Evaluation of egg quality traits in a synthetic coloured broiler female line

Abstract

Coloured broiler breeders are becoming popular in recent years because of the preference for a range of poultry products as well as the welfare issues in the poultry industry. The female broiler breeders are continuously improved for various economic traits. Amongst these, egg quality trait is very essential for the production of healthy and viable chicks. This study investigates the egg quality parameters in a synthetic coloured broiler breeder female line at different age groups. The study revealed that the egg quality is optimum for setting the eggs for hatching from 40 week onwards as the egg size and internal egg parameters attain the minimum standards for the production of a healthy chick.

Keywords:

• chicken
• coloured broiler breeder
• PB-2
• egg quality traits

1. Introduction

PB-2, a synthetic coloured broiler female line, is being used as a female parent line for producing commercial coloured broiler terminal cross viz. Krishibro™, which is a popular broiler for semi-intensive system of rearing in rural areas of India. This line has been maintained under selection pressure for improved body weight and better egg production for the past 18 generations. The selection has brought about gradual improvement in the traits subjected to selection.

The egg quality affects its acceptability to the consumers (Stadelman 1977). The success of the broiler parent farming depends on the total number of good quality chicks produced by a hen. The age of the breeders has a direct effect on the egg albumen characteristics, albumen/yolk ratio, embryo survival, hatchability, chick weight and chick health (Reis et al. 1997). The egg quality determines the price for both table and hatching eggs. The information on egg quality will be helpful for improvement and genetic exploitation of these traits. Hence, in the present study, an attempt was made to evaluate the egg quality traits (external and internal) at three different age groups viz. 32, 36 and 40 weeks to understand the quality of eggs for improving the number of chicks produced by a hen.

2. Materials and methods

2.1. Experimental population

The study was carried out on PB-2 flock under selection for 18 generations in the experimental farm of Project Directorate on Poultry, Hyderabad, India, located on latitude of 17°20′N and longitude 78°30′E. The annual maximum and minimum temperatures are 33.51°C and 21.35°C, respectively, during the period of study while the relative humidity ranged between 45.4 and 75.5%. An annual rainfall of 666 mm was recorded during the period of study. The birds were maintained under the standard managemental practices with ad lib feeding up to five weeks of age and thereafter subjected to restricted feeding regimen for obtaining optimum egg production. A total of 568 eggs collected from broiler breeder hens at different age groups, i.e., 32, 36 and 40 weeks, were included for studying the external and internal egg quality traits.

The eggs were weighed using an electronic balance to an accuracy of 0.01 g. The length and width of the eggs were measured using digital vernier calipers (least count, 0.01 mm). Subsequently, the eggs were broken, and internal traits viz. yolk weight, yolk height and albumen weight were recorded using the standard procedures. Haugh unit (HU) score, albumen height and yolk colour were measured using the egg quality tester machine (EMT 5200, Robotmation Co. Ltd. Japan).

2.2. Statistical analysis

The data were analysed using the Generalized Linear Model (GLM) procedure in SPSS 12.0 software. Significant differences between various age groups were tested by one way analysis of variance (ANOVA) (Sendecor & Cochran 1994).

3. Results and discussion

The egg quality traits of PB-2 birds at different age groups were evaluated. The means of the external and internal egg quality traits along with their standard errors are presented in Tables 1 and 2, respectively.

Table 1. External egg quality traits of PB-2 birds at different ages.

Traits	32 weeks (n = 169)	36 weeks (n = 203)	40 weeks (n = 196)
Egg weight (g)	51.97 ± 0.32^c	54.59 ± 0.32^b	55.93 ± 0.32^a
Egg length (mm)	52.39 ± 0.26^c	54.32 ± 0.21^b	55.71 ± 0.21^a
Egg width (mm)	40.21 ± 0.26^c	41.56 ± 0.14^b	42.49 ± 0.24^a
Shape index	0.77 ± 0.004	0.77 ± 0.003	0.76 ± 0.004

Note: Means within a row with no common superscript letters differ significantly (P ≤ 0.05).

Table 2. Internal egg quality traits of PB-2 birds at different ages.

Traits	32 weeks (n = 169)	36 weeks (n = 203)	40 weeks (n = 196)
Albumen height (mm)	5.93 ± 0.12	6.02 ± 0.12	5.97 ± 0.12
Albumen width (mm)	68.81 ± 0.63^c	72.88 ± 0.52^b	76.25 ± 0.64^a
Albumen weight (g)	33.21 ± 0.26	33.81 ± 0.29	34.15 ± 0.29
Albumen ratio	0.64 ± 0.002^c	0.62 ± 0.002^b	0.61 ± 0.002^a
Albumen index	0.091 ± 0.006	0.085 ± 0.002	0.081 ± 0.002
Haugh unit	77.20 ± 1.05	77.90 ± 0.90	77.17 ± 0.82
Yolk colour	8.44 ± 0.08^a	7.41 ± 0.07^c	7.91 ± 0.06^b
Yolk height (mm)	15.32 ± 0.11	15.62 ± 0.10	15.50 ± 0.10
Yolk width (mm)	35.31 ± 0.28^c	37.84 ± 0.12^b	39.42 ± 0.16^a
Yolk weight (g)	14.05 ± 0.09^c	15.68 ± 0.09^b	16.87 ± 0.09^a
Yolk ratio	0.27 ± 0.002^c	0.29 ± 0.002^b	0.30 ± 0.002^a
Yolk index	0.44 ± 0.005^c	0.41 ± 0.003^b	0.40 ± 0.003^a
Shell weight (g)	4.70 ± 0.04^c	5.12 ± 0.04^b	4.91 ± 0.04^a
Shell thickness (mm)	0.344 ± 0.002^c	0.353 ± 0.002^b	0.364 ± 0.003^a
Shell ratio	0.091 ± 0.0006^c	0.094 ± 0.0007^b	0.088 ± 0.0007^a

Note: Means within a row with no common superscript letters differ significantly (P ≤ 0.05).

3.1. External egg quality traits

3.1.1. Egg weight

The egg weight showed a significant variation (P ≤ 0.01) among age groups. The egg weight varied from 51.97 ± 0.32 g at 32 weeks to 55.93 ± 0.32 g at 40 weeks, with an average egg weight of 54.27 ± 0.20 g. There was a positive correlation between the egg weight and the age of the hen. Similar results were reported by Niranjan et al. (2008) in backyard chicken, Padhi et al. (1998) in Nicobari chicken, Chatterjee et al. (2007b) in white leghorn and Singh et al. (2009) in hill fowl. Rajkumar et al. (2009) reported higher egg weight in broiler-based naked neck chicken at different ages which ranged from 56.29 to 59.96 g at 32 and 40 weeks, respectively. The average egg weights in Nigerian local chicken ecotypes were lower than the present estimates and ranged between 34.25 and 38.98 g in birds of age group 20–32 weeks (Momoh et al. 2010). Haunshi et al. (2011) studied egg weights in Indigenous chicken, Aseel and Kadaknath which were significantly lesser than the egg weight of the broiler line used in the current study at both 32 and 40 weeks. The egg weights in the PB-2 flock are similar to the egg weights reported in other broiler-based populations.

3.1.2. Shape index

Shape index is the ratio between the width and length of the egg, which is a very good indicator of uniformity in size of the eggs. The higher the shape index, the more uniform the eggs are. In the present study, the shape index did not vary significantly at different ages. The average shape index was 0.77 ± 0.002 which is similar to that reported by Parmar et al. (2006) in Kadaknath breed, Chatterjee et al. (2006) in IWI (Indian White Leghorn-strain I) and IWK (Indian White Leghorn strain-K) strains of White Leghorn chicken, Niranjan et al. (2008) in Vanaraja, Gramapriya and other rural crosses, Rajkumar et al. (2009) in different naked neck genotypes, Singh et al. (2009) in hill fowl, Rajkumar et al. (2010) in dwarf chicken and Momoh et al. (2010) in different Nigerian local chicken ecotypes. Chatterjee et al. (2006) observed a higher shape index (0.81) in IWH (Indian White Leghorn strain-H) strain of White LegHorn (WLH). The length and width of the eggs also showed similar trend as that of the shape index. The higher shape index value in PB-2 breeders indicates better uniformity in the eggs which is essential for good hatchability and healthy chick production.

3.2. Internal egg quality traits

3.2.1. Albumen quality

Albumen contributes around 54% towards the total egg weight and thus has a major influence on the internal quality of the egg. Different parameters of albumen like height, width, weight, ratio and index were evaluated and described in Table 2. In this study, the albumen height, weight and index did not vary significantly in different age groups. However, the albumen width and ratio showed a significant variation among different age groups.

3.2.2. Albumen height

Average albumen height in the present study (5.98mm) is in accordance with the results of Niranjan et al. (2008), Rajkumar et al. (2009, 2010) and Momoh et al. (2010). Higher albumen height was reported by Olawumi and Ogunlade (2008) in exotic Isa Brown layer breeder (8.60 mm) and Zhang et al. (2005) in brown egg dwarf layer while lower heights were reported by Yakubu et al. (2008) in naked neck (4.65mm), Chatterjee et al. (2006) in WLH (5.59 mm) and Singh et al. (2009) in hill fowl (5.34 mm).

3.2.3. Albumen weight

The overall albumen weight was 33.75 ± 0.16 g, and it did not vary significantly over 32, 36 and 40 weeks of age. The albumen weight in the present study was higher than that reported by Islam et al. (2001) in naked neck, Chatterjee et al. (2007a) in indigenous fowls of Andaman, Niranjan et al. (2008) in improved backyard chicken, Singh et al. (2009) in hill fowl, Parmar et al. (2006) in Kadaknath and Momoh et al. (2010) in Nigerian local chicken. However, Rajkumar et al. (2009) and Olawumi and Ogunlade (2008) reported higher albumen weight in naked neck genotypes (35.11 g) and Isa Brown layer breeder (35.94 g), respectively.

3.2.4. Albumen index

Albumen index is an indicator of the firmness and viscosity of the egg white which is considered as most important factor for quality of eggs. The average albumen index in this study was 0.09 ± 0.001. The albumen index did not vary significantly between different age groups. These findings are in tune with the earlier results of Singh et al. (2009) in hill fowl (0.087) and Parmar et al. (2006) in Kadaknath chicken (0.085). However, lower albumen index was reported by Haunshi et al. (2011) in Aseel (0.076) and Kadaknath (0.072) native chicken.

3.2.5. Albumen ratio

The albumen ratio varied significantly between age groups. The highest ratio was observed at 32 weeks (64%), followed by 36 weeks (62%) and 40 weeks (61%). The albumen ratio reduced gradually with age. Similar ratio was reported by Olawumi and Ogunlade (2008) in Isa Brown layer breeder (64.24%). However, lower albumen ratio was observed in Aseel (56.88%) and Kadaknath (59.31%) by Haunshi et al. (2011). The higher ratio at early age indicates the firmness of the albumen.

3.3. Yolk quality traits

3.3.1. Yolk colour

The yolk colour exhibited a significant variation (7.41–8.44) with age. The highest yolk colour was noticed at 32 weeks followed by 40 and 36 weeks. The inconsistency in yolk colour may be due to varied deposition of carotenoid pigments and feed component variability among different chicken varieties. The yolk colour in the present study is in agreement with the reports of Niranjan et al. (2008) in improved rural varieties, Rajkumar et al. (2010) in naked neck and dwarf chicken and Haunshi et al. (2011) in Aseel and Kadaknath native breeds.

3.3.2. Yolk weight

The yolk weight showed a significant difference among different age groups. The average yolk weight was 15.61±0.07 g. The weight of yolk increased proportionately with age. Similar yolk weights were observed by Niranjan et al. (2008) in Gramapriya and Haunshi et al. (2011) in Aseel and Parmar et al. (2006) in Kadaknath. However, higher yolk weights were reported by Singh et al. (2009) in hill fowl, Momoh et al. in Nigerian local chicken, Niranjan et al. (2008) in Vanaraja and other rural crosses, Rajkumar et al. (2009, 2010) in naked neck and dwarf chicken, Yakubu et al. (2008) in naked neck and Chatterjee et al. (2007a) in barred desi and Frizzle fowl while lower yolk weights were observed by Haunshi et al. (2011) in Kadaknath, Islam et al. (2001) in naked neck and Chatterjee et al. (2007a) in brown and black Nicobari breeds of Andaman. The variation in yolk weight may be attributed to the size of the egg and also the breed/variety of the chicken studied.

3.3.3. Yolk index

The yolk index varied significantly among different age groups. The yolk index ranged from 0.40 to 0.44. Similar findings were reported by Padhi et al. (1998) in Nicobari fowl, Niranjan et al. (2008) in rural varieties, Momoh et al. (2010) in Nigerian local chicken whereas lower indices were observed by Rajkumar et al. (2009, 2010) in naked neck and dwarf chicken, Singh et al. (2009) in hill fowl, Parmar et al. (2006) in Kadaknath, Chatterjee et al. (2007a) in six breeds of indigenous chicken of Andamans, Haunshi et al. (2011) in Aseel and Kadaknath. However, higher index was noticed by Wani et al. (2007) in Vanaraja birds.

3.3.4. Yolk ratio

The yolk ratio is the ratio of yolk weight to the egg weight. The yolk ratio in the present study significantly increased gradually (0.27–0.30) with age. Similar ratio was reported by Haunshi et al. (2011) in Kadaknath and Laxmi et al. (2001) in WLH. Higher yolk ratio values were observed by Chatterjee et al. (2007b) in naked neck and white Nicobari fowl, Singh et al. (2009) in hill fowl and Haunshi et al. (2011) in Aseel native chicken.

3.4. Shell quality traits

3.4.1. Shell weight

Significant difference was noticed in the shell weights in different age groups. The shell weights ranged between 4.70 and 5.12 g. The weights in the present study were comparable with the reports of Bhutia et al. (2004) in coloured broiler, Haunshi et al. (2011) in Aseel, Rajkumar et al. (2010) in naked neck and dwarf chicken and Momoh et al. (2010) in Nigerian local chicken. However, lower shell weights were also observed by Haunshi et al. (2011) in Kadaknath chicken while higher shell weights were noticed by Singh et al. (2009) in hill fowl, Olawumi and Ogunlade (2008) in exotic Isa Brown layer breeder and Niranjan et al. (2008) in Vanaraja and other rural crosses.

3.4.2. Shell thickness

This is an important economic trait that controls the keeping quality of the egg and also it is breaking strength and transportability. The shell thickness varied significantly with age and it ranged between 0.34 and 0.36 mm. Similar shell thickness was observed by Islam et al. (2001) in naked neck chicken. The higher shell thickness than the present study was reported by Niranjan et al. (2008) in Vanaraja, Gramapriya and other rural crosses, Rajkumar et al. (2009, 2010) in naked neck and dwarf chicken, Yakubu et al. (2008) in naked neck chicken of Nigeria, Momoh et al. (2010) in Nigerian local chicken, Singh et al. (2009) in hill fowl. However, lower shell thickness was noticed by Parmar et al. (2006) in Kadaknath, Olawumi and Ogunlade (2008) in Isa Brown layer breeder, Nwachukwu et al. (2006) in crosses involving naked neck, frizzle and normal birds, Padhi et al. (1998) in Nicobari, naked neck and WLH. These variations in the shell thickness could be due to a difference in climatic zones, feed composition and breed variation.

3.4.3. HU score

HU is one of the important criterion for determining the internal quality of the egg. It is the most accepted and widely used measure to evaluate the albumen quality. Thus better the albumen quality, better the Haugh unit and better the internal egg quality. The differences for Haugh unit scores were not significant among the different age groups. The Haugh unit score varied within a very narrow range (77.17–77.90) in all the age groups up to 40 weeks of age, indicating uniform internal egg quality over the age. However, Rajkumar et al. (2010) reported that the Haugh unit values declined over age in both naked neck and dwarf chicken. HU scores comparable to the present study were reported by Momoh et al. (2010) in the Nigerian local chicken population, Haunshi et al. (2011) in Aseel and Kadaknath. Parmar et al. (2006) observed a wide range of HU scores from 62.6 to 90.0 in Kadaknath birds under field conditions. Niranjan et al. (2008) observed HU scores in rural indigenous chicken varieties varying between 74.6 and 79.4. Lower HU scores (59.6–71.6) were reported by Chatterjee et al. (2006) in different WLH lines. Ikeobi et al. (1999) also demonstrated lower HU scores (61.9) in Nigerian chicken. Padhi et al. (1998) reported HU scores in naked neck (73.2) and Nicobari (75.2) chicken. However, very high HU scores (100.3–106.3) were observed by Nwachukwu et al. (2006) in crosses of naked neck, frizzle and normal chicken. The variable HU scores may be due to the varied albumen quality in different chicken varieties.

4. Conclusion

It is concluded that the external and internal egg quality traits varied significantly (P ≤ 0.05) in different age groups. Age had a significant effect on egg weight, length, width, albumen width, albumen ratio, yolk colour, yolk width, yolk weight, yolk ratio, yolk index, shell weight, shell thickness and shell ratio. The egg quality characteristics observed in PB-2 breeders at 40 weeks of age are optimum to produce more number of quality chicks per hen which is desirable for better economics of farmers.

Funding

The authors are highly thankful to ICAR for providing financial support for conducting this research in the form of Institute project.

Additional information

Funding

Funding: The authors are highly thankful to ICAR for providing financial support for conducting this research in the form of Institute project.