Effects of egg weight on egg quality traits in partridge (Alectoris Chukar)

Abstract

In this study, the aim was to determine the internal and external quality traits of partridge (Alectoris chukar) eggs as well as the Pearson correlation coefficients among these traits. For use in this research, a total of 200 partridge eggs were collected over three sequential days. The partridges were housed at the Research Unit of Animal Science, Faculty of Agriculture, University of Akdeniz. The eggs were categorized according to weight and classified as ≤19.0 g, 19.1–20.0 g, 20.1–21.0 g and ≥21.1 g. Average eggshell thickness was highest in groups of 20.1–21.0 g and ≥21.1 g. In contrast, lowest eggshell weight was calculated in groups of ≤19.0 g and 19.1–20.0 g. In this study, egg shape index, yolk index, Haugh unit, albumen width and unit surface shell weight were not significantly affected by egg weight groups. Whereas egg length, egg width, shell weight, shell thickness, shell surface area, egg volume, yolk weight, yolk height, yolk width, yolk ratio, albumen height, albumen length, albumen weight, albumen index, albumen ratio and yolk/albumen ratio were significantly affected by egg weight groups. At the same time, there was found a significant relationship amongst the internal and external egg quality traits.

Keywords:

• partridge
• egg weight
• egg quality traits
• Pearson correlation

1. Introduction

Partridge breeding is becoming widespread because it enables high productivity in small breeding areas within a short time and without a large investment when compared with other winged breeding. Partridges are bred for a variety of purposes such as for eggs, meat and hunting preserves. Partridges can easily adapt to the environment in natural life.

Avian egg is not only a tool for reproduction but is also a valuable food source for humans. Moreover avian eggs are culturally accepted worldwide and are not subject to any religious or tradition prohibition. Nowadays, it is widely recognized that eggs are more than a source of nutrients, numerous studies describe biological properties potentially exploitable by the pharmaceutical, food-processing and cosmetic industries (Mine & Kovacs-Nolan 2004; Moulo et al. 2010). The egg size and internal quality of eggs are important for both table and hatching eggs. The nutrient content and composition of an egg can thus greatly influence the development of the embryo contained within as well as its success as a hatchling. Variation in the composition of avian eggs occurs among species (Finkler et al. 1998; Sekeroglu & Altuntas 2009; Moulo et al. 2010). The egg weight is affected by many factors such as heredity, breed, strain, age of hen, body size, feed and water consumption, temperature-humidity and diseases (Cook & Briggs 1997; Sekeroglu & Altuntas 2009).

Egg weight is in direct proportion to albumen, yolk and shell. The albumen is a major indicator of internal egg quality; air cell size, albumen and yolk quality and the presence of blood or meat spots in the eggs are the parameters, which determine the internal egg quality (De Ketelaere et al. 2002; Khurshid et al. 2003; Sarica et al. 2012). Egg yolk is still an important source of nutrients, and also used in non-food purpose like leather processing and a source of biologically active substances (Hartmann & Wilhemson 2001).

Partridge eggs weights vary from 16 g to 25 g, are oblong in shape, and are on average 42 mm long and 31 mm wide. Eggshell thickness of partridge eggs is about 0.228 mm, shell weight is between 2.34 g and 2.86 g (Woodard et al. 1982; Yannakopoulos 1992; Alkan et al. 2007).

The chicken egg has been extensively studied for its internal and external qualities as well as for its composition. However such information is not so well documented in other poultry species, for example, partridges. Thus, this study was conducted to investigate egg quality traits and Pearson correlation coefficients among the internal and external quality traits of partridge eggs.

2. Materials and methods

2.1. Measurements and formulas

In total 200 partridge eggs were randomly selected and evaluated in this study. The eggs were categorized according to weight and classified as ≤19.0 g, 19.1–20.0 g, 20.1–21.0 g and ≥21.1 g. The partridges were housed at the Research Unit of Akdeniz University, Department of Animal Science. The evaluated eggs were collected from partridge hens, and reared in a cage system. The partridge hens were about 52 weeks of age. The birds were fed a diet containing 21% crude protein and 2900 kcal/kg metabolic energy, and were provided with fresh water ad libitum during the laying period. In order to evaluate egg quality traits, eggs were stored for seven days in 15–18°C temperature and in 75–80% relative humidity conditions.

The eggs were first numbered and then weighed with an electronic balance to the nearest 0.01 g. Then egg length and width were measured by slide callipers sensitive to 0.01 mm. Next the eggs were broken onto a glass covered table in order to measure the yolk height, yolk diameter, albumen height, albumen length and albumen width by a three-legged micrometre (Model: 8567, USSR) with an accuracy of 0.01 mm. Following this, the yolk was separated from the albumen using a spoon and weighed. The albumen weight was calculated by subtracting yolk weight and shell weight from the gross egg weight. The eggshells were washed under slightly flowing water so that the albumen remains were removed. The washed eggshells were left to dry in the open air for 24 hours. Then, all eggshells were balanced together with the shell membrane. Finally, eggshell samples were taken from the sharp region, the blunt region and the equatorial parts of each egg were measured with micrometre to an accuracy of 0.01 mm, and the average eggshell thickness was obtained from the average values of these parts (Tyler 1961; Alkan et al. 2013). The other quality traits were evaluated according to the following equations (Yannakopoulos & Tserveni-Gousi 1986; Narushin 2005; Alkan et al. 2013):

2.2 Statistical analysis

The eggs were allocated according to their weight to ≤19.0 g, 19.1 – 20.0 g, 20.1 – 21.0 g, and ≥21.1 g groups. Data were analyzed using the one-way analysis of variance procedure of SPSS 17.0 (2008) and significant differences among the means were tested by Duncan's multiple range test. Also, the Pearson's correlations were calculated among the traits.

3. Results and discussion

Descriptive statistics of external and internal egg qualities and Pearson correlation coefficients among the external and internal egg quality traits are presented in Tables 1–3, respectively. There were found significant correlations among the external and internal egg quality traits.

Table 1. The effect of egg weight on external egg quality traits.

	Egg weight groups
Traits	≤19.0 g	19.1–20.0 g	20.1–21.0 g	≥21.1 g
Egg length (mm)	38.67 ± 0.19^a	39.72 ± 0.15^b	40.00 ± 0.12^b	40.62 ± 0.12^b
Egg width (mm)	29.44 ± 0.12^a	30.15 ± 0.06^b	30.59 ± 0.05^c	31.03 ± 0.05^d
Shell weight (g)	2.08 ± 0.03^a	2.15 ± 0.02^a	2.23 ± 0.01^b	2.32 ± 0.02^b
Shell ratio (%)	11.48 ± 0.20^b	10.97 ± 0.10^a	10.96 ± 0.07^a	10.74 ± 0.09^a
Sharp region thickness (mm)	0.256 ± 0.00^b	0.256 ± 0.00^b	0.250 ± 0.00^a	0.249 ± 0.00^a
Blunt region thickness (mm)	0.237 ± 0.00^b	0.236 ± 0.00^b	0.231 ± 0.00^a	0.228 ± 0.00^a
Equatorial region thickness (mm)	0.247 ± 0.00^b	0.246 ± 0.00^b	0.241 ± 0.00^a	0.239 ± 0.00^a
Average shell thickness (mm)	0.247 ± 0.00^b	0.246 ± 0.00^b	0.241 ± 0.00^a	0.238 ± 0.00^a
Shell surface area (cm^2)	33.02 ± 0.16^a	34.66 ± 0.05^b	35.72 ± 0.04^c	36.92 ± 0.05^d
Unit surface shell weight (g/cm^2)	0.063 ± 0.00^a	0.062 ± 0.00^a	0.063 ± 0.00^a	0.063 ± 0.00^a
Shape index (%)	76.24 ± 0.49^a	76.03 ± 0.40^a	76.54 ± 0.33^a	76.41 ± 0.32^a
Egg volume (cm^3)	18.54 ± 1.78^a	19.92 ± 0.76^b	20.61 ± 0.54^c	21.51 ± 0.77^d

Note: Means in rows with different letters differ significantly at P < 0.01.

Table 2. The effect of egg weight on internal egg quality traits.

	Egg weight groups
Traits	≤19.0 g	19.1–20.0 g	20.1–21.0 g	≥21.1 g
Yolk weight (g)	7.67 ± 0.12^a	7.77 ± 0.07^a	8.12 ± 0.07^b	8.45 ± 0.09^b
Yolk height (mm)	14.24 ± 0.10^a	14.40 ± 0.07^a	14.64 ± 0.08^b	14.94 ± 0.08^b
Yolk width (mm)	29.60 ± 0.15^a	30.46 ± 0.08^b	30.86 ± 0.12^b	31.30 ± 0.14^c
Yolk index (%)	48.19 ± 0.42^a	47.29 ± 0.25^a	47.55 ± 0.35^a	47.80 ± 0.34^a
Yolk ratio (%)	42.19 ± 0.72^b	39.62 ± 0.35^a	39.63 ± 0.35^a	39.15 ± 0.38^a
Albumen height (mm)	4.53 ± 0.14^a	4.86 ± 0.07^a	5.08 ± 0.09^b	5.26 ± 0.09^b
Albumen width (mm)	39.39 ± 0.60^a	39.51 ± 0.70^a	39.99 ± 0.20^a	40.89 ± 0.26^a
Albumen length (mm)	51.27 ± 0.60^a	52.31 ± 0.30^a	52.65 ± 0.30^a	53.45 ± 0.30^b
Albumen weight (g)	8.46 ± 0.17^a	9.67 ± 0.08^b	10.14 ± 0.08^c	10.79 ± 0.09^d
Albumen index (%)	10.05 ± 0.33^a	10.69 ± 0.20^ab	11.03 ± 0.20^b	11.19 ± 0.18^b
Albumen ratio (%)	46.33 ± 0.76^a	49.40 ± 0.36^b	49.57 ± 0.37^b	50.02 ± 0.40^b
Yolk/albumen ratio (%)	91.67 ± 2.93^b	80.86 ± 1.30^a	80.69 ± 1.35^a	78.89 ± 1.48^a
Haugh unit	85.14 ± 0.86^a	86.33 ± 0.41^a	87.07 ± 0.49^a	87.58 ± 0.51^a

Note: Means in rows with different letters differ significantly at P < 0.01.

Table 3. The Pearson correlation coefficients among the internal and external quality traits of eggs.

Traits	SW	YW	YH	YWDT	AH	AWDT	AL	EWDT	EL	ST	AI	YI	SI	SFA	SR	HU	EVL	AW	Y/A	YR	AR
EW	.512**	.455**	.384**	.539**	.339**	.149*	.245**	.802**	.494**	–.425**	.229**	–.038	.062	1.00	–.294**	.019**	.905**	.760**	–.276**	–.250**	.296**
SW		.277**	.131	.162*	.091	.109	.211**	.479**	.167*	–.107	.008	–.002	.139*	.512**	.598**	.013	.472**	.239**	.004	–.084	–.074
YW			.141*	.404**	–.068	–.054	.080	.322**	.368**	–.285**	–.048	–.146**	–.126	.452**	–.080	–.146*	.465**	–.220**	.717**	.741**	–.688**
YH				.075	.437**	.055	.164*	.196**	.454**	–.042	.395**	.755**	–.271**	.380**	–.171*	.395**	.414**	.324**	–.139	–.137	.156*
YWDT					.065	.076	.237**	.404**	.539**	–.293**	.015	–.583**	–.015	.542**	–.284**	–.019	.486**	.320**	.002	0.34	.026
AH						.146*	.149*	.196**	.313**	–.015	.903**	.310**	–.149*	.335**	–.170*	.987**	.331**	.424**	–.326**	–.023**	.352**
AWDT							.156*	.171*	–.004	–.067	–.209**	.001	0.91	.146*	–.002	.131	.132	.191**	–.147*	–.150*	.161*
AL								.137	.253**	–.038	–.069	–.014	–.125	.244**	.004	0.120	.248**	.193**	–.078	–.081	.073
EWDT									.080	–.326**	.107	–.110	.528**	.803**	–.201**	.074	.826**	.628**	–.262**	–.251**	.261**
EL										–.186**	.256**	.179*	–.797**	.494**	–.208**	.253**	.627**	.289**	–.007	.016	.026
ST											.026	.131	–.032	–.404**	.192**	.053	–.345**	–.275**	.048	–.011	–.065
AI												.306**	–.153*	.227**	–.174*	.903**	.231**	.297**	–.233**	–.229**	.255**
YI													–.221**	–0.044	0.043	.330**	.020	.054	–0.111	–.131	.109
SI														0.063	0.048	–.171*	–.039	.138	–.160*	–.172*	.144*
SFA															–.294**	.187**	.905**	.762**	–.280**	–.253**	–.299**
SR																–0.128	.269**	–.383**	.243**	.129	–.327**
HU																	.202**	.319**	–.296**	-.297**	.320**
EVL																		.649**	–.201**	–.180*	.212**
AW																			–.828**	–.799**	.841**
Y/A																				.985**	–.987**
YR																					–.967**

EW, egg weight; SW, shell weight; YW, yolk weight; YH, yolk height; YWDT, yolk width; AH, albumen height; AWDT, albumen width; AL, albumen length; EWDT, egg width; EL, egg length; ST, shell thickness; AI, albumen index; YI, yolk index; SI, shape index; SFA, shell surface area; SR, shell ratio; HU, Haugh unit; EVL, egg volume; AW, albumen weight; Y/A, yolk/albumen; YR, yolk ration; AR, albumen ratio.

* P < 0.05; **P < 0.01.

In this research, egg shape index ranged from 76.03% to 76.54%, indicating that the eggs had shown normal shape. Although egg shape index was the highest in the ≤19 g group (76.54%), the effect of egg weight on egg shape index was not significant. The egg shape index determined in this research was similar to that found in studies carried out by Tilki and Saatci (2004), Garip et al. (2010) and Ghasemi et al.(2014). However, the egg shape index was found to be higher than that reported by Alkan et al. (2007) and Krawczyk (2009). The difference among the egg shape index reported in the various studies may be due to variations in strain, stocking density, seasonal factors, feeding and watering systems and the age of birds studied. There was not found a significant correlation between egg weight and eggshell index (0.062). The results of studies concerning the relationship of egg weight with egg shape index are ambiguous. However, in many studies carried out on chickens, researchers reported a negative, although not always significant, correlation between the egg shape index and its weight (Nowaczewski et al. 2008; Begli et al. 2010; Tebesi et al. 2012) which would mean that heavier eggs are more elongated. In contrast, Nowaczewski et al. (2008) reported that Bernacki and Heller found heavier eggs were characterized by greater shape index in quinea fowls, these eggs were more ball-shape, and Kuzniacka et al. found a significant positive correlation between the shape of eggs and their weight (0.317).

Egg weight significantly affected eggshell thickness. Eggshell thickness was highest in the ≤19.0 g (0.247 mm) and the 19.1–20.0 g (0.246 mm) groups and lowest in the 20.1–21.0 g (0.240 mm) and the ≥21.1 g (0.238 mm) groups. Also, eggshell thickness was found to be highest in the sharp region and lowest in the blunt region implying that mineralization was higher in the sharp region. This research found a significant negative correlation between the egg weight and eggshell thickness (–0.425). Eggshell thickness value determined in our study was similar to that reported by Tilki and Saatci (2004), Song et al. (2000) and Kirikci et al. (2007), but was not in agreement with that found by Caglayan et al. (2009), Krawczyk (2009) and Garip et al. (2010).

The egg weight has an indirect relation with the shell quality of the egg. It has been stated by most researchers that the eggshell thickness has direct relation with the egg weight (Choi et al. 1983; Stadelmann 1995). Some researchers have mentioned positive correlations between the egg weight and eggshell thickness (Stadelmann 1995; Kul & Seker 2004; Nowaczewski et al. 2008). Also, Mohanty et al. (1986), Poggenpoel (1986), De Ketelaere et al. (2002) reported that egg weight increased significantly while shell thickness decreased. In this study, egg length and width values increased depending on the increase of the egg weight. Egg length (38.67 mm) and width (29.44 mm) values were lowest in the ≤19.0 g group.

The egg length and width values in this research were lower than those reported by Song et al. (2000), Alkan et al. (2007) and Alasahan and Gunlu (2012). The egg weight showed highly significant and positive correlations with egg length and width, and the values of correlation found were 0.494 and 0.802 for egg length and width, respectively. The significant and positive correlations indicated that the longer egg length had a positive effect on egg weight. In literature, egg length has also been reported to significantly affect egg weight (Monira et al. 2003). However, the relationship between egg weight and egg width was significant. This is probably attributed to the fact that egg yolk occupies the egg width area, thereby translating to heavier weight for eggs. This result supports the report of Abanikannda et al. (2007). These authors reported a phenotypic correlation of 0.78 and 0.84 between egg weight with egg length and egg width, respectively. Based on the correlations, they concluded that egg length and egg width were better predictors of egg weight when compared to egg shape index. The findings determined in this study are also in agreement with the reports of Nwagu et al. (2010), Obike and Azu (2012) and Tebesi et al. (2012). They found highly significant correlations between the egg weight with egg length and egg width. Also, Apuno et al. (2011) reported significant correlations between egg weight with egg length and egg width.

Yolk and albumen weights were affected by egg weight groups, and yolk and albumen weight values increased depending on the increase of the egg weight. This research found a high phenotypic correlation between egg weight and albumen weight (0.455), and also a highly significant correlation between egg weight and albumen weight (0.760). The findings determined in this research are in agreement with the reports of Tebesi et al. (2012), Alkan et al. (2013) and Khawaja et al. (2013). They found highly significant correlations between the egg weight with yolk weight and albumen weight. The yolk weight and albumen weight in this research was similar to those of reported by Kirikci et al. (2007), Caglayan et al. (2009) and Garip et al. (2010). These results indicate that the heavier weight of the yolk and albumen leads to increase in egg weight. Thus, selecting for egg weight will invariably select eggs with larger albumen and yolk weight, which is needed for embryo development.

Yolk weight had a significant correlation with yolk width (0.404). The yolk width possibly constitutes the yolk portion which may have influenced the yolk weight positively. There was also found a negative significant correlation (–0.583) between yolk width and yolk index. This result is similar to that reported by Obike and Azu (2012) and Nwagu et al. (2010), and these authors reported a negative and significant relationship (–0.656) between yolk index and yolk diameter. This result was expected, because yolk width is a very important factor in the determination of yolk index. Conversely, the correlation between yolk index and yolk height (0.755) was highly significant. Also, yolk index was found positively and significant correlated with albumen height (0.310). This indicates that improvement of albumen height, yolk height and yolk width will result in a better yolk index. Dependent on this result, egg freshness will be improved since yolk index determines egg freshness.

This research found a positive relationship between albumen index with albumen height (0.903), albumen weight (0.297) and albumen ratio (0.255), but a significant and negative correlation was found between albumen index and albumen width (–0.209). According to Ozcelik (2002), albumen index, albumen height, albumen weight and albumen ratio give an indication of the density of albumen quality and are used in the estimation of Haugh unit, which is an important factor in the internal quality of the egg.

There was found a positive and significant correlation between albumen index and yolk index (0.306). This result is in agreement with the findings reported by Ozcelik (2002), Kul and Seker (2004) and Obike and Azu (2012).

4. Conclusions

The correlations determined among the internal and external egg quality traits indicate that the parameters can be improved through selection. The chicken egg has been very well studied for its internal and external qualities as well as for its compositions, however such information is not so well documented in other poultry species i.e. partridges. Thus, it is important that poultry researchers study egg quality traits as much as the breeders who deal with partridge eggs breeding and improvement.

Acknowledgements

We would like to thank Sarah Bridgette Hill Karabag and Tally Pendragon for improving the English of the manuscript.