A Study on the Effect of Altitude on Shell Thickness in Goose Eggs

In poultry breeding, it is an important issue to produce eggs and ensure supply without any problem both to meet the consumer demand as food and to meet the chick demand of the breeders. According to the statement of Kocaeli Chamber of Commerce about egg waste; non-standard eggs (other than the market demand) the rate of wastage is 1%, the rate of dirty eggs is 4% and the cracked egg (eggs with a short storage period) is 3%. Until it is delivered from business to customer, the wastage, for Kocaeli, is between 1% and 2%. It is noted that the egg sector yields approximately 8% wastage and the majority of this is due to the egg internal composition and shell quality (KOTO 2020).
       
As in many living creatures, the survival of poultry depends on the quality of the embryonic egg yield. There is a need for a quality shell that protects the egg against external factors as well as a good internal composition that provides embryo development in a quality egg, which allows it to breathe and tries to prevent water loss. In determining the shell quality, protecting the shell against external factors and ensuring air intake from the outside and minimizing water loss are important criteria, which have a significant relationship with the shell thickness (Erensayýn 1991, Yamak et al., 2016, Veldsman et al., 2019).
       
The physical properties of the egg are effective on the physiology of the developing embryo and the energy production chain and greatly affect the incubation process. Any violation in this interaction chain can result in death of the embryo. And this makes physical features, such as; egg weight, egg shape, shell thickness and porosity, important when choosing hatching eggs. Hatching eggs have the possibility of successfully hatching when their physical propeties are at average. However, eggs with a shell thickness above the average value may have a more successful hatch (Carey 1994).
       
In commercial or hatching eggs, the shell thickness has an important role in the entrance of the gases (especially oxygen) required and in the discharge of harmful gases (especially carbon dioxide), in the protection of the water ratio and preventing the entrance of disease factors. As is known, these activities are provided through small pores on the egg and the number of these pores is closely related to the thickness of the shell. The effect of altitude on egg quality and egg composition is one of the important research subjects since the differences occur in altitude, atmospheric pressure and air gas composition. As altitude increases, there is a decrease in air pressure and oxygen level and due to this decrease, there are chemical and morphological changes in poultry eggs. When the poultry, which have already adapted to low altitude, are taken to high altitude areas, deaths under shell increase in incubation until they accommodate and the reason for these deaths is generally attributed to oxygen deficiency. The gaseous environment in the shell is hypoxic, hypocapnic and its humidity is low at 4000 m and at higher altitudes, these adversities gradually increase. In these conditions, embryonic physiological features that support growth and development become important. In poultry species at high altitudes, the egg shell is thick and since the number of pores are few, they have adapted to water loss (Rahn et al., 1977, Sotherland et al., 1980, Black and Snyder 1980, Linden 2013).
       
There are formulas that can calculate the number of pores depending on the thickness of the shell. Studies disclosed observed that there is an inverse proportion between the thickness of the shell and the number of pores (Carey 1980, Balkan and Biricik 2006, Portugal et al., 2014). Indeed, egg shell thickness is not the same in all parts of the egg and thickening from blunt end to sharp end. Pores are condensed in the thin part (Balkan and Biricik 2006).
       
The fact that the egg shell is thicker in bird species living at high altitudes brings the idea of whether altitude has an effect on the egg shell thickness. Although there is not enough study to explain this idea, Agelaius phoeniceus, which has the ability to live at different altitudes, the eggs of which at different altitudes have been studied and no difference has been found (Rahn et al., 1977).
       
Geese, like Agelaius phoeniceus, are poultry species which are capable of living at different altitudes (Knight 2016). Similar study on goose eggs may disclose the effect of altitude on the thickness of egg shell. Because the hatching of goose eggs requires the implementation of tough rules and yet the rate of unexplained deaths is high. Karabulut et al., (2017) found 34% embryonic and 14% deaths under shell in their study on goose eggs collected from breeders.
       
In studies investigating the factor effecting shell quality, the average shell thickness in geese was found to be around 0.44 - 0.55 mm (Carey et al., 1990, Tilki and Ýnal 2004, Ahmad et al., 2017). Saatçi et al., (2002) found the average shell thickness as 0.72, the highest as 0.94, the lowest as 0.45 and the precentage Coefficient of Variation (CV%) as 15.
       
The egg shell is not in the same thickness in all areas of the egg and generally shows thickening from blunt to sharp end. In their study on goose eggs, Zhang et al., (2017) measured the blunt end as 0.479 mm, equatorial 0.510 mm and the sharp end 0.510 mm. Fiialovych and Kyryliv (2016) found the blunt end as 0.52 and the sharp end as 0.53 mm.
       
With the ration regulation, a significant increase in the thickness of the shell was achieved. An increase of 0.4% to 1.4% has been achieved in studies in laying quails, hens and geese and it is reported that the level of copper and zinc in the ration has an effect (Kaya et al., 2004, Bayram et al., 2008, Roy and Mishra 2010, Swain et al., 2014, Olgun et al., 2015, Fiialovych and Kyryliv 2016, Zia et al., 2016). There was no significant change in shell thickness during incubation in geese and hens (Bingöl et al., 2016, Yildirim 2018). No significant change in the shell thickness of 1-year-old geese was found when compared to other ages (Tilki and Ýnal 2004).
       
In this study; the effect of altitude, which has yet not been fully explained, on egg shell thickness, the most important element of shell quality, is to be investigated.

Materials
 
Eggs of native goose breed of Aksaray used in this study were collected from the localities laid out between the Tuz Lake (Salt Lake) and Hasan Mountain at 2018. The altitude in these regions is 900-1500 m and annual average temperature is approximately 10°C and the highest temperature does not exceed 30°C (Kopar 2008, Yayvan et al., 2008).
       
Tuz Lake is an A class wetland area with important and international criteria in terms of biodiversity conservation and is home to geese and many migratory birds (TVK 2018). The annual average temperature in this region is approximately 14°C and the highest temperature reaches 40°C (Karadavut 2009).
       
Lakes around Hasan Mountain and Mamosin Pond are also home to some other water birds. The majority of birds that come in summer and autumn are Flamingo and wild ducks. At time, this place is also a nest for ruddy Tardona ferruginea, pelicans, cormorants, water hen and wild geese. The lake and ponds here have a volcanic ground and are fed fresh water sources. The altitude in these regions is 1000-1500 m and annual average temperatures are approximately 10°C and the highest temperature does not exceed 30°C (Kopar 2008, Yayvan et al., 2008). In the researches on the heavy metals and minerals in the lake waters in this region, the salt ratio is low, rich in boron element and it is at a level that will not cause damage in terms of heavy metals and other minerals (Karadavut 2009).
       
A total of 103 eggs were randomly collected from the settlements at different (Table 1). Altitude of the region varies from 915 m to 1350 m.
 


Method
 
Goose breeders collected eggs from nest and handed over to the author. Eggs are numbererd according to the regions and incubated after disinfection. Egg shells coming out of the hatching machine at the end of incubation were used in the study.
       
The measurement of egg shell thickness was made as previously described. For this purpose, the endest points of the wide part of the egg equatorial part, the blunt end and the sharp end sides were used (Saatçi et al., 2002, Tilki and Ýnal 2004, Balkan and Biricik 2006). General shell thickness is the arithmetic average of the parts of each egg. The shell was removed from the inner membranes and thickness was measured with a micrometer with a pericision on 0.01 mm.
 
Statistical evaluations
 
The comparison between the measurements made from the blunt, equatorial and sharp end of the egg was made by dependent T-test, the difference between the altitudes was made by oneway analaysis of variance and altitude and egg shell thickness was correlated by using pearson correlation. Statistical calculations were made in SPSS package program (IBM 2013). Statistical significance was set at P<0.05.

The average shell thickness of all collected eggs was 0.58 ± 0.003 mm and at level of CV% 8.4. The highest measured shell thickness was 0.68 mm and the lowest was 0.47 mm.
       
The measurements taken from different part of the egg shell were compared and the results are presented in Table 2. A marked difference was found between the shell parts and theaverages values were as follow; blunt end 0.54 ± 0.004 mm, Equatorial part 0.58 ± 0.004 and sharp end 0.60 ± 0.004 mm. In other words, the thickness of the egg shell raised from blunt end to sharp end. The CV% levels for the blunt end, equatorial part and sharp end are 7.40, 6.84 and 7.03 respectively.
 

       
The effect of altitude on egg shell parts and general shell thickness and their importance are given in Table 3. While the effect of altitude was not observed on the blunt and general shell thickness, the impact on the equatorial part was found to be marked. It was noted that at the sharp end, the highest average shell thickness was 0.56 mm at the altitude of 935 m and the lowest average was 0.51 mm at the altitude of 1150 m, the highest average shell thickness at the equatorial part was 0.61 mm at the altitude of 960 m and the lowest was 0.53 mm at the altitude of 995 m, the highest average shell thickness at the sharp end was 0.63 mm at the altitude of 968 m and the lowest was 0.54 mm at the altitude of 995 m. As for general avarage of Shell thcikness the highest value was 0.66 mm at the altitude of 935 m and the lowest was 0.53 mm at the altitude of 1150 m.
 

       
When looking at the variances, the egg parts were generally at the lowest level at 915 m altitude and the highest CV% occured at the blunt end at 968 m altitude. Percentage variance exceeds 10% in 4 places, 3 were at blunt end and one was at the sharp end. When altitude is taken into account, the values were close between the egg parts and the general shell thickness except for 939 m. At the mentioned altitude, the highest was at blunt end (10.12), while the lowest (5.31) was at the sharp end.
       
The correlations between the overall shell thickness and the shell thickness of the egg parts and altitude were examined and the result are given in Table 4 and the correlation was insignificant for all parameters (p>0.05).
 

       
In this study, the average shell thickness of the eggs collected from the breeders were similar to the results of previous studies (Carey et al., 1990, Saatçi et al., 2002, Tilki and Ýnal 2004, Ahmad et al., 2017). However, studies in shell thickness in the rehabilitated breeds in Turkey is lower than that of native breeds. Rehabilitated breeds spawn more than domestic breeds and therefore, they need more calcium. If a proper ration program is implemented, this need can be met and the thickness of the shell can be increased (Kaya et al., 2004, Bayram et al., 2008, Fiialovych and Kyryliv 2016).
 
Percentage varience determined in this study was lower than that of Saatçi et al., 2002. This may indicate that the change in the thickness of the egg shells in the study was in accordance with reference values and that the results may be more reliable.
       
The shell was differentiated according to the egg parts and it was observed that there was a thickening from Blunt end to Sharp end as reported previously (Balkan and Biricik 2006, Fiialovych and Kyryliv 2016, Zhang et al., 2017). The difference between parts in this study was found to be much more distinctive than the earlier studies (p<0.001). The reason for this may be genetic or a common effect of climate, altitude and nutrition. Although the effect of altitude on shell thickness was observed in general, some genetic and environmental conditions such as seasonal effects and nutrition may have overshadowed the effect of altitude (Kaya et al., 2004, Tilki and Ýnal 2004, Bayram et al., 2008, Kopar 2008, Yayvan et al., 2008, Karadavut 2009, Fiialovych and Kyryliv 2016, TVK 2018). It is well documented that the physiologically and morphologically explicit effects of altitude occur in eggs at an altitude of 4000 m (Rahn et al., 1977, Black and Synder 1980, Sotherland et al., 1980, Linden 2013).
       
As is known, there are pores on the egg and these pores have two important functions. First; to expel the harmful gases accumulated in the egg and to take the gases it needs. The second is to keep the egg moisture in balance. The vital majority of pores are located at the blunt end. Based on these criteria, the studies indicate that the negative effects of incubation due to altitude may be caused by the failure of adaptation in blunt end. However, in this study, there was no difference emerged in the blunt end, but it was in the Equatorial part and in the sharp end. Since there is no available information to explain this difference, it should be matter of further reseach. Researchers must be designed to evaluate the change of salinity in the soil to volcanic formations and how microclimate will affect the physiology of geese as bred in between Tuz Lake to Hasan Mountain.
       
The significant difference that emerged in equator and sharp end may not be caused by altitude. If it was caused by altitude, there would have been a harmony between the altitude change and the thickness of the the shell as the correlation between altitude and egg shel thiikness was poor in our study (Table 4).

In conclusion, the effect of the altitude factor on the egg shell seems insignificant. Further studies investiagating effect of genetic, environment and management practices are needed to define the effect of altitude on eggshell thickness.