Egg quality of laying hens in different conditions of storage , ages and housing densities

The objective of this research was to evaluate the quality of eggs from Dekalb White hens under different temperatures (room temperature, 25 oC; and refrigeration, 8 oC), storage times (7, 14 and 21 days), age of birds (35, 40, 45 and 50 weeks) and housing densities (625, 500, 416.6 and 357.14 cm2/birds). Haugh unit (HU) values and albumen height of 1,120 eggs from 528 laying hens, randomly allocated to four groups with different population densities were evaluated. The results showed a significant effect on Haugh units, between the time and storage conditions and between the ages of laying hens and storage condition. Eggs stored in refrigeration showed less weight loss and better Haugh unit indices when compared with eggs stored at room temperature. The increased time of storage, regardless of the temperature, caused loss in their quality. According to the results of this study, based on the evaluation of the albumen height, temperature, storage time, density and age of the layers influence the values of Haugh unit.


Introduction
The chicken egg is one of the finest foods, offering men an almost complete balance of essential nutrients with proteins, vitamins, minerals and fatty acids of great biological value (Brugalli et al., 1998).In addition to being one of the foods of lowest cost, it increases the consumption of food of high nutritional value for the low-income population (Pascoal et al., 2008;Menezes, 2009).
In Brazil, because refrigeration is not mandatory, commercial eggs are packed from the moment they are laid and stay until the final distribution at room temperature, and in some cases, refrigerated only in the homes of consumers.Although the Brazilian law determines minimum internal traits, only the weight and characteristics of the shell have been considered (Brasil, 1997).
The use of Haugh units has been accepted as a measure of the quality of the albumen in various studies on egg quality (Eisen et al., 1962).The Haugh unit value of fresh eggs decreases with increasing age of the hen (Cunningham et al., 1960;Fletcher et al., 1981Fletcher et al., , 1983;;Silversides et al., 1993;Ramos et al., 2008), and the albumen height decreases as birds age, as well (Carvalho et al., 2003;Ramos et al., 2008).According to Campos & Baião (1975), Sauveur (1993) and Santos (2005), temperature and storage time negatively influence the quality of eggs and significantly reduce the Haugh unit, because of the continuous loss of CO 2 .Davis & Stephenson (1991), Morais et al. (1997) Leandro et al. (2005) and Menezes et al. (2009) report that the temperature and relative humidity are the most important factors that affect egg quality during storage.Barbosa et al. (2004), evaluating the effect of temperature (ambient and refrigerated) and storage time (0, 7, 14, 21, 28 and 35) on egg quality, verified that the increase of storage time caused reduction in Haugh unit and egg weight.They also reported that the storage time affects the quality of eggs, exerting a negative influence on the Haugh unit.

Material and Methods
aspects, raised in a single nutrition program in the starter, growth, and production phases.Hens were housed in cages measuring 100 × 50 × 40 cm and randomly allocated in four groups (cages) of different densities: 8 birds at 625 cm²/bird; 10 birds at 500 cm²/bird; 12 birds 416.6 cm²/bird; and 14 birds at 357.14 cm 2 /bird.
All groups received the same treatment according to the requirements of the strain for each week of age.The specifications provided by the producer and by the manual of raising of the DeKalb White hen were followed without alterations.
The aviary is built with precast material in its structure and covered with wood and with shingles of asbestos cement, with the floor cemented and the open sides.The cages were the same used in industries (commercial type), without any enrichment.Nipple-type drinkers and metal trough feeders were placed in front of and outside the cage.The distribution of the feed was changed every day, in an amount according to age and recommendation of the bird supplier.The diet given to birds was produced at the feed mill of the poultry company where the experiment was conducted, under the guidance of the supplier of vitaminmineral premix, as to its formulation.
During the research, the temperature inside the shed ranged between 19 and 32 ºC and the relative humidity ranged between 75 and 90%.
The collection of eggs occurred at intervals of five weeks.Two hundred and eighty eggs were used for each shipment, totaling 1120 eggs.After packaging in cardboard trays with up to 30 eggs each, they were stored at room temperature (average 25 °C) and refrigeration (average 8 ºC).Eggs were collected in the morning, identified and analyzed for the following variables: egg weight, albumen height and Haugh unit.Laboratory tests were performed at the Departamento de Morfologia e Fisiologia Animal of Universidade Federal Rural de Pernambuco, Brazil.
The eggs were individually weighed on an analytical balance, accurate to 0.01 g each time after storage (7, 14 and 21 days).They were then broken and weighed without the shell on a flat glass measuring 20 × 20 cm.Albumen height measurement was performed with a digital caliper.The egg yolk was removed and the weight of the albumen was recorded, obtaining the egg yolk weight difference between the weights.The shell thickness was measured at three points of the equatorial region of the egg, using a digital caliper.The shell weight was recorded after a previous treatment for at least four hours in an oven at 60 °C.
The effect of the interaction of factors type of storage (temperature and refrigeration), storage time (7, 14 and 21 days), age of birds (35, 40, 45 and 50 weeks) and population density (625, 500, 416.6 and 357.14 cm 2 /bird) were studied.The experimental design was completely randomized and the analysis of variance was conducted using program ASSISTAT (Silva, 2009) and the comparison between pairs of means was done by the Tukey test at 5% probability.

Results and Discussion
The higher the value of the Haugh unit (Table 1), the better the quality of eggs, which are classified according to the United States Department of Agriculture (USDA) as AA (100 to 72), A (71 to 60), B (59 to 30) and C (below 29) (USDA, 2000), in which the refrigerated eggs are classified as AA.
The age of the hens (35, 40, 45 and 50 weeks) and storage temperature (8 and 25 °C) had an influence on albumen height, with higher values (P<0.05) in eggs from younger hens of up to 35 weeks of age (5.836 mm), compared with the hens of 40 (5.455 mm), 45 (5.153 mm) and 50 (4.487mm) weeks of age.The results from this study are in line with those reported by Carvalho et al. (2003) and Ramos et al. (2008), who found that the albumen height is negatively affected as the age of the laying hens increases.Silversides & Scott (2001), evaluating different strains of laying hens, showed that the percentage of albumen was lower in older birds in any of the tested strains.
Concerning the eggs in refrigeration for 7 days of storage, there were significant differences (P<0.05) in birds of 50 weeks of age housed in groups with different densities (625, 416.6 and 357.14 cm²/bird) and between Analyzing the temperatures of storage according to the age of the laying hens, it was found that at ambient temperature, the eggs of the birds at 35 weeks of age reached higher values for albumen height (Table 1) and Haugh unit (Tables 2, 3, 4) in relation to the other groups.The eggs in refrigeration showed lower values of this variable in older birds, indicating that regardless of the storage temperature, there is decrease of the albumen height (Table 1) and Haugh  unit (Tables 2, 3, 4) with advancing age of the laying hens.These results reinforce the findings of Cunningham et al. (1960), Fletcher et al. (1983), Silversides et al. (1993) and Ramos et al. (2008), who found results similar to those found in this study.The albumen height and Haugh unit are important for assessing the quality of eggs.Among the densities evaluated in our study (625, 500, 416.6, 357.14 cm²/bird), the density of 625 cm²/bird showed the best mean values for albumen height and Haugh unit, and therefore presented better egg quality.
There was a statistically significant difference (P<0.05) of the Haugh unit of eggs from hens between the ages (35, 40, 45 and 50 weeks) and between the storage temperatures (8 and 25 ºC) (Table 5).Mean values were decreasing with age in both storage conditions: with and without refrigeration.All mean values of Haugh unit of the eggs in refrigeration were higher than those stored at room temperature.The birds at 35 weeks of age had higher quality for the eggs in refrigeration (94.166), and birds at 50 weeks of age had the lowest egg quality, both at room temperature (63.092) and age groups (625, 500, 416.6 cm²/bird) (Table 2).The laying hens housed at a density of 500 cm²/bird) had higher mean value of Haugh unit (93.98).
The Haugh unit of eggs stored at room temperature showed significant difference (P<0.05) in the birds of 45 weeks in the groups with densities of 416.67 and 357.14 cm²/ bird.The highest mean value was recorded in the group of density of 625 cm²/bird at all ages tested.The coefficient of variation showed low values, ranging from 0.27 to 6.07%, which shows that it is a stable variable.
Regarding eggs in refrigeration at 14 days of storage, there were significant differences (P<0.05) in the groups housed at densities of 500, 416.67 and 357.14 cm²/bird (Table 3).The highest values occurred at a density of 625 cm²/bird.In eggs stored at room temperature, the difference was statistically significant (P<0.05) at the density of 416.67 cm²/bird.The highest mean value was observed at the density of 625 cm²/bird (69.47).Therefore, the birds housed at this density showed better results in terms of egg quality.
Concerning the eggs in refrigeration at 21 days of storage, there were significant differences (P<0.05) in groups housed at densities of 416.67 cm²/bird with 45 weeks (Table 4).
In eggs stored at room temperature, the difference was statistically significant (P<0.05) at the density of 500 cm²/ bird.The higher mean values for eggs under refrigeration (89.74 HU) and for eggs stored at room temperature (62.60 HU) was at the density of 625 cm²/bird.in refrigerated environment (85.882).These results can be attributed to physical and chemical reactions that occur, leading to protein degradation.Ramos et al. (2008), analyzing the Haugh unit of the eggs stored at room temperatures and in different types of containers for 21 days, indicated that the room temperature and storage time adversely affect the average of Haugh unit, reducing the average of Haugh units with increasing storage time, corroborating the results found in this study.
In eggs in refrigeration, there was a decrease in internal quality, but this reduction was greater in eggs that were stored at room temperature.Similar results were observed by Frazier (1976) and Pombo (2003), who report that water loss in eggs takes place by evaporation and varies as a function of storage time, temperature, relative humidity and porosity of the shell.These authors also report that all eggs stored under refrigeration (8 °C), were classified as AA, or excellent quality, according to the quality control recommended by the USDA (2000).There were no statistically significant differences (P<0.05) between the densities studied at 14 and 21 days of storage (Table 6).However, there was a significant effect (P<0.05) between storage periods.After 21 days storage, the lowest mean values of Haugh units were found, in contrast to the values found at 7 and 14 days.All mean values of Haugh units decreased with increasing storage time, demonstrating that storage time and population density influence this variable.The coefficient of variation showed low values for storage time (1.03 to 1.64) and density (5.75 to 6.74); this indicates that the variable studied is very stable, with better results for the density of 625 cm²/bird at 7 days of storage.Morais et al. (1997) observed reduction in the mean values of Haugh unit of eggs at 21 days of storage.According to Stephenson et al. (1991) and Cherian et al. (1996), when the eggs are stored for long periods,the egg weight can also decrease due to water loss and centralization of the yolk.Campos & Baião (1975), Sauveur (1993) and Santos (2005) mentioned that the temperature and storage time negatively influenced the quality of table eggs and verified that these parameters exert a significant reduction in Haugh unit, mainly by continuing losses of CO 2 .In this experiment, when evaluating the effect of storage temperature within each age group, it was found that, at any age, there is better preservation of the internal quality of the eggs when they are kept under refrigeration.Barbosa et al. (2004) studied the effect of temperature and storage time on the internal quality of commercial eggs, and observed linear increase in the percentage of egg yolk as a function of storage time.In a place where the room temperature is high and the eggs are not refrigerated, they should be consumed within one week after laying.Studies on the effects of tropical climate showed that the two most important factors affecting egg quality during storage are  temperature and relative humidity (Davis & Stephenson, 1991;Morais et al., 1997;Leandro et al., 2005).The Haugh unit is considered a standard measure of quality (Williams, 1992;Eisen et al., 1962).According Silversides et al. (1993Silversides et al. ( , 1994)), the Haugh unit of eggs obtained from hens at 26 weeks of age was 88.48±0.44,and at 65 weeks, the value was 77.40±0.44.Pope et al. (1960), Cunningham et al. (1960), Fletcher et al. (1981, 1983) and Belyavin (1988) are unanimous on Haugh unit and age of the hen, and stated the Haugh unit decreases with increasing age.Romanoff & Romanoff (1963), Campos et al. (1973) and Fennema (1993) stated that in eggs stored at room temperature or higher temperature, the quality can be preserved provided that the shell is impermeable to carbon dioxide loss.

Conclusions
According to the results obtained and the conditions in which this experiment was carried out, density, temperature and time of storage and age of the birds have an influence on the values of Haugh unit.Thus, it is recommended that eggs be stored in refrigeration in order to maintain the internal quality for a longer period.The recommended density population for Dekalb White hens is 625 cm²/birds.

Table 1 -
Mean albumen height, Haugh unit and shell percentage according to age and storage temperature of the eggs from Dekalb White hens Means followed by same letter in columns do not differ statistically from one another by the Tukey test at 5% probability.CV -coefficient of variation.

Table 3 -
Mean Haugh units of eggs from Dekalb White hens at 14 days of storage according to age, storage temperature and population density (cm²/bird) Means followed by the same lowercase letter in the columns and uppercase letter in the rows do not differ statistically from one another by the Tukey test at 5% probability.CV -coefficient of variation.

Table 2 -
Mean Haugh units (HU) of eggs from Dekalb White hens at 7 days of storage according to age, storage temperature and population density (cm²/bird) Means followed by the same lowercase letter in the columns and uppercase letter in the rows do not differ statistically from one another by the Tukey test at 5% probability.CV -coefficient of variation.

Table 6 -
Mean Haugh units (HU) of eggs from Dekalb White hens according to population density and storage time Means followed by the same lowercase letter in the columns and uppercase letter in the rows do not differ statistically from one another by the Tukey test at 5% probability.CV -coefficient of variation.

Table 5 -
Mean Haugh units of eggs from Dekalb White hens according to bird age and condition of storage Means followed by the same lowercase letter in the columns and uppercase letter in the rows do not differ statistically from one another by the Tukey test at 5% probability.CV -coefficient of variation.

Table 4 -
Mean Haugh units of eggs from Dekalb White hens at 21 days of storage according to age, storage temperature and population density (cm²/bird) Means followed by the same lowercase letter in the columns and uppercase letter in the rows do not differ statistically from one another by the Tukey test at 5% probability.CV -coefficient of variation.