INTRODUCTION
In the Turkish egg production sector, there are about 85 million laying hens with an annual production of 15 million eggs (about 1 million kg) produced in 2012 (TUIK, 2013) and 61 billion kg produced annually worldwide (FAO, 2011). Currently, laying hen husbandry with a cage system is the most common method of commercial egg production in Turkey, in parallel with the trend worldwide.
The indoor air quality in laying hen houses is crucially important to the hens’ egg production as well as emitting less pollutant gas and providing a healthier environment for workers. Pollutant gas concentrations, indoor environmental conditions such as, temperature, relative humidity, light intensity and airflow are major characteristics of indoor air quality in laying hen houses. Ammonia (NH3) is dominant pollutant gas in poultry houses. Furthermore, NH3 plays an essential role in the atmosphere with contribution to the nitrogen cycle as well as in indoor air quality (Arogo et al., 2006). Also, high concentrations of NH3 (e.g. >20 ppm) may cause respiratory diseases (e.g., coughing, upper respiratory tract bleeding, excessive secretions, and lung bleeding or inflammation) (Smith, 1998; Dong et al., 2009).
Ammonia in laying hen houses emitted mainly from manure, whereas CO2 formation commonly comes from the bird's respiration. The magnitude of NH3 concentration in buildings mainly depends on husbandry systems (cage, on litter or alternative systems), capacity of house, density (in cage or on unit floor area) and feed content. The NH3 concentration increases in cases of higher density and feed with higher protein.
There are a few studies to determine NH3concentrations in animal barns in Turkey. In these studies, NH3 concentration was measured in broiler houses (Atilgan et al., 2010; Simsek et al., 2013), dairy barns (Simsek et al., 2012) and laying hen houses (Kocaman et al., 2006). On the contrary, many of studies have been conducted to quantify NH3 concentrations in laying hen houses in Europe and in the US.
Gao et al. (2013) estimated NH3 concentration and emissions in a laying hen house in China. The emissions factor for laying hen houses was found as 164 mg·hen−1·year−1 in this study. Groot Koerkamp et al. (1998) and Nicholson et al. (2004) measured NH3 emissions from different manure handling systems in four European countries and UK, respectively. They measured NH3 concentrations as 8.3 ppm in England, 29.6 ppm in the Netherlands, and 25.2 ppm in Denmark. Fabbri et al. (2007) reported NH3 and greenhouse gases (GHG) concentrations and emissions from two different laying hen houses in Italy. The average NH3 concentration in summer months was about 2 ppm in their study. Wang-Li et al. (2013) monitored two tunnel-ventilated high-rise layer houses in North Carolina, USA to determine NH3 concentrations and emissions. They found that NH3 concentrations were 23 ppm for laying hen houses. Lin et al. (2012) addressed NH3 and other pollutant gas concentrations and emissions from high-rise laying hen houses in California, USA. The NH3 emission from Californian laying hen houses was calculated 0.95 g·d−1·bird−1 during two years measurement. Kilic et al. (2011) estimated using nitrogen balance method NH3 concentration in US high-rise laying hen houses. NH3 emissions was calculated as 0.16 kg·birds−1·year from laying hens house in Kilic et al. (2011).
The aim of this study were to quantify NH3 and CO2 concentrations gases and determine effects of indoor environmental conditions on pollutant gas concentrations during summer seasons for a naturally ventilated laying hens house located in Bursa, west Turkey.
MATERIALS AND METHOD
House characteristics
A cage layer farm in Bursa, western Turkey, was selected in this study to monitor NH3, and CO2 concentrations and emissions. Selection of the farm was based on its production scale and management practices being representative of the current and growing trend of egg production facilities in Bursa region. The farm had a total of two naturally ventilated houses.
The monitored house had a dimension of 39×12 m (L×W) with a north-south orientation. The monitored house contained five cage rows and each cage row had three tiers, with a total holding capacity of approximate 12,000 laying hens (Figure 1). Each house had 10 air inlet openings (0.5×2.1 m each) spaced at 1.6 m intervals along each east and west sidewalls. There was an opening on ridge throughout length of building.
Fresh air enters the building through both sets of sidewall openings and exits the building through the ridge opening (Figure 1). Operation of the ventilation windows and ridge vents was based on the target house temperature, which was 25°C in summer and was adjusted manually.
The leghorn hens were fed with commercial standard diets three times a day at 06:00, 12:00, 18:00, and 24:00 h and had free access to drinking water. Feces dropped to the manure belt beneath the cages and were scraped out to a manure collection channel at the end of each cage row. The removed manure was taken from the manure collection channel to a trailer outside the house.
The cage density was five birds per cage. Bird performance data (feed consumption, bird age, and egg production) were taken from farm records during the experiment.
Egg, feed and manure samples from each cage rows were collected. Their physical and chemical properties, including dry matter and total nitrogen contents, were analyzed in a certified analytical lab (TUBITAK, BUTAL) in Bursa.
Pollutant gas concentration and environmental conditions measurement
In this study, NH3 and CO2 concentrations and indoor environmental conditions such as temperature, and relative humidity was measured for five consecutive days in first, medium and last week of each month in summer of 2013. The laying hen age during the summer measurement period was 56 weeks. A multi-gas analyzer (MultiRAE IR Lite, RAE systems, San Jose, CA, USA) with electrochemical and NDIR sensors was used for pollutant gas concentrations. Two multi-gas analyzers were located at the inlet and exhaust openings and measured pollutant gas concentrations at 5 min intervals. Indoor and outdoor air temperatures, relative humidity (RH) and air velocity in monitored house were measured at 5 min intervals throughout the experiment using portable temperature/RH/air velocity meter with hot-wire probe (Model 435-2, Testo, Germany). Outdoor temperature/RH/air velocity data was taken from a meteorology station near the monitored layer house. The distance between the house and station is approximately 14 km.
Airflow rates calculation
Calculation of airflow rates in naturally ventilated facilities is highly difficult during the summer season. Therefore we used an indirect method to calculate airflow rate. The house ventilation rate was calculated using a CO2 balance method based on CO2 production of laying hens given below (Albright, 2000).
Where; VCO2 is CO2 generation rate of the hen house (m3·h−1·house−1), Ce, CO2 and Ci, CO2 are exhaust and inlet CO2 concentrations of the hen house at 20°C (mg·m−3), and ρCO2 is CO2 density (1.977 kg·m−3 at 20°C).
Data analysis
The data obtained from the monitored laying hen house was statically analyzed using JMP 7. The general linear model was used to determine significance of differences among pollutant gas concentrations and also regression analyze was done to reveal relationship between environmental indoor conditions and pollutant gas concentrations.
RESULT AND DISCUSSION
Egg production parameters
The number of hens, average body weight, bird age, mortality, egg production and daily feed intake parameters in egg production during the study period are summarized in Table 1. Feed intake increased with hen age from 56 to 65 weeks. The lowest feed intake was found in June 2013. The highest mortality occurred in July 2013 due to environmental conditions. In the study period, egg production was affected by mortality.
Feed, egg and manure samples were analyzed weekly during each month in the summer of 2013. The results are listed in Table 2.
Ambient and indoor environmental conditions
The descriptive statistics of indoor and ambient air temperature, relative humidity, air velocity and airflow rate are given in Table 3. The indoor temperature varied from 16.80°C to 34.71°C while relative humidity ranged between 34.60% and 86.18%. The indoor temperature and relative humidity in August 2013 were significantly higher than other months in summer. The air velocity and airflow rates varied from 0.04 to 0.54 m·s−1 and from 8 to 37 m3·s−1·house−1, respectively. The maximum airflow rate was obtained in July and August 2013.
The diurnal variation was observed on indoor environmental conditions during study period (Figure 2). The average daytime and night time indoor air temperatures (T), relative humidity (RH) and velocity (V) were 26°C and 22°C, 59% and 69%, 0.20 and 0.18 m·s−1 respectively. Also, the differences between daytime and nighttime variables were statistically significant for T, RH (p<0.01) and V (p<0.05).
Ammonia and carbon dioxide concentrations
The descriptive statistics of measured gas concentrations during the summer 2013 are presented in Table 4. The average exhaust or inlet NH3 and CO2 concentrations were defined as the average of the hourly mean concentrations measured at inlet and exhaust levels.
When the inlet concentration measurement location was in front of the inlet on the side wall, pollutant gas concentrations were higher than ambient air surrounding the house because it was most likely affected by the emissions from the hen house itself. Pollutant gas concentrations at this inlet location varied from 4.00 to 8.67 ppm for NH3 and from 510 to 824 ppm for CO2.
Pollutant gas concentrations were generally higher in exhaust than that of inlet concentrations. The average NH3 and CO2 concentrations were calculated using hourly mean data. The minimum, average, maximum and standard deviation values of pollutant gas exhaust concentrations were measured as 6.98, 8.05, 10.58, and 2.48 ppm for NH3, 609, 732, 904, and 69 ppm for CO2 throughout study, respectively. The maximum NH3 and CO2 exhaust concentrations were observed on June 2013 while minimum exhaust concentrations were measured on August 2013 for NH3 and July 2013 for CO2.
According to average hourly pollutant gas concentrations (Figure 3), inlet concentrations for NH3 and CO2 illustrated no clear diurnal variations. However, exhaust concentrations for NH3 and CO2 showed a clear diurnal pattern depending on bird activity, ambient temperature and house airflow rate. The average NH3 and CO2 exhaust concentrations in day time were 9.03 and 790 ppm, respectively. Consequently, the average NH3 concentration was lowest in early morning (2.42 ppm) while average CO2 exhaust concentration was lowest in early noon (467 ppm). The maximum exhaust concentrations for NH3 and CO2 were measured after noon. Since the inside and exhaust NH3 and CO2 concentrations are substantially affected by house airflow rates and the airflow rate varies with ambient temperature, this interaction among environmental conditions created diurnal patterns of NH3 and CO2 concentrations.
The magnitude of ammonia concentration in laying hen houses is more important comparing with other animal houses, e.g., dairy and swine (Koerkamp et al., 1998). In a study in the USA, NH3 concentrations varied between 2 and 10 ppm in broiler houses under summer conditions, (Redwine 2003). Cheng et al. (2011) measured NH3 concentration in layer houses with a cage system and their results for NH3 concentration ranged from 0.5 to 12.5 ppm. These concentration values for NH3 were comparable to the results of this study. The layer houses with a manure belt and high rise (HR) cage systems in North Carolina, USA were monitored continuously during two years. The results of Wang-Li (2013) stated that the 2-year mean NH3 concentrations (23 ppm) at the exhaust fans in the HR houses were higher than results of this study, while the results (3 ppm) of a study from China (Zhu et al., 2011) were similar.
NH3 concentrations affect workers’ health as well as laying hens in house. Different countries worldwide have some regulations to protect workers’ health in animal barns. These regulations set limits for a time-weighted average (TWA) over 8 h and a short exposure threshold limits. According to Turkish regulations on workers’ health, the exposure limit of NH3 was established as 20 ppm for short-term exposure and 50 ppm for TWA over 8 h (Kilic, 2013). Indicative Occupational Exposure Limit values by European Union (Directive 2009/161/EU) are similar to the Turkish limits (Anonymous, 2009). Additionally, NH3 exposure limit for animals in barns in Sweden is 10 ppm (Anonymous, 2010).
The average summer CO2 concentration was measured as 732 ppm in this study. This value is similar to some European studies while it is lower than some studies in USA. Dobeic and Pintaric, (2011) measured average CO2 concentrations was 758 ppm in exhaust air in monitored seven layer hen houses in Slovenia. The average summer ammonia concentration was found 1,012 ppm in four laying hen houses with manure belt in Iowa in USA (Liang et al., 2005; Green et al., 2009).
CO2 is one of the GHG involved in global warming. In this study, average CO2 concentration per 1,000 bird was measured 66.54 ppm for the Bursa region. According to data obtained from the Turkish Statistical Institute (TUIK, 2013), the number of laying hens in Bursa region and Turkey for 2012 year was 4.2 million and 84.6 million, respectively. When the effect of a laying hen house on global warming is estimated using this study results, the contribution of CO2 concentration produced in laying hen houses to atmospheric CO2 concentrations is approximately 280,000 ppm regional wide and 5.6 million ppm national wide. However, under Turkey’s conditions, more studies are required to more accurately estimate the CO2 contribution to global warming.
Relationship of pollutant gases concentration and environmental conditions
Regression models were developed for NH3 and CO2 concentrations using the data obtained from this study (Eq 1 and Eq 2). The indoor air temperature (T), indoor air velocity (V) and indoor relative humidity were considered as independent variables. The regression analyze was used to develop these models. The descriptive statistics of these models were given in Table 5.
Only indoor air temperature among all variables had a significant effect on pollutant gas concentrations in the laying hen house. This study revealed that increased T was associated with higher NH3 and CO2 concentrations (Table 5). The source of pollutant gas in laying hen houses can explain this finding in the model. NH3 concentrations are mostly emitted from manure and urine on the manure belt. Indoor air temperature and pH have been reported as two of the most important factors that influence NH3 volatilization from manure (Sommer et al., 1991; Arogo et al., 2006).
The producers in Bursa region can use these equations to estimate concentration level of NH3 and CO2 in their laying hen houses. They firstly need to measure indoor environmental conditions, such as temperature, relative humidity, and air velocity. They can easily estimate concentration level of NH3 and CO2 in their house via only these parameters in the equations and decide whether NH3 and CO2 concentration in their laying hen house exceed exposure limits for bird and workers’ health. Therefore, producers can determine and implement the most reliable mitigation strategy to reduce these gases concentrations in their conditions. Also, the measurement of indoor environmental conditions is less expensive than air quality measurements in animal barns. When producers use these equations, they can easily determine NH3 and CO2 concentrations using this less expensive method.
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