Scientific hypothesis: balanced results selected indicators of table eggs in small-scale breedings, due to the small numbers of animals in breeding and outdoor free-range for carrying out natural activities.

Our object of study was eggs, shell, damage, and contamination of table eggs. Four small-scale breedings were randomly selected in Slovakia. These breeds were alternatively with an outdoor free-range.

Laying hens Dominant was bred in conditions of 4 small-scale breeders in Slovakia. Breeding conditions as well as nutritional conditions were ensured in these small-scale breedings of small-scale breeds in accordance with laying hens needs. Laying hens Dominant was reared in small-scale breedings No. 1, No. 2, and No. 3 in the 1^st laying cycle, and No. 4 in the 2^nd laying cycle. Henhouse with deep litter and free-range was a breeding house for laying hens. Laying hens had the opportunity to run daily in the summer from 6:00 am to about 7:00 pm. pm and in winter until 5:00 pm. The hen house equipment consisted of a watering-place, a feeder, a nest, and perch. To lay eggs, a nest was made for them to be made by hand collection. Drinking water and feed were part of the free-range. Laying hens were fed with a conventional feed mixture intended for laying hens, which was replenished at least 2 times a day. Sometimes laying hens were fed with food from the kitchen or crushed eggshells. Drinkers and feeders were washed daily. The eggs produced were harvested once a day in the summer in the afternoon and twice a day in the winter in the morning and afternoon.

Egg samples of 80 pieces were obtained from four selected small-scale breeders, i.e. 20 eggs from each small-scale breeder. Investigation of egg samples was carried out in a laboratory at the Department of Food Hygiene and Safety.

Physical indicators of table eggs from small-scale breeders No. 1, No. 2, No. 3 and No. 4:

Contamination and egg damage under the light of a 100W table lamp from small-scale breedings 1, No. 2, No. 3, and No. 4: blood spots, droppings, pigment dots, other deposits, calcium deposits, bumps on the surface, and deformed egg shape.

The results in the study are presented as mean – arithmetic mean (x), variance range (R), which determines the difference between the minimum value (Min) and the maximum value (Max), the standard deviation (SD), and the coefficient of variation (cv, %).

Hypotheses about equality of mean values were tested using a one-factor analysis of variance (F) at significance levels α = 0.05, α = 0.01 and α = 0.001. One-factor variance analysis (ANOVA) is the simplest form of ANOVA that examines the relationship between interval and nominal variables. It tests the null hypothesis of the mean equivalence, assuming that the selections have the same variance. The null hypothesis indicates that there is no relation between the interval and the nominal variable. If the calculated statistical value F is greater than the corresponding character value that divides the statistical set of a group with the same number of Fisher-Snedecor distribution elements FI-1, n-I, the hypothesis of equality of mean values is rejected.

Scheffe's test was used at a significance level of α = 0.05 to compare the difference in the indicator between small-scale breedings. The Pearson correlation coefficient (r) reflects the relation between the two egg variable variables. The Pearson correlation coefficient (r) reflects the degree of the linear relation between the data of the two egg indicators. Its value is between -1 and +1. A +1 indicates that there is a high positive linear relationship between the two indicator data. A value of -1 means that there is a high negative linear relation, and value of 0 means that there is no linear relation between the two indicator data. The interpretation of the size of the correlation coefficient is given by Cohen (1988).

Values of correlation coefficient (r) and strength of dependence between two variables: below 0.1 trivial (simple, light), 0.1 – 0.3 weak, 0.3 – 0.5 medium, above 0.5 strong. It is often reported in the publications that the correlation coefficient values of 0.7 – 0.9 represent a very strong relation and 0.9 – 1 as an almost perfect relation between two variables. The correlation coefficient results are statistically significant at α = 0.05, α = 0.01 and α = 0.001. The SAS statistical package, version 8.2, was used to statistically evaluate the results.

Average egg weight in individual small-scale breedings is given in Figure 3. Statistically evaluation of egg weight in individual small-scale breedings is given in Table 1.

The average egg weight was found to be either the same or relatively balanced in small-scale breedings No. 1, No. 2 and No. 3. The measured values of egg weight were largely balanced in small-scale breeding No. 4. The values of the egg weight in this small-scale breeding were statistically significant (p <0.05) higher compared to the values of the egg weight of small- scale breedings No. 1, No. 2, and No. 3. Conclusions of the research and the knowledge published in scientific journals are not uniform as regards the impact of factors on eggshell quality.

Huber-Eicher and Sebö (2001) took the view that they showed a higher weight of eggs and their egg components, which were in a negative correlation with the stocking intensity (r = -0.27, p <0.01). The authors pointed out that if laying hens produced more eggs under industrial conditions, the lower the egg weight was recorded. At the end of their investigation, the authors concluded that laying hens that were kept under organic farming conditions, they laid eggs which were generally heavier due to the lower production intensity.

Average eggshell weight in individual small-scale breedings is given in Figure 4. Statistically, evaluation of eggshell weight in individual small-scale breedings is given in Table 2.

Egg colour is also an important factor in egg production, in our case brown. Colour shell of eggs can affect consumer choice due to regional or national cultural preferences for different colours, directly affecting eggs' production (Wei and Bitgood, 1990; Joseph et al., 1999).

Thus, the determination of egg colour and eggshell strength is of importance. The average weight of eggshell was found to be either the same or relatively balanced in small-scale breedings No. 1, No. 2 and No. 3. The measured values of eggshell weight were largely balanced in small-scale breeding No. 4. The values of the eggshell weight in this small-scale breeding were statistically significant (p <0.05) higher, compared to the values of the eggshell weight of small-scale breedings No. 1, No. 2 and No. 3. Conclusions of the research and the knowledge published in scientific journals is not uniform as regards the impact of factors on egg shell quality.

Authors Monira et al. (2003); Alsobayel et al. (2003) and Anderson et al. (2004) agreed in a statement that the quality of the eggshell is sufficiently affected by the genotype and age of laying hens. In characterizing the effect of genotype on egg shell quality, the authors emphasize the significance of genotypic differences in egg weight and shell quality.

Such contradictory aspects may also be related to ensuring that laying hens are kept in line with their needs. Therefore, in our research, we focused on characterizing the laying hens and compared them with four small-scale breeders in Slovakia with a focus on selected indicators of the table eggs. Avian eggshells are commonly used in studies focusing on bioindication and environmental monitoring (Lam et al., 2005; Ayas et al., 2008; Kim and Oh, 2014; Khademi et al., 2015; Simonetti et al., 2015).

The average thickness in the equatorial plane of egg in individual small-scale breedings is given in Figure 5.

Statistically evaluation of shell thickness in equatorial plane of egg is given in Table 3.

The average thickness in equatorial plane of egg was found to be either the same or relatively balanced in small-scale breedings No. 1, No. 2 and No. 3. The measured values in the three parts of the equatorial plane of egg were largely balanced in small-scale breeding No. 4. The values of the equatorial plane of the egg in this small-scale breeding were statistically significant (p <0.05) higher compared to the values of the equatorial planes of egg of small- scale breedings No. 1, No. 2 and No. 3

Correlation relation between indicators of the eggs in small scale breedings and statistically significant difference between the two variables are given in Table 4. Middle, a positive linear relation (small-scale breeding No. 1 and at the lower limit a strong positive linear relation (small-scale breeding No. 4) was found between egg weight and eggshell weight, statistically significant (p <0.05). A very strong relationship in all small-scale breedings (p <0.01, p <0.001) was found between eggshell weight and shell thickness in the equatorial plane of the egg.

Shell thickness in individual parts of the equatorial plane of the egg in small-scale breedings

Average shell thickness in individual parts of the equatorial plane of the egg in small-scale breedings is given in Figure 6. A statistically significant difference between the two variables is given in Table 5. The average thickness in equatorial planes 1, 2, and 3 of the egg was found to be either the same or relatively balanced in small-scale breedings 1, No. 2, and No. 3. The measured values in the three parts of the equatorial plane of egg were largely balanced in small-scale breeding No. 4. The values of the equatorial planes of the egg in this small-scale breeding were statistically significant (p <0.05) higher compared to the values of the equatorial planes of the egg of small- scale breedings No. 1, No. 2, and No. 3.

The eggshell is a natural protection for the egg, and thus it is significant to get a high value of eggshell strength (Bain, 1990).

The eggshell strength, reflecting the resistance ability to damage, can protect eggs when they are in collecting, packaging, storage, and transportation. It can be found the higher the eggshell strength, the stronger the resistance to damage. Cracked eggs can finally cause economic loss in two ways, one is that they cannot be sold at a high price, another is cracked eggs may raise the risk of bacterial contamination to intact eggs, which can even produce food quality and safety problems (Bain, 2005; Mertens et al., 2006; Li, Dhakal and Peng, 2012).

Correlation relation between shell thickness in individual parts of the equatorial plane of the egg according to small-scale breedings and statistically significant difference between the two variables are given in Table 6.

In shell thickness between individual parts of the equatorial plane of the egg in small-scale breedings, No. 1, No. 2, No. 3, and No. 4, an almost perfect positive linear relation was found, statistically very highly significant (p <0.001).

Correlation relation between shell thickness in individual parts of the equatorial plane of the egg together for all small-scale breedings and statistically significant difference between the two variables is given in Table 7.

Almost perfect positive linear relation, statistically very high significant (p <0.001), was found in the shell thickness between the individual parts of the equatorial plane of the egg in all examined small-scale breedings together.

The percentage and number of eggs with damaged egg surface but also deformed and contaminated on the eggshell are given in Table 8.

Table eggs obtained from a small-scale breeder were subjected to an assessment of the hygiene aspect of the breeding environment. Table eggs can be considered as naturally packaged food. The eggshell serves to contain the egg contents. It is also the first barrier against bacterial penetration and must be free from defects in the order to optimize the safety of human consumption (Mabe et al., 2003).

We found that table eggs were contaminated with blood (from 5 to 45%) and dropping (from 20 to 60%). We found sediments, pigment dots and calcium deposits on the surface of table eggs. Also table eggs from two farms had a deformed shape.

Solomon (2010) reported that the coated eggshell, it is common surface defect observed on the eggshell. There are observed additional calcium deposits or extra-cuticular coverings and possibly reflects the timing and magnitude of the stress or disturbance experienced by the flock. It is commonly observed an incidence of this defect of 1% and could be caused by the age of the laying hens, often younger flocks coming into production (Coutts and Graham, 2007).

These damaged table eggs, but also deformed and contaminated on the surface, are related both to internal factors and to external factors, which the farmer can influence and take measures to improve laying hens living conditions. Hincke et al. (2000) reported that there are multiple factors affecting eggshell quality like the genetics of the hen, nutrition, and management of feed intake, disease, and environment challenge, and also equipment insult.

A decline in eggshell quality is detected as hens approach the end of a laying period (Mazzuco and Hester, 2005). In this way, the condition of the eggshell at the oviposition time can influence the incidence of shell breakage. An interesting insight presents Alves et al. (2007). When the laying hens are raised in conditions of greater thermal comfort, it can promote eggshell quality and decrease egg losses through cracks.

Hulzebosch (2004) states in his study that eggshell plays a very important role. It must form a good barrier against the intrusion of microorganisms into the internal egg content. Many research results confirm increased microbial contamination in alternative breeding compared to laying hens.

In alternative breeding, laying hens lay eggs more extensively outside the nest, into the litter. Such eggs show excessive contamination of their surface. Such eggs have a damaged shell, which can lead to the deterioration of the internal content of the egg and its contamination. There are two ways in which the contents of a table egg can be infected. It can be infected by an endogenous route and an exogenous route. Engelmaierová, Tůmová and Charvátová (2010) state that endogenous contamination occurs through sick laying hens, which affect the egg through the bloodstream. Exogenous contamination of table eggs is caused by microorganisms that are in the outdoor environment.

Görner and Valík (2004) in the study point out that there is a large number of spores on the surface of the eggshell that are highly permeable to air. The cuticle is an outer layer whose main function is to prevent microorganisms from entering the egg. When the eggs are brought into contact with the air, the cuticle is drawn into the spores, changing its shape, which results in deformation, causing penetration of the microorganisms through the shell into the internal contents of the egg. An important protective barrier is also represented by the membrane membranes. Their fibrous structure acts as a filter.

Their protective properties are associated with the chemical action of lysozyme and ovotransferrin. Microorganisms, by means of proteolytic enzymes, disrupt the membranes and penetrate the whites. The main role of egg white is to protect the egg yolk from contamination. Gram-positive bacteria are affected by egg white due to their antimicrobial and bactericidal effects. Egg yolk that has no antimicrobial properties is the perfect breeding ground for the reproduction of microorganisms. If a high incidence of contamination has been observed on the surface of the eggshell, there is a higher risk of contaminants penetrating the egg content. Křepelka (2012) points out that contaminated eggs are a major problem in terms of consumer protection, which must be constantly eliminated. In most cases, gram-negative bacteria, e.g. Pseudomonas spp., Alcaligenes spp. Salmonella enteritidis and Escherichia coli and gram-positive bacteria such as e.g. Bacillus spp. and Staphylococcus.