THE EFFECT OF NATURAL ZEOLITE DIETARY SUPPLEMENTATION ON THE EGG QUALITY OF JAPANESE QUAILS (Coturnix japonica) DURING THE LAYING PERIOD

also by age of quails (P≤0.001). At the beginning of the laying, the weight of the eggs (age 1) was significantly lower (12.07±0.12 g at the beginning, 12.38±0.12 g in the middle and 13.38±0.12 g in the end) (P≤0.001). The albumen weight and Haugh unit were significantly influenced by the age of the females. The albumen weight increased with female age (from 6.88 to 8.10±0.09 g). The HU was significantly lower (89.52±0.30) at the age 1 than in age 2 (90.50±0.30) and age 3 (90.57±0.30) (P≤0.05). The yolk index was significantly affected by both diet and age of animals. The significant difference was between C and Z1 (P≤0.05). The highest yolk index was found in youngest female (P≤0.01). The egg quality was mainly affected by age of females. Diet affected investigated traits to a smaller extent.

The important part of egg production as well as their quality is egg number.The egg quality is conditional upon a number of factors such as poultry species, genotype, nutrition, oviposition time, environment and age of laying hens.Johnston and Gous (2007) and Zita et al. (2009,2012) showed that the egg weight increased with hen's age.The egg weight was also affected by the age of the quails.Nazligul et al. (2001) and Orhan et al. (2001) found that egg weight increased with the age of the quail.Quality of poultry products, especially eggs, is a very important issue for both the producers and consumers.Egg quality has been defined as the characteristics of an egg that affect its acceptability by the consumers.Egg quality is the more important price contributing factor in table and hatching eggs.Therefore, the economic success of a laying flock solely depends on the total number of quality eggs produced (Monira et al., 2003).Egg quality is composed of those characteristics of an egg that affects its acceptability to consumers, it is therefore important that attention is paid to the problems of preservation and marketing of eggs to maintain the quality (Hrnčár et al., 2014).Gonzales (1995) were analysed the external and internal egg quality of Japanese quails during 6 months of lay.Egg weight, egg length, yolk height and yolk index increased as quail aged.Specific gravity, eggshell plus membrane thickness, egg shape index, albumen height and internal quality unit (IQU) decreased at the end of the experiment.Highest values of eggshell thickness (0.201 mm) and internal quality unit (69.68) obtained at 17 and 8 weeks of age, respectively, indicated that a better quality of egg was attained at the beginning of lay.The aim of the study was to investigate the effect of supplementing natural zeolite on the laying characteristics and on the internal and external egg quality during laying period of Japanese quails.

Animals and diet
The experiment was carried out on the Department of Small Farm Animals of the National Agricultural and Food Centre -Research Institute for Animal Production in Nitra.Japanese quails of meat line were included in the experiment.Japanese quails were kept in cage with three females per cage.A cycle of 14 h of light and 10 h of dark was used throughout the experiment.They were fed with commercial diets (TEKRO Nitra, Ltd.Slovak Republic).The quails were divided into three groups as follows: the control group received commercial diets without additives (C), the experimental group Z1 were fed a commercial diet enriched with supplement of 1 % natural zeolite and experimental group Z2 were fed a commercial diet enriched with supplement of 2 % natural zeolite.The animals had the feed and water at libitum.The natural zeolite (ZeoFeed) was supplied by Zeocem Company (Zeocem a.s., Bystré, Slovakia) from the quarry of Nižný Hrabovec, Slovakia.Zeolite used in the experiment had a particle size of 0.2 -0.5 mm and contained more than 80 % of clinoptilolite, as determined by X-ray powder diffraction.Its chemical composition was as follows: SiO2 -70.98%,Al2O3 -11.72%,Fe2O3 -1.26%, CaO -2.89%, MgO -0.53%, K2O -3.25%, Na2O -0.56% and loss on ignition -7.17%.Table 1 shows the list of the ingredients and nutrient content of the basal diets formulated to provide the nutrient requirements of quails according to the recommended reference levels.The feed mixture was produced without any antibiotics and coccidiostats.

Egg quality
The laying was recorded daily from 8 weeks of age until the end of 50 weeks of age (from June (VI) to March (III)).We monitored the effect of the natural zeolite addition on the laying parameters of Japanese quail during the experiment.At the age of 14 (age 1), 23 (age 2) and 45 (age 3) weeks of females, we performed an analysis of eggs.Total 279 eggs were analysed; 31 eggs from each group were analyzed in three different laying periods.Egg weight was individually determined with 0.001g accuracy using a laboratory scale Kern 572-32.Egg length (along the longitudinal axis) and egg width (along the equatorial axis) were measured with a micrometer.Egg shape index was calculated as the ratio of egg width to egg length (%) by method of Anderson et al. (2004).After the eggs were broken, eggshells were washed with water and dried in order to clean the remaining albumen.Shell thickness (with membrane) was measured at the sharp poles, blunt poles and equatorial parts of each egg.The albumen weight was calculated as the difference between the egg weight, and the yolk and eggshell weight.Individual Haugh unit score (Haugh, 1937) was calculated using the egg weight and albumen height as follows (Monira et al., 2003).Yolk weight with 0.001 g accuracy was determined using a laboratory scale Kern 572-32 and its percentage proportion was calculated.Yolk colour was determined with La Roche scale (Hoffman-La Roche, Switzerland).Egg length (along the longitudinal axis) and egg width (along the equatorial axis) were measured with a micrometer.Egg shape index was calculated as the ratio of egg width to egg length (%) by method of Anderson et al. (2004).

Statistical analysis
Statistical analysis was done using the SAS 9.2 statistical software (2009).The GLM model was applied to study the influence of effects causing variation of individual egg quality parameter and age in Japanese quail.The following model was applied: Differences among means were obtained using Tukey´s test for the same number of observations in each class of individual effects.

RESULTS AND DISCUSSION
The result of laying performance (average laying eggs per hen and laying intensity) of control group (C) and group with addition of different concentration of natural zeolite (Z1, Z2) in Japanese quails diet are given in table 2. As we can see from the table, the laying and average eggs per female was lower in control and Z1 experimental groups compared with the Z2 experimental group.These parameters were relatively balanced throughout the whole experiment.In  The egg weight is among the most important parameters not only for consumers, but for egg producers as well (Genchev, 2012).In our experiment, average egg weight was significantly affected by diet (P≤0.05) and also by age of quails (P≤0.001).The Japanese quails of experimental group Z2 (adding of 2% natural zeolite) had significantly lower egg weight than experimental group Z1(P≤0.05).At the beginning of the laying, the weight of the eggs (age 1) was significantly lower (12.07±0.12g at the beginning, 12.38±0.12g in the middle and 13.38±0.12g in the end of lay) (P≤0.001).Similar results found Hanusová et al. (2021) by hens at 7, 8 and 13 months of age.The average egg weight was significantly increased with the age of the laying hens (P <0.001, P = 0.0076).(2014) found in laying hens that the young hens had significantly lower eggshell weight (6.76±0.19g) than the old one (7.74±0.19g).They followed apart age also effect of strain, temperature and oviposition on the eggshell weight.They confirmed that only age had significant effect on these traits.The most important quality traits of the eggshell are its thickness.We did not find the significant differences in eggshell thickness between groups.This is in agreement with works of The important internal egg quality traits are mainly the albumen weight, Haugh unit and yolk weight.The internal quality of albumen is assessed according to the content and consistency of the solid albumen bag by the albumen.The albumen index is an indicator of egg freshness (Halaj and Golian, 2011).Haugh unit expresses a more complex quality of albumen in relation to its weight (Halaj and Golian, 2011).As we can see from our experiment the addition of natural zeolite did not affect the albumen quality.The albumen weight and Haugh unit was significantly influenced by the age of the females.The albumen weight increased with female age (from 6.88±0.09g to 8.10±0.09g).The Haugh unit was significantly lower (89.52±0.30)at the age 1 than in age 2 (90.50±0.30)and age 3 (90.57±0.30)(P≤0.05).The weight of the egg yolk was not affected by diet or age.The yolk index was significantly affected by both diet and age of animals.We found significant differences between the control group and the experimental group Z1 (P≤0.05).At the beginning of the laying, the yolk index was significantly higher than in older age (P≤0.01).The addition of natural zeolite did not significantly affect the yolk colour.However, in our experiment, the age of the females had a significant effect on the yolk colour.With increasing age, the yolk colour was significantly darker (from 5.67±0.11 to 7.92±0.11,P≤0.001).In our experiment the colour of yolk was darker as compared with Zita et al. (2012) (4.87±0.07).
In conclusion, we can state that the addition of natural zeolite to the feed ration at a concentration of 1% or 2% does not negatively affect the internal and external egg quality.Öztürk et al. (1998) also did not observed significant effect of adding natural zeolite in to diets of hens on their egg quality parameters.

CONCLUSION
Feeding natural substances to Japanese quails did not negatively influence laying parameters.The addition of 2% of natural zeolite had positive effect on laying performance of Japanese quails.The submitting of natural zeolite to the feed ration at a concentration of 1% or 2% did not negatively influence the internal and external egg quality of Japanese quails.The internal and external egg quality was more affected by age of laying female than by supplementing natural zeolite.
agreement with works of Baumgartner and Hetényi (2001) and Hanusová et al. (2013), the laying of Japanese quails was the most intensive until 20 weeks of age.The laying gradually decreased in C and Z1 decreases with increasing age.
Naharjan et al. (1991), Gonzales (1995), Altan et al. (1998), Zita et al. (2012, 2013) found that the egg weight increased with the age of Japanese quails.Peric et al. (2017) found significant effect of hen age (P<0.01) on egg weight, shell strength, albumen height and Haugh unit (HU).Zita et al. (2012) show that egg weight was affected by the age of the hens and quails (overall means 61.13 and 12.52 g, respectively).Despite frequents fluctuations, as the age of the laying hens and quails increased, the yolk index and yolk proportion increased as well, while the albumen index, eggshell strength and shell thickness decreased.The important indicator of the external quality of eggs is the eggshell.A lot of authors have reported that eggshell weight increases and eggshell thickness decreased with quails' age (Gonzales, 1995; Altan et al., 1998; Nazligu et al., 2001; Orhan et al., 2001; Zita et al., 2013).Similar results found Kermanshahi et al. (2011) in hens.The eggshell weight was significantly increasing with age, the lowest was at the beginning of the laying (1.08±0.01g) and the highest at the end of the laying (1.17±0.01g).Tůmová et al.

Table 1
Composition of basal diet and nutrient content of feed mixture per kg of diet(KKZ HYD 11)

Table 2
Laying characteristics of Japanese quailLeast squares means and standards errors for external and internal egg quality are given in table3.The table shows that the eggs quality is more influenced by age than by the supplementing natural zeolite.The significant effect of the natural zeolite addition in comparison with the control group was found in the eggshell weight and the yolk index.The weight of eggshell of the control group (1.10±0.01g) was significantly lower than the eggshell weight of experimental -least squares mean,   -standard error, + -P<0.05,++ -P<0.01,+++ -P<0.001

Kralik et al. (2006) and Emam et al. (2019).
We found that eggshell thickness decreased with female age in all measurement sites.The average eggshell thickness significantly decreased from 224.52±0.93µm at the beginning of the laying, to 219.39±0.93µm in the middle of the laying up to the value of 216.42±0.93µm.These agree with results of Hanusová et al. (2021).The thickness of eggshell was demonstrably thinner in all measured positions of the egg with increasing age of laying hens.