Introduction

Poultry meat production has been taken into consideration since the red-meat crisis in the world. People have perceived poultry meat as healthier than beef for being lighter and having a lower fat content (Ramirez et al. 2006). Total world chicken meat production in 2012 was 92 million t, from which the USA, China, and Brazil were the main producers, and Iran, with its production of 1.9 million t, was the 7th largest chicken meat producer in the world (FAOSTAT 2012). The total white meat production of Alborz province was reported as 13,000 t (Anonymous 2015). Alborz province is situated 35 km west of Tehran, the most populated city and capital of Iran. In this situation, Alborz province plays an important role in Tehran’s food security. Energy as one of the most important inputs for economic growth and human development is used in agricultural production widely. In livestock farming, energy is mostly necessary to implement equipment, heating, cooling, lighting, and many other appliances. Until recently, most in-depth energy analyses for agricultural systems have been focused on energy use of farm crops (e.g., wheat, vegetables, forages) while livestock farming (e.g., dairy cattle, poultry) has been disregarded. The energy analysis is one of the most useful methods for evaluating the potential long-term sustainability for various agricultural practices (Atilgan and Koknaroglu 2006). There are various benefits of improving the energy efficiency, such as helping in the promotion of competitiveness through cost reduction, resulting in minimized energy-related environmental pollution, and therefore positively contributing towards sustainable development (Moore 2010). Since global warming poses one of the major environmental issues now and in the future, greenhouse gas (GHG) emission is the main factor of this challenge. Ruminant animal operations are a source of GHG emissions, although the contributions of poultry activities are far lower (Skunca et al. 2015). These gases include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) which absorb energy (heat) of specific wavelength bands in the thermal infrared radiation (Xin et al. 2011). Some researchers have done studies on the energy use, economic, and GHG emission pattern of poultry production (Leinonen et al. 2012; Pelletier 2008; González-García et al. 2014; Nielsen et al. 2011; MacLeod et al. 2013; Heidari et al. 2011; Seguin et al. 2011; Kalhor et al. 2016). With respect to the fact that when designing production systems, economic profitability is the main objective, it is essential to perform economic, energy, and environmental assessments together. It gives a better view to policy makers and producers and helps them to better understand the production system. To the best of our knowledge, energy, economic, and GHG emission assessments have not been studied before on an individual farm level. Initial observation in the research region showed that herd size has a significant effect on input and output variability, and some researchers studied this effect on energy usage in poultry farms (Alaw Qotbi et al. 2011; Atilgan and Koknaroglu 2006). Knowing the effect of farm capacity on the variability of energy, economic, and environmental indices helps to identify the most productive farm capacity. Due to the importance of Alborz province in supplying Tehran’s white meat needs and the lack of similar studies, which were focused on all aspects of broiler chicken production, the aim of this study was to investigate the energy use, economic, and GHG emissions pattern in Alborz province of Iran. Moreover, we assessed the effect of farm capacity on the variability of energy, economic, and environmental indices.

Material and methods

Data collection, functional unit, and system boundary

We collected data on broiler chicken from 60 broiler chicken farms in the province of Alborz (35.68 to 36.37° N and 50.23 to 51.43° E) in Iran. To collect data, farmers were asked about the amount of their farm input utilization and output yield during one period of broiler production process (almost 60 days) during the winter season (in 2014). A simple random sampling method was used to find the required sample size (see Supporting Information file). The most common commercial broiler hybrids in Iran are Arbor Acres, Arian, Cobb, Hubbard, Lohmann, and Ross. Cobb and Lohmann hybrids are the most common hybrids in Alborz province.

The functional unit was 1000 chickens at the farm gate, i.e., the system boundary was from cradle to broiler chicken farm gate. To compare the environmental assessment results with other similar research, we used ton of carcass and kilogram live weight as functional units. To study the effect of farm capacity on energy, economic, and GHG emission indices, farms were classified (based on the frequency of farms) into three groups: small (<16,000 birds which were 19 farms), medium (between 16,000 and 20,000 birds which were 21 farms), and large (>20,000 birds which were 20 farms).

Energy analysis

Table 1 shows the energy equivalents that were used to estimate the energy content of inputs and output. Energy inputs, which were considered in broiler production, were machinery and equipment, diesel fuel, natural gas, electricity, human labor, chick, and feed, while output energy source was broiler chicken meat. Electricity, diesel fuel, chick (1-day-old chicken with average weight of 47.5 g), and broiler meat energy content were calculated by multiplying the amount of inputs (or output) and their corresponding energy coefficients (Table 1). The details of calculations for the energy coefficients of machinery and equipment, diesel fuel, natural gas, electricity, and chicken meat can be found in the Supporting Information file. The energy coefficient of feed ingredients is the total energy consumption to produce 1-kg feed. Since the usage of veterinary resources and chemicals were negligible, and reliable energy coefficients were not found for them, veterinary resources and chemicals were not included in the energy analysis. Output energy in Table 1 is the metabolized chicken meat energy. To calculate the metabolized chicken meat energy content, energy-producing constituents of chicken meat in the human body were calculated and multiplied by their corresponding energy contents. Table S2 shows all related values and calculations (see Supporting Information file).

Table 1 Energy coefficients of inputs and output
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In order to compare different production systems, various energy indices including energy use efficiency (EUE), energy productivity (EP), specific energy (SE), and net energy (NE) were used (see Supporting Information file).

Economic analysis

To carry out the economic analysis, the price of all inputs and output was explored. Net return (NR), gross return (GR), and benefit to cost ratio (BCR) as economic indices were calculated by using Eqs. (1–5) (Pishgar-Komleh et al. 2011):

$$ \mathrm{Total}\ \mathrm{production}\ \mathrm{value}\ \left(\mathrm{TPV}\right)=\mathrm{Broiler}\ \mathrm{meat}\ \mathrm{yield}\ \left(\mathrm{kg}\ {\left(1000\ \mathrm{birds}\right)}^{-1}\right)\times \mathrm{B}\mathrm{roiler}\ \mathrm{meat}\ \mathrm{price}\ \left({\$\ \mathrm{kg}}^{-1}\right) $$
(1)
$$ \mathrm{Gross}\ \mathrm{return}\left(\mathrm{GR}\right)\kern0.75em =\kern0.5em \mathrm{Total}\ \mathrm{production}\ \mathrm{value}\ \left(\$\ {(1000)}^{-1}\right)-\mathrm{Variable}\ \mathrm{cost}\ \mathrm{of}\ \mathrm{production}\ \left(\$\ {(1000)}^{-1}\right) $$
(2)
$$ \mathrm{Net}\ \mathrm{return}\left(\mathrm{NR}\right)=\mathrm{Total}\ \mathrm{production}\ \mathrm{value}\ \left(\$\ {(1000)}^{-1}\right)-\mathrm{Total}\ \mathrm{production}\ \mathrm{cost}\ \left(\$\ {(1000)}^{-1}\right) $$
(3)
$$ \mathrm{Benefit}-\mathrm{cost}\ \mathrm{ratio}\left(\mathrm{BCR}\right)=\frac{\mathrm{Total}\ \mathrm{production}\ \mathrm{value}\ \left(\$\ {\left(1000\ \mathrm{birds}\right)}^{-1}\right)}{\mathrm{Total}\ \mathrm{production}\ \mathrm{cost}\ \left(\$\ {\left(1000\ \mathrm{birds}\right)}^{-1}\right)} $$
(4)
$$ \mathrm{Economic}\ \mathrm{Productivity}\left({\mathrm{P}}_{\mathrm{e}}\right)=\frac{\mathrm{Broiler}\ \mathrm{meat}\ \mathrm{yield}\ \left(\mathrm{kg}\ {\left(1000\ \mathrm{birds}\right)}^{-1}\right)}{\mathrm{Total}\ \mathrm{production}\ \mathrm{cost}\ \left(\$\ {\left(1000\ \mathrm{birds}\right)}^{-1}\right)} $$
(5)

GHG emission analysis

To estimate the GHG emissions of broiler chicken production, CO2, CH4, and N2O emissions were calculated and the results were expressed in carbon dioxide equivalents (CO2-eq). Global warming potentials (GWPs) were used to aggregate the contribution of different relative warming forcing values of GHGs of a product. GWP values of 1, 28, and 265 kgCO2-eq were used for CO2, CH4, and N2O, respectively (Myhre et al. 2013). The life cycle assessment (LCA) for broiler chicken production begins with the production of crop inputs and passes through the phases of crop production, chick production, and chicken rearing, including all transport phases up to broiler chicken farm gate. The production of chicken houses, buildings, and machineries was included. For buildings and machineries, the amount of steel, aluminum, glass, building, polyethylene, which are used in the construction and equipment were inserted into Simapro software and by using Ecoinvent 3.1 database (Weidema et al. 2013), the amount of production emission was calculated. Inventory data for crop production in Iran was based on Sefeedpari et al. (2013), Banaeian and Zangeneh (2011), and Mousavi-Avval et al. (2011). The grain drying and processing and feed manufacturing were not included. We considered that a portion of the crops is produced for chicken feeding uses chicken manure coming from studied systems. Thus, the chicken manure was not included. Seven main GHG emission sources of broiler production were identified, namely construction and equipment, diesel fuel, natural gas, electricity, feed, chick and chicken rearing emission. We used Ecoinvent 3.1 database to calculate the GHG emissions of diesel fuel, natural gas, and electricity production. Table S3 shows the inventory data of broiler chicken farms in Alborz province (see Supporting Information file). All emissions related to production, transportation, and application of inputs were calculated by using Ecoinvent 3.1 database.

To calculate all energy and economic indices, Excel spreadsheets were used, and GHG emission calculations were done using SimaPro 8. To find the meaningful differences of values in all three farm size categories, an ANOVA test and Duncan compare mean were performed in SPSS 18 software.

Results and discussion

Energy analysis

Table 2 shows the inputs and output energy contents of broiler chicken farms in Alborz province. The total energy input average was almost 194 GJ per 1000 birds. An amount of 186 GJ was reported in a similar research for broiler chicken farms in Yazd province of Iran (Heidari et al. 2011). This discrepancy can be explained by the colder weather of Alborz in comparison to Yazd province, which increases the amount of energy usage for heating. Diesel fuel contributed most to the total energy use, i.e., on average 49%, followed by feed (25%), natural gas (22%), and electricity (3%). Diesel fuel, natural gas, and electricity were applied to run the equipment, for heating and ventilation purposes. The same pattern was affirmed by Heidari et al. (2011) and this is in agreement with the results of the research by Alaw Qotbi et al. (2011) and Atilgan and Koknaroglu (2006). In a similar study (Alaw Qotbi et al. 2011), feed was reported as the second most important energy input in the broiler farms. The total average of broiler live weight was 2868 kg (1000 birds)−1 and the corresponding total energy output was approximately 31 GJ (1000 birds)−1. The results of the analysis of the farm size impact on energy consumption showed that total energy input decreases significantly as farm size increases. This reduction can be explained by more efficient energy use for heating (diesel fuel), ventilation, and lighting (electricity) purposes in medium and large farms. This result was in agreement with the results of similar studies (Alaw Qotbi et al. 2011; Atilgan and Koknaroglu 2006). Electricity is consumed in different operations, but lighting is the major use of electricity in poultry industry. It was seen that in small farms, producers use normal light bulbs, while most of the others use energy saving light bulbs. For machinery energy input, an increase of the farm size increases the energy usage. This trend is due to the use of more mechanized production systems in large farms, which increases machinery energy usage and thus decreases human labor energy usage significantly.

Table 2 Energy analysis in three farm capacities for broiler chicken production in Alborz
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Energy indices, consisting of EUE, EP, SE, and NE for broiler chicken production in Alborz province, are presented in Table 3. The EP showed that to produce 1 kg of chicken meat, 67.72 MJ is needed (Table 3). The average EUE was 0.16. The less than unity value of EUE does not show the inefficient use of energy in broiler chicken farms in Alborz province. The EUE index shows that the broiler chicken production is an energy use process. To improve the production in the viewpoint of energy, two major guidelines can be used, including (i) using less energy input and/or (ii) increasing the farm yield (output energy). Various methods for decreasing energy inputs in regard to less diesel fuel, natural gas, and feed diet (i.e., using diets with high fiber and lower protein and lysine) can be suggested. Replacing diesel fuel heaters with ones that burn natural gas is another option, which may decrease the total heating energy consumption. The effect of farm capacity on energy indices showed that large farms with a larger capacity had better EUE than the other groups, due to their lower total energy consumption.

Table 3 Average energy indices in broiler chicken farms in Alborz
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Economic analysis

Table 4 shows the economic analysis of broiler farms in three different farm sizes. Feed accounted for a significant share of the average total cost. Due to the importance and the skyrocket conditions of feed intake of poultry production in Iran, determining the amount of required feed called as optimized diet is of particular importance. After that, chicks (413 $ (1000 birds)−1) and vaccination (276 $ (1000 birds)−1) were found to be costly inputs. Despite the high energy consumption in diesel fuel and electricity supply, they had a small share in variable costs, which is due to low price of fossil fuels and the subsidizing policy in Iran. These results are consistent with the findings reported by Heidari et al. (2011). The total costs (sum of variable and fixed costs) were estimated to be 4532 $ (1000 birds)−1 which is about 24% higher than the estimate reported by Heidari et al. (2011). A significant decrease was observed in the cost per 1000 birds of diesel fuel as the farm size increases. As it can be seen, for major cost inputs such as feed and chick, no significant difference was found among herd size groups.

Table 4 Economic analysis in three farm capacities for broiler chicken production in Alborz
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The economic indices per 1000 birds are given in Table 5. The average gross value was 5031 $ (1000 birds)−1. The variation of variable and fixed costs was found to be almost constant as capacity increases. Fixed and variable costs were around 5 and 95% of total costs, respectively. The results revealed that, for all economic indices, there is no significant difference between the herd size groups. The average value for benefit to cost ratio was 1.11. This index was 1.38 in the farms surveyed by Heidari et al. (2011). Colder weather, which increases heating needs and feed cost in Alborz province, are the main reasons of less benefit to cost ratio of our target farms in comparison to Heidari et al. (2011) research results.

Table 5 Economic indices based on three farm capacities for broiler chicken production in Alborz
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GHG emission analysis

Table 6 shows the GHG emissions of broiler farms in Alborz province. The total GHG emission was 19.13 t CO2-eq per 1000 birds. Feed contributed most to the total GHG emission, i.e., on average 43%, followed by diesel fuel (32%), and natural gas (10%). These findings are similar to Leinonen et al. (2012) research. They found that feed production, processing, and transport resulted in greater overall environmental impacts than any other components of broiler chicken production (71 to 72% of GWP). In 2006, Williams et al. (2006) accounted for the environmental burdens and impacts for the UK poultry meat production system and estimated the GWP100 value as 4.6 t CO2-eq per t of carcass. In our study, the GWP100 value was estimated as 8.50 t CO2-eq per t of carcass. The difference can be explained by the larger amount of material and energy usage and lower output in Alborz province. The broiler chicken production system in Iran is less modern and efficient in comparison to that of Europe. Moreover, our study was carried out during the winter season, and thus, more fuel and feed were used to maintain the temperature needed for chickens. Katajajuuri et al. (2008) found the total GHG emission of 1.3 kg CO2-eq per kg live weight for chicken meat production in Finland, which was lower than our result (6.83 kg CO2-eq per kg live weight). A comparison of GHG emissions based on herd size showed that as the herd size increases, the GHG emissions decline. The significant difference between large, medium, and small farms was observed in the total GHG, diesel fuel, and electricity emissions (Table 6).

Table 6 GHG emission analysis in three farm capacities for broiler chicken production in Alborz
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To sum up the study’s key findings, we can include feed as the most important input in broiler chicken production in Alborz province. Feed contributed most to total energy consumption, GHG emission, and total cost. As it was seen, in all herd sizes, there was no significant difference for feed input between different farm sizes, which shows a high consideration of farmers on feed input. Diesel fuel input had the least amount of energy consumption, cost, and GHG emission in large farms. Based on our field observations, a low level of building isolation and applying low efficient heaters are two major reasons for the high consumption of diesel fuel in small farms of Alborz province. Applying old heaters with low efficiency increases the amount of fuel consumption, and this results in more emission. More emission subsequently increases the ventilation needs. As it was observed in the research area, with the increase of the farm size, fuel usage rises up progressively, and in this situation, farmers use more efficient heaters, therefore causing a decrease in fuel consumption in comparison to small farms.

Limitations and uncertainties

Several assumptions were needed to calculate the GHG emission of broiler production leading to some uncertainties. The grain drying and processing and feed manufacturing were not included in GHG emission calculations. Moreover, the chicken manure was not included. We used the Ecoinvent database for emissions of inputs. In some cases, no exact data for Iran were available and we relied on world averages, such as for natural gas, diesel fuel, and construction. Future research would benefit from the application of Iran-specific data for all emissions.

Conclusion

This study shows the energy, economic, and GHG emission flow of broiler chicken farms in Alborz province, Iran. Therewith, comparisons based on different capacities of broiler chicken farms were performed. Based on the results, some conclusions were drawn, and their corresponding recommendations are as follows:

  1. 1.

    The total average energy input was calculated as 194 GJ (1000 birds)−1, among which diesel fuel, feed, and natural gas had the greatest share. The EP was 67.72 MJ kg−1 in the surveyed area and revealed that to produce 1 kg chicken meat, 67.72 MJ is needed. Results showed that large farms had better energy management, so they had the highest amount of EUE values among other farm categories.

  2. 2.

    The total average cost and income were 4532 and 5031 $ (1000 birds)−1, respectively. Feed was the most important input in the economic analysis of the present study. BCR was reported as 1.11 and there was no significant difference among broiler chicken herd size groups for BCR.

  3. 3.

    The total GHG emissions based on different functional units were 19.13 t CO2-eq per 1000 birds, 8.5 t CO2-eq per t of carcass and 6.83 kg CO2-eq per kg live weight. Feed had the highest impact on total emission. In large farms, we saw lower amounts of emissions for diesel fuel, electricity, and total emissions.

  4. 4.

    In this study, it was not possible to definitely determine the impact of the improvement or worsening of energy efficiency or GHG emissions as a result of the management changes on broiler yield, or the impact of changes in the inputs use on the yield, but we can posit some likely explanations for the farm-wide patterns observed. It was concluded that energy consumption, and subsequently the GHG emission situation, was better in large farms. A better management of inputs and less bird losses were the reasons of this fact. Large farms with more investment had modern heaters (with higher efficiency), which decreases the diesel fuel and natural gas consumption. It was observed that in almost all the large and medium farms, farmers are experienced in broiler chicken production; therefore, they had better input management and also less chicken losses. As a result of our study, it is recommended to support small-scale broiler producers by providing subsidies to use high-efficiency equipment. In order to decrease the amount of energy usage and GHG emission, replacing heaters (which use diesel fuel) with natural gas heaters may be considered. Natural gas has lower emission and decreases the amount of ventilation needed in the poultry buildings. It was seen that in small farms, producers use normal light bulbs, while others use energy saving light bulbs. Apart from the other factors (such as ventilation and water pumping), light bulbs have caused small farms to experience higher energy consumption.