Effect of Different Breeding Densities and Inclusion of Soybean Oil on Performance, Carcass Trait and Heat Loss in Meat Quails

Quails are homeothermic animals, in countries with a tropical climate, such as Brazil, birds face great difficulties in controlling body temperature inside the sheds. Several practices are being studied in order to keep these animals within the thermal comfort zone, and thus, to minimize the effects of thermal stress, partial substitution of carbohydrates by oils and changes in density are some of them. The objective of this study was to evaluate the different breeding densities and inclusion levels of soybean oil in performance, carcass characteristics and heat loss in quail. 450 quails, seven days old, distributed in a completely randomized design in a 3 × 2 factorial scheme, two densities (215.6 cm bird and 188.6 cm bird) and three inclusion levels of soybean oil (0, 2, 4%) were used, totaling six treatments with five replicates each. The heat loss by radiation was estimated with the aid of infrared thermography. The results showed that there was an effect of the density on feed consumption, which was lower for birds raised in the density of 188.6 cm bird (783.78 g of feed), but without its effect on weight gain and food conversion. No effect of inclusion levels of soybean oil was observed on any performance variables. There was no statistical difference (P > 0.05) between treatments for any variables of carcass yield and parts, and heat loss by radiation analyzed. Therefore, it is concluded that soybean oil inclusion levels do not affect the performance and yield of quails, nor do they influence the loss of heat throughout the life cycle of these animals. The birds raised in the density of 188.6 cm bird obtained the lowest average dietary intake, with no impact on weight gain and feed conversion, allowing the creation of a greater number of birds per box.


Introduction
In the last years, coturniculture has presented a very high development, adapted to the new techniques and production technologies, in which a subsistence activity starts to occupy a highly technified activity scenario (Pastore et al., 2012). According to the Instituto Brasileiro de Geografia e Estatística (IBGE, 2014), the effective quail in 2014 had an increase of 11.9% compared to that found in 2013, going from 18.2 to 20.3 million heads.
Some elements such as management, sanity, genetics, nutrition and ambience are pointed out as the support structure of poultry farming as an economic activity and indispensable in the production of affordable foods of high nutritional quality. However, in order to be successful, it is necessary to adopt new management practices, in order to prioritize animal welfare.
The greater heat tolerance is related to physiological particularities and adaptability of farm animals (Habibu et al., 2016), the higher heat tolerance, the greater the possibility of achieving the most productive index, since the maintenance of body temperature outside the thermal comfort zone requires energy expenditure, due to the physiological and behavioral effects performed to ensure the survival of the animals (Marques et al., 2018;Machado et al., 2019). Several strategies can be used to minimize the thermal discomfort of these animals, one of them is the use of foods in the diet that offer energy with low caloric increment, that is, diets in which the amount of oil of the rations is modified (Menten & Pedroso, 2001;Machado et al., 2018).
Several lipid sources are used in poultry feed, especially vegetable oils, which are sources rich in essential fatty acids. The partial substitution of carbohydrates by oil is based on the reduction of the caloric increment of the feed through the use of lipids as energy source. Thus, diets with higher lipid content may cause lower heat production by birds. Among the oils most used for this purpose is the soybean oil that is rich in phospholipids which are a special group of essential lipids in the use of fats by the animal organism.
According to Leandro et al. (2005), there is great pressure to reduce production costs, and to meet this requirement one of the alternatives being used is the increase in bird population density, this strategy may be a good option to increase the productive yield of the stock. The adequacy of the stocking density of the animals guarantees the use of space in the sheds, contributes to the maximum performance of the birds and favors issues related to animal welfare. In this context, the objective of this study was to evaluate the effect of different soybean oil inclusion levels on the diet and different breeding densities on performance, carcass characteristics and heat loss in quail.

Location and Experimental Animals
The experiment was carried out in the poultry sector of the Agricultural Science Center of the Federal University of Ceará (UFC), Campus do Pici, located in the city of Fortaleza-CE, latitude (3º44′ S), longitude (38º34′ W) and altitude (19.6 m), with climatic classification, according to Köppen (1936) of Aw', defined as tropical rainy. The study was carried out between November 19/2016 to December 30/2016, with a duration of 42 days. A total of 450 quails, seven days old, were housed in a conventional shed for quail rearing divided into 30 boxes of 0.6 × 0.6 × 0.6 m (length × width × height), covered by nylon, with floor covered by bed, each box equipped with a tubular type feeder and a drinker type glass pressure.

Experimental Design and Treatments
The birds were distributed in a Completely Randomized Design (CRD) in a 3 × 2 factorial scheme, counting six treatments with five replicates each. The factors were three inclusion levels of soybean oil: 0, 2, 4% and two breeding densities: 14 birds/box (215.6 cm 2 bird -1 ) and 16 birds (188.6 cm 2 bird -1 ). The experimental rations (Table 1) were formulated according to the composition of the ingredients presented by Rostagno et al. (2011) and considering nutritional requirements for quails as recommended by Silva and Costa (2009), so that the rations were isoenergetic and isoproteic. In this way, the treatments were divided as follows: T1 = Reference Ration + density 14 quails; T2 = Reference feed + density 16 quails; T3 = Inclusion of 2% soybean oil + density 14 quails; T4 = Inclusion of 2% soybean oil + density 16 quails; T5 = Inclusion of 4% soybean oil + density 14 quails; T6 = Inclusion of 4% soybean oil + density 16 quails.

Procedures and Variables Analyzed
In order to evaluate the performance, the following variables were measured: -Feed consumption (g/bird): the feed provided at the beginning of the breeding phases and the leftovers at the end of the stages were weighed and, by difference, the feed intake was calculated for each repetition; Weight gain (g/bird): the birds of each replicate were weighed on the 7th day and 42nd day so that the average weight gain of each plot was calculated by the difference of the final weight minus the initial weight; Food conversion: it was calculated by dividing the feed intake by the weight gain of the birds. Throughout the experimental period ration and water were provided at will, mortality was recorded for correction of feed intake and, consequently, feed conversion (Sakomura & Rostagno, 2007).
To evaluate the carcass characteristics, at 42 days of age two birds from each experimental unit, one male and one female, were selected based on the average weight of the plot and submitted to a 6-hour fasting. After this period the birds were weighed, desensitized, bled, scalded, plucked, eviscerated and removed from the head, neck and feet to determine the carcass yield in relation to the body weight of the fasting bird. Subsequently, the carcasses were cut and the parts weighed to determine the yield of breast, thigh + overcoat and percentage of abdominal fat, which were calculated in relation to the weight of the warm carcass, and liver that was calculated in relation to the weight of the fasting bird.
In order to obtain air temperature (Ta) and relative air humidity (UF), Meteorological Minidimensions and Data logger (onset® Mark, model U23-001 HOBO® Pro v2) were positioned, positioned at the height of the quails, inside the boxes in that they were during the whole experimental phase. For this purpose, this equipment was previously programmed to record the values of air temperature (Ta, °C) and relative air humidity (RH, %) at 10 minute intervals, from the 1st to the 42nd day of life of the quails. Three Data loggers were installed throughout the shed, one at the beginning, the middle and the other at the end of the shed.
To obtain the body surface temperature (Ts, ° C) of the quails an infrared thermographic camera was used (Flir Systems brand, model Flir i3, resolution 60 × 60 pixels, precision +/-2% or 2 ºC). Three individual thermograms were performed per plot at 42 days of life of the quails, one meter away from the animals, according to the manufacturer's recommendation. An emissivity of 0.98 was considered, which is indicated by the manufacturer for biological tissues. Later, these thermographic images were analyzed by the software Flir QuickReport© 1.2, to obtain the average surface temperature of the entire body surface of the birds. For the calculation of the individual mean surface temperature (Ts) of the animals, 30 random points were marked along the whole body surface of the birds in thermographic images. The loss of sensible heat was considered as the loss of heat by radiation. The surface area calculation was performed using Equation 1 (Curtis, 1983;Silva, 2000). Thus, the surface in 0.151 m 2 . From this data the estimation of heat loss by radiation (Qs = Qr) was carried out to measure the amount of heat loss from birds to the environment. Qr was calculated using Equation 2 (Meijerhof & Van Beek, 1993;Yahav et al., 2004).

Statistic
For statistical analysis of performance and carcass yield, parts and heat loss, the data were submitted to analysis of variance and the means compared by the SNK test at 5% significance, using the program "Statistical Analyzes System" (SAS, 2000)

Performance
During the experiment the minimum and maximum averages recorded inside the shed were 30.3 °C and 33 °C for air temperature and 58.2% and 72.3% for relative humidity, respectively. The performance data for cutting quails, from 7 to 42 days of age, submitted to diets with different levels of soybean oil and breeding densities are described in Table 2.
In the analysis of variance, it was verified that there was no significant interaction among the factors, soybean oil levels and breeding densities, on feed intake (CR), weight gain (GP) and feed conversion evaluation period. It was also possible to observe that diets did not significantly influence these variables during the study. However, there was a difference between rearing densities over feed consumption, but the same was not observed for the other variables (GP and CA).
Considering that the inclusion of the energy level has been studied as the main factor that influences the voluntary consumption of feed by the birds (Freitas et al., 2011), it can be inferred that the lack of significant effect of the inclusion of soybean meal on feed consumption may be associated with a good evaluation of the metabolizable energy value of the food, considering that the rations were calculated to be isoenergetic considering the values of metabolizable energy of soybean oil determined for the quails during the period studied. Note. 1 CV = coefficient of variation. Means followed by the same lowercase letters in the columns do not differ statistically from one another by the SNK test (P < 0.05).
For the feed intake variable, it was possible to observe that there was a significant difference at 5% of significance for the different breeding densities used in this experiment. The data show that a lower consumption (783.78 g/bird) occurred in the highest density of animals (188.6 cm 2 bird -1 ). According to Goldflus et al. (1997), the gradual increase in the rates of densification during the rearing period reduces the feed intake of the animals. Lima et al. (2012) report that high housing densities can cause competition among birds for food, which can affect consumption and decrease feed intake by animals.
As for the variable weight gain, the results obtained in this research for quails, resemble those found by Vieira et al. (2002), who did not observe a significant difference (P > 0.05) in the weight gain of broiler chickens reared from 8 to 42 days old, consuming rations containing soybean oil of 2 and 4% concentrations. Lana et al. (2001) studied the effect of density and feeding programs on the performance of broiler chickens, in which it was possible to verify worsening of feed conversion of these birds with increasing density, this fact differs from the results found in this study, since there was no significant difference for this variable.
The results for the effect of density on weight gain obtained in this research do not agree with those described by Moreira et al. (P < 0.05). The results of this study show that the effect of the population density on performance, carcass yield and meat quality in broiler chickens of different commercial strains, observed that the densities influenced weight gain (P < 0.05); in which the birds raised in the density of 10 birds/m 2 presented better gain than those created in the densities of 13 and 16 birds/m 2 .

Carcass Characteristics
Data on the percentage of carcass traits, noble cuts, abdominal fat and liver for meat quails, slaughtered at 42 days of age, submitted to diets with different levels of soybean oil and rearing densities are described in Table 3. For the carcass characteristics, it was observed that there was no significant interaction between the factors, levels of soybean oil and breeding densities, on any of the evaluated variables. It was also observed that the treatments did not significantly influence the carcass characteristics evaluated. Note. 1 CV = coefficient of variation. Means followed by the same lowercase letters in the columns do not differ statistically from one another by the SNK test (P < 0.05).
According to Freitas et al. (2006), when the nutritional value of the food is well evaluated, the probability that the carcass characteristics are influenced by the inclusion of that food in the isonutrientes diets becomes very unlikely. However, if the metabolizable energy value of the food is disregarded, its inclusion in the diet may cause alterations in the energy: protein ratio of the feed, and thus, cause changes in carcass yield and even carcass cuts. Therefore, it can be deduced that increased soybean oil levels in the diet were not sufficient to alter the energy: protein correlation of the diet to the point of causing significant variation on carcass characteristics and parts of quail observed in this study. According to the literature the carcass yield of quails can range from 57 to 74% (Móri et al., 2005;Oliveira et al., 2005;Santos et al., 2006;Silva et al., 2007;Corrêa et al., 2008), the values found in this study were similar to the maximum value described above by the authors.
The results obtained by Lara et al. (2006) according to these authors, the lipid sources of plant origin do not influence the carcass yield, viscera and cuts (chest and thigh) or the percentage of abdominal fat. According to Oliveira Neto et al. (2000), who evaluated the effect of ambient temperature on performance and carcass jas.ccsenet.org Vol. 11, No. 7;2019 characteristics of broilers fed a controlled diet and two levels of metabolizable energy, observed a decrease in carcass, breast and liver yield of broiler chickens as the feed oil level increased. These results differed from those found in the present study.

Journal of Agricultural Science
As for the percentage of abdominal fat, the results obtained for quails in this research differed from those found by Meza et al. (2015). According to these authors, the levels of metabolizable energy and digestible lysine on the composition and carcass yield of broilers, it was observed that the values of abdominal fat increase proportional to the increase of energy level in the diet. This difference in results can be explained by Café (2001), where it is stated that manual removal of abdominal fat from the carcass causes significant variation in the values, causing high coefficients of variation and decreasing the sensitivity of the statistical test to detect significant differences.
The data obtained in this research are similar to those reported for broiler chickens by Moreira et al. (2004), where the effect of the population density, 10 to 16 birds/m 2 , on yield of different commercial strains, did not observe a significant difference (P > 0.05) for any variable with the elevation of breeding density. As well as the results found by Goldflus et al. (1997), in which studying the effects of population density and diet energy on the performance of broiler chickens also noticed that when varying the densities of 10 to 22 birds/m 2 , no differences were observed for carcass yield. Table 4 shows the values of Qr, loss of heat sensitive by radiation, between treatments and during the 2nd, 3rd, 4th, 5th and 6th week of life of the quails. As shown in Table 4, it can be observed that there was no significant difference for the Qr variable in any evaluated week. It is suggested, then, that the oil inclusion levels and the different densities did not influence to increase or decrease the radiation heat loss in the birds.

Heat Loss
According to Lehninger (2002), in general, oils and fats with the highest number of unsaturated bonds in their structure, such as soybean oil, tend to present higher metabolic heat production from their break, this fact was not observed in this study, since there was no difference in relation to the different concentrations of soybean oil in the diet. A fact to be mentioned regarding the explanation of not obtaining significant difference for heat loss from the addition of the different levels of soybean oil, can be attributed to the presence of feathers in the birds, they play an important role in the thermal balance between the organism and the environment, implying peculiarities in the regulation of thermal equilibrium.
According to Malheiros et al. (2000), the feathers directly interfere in the loss of heat by radiation, conduction and radiation as a mechanism of elimination of heat and considering tropical climate locations the temperature differential between the environment and the body surface of the animals is small. According to Nascimento (2010) when the air temperature is at levels close to 21 °C, the bird can lose up to 75% of heat through sensible heat: radiation, conduction and convection.
However, when the ambient temperature approaches the surface temperature of the birds, its main means of heat loss becomes the release of latent heat through panting. Souza Júnior et al. (2013) mentioned that birds' feathers have good insulating properties, blocking most of the infrared emission from the skin and the use of thermography is a good tool to perform the thermal mapping. These same authors have mapped the temperature of Japanese quails using infrared thermography and concluded that these birds present differences in the surface temperature according to the body region, and the areas without feathers are considered important sites of thermolysis, area favorable to heat loss, under heat stress conditions. Note. Means followed by equal letters, uppercase in the column and lowercase in the row, do not differ from each other by the SNK test (P < 0.05).

Conclusion
Up to 4% levels of soybean oil can be included in the feed and use rearing densities of 215.6 cm 2 bird -1 and 188.6 cm 2 bird -1 without affecting the performance, carcass characteristics and heat loss by radiation of meat quails from 7 to 42 days of age.