Factors that Influence the Production , Environment , and Welfare of Broiler Chicken : A Systematic Review

The objective of the present study was to characterize the scientific production regarding the factors that influence broiler chicken production, and that were published from 2000 to 2015 in journals indexed in the database of Google Scholar, Scielo, and ScienceDirect. The research was done in the Thermal Comfort Laboratory at FEAGRIUNICAMP, and the concept of the systematic review was applied. The research criterion was initially defined (the keywords) aiming to identify and evaluate the variables that describe the experimental characteristics and the animals. The primary keywords identified were: broiler chicken from commercial strains, broiler production, rearing conditions, thermal environment, air quality, acoustic environment, light intensity, management, and heat stress. Those were the key words searched in the database of the online libraries. The selected articles were registered into an electronic spreadsheet with the title, the name of the authors, year of publication, language, the journal where it was published, the keyword, the period when the research was done, source/ database, and the abstract. A total of 167 articles were selected, and only 34 were added to the review. The use of the systematic review of the literature allowed identifying the main variables that positively influence the broiler performance, such as the temperature near the thermal comfort, the use of roof lining, besides the use of adiabatic cooling and cast bricks in the laterals. The presence of positive ventilation, as well as the use of yellow curtains and constant lighting, has also influenced a better performance to broilers.


INTRODUCTION
Brazilian poultry industry is highly relevant for the country economy.In 2016 a total of 13 million tons of broiler meat was produced, and nearly 35% was exported.(ABPA, 2017).Broiler production is carried out in several variations of house design.However, most of the production in the integrated system is done in open-sided houses with lateral polypropylene curtains, and with solar orientation East-West.The inside cooling is a combination of natural and forced ventilation (axial fans) associated with the fogging system.Modern houses adopt the closed sides using a more resistant curtain, and the inside ventilation may be done with positive pressure by using axial fans or exhausting fans associated with adiabatic cooling.
The systematic review (SR) of literature is the scientific technique that aims to review and evaluate the published literature using methods to identify and select the studies that are relevant.This technique has been used by authors in various circumstances.Kerr et al. (2013) used the systematic review to identify the effectiveness of competitive exclusion and its effect on the prevalence of salmonella in broiler breeding.Rodrigues Filho & Gonçalves (2015) applied the systematic review to identify the contribution of legal metrology to control processes, in addition to identifying the research needs of the sector.Offedo et al. (2016) reviewed the impact of interventions in the poultry market, aiming to reduce the contamination of humans by Avian Influenza, based on published scientific evidence.Średnicka-Tober et al. (2016) used the systematic review and meta-analysis from sixty-seven published papers to compare the nutrient content in organically produced beef compared to meat produced traditionally.Clarck et al. (2016) conducted a systematic review of scientific studies focusing on the reaction of consumers when informed about diseases in animal production in intensive systems.Clune et al. (2017) presented the results of a systematic review of the literature on greenhouse gas emissions for different food types, which offered the life cycle computation, aiming at recommending a sustainable food type.
The present study aimed to characterize the scientific publications on the topics of the factor that influences broiler production published between 2000 and 2015 in journals indexed in the databases of Google Scholar, Scielo, and ScienceDirect.

MATERIALS AND METHODS
The literature review was carried out at the Thermal Comfort Laboratory of FEAGRI-UNICAMP, using the concept and method of the systematic review.Figure 1 shows the flow of information from the systematic review used.
The research criteria and the keywords were initially defined with the purpose of identifying and evaluating the variables that describe the experimental and animal characteristics.The main keywords identified were: commercial broilers, production, lodging conditions, thermal environment, air environment, acoustic environment, luminosity, handling, thermal stress) in databases (Google Scholar, ScienceDirect, and SciELO).
Table 1 shows the keywords used to search within the databases.The articles selected using the criteria were organized through the association of a database using a spreadsheet.The list contained the title, author, year of publication, language, and journal in which the title was published (inserted in the database), a period in which the research was carried out, the source/ database, and the summary of the article (Andretta, 2011;Offedo et al., 2016).The research criteria and the keywords were initially defined with the purpose of identifying and evaluating the variables that describe the experimental and broiler characteristics.The main ones were the commercial broilers, production, housing conditions, thermal environment, air quality and conditions, acoustic environment, luminosity, handling, and thermal stress in the studied databases (Google Scholar, ScienceDirect, and SciELO).
The second step was to check the titles and summaries of the articles to identify the articles that were related to influence factors in the production of broiler chicken, as suggested by Średnicka-Tober et al. (2016).The third step was to analyze each article to decide inclusion and exclusion criteria (Table 2).

RESULTS
A total of 167 scientific articles were identified (Figure 2) using a critical analysis as recommended by Riera et al. (2006).From the total scientific articles selected, 22 articles were found in the Google Scholar database, 92 on ScienceDirect, 53 on SciELO.A total of 99 articles were in English and 68 in Portuguese.The year that presented the highest number of publications was during 2010 (24 articles), followed by 2014 (21 articles), as shown in Figure 3.The year 2014 was the one that presented the most significant number of articles published in English, and in Portuguese was in the year of 2010 (Figure 4).The higher number of papers published may not reflect qualitative advances.Therefore, systematic reviews have become essential tools for tracking evidence that accumulates in a particular field of interest (Andreta, 2011).Amongst the most various journals that publish articles on broiler production, the following may be highlighted: Applied Behavior (15%), Engenharia Agrícola/Agricultural Engineering (12%) and Brazilian Journal of Animal Science (12%).From the 167 articles selected, after applying the critical review (Figure 1) only 34 were considered in the review (Table 3).

DISCUSSION
The discussion is presented relating the effects identified in the systematic review.et al. (2000) reported that the ambient temperature influenced the weight gain, which was 16% lower in birds kept under heat stress (32.3 ± 0.31ºC) than those maintained in thermal comfort (23.3 ± 0.58ºC).Similar to the weight gain, it was verified that the high temperature (32ºC) determined a 19% increase in the feed conversion rate of the birds.

Neto
For Sartori et al. (2001) the weight and the weight gain of the birds reared in the warm environment were lower than those of the birds kept in the thermoneutral and cold environment.These results probably occurred due to the lower feed intake of the birds in the heated chamber when compared to the birds raised in the thermoneutral and cold climatic chambers.Among the birds housed in the thermoneutral and coldchambers, feed intake was lower for birds housed in the thermoneutral chamber, indicating that the   cold temperature caused an increase in the voluntary consumption of food.The ambient temperature affected the broiler performance.Oliveira et al. (2006) indicates that, in all the analyzed periods, birds kept in the thermal comfort environment presented the highest values of feed intake and weight gain and the worst feed conversion.According to the authors (Oliveira et al., 2006), the best results of weight gain and absolute weights of the breast, thigh, and carcass of male broilers of the Avian Farms strain were obtained in the birds reared at inside temperature from 24 to 26, 3°C.Ambient temperatures below 24ºC and above 26.3ºCnegatively influenced the weight gain and the absolute weights of chest, thigh, and carcass.
Heaters provide a reliable, low-maintenance source of heat for young birds.Cordeiro et al. (2010) showed that the heating system conjugating several radiant heaters is more efficient because it maintains the house in better thermal conditions on condition that offers welfare for the birds in the first and second weeks of grow-out, which provides improved productive performance.The system with minimal ventilation significantly reduces the temperature inside the house, compromising thermal comfort and damaging animal performance, evaluated through feed conversion, Betin PS, Moura DJ Factors that Influence the Production, Environment, and Welfare of Broiler Chicken: A Systematic Review slaughter weight and productive efficiency (Vigoderis et al., 2010).
Broilers reared close to the ventilation system presented better performance in a hot environment (Bilal et al., 2014).
Effect of the housing, flock density, and the use of adiabatic cooling Houses with evaporative cooling systems associated with ventilation provided higher values of broiler weight gain and lower values of feed conversion and mortality (Sartor et al., 2001).Bueno & Rossi (2006) observed in both housing systems (conventional and high density) that the daily weight gain was below, while the feed conversion was above the Ross lineage standard (Agroceres Ross, 2000).The analysis of the primary variables the highdensity housing showed, on average, better results when compared to those of the conventional shed.Furtado et al. (2006) in an experiment evaluating three systems (sprinkler system, ventilation system, misting system) reported that the values observed and the productive indexes remained within the ideal ranges for the chicken industry.In the positive pressure system, the best results were obtained for the performance indexes of the birds, for the parameters live weight and feed conversion (Menegali et al., 2010).On the other hand, according to Vigoderis et al. (2010) in non-ventilation sheds, birds presented better performance.
Results from two different cooling systems wetted porous plates of cellulose associated with fogging and moistened plates of plastic shade related to fogging, and did not differ from the values of feed intake, weight gain and feed conversion (Damasceno et al., 2010).
Different ventilation systems used by Abreu et al. (2011), did not show significant differences in poultry performance, mortality rate and the presence of foot injuries.Barbosa et al. (2012) detected that the use of the evaporative adiabatic cooling system was more efficient when associated with the evaporative system of wet hollow bricks, providing a more comfortable and homogeneous environment showing the effect on the performance parameters, and favoring feed conversion.
The semi-intensive breeding system provided conditions that increased bird welfare, positively influencing performance, even under conditions of thermal stress (Silva et al., 2003).In studies conducted by Lima & Naas (2005) comparing two systems of broiler breeding (Conventional-A and Semi-extensive-B), feed conversion was 1.97 and 2.98 in A and B, respectively.Conventionally bred broiler chickens had better feed conversion than broiler chickens in the semi-extensive system.Wood et al. (2010) reported that data on weight gain, feed intake, feed conversion, and mortality were not affected by the breeding system (confinement and semi-confinement).
In studies by Souza et al. (2010) non-automated sheds and during winter and spring, birds presented better performance.Furtado et al. (2010), analyzing two sheds (ceramic tile and another with fiber cement tile) did not observe a significant difference between the mean values of the variables live weight, daily weight gain, feed conversion and mortality rate in the two systems analyzed.

Other identified effects
Roof insulation Oliveira et al. (2000) observed that the use of roof thermal insulation gave birds greater feed intake, higher weight gain and better feed conversion than the environment without thermal insulation.There was a decrease of 4.06% in poultry mortality in the housing with thermal insulation compared to the house without thermal insulation.Abreu et al. (2007) reported that the use of the polyethylene on roof insulation of the house, results in better conditions of thermal comfort for the birds and better results of live weight, weight gain and feed consumption and feed conversion not was influenced by the use of the roof insulation.

Genetic strains and sex
In the study presented by Stringhini et al. (Ross, Cobb, Arbor Acres and Avian Farms) showed a proper performance and the Ross strain had the weight gain and slaughter weight superior to the other strains at 44 days of age; however, the result was not the same in the different phases.The Avian Farms and Arbor Acres strains showed higher cumulative feed intake at 48 days of age.At this stage, Arbor Acres and Avian Farms chickens had a cumulative feed intake statistically superior to the Cobb strain at 168.65 and 148.49g, respectively.The Ross strain showed better feed conversion (1.667) about Avian Farms (1.779) and Arbor Acres (1.780) from 1 to 44 days of age.Males had superior performance and carcass weight than the females, but carcass yield characteristics were similar.According to Amaral et al. (2011), higher body mass was found in males when compared to females.

Semi-intensive and extensive way of rearing
Data from broilers reared in a semi-intensive mode, data of weight gain of the birds was influenced by the genetic strain and birds of the Ross strain presented more significant weight gain when compared to the Master Griss and Vermelhão Pesado strains, which did not differ from each other.Label Rouge birds had lower weight gain, according to Madeira et al. (2010).Zhao et al. (2014) showed that the mortality rate of broiler breeder raised outdoors was significantly higher than for those reared inside the housing.
Flock density and season of the year Silva et al. (2005) researched broilers with flock densities from 10 to 14 birds m -2 and observed that the flock density did not affect the feed conversion in any of the grow-out phases.However, the increase in flock density reduced the weight gain in 19-38 days of grow-out and the total time of growth, and in the fall feed conversion was high, on average, 3.27.Gopinger et al. (2015) increased density from 11.08 to 13.20 m -2 birds and observed that the flock density did not affect broiler performance in the tested range.

Lighting
The live weight of the birds was higher in the treatment with increasing light, and the feed consumption was lower, according to Moraes et al. (2008).Abreu et al. (2011) a program of almost continuous lighting and yellow curtains provide better performance of broilers.However, this program causes increases in the mortality rate and the consumption of electricity.Santana et al. (2014) showed that the use of LEDs of different colors had the same effect of fluorescent lamps on the performance and carcass yield of broilers.

Floor
The research presented by Abreu et al. (2011), showed that there is no difference in the performance parameters in broilers raised on two types of floors (concrete and dry land).Wang et al. (2015) reported that chickens reared in three types of poultry facilities using multiple layers of cages, compared to broiler chickens raised on slatted plastic, were not affected by the housing or floor condition.
Table 4 shows the summary of the primary variables that positively influenced broiler performance.

CONCLUSIONS
The use of systematic review of the literature allowed us to identify the primary variables that influence the performance of the broiler chicken.These are related to the maintenance of temperatures close to the thermal comfort of the birds, which can be achieved with the use of roof thermal insulation, as lining, besides the use of adiabatic cooling and the use of brick cast on the sides.The presence of positive ventilation, as well as the use of yellow curtains and the continuous lighting, also positively influences the performance of the broiler chickens.The sex of the chicken seems to influence the performance.

Figure 1 -
Figure 1 -Scheme of the systematic review process of scientific articles considered in the current study.(Adapted from Rodrigues Filho & Gonçalves, 2015).

Figure 2 -
Figure 2 -The total of scientific articles identified in the studied databases.

Figure 3 -
Figure 3 -The total of scientific articles found in the studied databases in each year.

Figure 4 -
Figure 4 -Total of scientific publications by the year and the language.

Factors
Betin PS, Moura DJ Factors that Influence the Production, Environment, and Welfare of Broiler Chicken: A Systematic Review

Table 1 -
Keywords used in the systematic review.
Frango de Corte e Alojamento Broiler and Housing Frango de Corte e Produção Broiler and Conditions Frango de Corte e Bem-Estar Broiler and Stress Frango de Corte e Luminosidade Broiler and Management Frango De Corte e Ambiência Aérea Broiler and Lighting Frango de Corte e Temperatura Broiler and Heat Stress Frango de Corte e Estresse Térmico Broiler and Production Frango de Corte e Ambiência Acústica Broiler and Acoustic Environment Frango de Corte e Ambiência Térmica Broiler and Thermal Environment

Table 2 -
Adopted criteria for inclusion and exclusion of the keywords

Table 3 -
Scientific articles selected for the systematic review, following the established criteria.
Title Author Year of publication Language Journal, volume , and issue Desempenho Produtivo e Bioeconômico de Frangos de Corte Criados em Diferentes Sistemas de Aquecimento Abreu et al. 2000 Portuguese Rev. Bras.Zootec.v.29 n.1 Efeito da Temperatura Ambiente e da Restrição Alimentar sobre o Desempenho e a Composição da Carcaça de Frangos de Corte Lana et al.

Table 3 -
Scientific articles selected for the systematic review, following the established criteria.

Table 4 -
Main variables that positively influenced broiler chicken performance Variables Thermal comfort Environmental temperature of 24 to 26.3ºC Roof thermal insulation Increased lighting Brooding heating system Non-automatic ventilation system -cold season Positive ventilation system Low ventilation during the winter Male broiler Yellow curtains and continuous lighting Adiabatic evaporative cooling +hollow clay bricks