affect the health, welfare, and productivity of poultry. Large-scale (>250,000 hens per house) commercial laying hen housing with manure-drying tunnels has gained large interest in the past decades and is a common housing type in the global egg industry; thus, it is important to evaluate the interior thermal environment and air quality parameters for layer housing with manure-drying tunnels.

The Portable Monitoring Unit (PMU) was designed and developed for measuring air temperature, NH3, CO2 concentrations, and building static pressure in livestock and poultry buildings (Gates et al., 2005) and had been widely used in air quality assessment in poultry houses (Li et al., 2005, Liang et al., 2005, Wheeler et al., 2006, Gates et al., 2008). The use of the first-generation PMUs entailed a substantial degree of manual setup and data processing, making field deployment of multiple PMUs simultaneously a logistical challenge. To improve the functionality and data processing of the PMUs, the PMU design was upgraded to the Intelligent Portable Monitoring Unit (iPMU) as reported in the study by Ji et al. (2016). The newer generation iPMUs are capable of measuring the NH3 (uncertainty: ±3 ppm) and CO2 (accuracy: 1.5% of range and 2% of reading) concentrations and air temperature (accuracy: 0.75% of reading) simultaneously and providing real-time data processing and display and wireless data transfer.

The objectives of this article were 1) to assess the values and variability of interior air temperature and NH3 and CO2 concentrations monitored over 6 months inside a commercial laying hen barn with manure-drying tunnels and 2) to compare the NH3 and CO2 concentrations at the hen level (measured inside cages) and in the adjacent aisle (measured between cages in the hallway).

Materials and methods

Description of the Layer Barn

This study was conducted in a commercial laying hen house with enrichable cages and manure-drying tunnels, in the Midwest United States. The layer barn measured 27.8 m wide, 164.6 m long, and 10 m high, with a floor halfway between the ground and ceiling forming the top and bottom floors. The barn's interior contained 10 rows of enrichable cage stacks, with each stack consisting of 12 tiers (6 tiers on each floor) and with a manure belt under each cage. The building housed about 425,000 laying hens (White Leghorns W-36) at the time of this study. Two manure-drying tunnels with the same dimension (4.9 m wide × 85 m long) were constructed at both sides of the building. Building layout and fan placements for the barn's ventilation system are illustrated in Figure 1. There were 31 fans with shutters and cones (1.32 m diameter; Officine Facco & C SpA, Via Venezia, Italy) on each sidewall, of which 10 were variable speed fans (Figure 1, minimum variable speed fans). In addition, a total of 130 constant-speed fans (1.32 m diameter; Officine Facco & C SpA, Via Venezia, Italy) were vertically placed in five rows at the building south end wall, and cooling pads were placed at the other end for hot weather operation. The designed values of minimum and maximum ventilation rate of the barn were approximately 0.6 m3 h−1 per bird and 12.4 m3 h−1 per bird, respectively, per the onsite manager. The barn ventilation operated in one of 2 modes: 1) during cold conditions, fresh air entered the barn through evenly distributed ceiling air inlets, and barn air exhausted through the fans placed along both sidewalls (mode 1); and 2) during hotter conditions, fresh air entered the barn through the evaporative pads placed at the building north end wall and barn air exhausted through tunnel fans at the south end wall and both sidewalls (mode 2). In both modes, stages of fans were sequentially activated as interior temperature rose above targeted room temperature.

Figure 1.

Figure 1

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Barn layout, ventilation system, fan placements, sensor locations, and sampling points. The barn measured 27.8 m wide × 164.6 m long and had 2 floors (12 tiers of cages) and housed about 425,000 laying hens (White Leghorns W-36). Two manure-drying rooms with the same dimension (4.9 m wide × 85 m long), each contains a perforated manure-drying belt, were constructed at both sides of the building. Temperature measurements include at the tunnel ventilation inlet end (TTIE), at the tunnel ventilation fans end (TTFE), at the center of the barn in the middle across the width (TC,M, TCT2, and TCT3, from the building center to the manure-drying tunnel side), and at the middle height of the first floor (TC,B) and the second floor (TC,T). A–D indicate the 4 locations where barn air was sampled for ammonia and carbon dioxide concentrations.

A portion of each sidewall was connected to an extended room (4.9 m wide × 85 m long) that functioned as a manure-drying room (Figure 2). The manure-drying room contains a 10-tier perforated belt (drying tunnel) that was designed to continuously dry feces produced in the barn by using the ventilation system and six exhaust fans and a curtain located on both exterior sidewalls of the manure-drying rooms. Barn air left the poultry house and entered the manure-drying tunnel, circulating upward through the feces on aerated manure belts to promote moisture removal and eventually exited the building. A proper balance of the static pressures between the hen occupied zone, the manure-drying tunnels, and the outside air is critical for proper operation of this system.

Figure 2.

Figure 2

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Partial (one-half) building cross-section view demonstrating the manure-drying system, sampling locations, manure-drying tunnel, exhaust fan, and curtain locations on the exterior wall. Temperature measurements include at the tunnel ventilation inlet end (TTIE), at the tunnel ventilation fans end (TTFE), at the center of the barn in the middle across the width (TC,M, TCT2, and TCT3, from the building center to the manure-drying tunnel side), and at the middle height of the first floor (TC,B) and the second floor (TC,T). A–D indicate the 4 locations where barn air was sampled for ammonia and carbon dioxide concentrations.

Interior Environmental Monitoring

Interior air temperature, NH3 and CO2 concentrations, and building static pressures were monitored from February to July 2016. The top and side views of the environmental measurement locations are shown in Figures 1 and 2.

Seven temperature dataloggers (HOBO U12-012, Onset Computer Corp., Bourne, MA) were used to measure the interior air temperatures from March 12th to July 26th, 2016. The temperature dataloggers were installed in the following directions inside the barn to characterize a three-dimensional temperature profile of the barn: 1) longitudinal direction measurements included one at the tunnel ventilation inlet end (TTIE) and one at the tunnel ventilation fans end (TTFE); 2) lateral direction measurements included 3 in the center of the barn and in the middle across the width (TC,M, TCT2, and TCT3, from the building center to the manure-drying tunnel side); and 3) vertical direction included 2 other temperature dataloggers located in the center lane and in the middle height of the first floor (TC,B) and second floor (TC,T). Another datalogger was set outside to record the ambient air temperature (TOUT) during the experiment period. All temperature data were recorded every 10 min.

Four iPMUs were used to simultaneously measure NH3 and CO2 concentrations in the center of the building (approximately the same height as the ceiling level of the sixth tier cage, 4.1 m above the floor). Barn air was sampled at 4 sampling points, including inside the cage to represent air conditions at the hen level (point B; Figures 2 and 3A); between cages to represent the adjacent aisle conditions (point C; Figures 2 and 3B); and above 2 continuously running minimum ventilation exhaust fans (points A and D; Figures 1 and 2). The iPMUs were programmed to collect data at a 10-s sampling interval for 5 min, following by a 55-min purging cycle in which fresh air from outside was drawn into the sensors. The sampling cycle continued for 24 h, then was followed by a 48-h fresh air purge, after which the process repeated. Building static differential pressure between bird production area, manure-drying tunnel (bird area to perforated belts), manure-drying room (perforated belts to drying room exterior wall), and outside was regularly measured using a handheld differential pressure meter (Testo, 512, 0–20 hPa, Testo SMI Sdn Bhd, Malaysia). The static pressure in each location was collected along with other environmental data.

Figure 3.

Figure 3

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Sampling locations of barn air: (A) inside hen cages to represent air conditions at the hen level (sampling point B) and (B) between cages to represent the adjacent aisle (hallway) air conditions (sampling point C). Sampling points B and C with dust cup filters installed were at the same heights and locations of the two dust cup filters are shown in the red circles.

All environmental measurement sensors deployed in this study were checked and calibrated. The air temperature sensors were calibrated using a National Institute of Standards and Technology-certified Heating and Cooling Temperature Calibrator (CL134-1; OMEGA Engineering, Inc., Norwalk, CT) before and about every 4 wk during the experiment. The NH3 and CO2 sensors in the iPMUs were calibrated using calibration-grade reference gases before farm installation.

Data and Statistical Analysis

The following statistical analyses were performed using SAS (version 9.4; SAS Institute Inc., Cary, NC) and RStudio (version 1.2.5001; RStudio Inc., Boston, MA). The air temperature distribution inside the barn was represented as follows: 1) longitudinally by comparing TTIE, TC,M, and TTFE; 2) laterally by comparing TC,M, TCT2, and TCT3; and 3) vertically by comparing TC,B, TC,M, and TC,T. The daily means (± SD) of the interior temperatures and the outside temperature were analyzed and plotted over the 2 monitoring periods associated with ventilation mode 1 (March 12th–May 22nd) and mode 2 (May 23rd–July 26th). The means and the SD of these temperature measurements during the 2 monitoring periods were tabulated. TOUT was included in the temporal distribution plot for reference. A Tukey mean separation was performed by PROC ANOVA in SAS for the daily mean air temperatures to explore if temperature variation presented in the directions listed previously with significant effects acknowledged at P < 0.05.

The daily means of the interior CO2 and NH3 concentrations were evaluated for seasonal and spatial effects, based on daily average ambient temperatures recorded. The daily average TOUT (noon to noon) was categorized into 4 thermal ranges, that is, <0, 0–10, 10–20, and >20°C. Analyses of the interior CO2 and NH3 concentrations were sorted into the TOUT categories, and the number of monitoring days experiencing the TOUT categories was tabulated. The daily means of the NH3 and CO2 concentrations at each sampling point were averaged and tabulated for each TOUT category. The mean values (±SD) of the indoor air temperatures, CO2, and NH3 were analyzed by analysis of variance (ANOVA) for effects of TOUT category, sampling point, and TOUT category × sampling point interaction. The analyses were carried out by two-way ANOVA in RStudio. Normality of the dependent variable for each TOUT category was verified and accepted at P > 0.01. The Tukey-Kramer test for differences of least square means was used to determine significant differences between variable means (P < 0.05) due to unequal sample sizes between TOUT categories. A box-whisker plot was created for the daily means of the interior CO2 and NH3 concentrations measured at the 4 sampling points and the TOUT categories. The CO2 and NH3 concentrations were further explored for sampling points B (hen level) and C (cage aisle) by plotting the concentrations against date of the experiment and the TOUT to depict the characteristics of their temporal and thermal profiles at the hen level and at cage aisle. A linear regression was fitted for the average concentrations between points B and C, for TOUT < 20°C (ventilation mode 1), and for TOUT > 20°C (mode 2), respectively. The results of the slope, the intercept, and the coefficient of determination (R2) of the linear model were included. The average building static pressure in each location was used as supplemental information to understand the barn ventilation management.

Results and discussion

Temperature Distribution

Daily average air temperatures computed from measurements at different locations inside the barn and the ambient temperatures during the monitoring period are shown in Figure 4. Table 1 provides a summary of descriptive statistics (mean ± SD) and the results of the mean separation analysis for the interior air temperatures measured at different sampling locations during the 2 monitoring periods that were associated with ventilation mode 1 and mode 2, respectively.

Figure 4.

Figure 4

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Daily average air temperature at different sampling locations (as indicated in Figure 2) over the experiment period: (A) longitudinal temperature distribution including TFIS, TC,M, and TTFS; (B) lateral temperature distribution including TC,M, TCT2, and TCT3; and (C) vertical temperature distribution including TC,B and TC,T. The ambient air temperature measured outside of the barn (TOUT) is included.

Table 1.

Summary of descriptive statistics (mean ± SD) and the results of the mean separation analysis for the interior air temperatures measured at different sampling locations during the 2 monitoring periods that were predominantly associated with ventilation mode 1 and mode 2.

Testing period TOUT (°C) Daily average air temperature1 (°C, mean ± SD)
TTIE TC, M TTFE TCT2 TCT3 TC, B TC, T
3/12-5/22 13.0 ± 4.8 22.9 ± 1.3D 26.3 ± 1.1B 22.1 ± 2.1E 25.2 ± 1.3C 25.1 ± 1.1C 26.5 ± 1.4B 28.1 ± 1.1A
5/24-7/26 26.0 ± 3.1 25.7 ± 1.4D 28.2 ± 1.2C 28.6 ± 2.2B,C 27.9 ± 1.3C 27.9 ± 1.3C 29.1 ± 1.1A,B 29.6 ± 1.2A
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Different superscript uppercase letters within the same row indicate that means under the same testing period differ significantly (P < 0.05) using the Tukey test for difference of the means.

1

Temperature measurements include at the tunnel ventilation inlet end (TTIE), at the tunnel ventilation fans end (TTFE), at the center of the barn in the middle across the width (TC,M, TCT2, and TCT3, from the building center towards the manure-drying room), and at the middle height of the first floor (TC,B) and the second floor (TC,T).

During monitoring, the daily average TOUT ranged from 3.7°C to 22.4°C and 17.2°C to 30.3°C for testing periods March 12th–May 22nd and May 23rd–July 26th, respectively. All interior temperature measurements (longitudinal and lateral) paralleled the ambient temperature. During the first testing period, there was a spatial variation in temperature distribution for all 3 directions, indicating the thermal environment was not uniform in the barn. In the longitudinal direction, temperatures measured at the barn center (TC,M), the tunnel ventilation inlet end (TTIE), and the tunnel ventilation exhaust fans end (TTFE) were all different (P < 0.05), with TC,M consistently being the highest and TTFE being the lowest. When tunnel ventilation fans were not running, the tunnel fans end was 0.8°C colder than the tunnel inlet end, and both ends were colder than the middle by 3.4°C–4.2°C. In the lateral direction, the warmest temperatures were measured at TC,M (P < 0.05), while no difference was observed between TCT2 and TCT3 located in the middle across the width toward the manure-drying tunnel wall. Vertically, the mean temperature at the center lane on the top floor (TC,T) was 1.6°C and 1.8°C greater (P < 0.05) than that at the middle or at the bottom floor (TC,M and TC,B), respectively, indicating a vertical temperature difference, and although this was reduced in the second testing period, it was not eliminated. During the second testing period, a temperature difference in the longitudinal direction was noticed (P < 0.05), with the tunnel ventilation inlet end temperatures (TTIE) consistently lower than the barn center (TC,M) or the tunnel ventilation exhaust fans end (TTFE) as evaporative cooling operated, and a mean temperature rise of 2.6°C between TTFE and outside air (TOUT). No difference was noted for temperature measurements in other directions. It should be noted that air temperatures were measured at only 7 locations in this study. When appropriate, both air temperature and RH should be measured at more testing locations for comprehensive assessment of spatial distribution inside modern size commercial layer barns.

As TOUT gradually increased during the year, the barn ventilation transitioned to mode 2, from May 22nd to June 11th and June 28th to July 7th, and was conducted completely in mode 2 from June 12th to June 28th and July 8th to July 26th. Our results showed that the tunnel ventilation inlet side consistently recorded the lowest air temperatures of these testing periods. Wang et al. (2019) noted a similar pattern of temperature distribution along the building length direction in a poultry house operated with tunnel ventilation system. Their results showed that the air temperature greatly increased along the building length direction in the poultry house with tunnel ventilation system, that is, cooler near the inlets and warmer near the fans, and the temperature at the three different sampling locations increased along the length of the barn because of the addition of sensible heat produced from the laying hens (Wang et al., 2018, Wang et al., 2019). Regardless of the longitudinal gradient observed, there was no difference found laterally (among TC,M, TCT2, and TCT3) or vertically (between TC,B and TC,T), indicating uniform air temperature distribution along these directions and suggesting that tunnel ventilation effectively encouraged more fresh air distribution inside the barn and created a more uniform thermal environment than during the winter. A similar pattern of uniform temperature distribution along the width and the height of a poultry barn with tunnel ventilation in the summer was also reported by Webster and Czarick (2000). This is due to the air flow coming from the evaporative cooling pads (tunnel ventilation inlet end), which were installed on the gable wall or/and both sidewalls in one end of the building, while fans were installed on the other end. Thus, continuous airflow from the evaporative cooling pads to the exhaust end was noted and provided air with uniform temperature along the width distribution of a poultry house (Hui et al., 2016, Freitas et al., 2018, Freitas et al., 2019), with a linear increase from bird heat production (Gates et al., 1992).

Carbon Dioxide Concentrations

The daily mean CO2 concentrations measured at sampling points A, B, C, and D are provided in Table 2, along with a summary of descriptive statistics (mean ± SD) and the results of the mean separation analysis for the daily CO2 concentrations at different sampling points under different ambient thermal categories. Any difference in CO2 concentrations between the hen level and the adjacent aisle was useful to assess the gas environment experienced by laying hens and was further explored by plotting the temporal profile of daily CO2 concentrations (Figures 5A, 5B) and its relationship with ambient temperatures (Figure 6). The daily CO2 concentrations were regressed for the ventilation mode 1 (TOUT < 20°C) and mode 2 (TOUT > 20°C).

Table 2.

Descriptive statistics (mean ± SD) of CO2 and NH3 concentrations at 4 different testing sampling locations (A, B, C, and D).

Gases Daily average ambient temperature range (°C) (days encountered this range) Daily mean concentration (mean ± SD, ppm)
 TOUT × location interaction
Sampling point A Sampling point B Sampling point C Sampling point D
CO2 <0 (4 D) 2,924 ± 416b,A 3,352 ± 487a,A 3,214 ± 421a,A 3,046 ± 466b,A 1
0 to 10 (8 D) 1,896 ± 358c,B 2,389 ± 395a,B 2,239 ± 375b,B 2,350 ± 448a,B
10 to 20 (16 D) 1,501 ± 357c,C 1,786 ± 465a,C 1,689 ± 410b,C 1,789 ± 418a,C
>20 (20 D) 707 ± 307c,D 1,030 ± 284a,D 917 ± 281b,D 995 ± 363a,D
NH3 <0 (4 D) 7.8 ± 2.8d,A 22.0 ± 5.2b,A 20.4 ± 4.5c,A 28.1 ± 4.7a,A 1
0 to 10 (8 D) 2.4 ± 2.2d,B 14.6 ± 5.2a,B 11.1 ± 4.1c,B 12.8 ± 3.7b,B
10 to 20 (16 D) 1.4 ± 2.3c,B 11.7 ± 6.0a,C 9.5 ± 4.6b,C 10.1 ± 5.1b,C
>20 (20 D) 0.0 ± 0.0d,C 2.0 ± 2.6a,D 0.8 ± 1.9c,D 1.2 ± 2.2b,D
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Results of the two-way ANOVA for effects of sampling location and TOUT categories and sampling location × TOUT on CO2 and NH3 concentrations are included.

Different superscript lowercase letters within the same row indicate that means under the same thermal category differ significantly (P < 0.05) using the Tukey test for difference of the means.

Different superscript uppercase letters within the same column indicate that means under the same sampling location differ significantly (P < 0.05) using the Tukey test for difference of the means.

1

There is a significant interaction effect of the outside temperature categories and the sampling locations (P < 0.001).

Figure 5.

Figure 5

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(A) Distribution of daily average CO2 concentrations measured at sampling points A–D under 4 different TOUT thermal categories that were monitored from February 9th–July 27th, 2016. Different letters “a–d” within the image indicate that different sampling locations had significantly different means (P < 0.05) using the Tukey test for difference of the means. (B) Daily average CO2 concentrations at sampling points B (hen level) and C (adjacent aisle) measured by the iPMUs from February 9th–July 27th, 2016.

Figure 6.

Figure 6

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Relationship between daily average CO2 concentrations measured at hen level (sampling point B), at adjacent aisle (sampling point C), and the corresponding ambient temperatures (TOUT). The CO2 concentrations were regressed for the ventilation mode 1 (TOUT < 20°C) and mode 2 (TOUT > 20°C).

The daily average CO2 concentrations ranged from 400 to 4,981 ppm among the 4 sampling locations. Results indicate that CO2 concentrations were significantly different for both the TOUT category and sampling location (P < 0.001), as well as the interaction of TOUT category × sampling location (P < 0.001). The daily mean CO2 concentrations at all sampling points decreased with increasing TOUT. When operated under ventilation mode 1, relatively high indoor CO2 concentrations (means of 2,924 ppm, 3,352 ppm, 3,214 ppm, and 3,046 ppm for points A to D, respectively) were found in cold weather due to the low ventilation rate to maintain room temperature, with a strong linear decrease with outside temperature (Figure 6, mode 1). When the barn ventilation switched to mode 2, low CO2 concentrations at ambient levels (approximately 400 ppm) were observed during warm temperatures (Figure 6, mode 2). The results were similar to those from the study by Ni et al. (2012), who reported high daily mean CO2 concentrations between January and March (winter) and low values during July and August (summer). When the ambient temperature exceeded 25°C, the barn was operated with tunnel ventilation (mode 2), and the CO2 concentrations remained at reasonably low levels (<1,000 ppm). Ni et al. (2012) and Zhao et al. (2013) also observed low CO2 levels with increased air temperature, presumably from the increased house ventilation rates with increased interior temperatures during summer conditions.

Within each TOUT thermal category, differences in CO2 measured concentrations at different sampling points were observed (P < 0.05). For TOUT below 0°C, CO2 concentrations measured at the minimum ventilation sidewall fans (sampling points A and D) were lower (P < 0.05) than those measured in the barn's center (points B and C). As ambient temperature increased, the CO2 concentrations measured at different sampling points followed a similar pattern, with sampling point A having the lowest CO2 concentrations and sampling points B and D the highest concentrations (P < 0.001). Among all the sampling locations inside the barn, sampling point A consistently had the lowest CO2 concentration for all TOUT categories (P < 0.001). One explanation for this was that the sampling location was located on the tunnel ventilation inlet end, where fresh air was drawn into the barn during warmer weather (mode 2). For cold weather (mode 1), CO2 levels at sampling point A were lower than those at sampling point D. This could be explained by that the pressure difference for fans at sampling point A that exhaust directly to the exterior was lower (16 ± 9 Pa) than that at sampling point D that exhaust to the manure-drying tunnel (29 ± 10 Pa). Compared with the CO2 concentration at point C, higher concentration was detected at point D for TOUT greater than 0°C (P < 0.05). The mean CO2 concentrations measured in the cage (point B) were slightly greater (P < 0.001) than those in the adjacent aisle (point C) (1,898 ± 787 ppm and 1,781 ± 758 ppm, respectively).

Ammonia Concentrations

Mean (±SD) daily NH3 concentrations at sampling points A, B, C, and D and the results of the two-way ANOVA with mean separation analysis for the daily NH3 concentrations at different sampling points under different ambient thermal categories are provided in Table 2. Figures 7A, 7B illustrate the distribution of the daily mean NH3 concentrations of each sampling point for each TOUT category. Difference comparisons of NH3 concentrations between the hen level and the adjacent aisle is useful to assess the gas environment experienced by laying hens and was further explored by plotting the temporal profile of daily NH3 concentrations (Figure 7B) and its relationship with ambient temperatures (Figure 8). The daily mean NH3 concentrations were regressed for the ventilation mode 1 (TOUT < 20°C) and mode 2 (TOUT > 20°C).

Figure 7.

Figure 7

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(A) Distribution of daily average NH3 concentrations measured at sampling points A–D under 4 different TOUT thermal categories that were monitored from February 9th–July 27th, 2016. Different letters “a–d” within the image indicate that different sampling locations had significantly different means (P < 0.05) using the Tukey test for difference of the means. (B) Daily average NH3 concentrations at sampling points B (in cage) and C (adjacent aisle) measured by the iPMUs from February 9th–July 27th, 2016.

Figure 8.

Figure 8

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Relationship between daily NH3 means for the hen level (point B) and cage adjacent aisle (point C) and the corresponding ambient temperatures (TOUT). The NH3 concentrations were regressed for the ventilation mode 1 (TOUT < 20°C) and mode 2 (TOUT > 20°C).

Figure 7A shows that the NH3 in the layer hen house exhibited a wide range of daily mean concentrations over the course of this study. The daily NH3 concentrations recorded within the barn ranged from 0 to 28.1 ppm on average, with extreme values above 40 ppm observed during colder outside temperatures. The patterns of the seasonal distribution and variation of NH3 concentrations shown in Figures 7A, 7B resemble those of the CO2 concentrations (Figure 5). Daily mean NH3 concentrations were significant for TOUT category and sampling location effects (P < 0.001) and the interaction of TOUT category × sampling location (P < 0.001). NH3 concentrations in other layer barns are also affected by ventilation rate, which is largely influenced by outside air temperature (Lin et al. 2017). At the same sampling location, TOUT categories greatly impacted the indoor air NH3 concentrations (Figure 8), where lower NH3 concentrations always corresponded to higher TOUT, and higher NH3 concentrations associated with lower TOUT, during which the barn ventilation rates were reduced to a minimum value (0.6 m3 h−1 per bird) to conserve energy while maintaining adequate indoor air quality. A few studies were previously conducted to assess NH3 concentrations inside layer facilities, with different layer farms showing unique characterization of their interior NH3 conditions. Wathes et al. (1997) monitored a NH3 concentration range of 12–24 ppm in a layer barn, and Cheng et al. (2011) measured NH3 concentrations in layer houses with cage systems, of which the NH3 concentration ranged from 0.5 to 12.5 ppm. NH3 concentrations were positively correlated to the moisture contents of the air (Ni et al. 2017), and higher in-house NH3 concentrations in winter were caused by lower ventilation rates and wetter litter conditions due to insufficient drying.

Regardless of the TOUT categories, NH3 concentrations also varied among different sampling locations. From Table 2, sampling point A consistently had the lowest daily NH3 concentrations compared with the other three sampling locations (P < 0.001). The overall mean NH3 concentrations measured in the cage (point B) and near the cage (point C) were 12.5 ± 4.75 ppm and 10.4 ± 3.80 ppm (P < 0.001), respectively. During all TOUT conditions, sampling points B and D consistently had the highest NH3 concentrations (P < 0.001), with the highest mean NH3 concentration of 42.3 ppm during the entire course of the monitoring recorded at sampling point D (above the minimum exhaust fan adjacent to the manure-drying tunnel) for TOUT < 0°C.

Ventilation Management

As reported by the producer, the ventilation was mainly conducted in mode 1 from March 12th to May 22nd in 2016 (solely in mode 1 from March 12th to May 5th, and predominantly in mode 1 from May 5th to May 22nd). During cold weather (ventilation mode 1), we observed lower temperature toward the tunnel fans end and a higher ammonia concentration measured at sampling point D near the manure-drying tunnel. Ventilation design and management can potentially explain this. Based on our observation, during ventilation mode 1, fresh air was drawn into the barn through ceiling inlets and distributed to the barn interior. Air then exited through the continuously running side-wall fans and into the manure-drying tunnels, which were pressurized above atmospheric conditions. Referring to Figure 9, the static pressures at the manure-drying tunnel (P3) and manure-drying room (P2) were above atmospheric pressure (P0). This back pressure allows higher concentration ammonia air to leak into the bird area (sampling location D) through fan louvers and other cracks. Ideally, to alleviate this situation, the fans on the exterior walls of the manure-drying room should pull a greater suction (P0–2) than the sidewall fans that blow into the manure-drying room (P3–1 and P2–1). In fact, the average measured value of P0–2 was only 1 ± 4 Pa during both ventilation modes, whereas P3–1 and P2–1 were 29 ± 10 and 17 ± 10 Pa, respectively, during mode 1 from March 12th to May 22nd. However, the pressure difference for fans such as those at sampling point A that exhaust directly to the exterior (P0–1) was lower (16 ± 9 Pa). Consequently, the amount of airflow from these fans was reduced, resulting in higher air temperatures recorded in the barn center than in both ends of the barn (TTIE and TTFE). Warmer temperatures observed on the top floor indicated that there was insufficient fresh air circulation at higher elevations in the barn as compared to the bottom floor. Leakage of air caused by back pressure between the manure-drying tunnel and the bird area could also explain the relatively high NH3 concentrations at sampling point D. Management practices to adjust operational static pressure differences, which fans to operate during coldest conditions, and methods to reduce back pressure induced leakage were suggested to the producer.

Figure 9.

Figure 9

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Schematic of static pressures in the layer barn (partial elevation shown) interior, manure-drying tunnel, and the ambient environment during cold weather conditions. Normally, P0 > P2 ≥ P3 > P1. Higher pressures at P3 and P2 created a back pressure that can induce air flows through nonoperating fan louvers and back into the bird area.

Conclusions

The following conclusions were drawn from the assessment of interior air temperature, NH3, and CO2 concentrations in a commercial caged layer barn with manure-drying tunnels and comparison of the NH3 and CO2 concentrations between inside cages (hen level) and the adjacent aisle:

  • 1.

    During ventilation for cold conditions (March 12th–May 22nd), there was a variation in temperature distribution longitudinally, laterally, and vertically. Temperatures at the barn center were consistently the highest (26.3°C ± 1.1°C), whereas the tunnel inlet end and tunnel ventilation fan end were lower (22.9°C ± 1.3°C and 22.1°C ± 2.1°C, respectively). Vertically, temperatures measured at the barn center on the top floor were significantly greater (P < 0.05) than those measured on the bottom floor. During ventilation for warmer outside temperatures (May 23rd–July 26th), only a variation in the longitudinal direction was noted (P < 0.05).

  • 2.

    The CO2 and NH3 concentrations varied significantly with the sampling location inside the building and with outside temperature. Both CO2 and NH3 decreased linearly with increasing TOUT (approximately 77 ppm CO2 and 0.6 ppm NH3 per °C rise for TOUT < 20°C).

  • 3.

    The CO2 and NH3 concentrations measured inside the cages were higher than those in adjacent aisle (P < 0.001), except for when average daily TOUT < 0°C.

  • 4.

    Air leakage through the nonoperating fans shutters from the manure-drying tunnel to the barn, probably from excess back pressure between the drying tunnel and the barn, caused higher NH3 concentration near the sidewalls in bird production area.

Acknowledgements

This work was funded in part by USDA-NIFA Program (award no. 5020-32000-011-16) and multistate Project NE1442: Poultry Production Systems and Well-being: Sustainability for Tomorrow. The authors wish to express appreciation to the International Postdoctoral Exchange Fellowship Program by the Office of China Postdoctoral Council (2013OCPC) for supporting postdoctoral research associate exchange. Mention of commercial products in this article is solely for providing scientific information and does not imply recommendation.

Conflict of Interest Statement: The authors declare that they have no conflicts of interest to this work.

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