Genetic analysis of egg quality traits in White Leghorn chicken

Abstract

Aim: The present study was undertaken to estimate the genetic parameters and to assess the inheritance pattern of egg quality traits in White Leghorns. Materials and Methods: Data on 480 eggs produced by 40 week old pullets of 4 genetic groups were used for studying egg quality traits. Heritabilities and correlations were estimated by full sib correlation method using Mixed Model Least Squares and Maximum Likelihood (LSMLMW) computer program. Results: The egg weight, haugh unit, yolk index, albumen index, yolk weight, albumen weight, shell weight and shell thickness ranged from 50.01 ± 0.48 to 53.89 ± 0.43 g, 65.38 ± 0.92 to 80.98 ± 1.01, 0.341 ± 0.003 to 0.353 ± 0.003, 0.056 ± 0.002 to 0.087 ± 0.002, 14.16 ± 0.13 to 15.58 ± 0.12 g, 30.92 ± 0.39 to 33.18 ± 0.39 g, 4.32 ± 0.05 to 5.12 ± 0.05 g and 0.336 ± 0.003 to 0.376 ± 0.003 mm, respectively. Heritability estimates for egg weight, yolk index, albumen index and albumen weight ranged from low to medium while those of haugh unit, yolk weight, shell weight and shell thickness ranged from low to high. The genetic and phenotypic correlations of egg weight with other egg quality traits except shell quality traits were mostly positive and moderate to high. High positive genetic and phenotypic correlations between haugh unit and other traits were observed. Genetic correlation of yolk weight with albumen weight was positive while that with shell quality traits was mostly negative. Shell weight was positively correlated with shell thickness. Conclusion: Significant genetic group differences were observed for various egg quality traits studied. The heritability estimates for different egg quality traits were low to moderate. The association among egg quality traits was positive in general.

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How to cite this article:
Sreenivas D, Gnana Prakash M, Mahender M and Chatterjee RN (2013)
, Vet. World 6(5):263-266, doi:10.5455/vetworld.2013.263-266
Genetic analysis of egg quality traits in White leghorn
chicken
Introduction collected and used for studying external and internal
egg quality traits. Each sire mated to two dams
Poultry farming occupies a pivotal position in contributed to 6 progeny at the rate of three progeny per
bringing about rapid economic growth. In India, during dam.
the last five decades, poultry has evolved from subsis- Eggs were weighed individually to the accuracy
tence farming to an integrated and highly commercial of 0.01 g. Thereafter, the eggs were broken and
business oriented enterprise, the development of which albumen height, haugh unit (HU) etc. were measured
was not only in size but also in productivity, using Egg Quality tester (EMT 5200, Japan). Length
sophistication and quality [1]. India is the third largest and width of thick albumen were measured at the
producer of eggs and fifth largest producer of poultry longest point by Vernier Callipers with an accuracy of
meat in the world, producing 55.64 billion eggs and 0.05 mm. Width of the yolk was measured twice at the
about 648,900 tons of poultry meat in 2008 [2]. The right angles to each other and averaged. Height of the
overall quality of egg has been considered as the most yolk was measured at the highest part by Ames
important trait by the producers and consumers as well micrometer with an accuracy of 0.1 mm. Yolk was
for which continuous genetic evaluation of different separated from albumen and weighed nearest to 0.1 g.
egg quality traits has become essential in the present The shells of broken eggs were dried at room
market scenario. Therefore, this investigation was temperature before shell weight was recorded to 0.1 g
taken up to estimate the genetic parameters and to accuracy. Shell thickness was measured nearest to 0.01
assess the inheritance pattern of various egg quality mm using a dial thickness gauge at two places on the
traits in three strains and control population of White shell (at broader and at narrower ends) and averaged.
Leghorns. Albumen and yolk indices were determined as the ratio
Materials and Methods of height to width of albumen and yolk as per standard
procedures suggested [3,4]. Albumen weight was
A total of 480 eggs produced by 40 week old calculated by subtracting the total weight of the two
pullets (120 from each of the three pure lines and one components (yolk + shell) from the egg weight.
control line of White Leghorns) mated to 20 sires were
www.veterinaryworld.org 263
doi:10.5455/vetworld.2013.263-266
Genetic analysis of egg quality traits in White Leghorn chicken
College of Veterinary Science,
Sri Venkateswara Veterinary University, Rajendranagar, Hyderabad - 500 030, Andhra Pradesh, India
Corresponding author: email: dasari117@rediffmail.com
Received: 10-08-2012, Accepted: 15-09-2012, Published online: 12-02-2013
Dasari Sreenivas, Manthani Gnana Prakash, Mallam Mahender and Rudra Nath Chatterjee
Sreenivas Dasari,
Abstract
Aim: The present study was undertaken to estimate the genetic parameters and to assess the inheritance pattern of egg quality
traits in White Leghorns.
Materials and Methods: Data on 480 eggs produced by 40 week old pullets of 4 genetic groups were used for studying egg
quality traits. Heritabilities and correlations were estimated by full sib correlation method using Mixed Model Least Squares
and Maximum Likelihood (LSMLMW) computer program.
Results: The egg weight, haugh unit, yolk index, albumen index, yolk weight, albumen weight, shell weight and shell
thickness ranged from 50.01 ± 0.48 to 53.89 ± 0.43 g, 65.38 ± 0.92 to 80.98 ± 1.01, 0.341 ± 0.003 to 0.353 ± 0.003, 0.056 ±
0.002 to 0.087 ± 0.002, 14.16 ± 0.13 to 15.58 ± 0.12 g, 30.92 ± 0.39 to 33.18 ± 0.39 g, 4.32 ± 0.05 to 5.12 ± 0.05 g and 0.336 ±
0.003 to 0.376 ± 0.003 mm, respectively. Heritability estimates for egg weight, yolk index, albumen index and albumen weight
ranged from low to medium while those of haugh unit, yolk weight, shell weight and shell thickness ranged from low to high.
The genetic and phenotypic correlations of egg weight with other egg quality traits except shell quality traits were mostly
positive and moderate to high. High positive genetic and phenotypic correlations between haugh unit and other traits were
observed. Genetic correlation of yolk weight with albumen weight was positive while that with shell quality traits was mostly
negative. Shell weight was positively correlated with shell thickness.
Conclusion: Significant genetic group differences were observed for various egg quality traits studied. The heritability
estimates for different egg quality traits were low to moderate. The association among egg quality traits was positive in
general.
Keywords: egg quality traits, heritability, White Leghorn

Heritabilities and correlations were estimated by also reported in different breeds [14-16].
full sib correlation method using Mixed Model Least Yolk index and albumen index were highest in
Squares and Maximum Likelihood (LSMLMW) computer IWI strain (0.353±0.003 and 0.087±0.002, respecti-
program [5]. vely) and lowest in IWK strain (0.341±0.003 and 0.056
±0.002, respectively). There were reports of higher
Results and Discussion yolk index value (17) and higher albumen index value
Phenotypic means: Significant differences (P<0.01) (11) and very lower albumen index values [7, 8 and 10]
were observed among the three strains and control in comparison to the present findings. The weights of
population with respect to various egg quality traits yolk, albumen and shell and their percent weights over
(Table-1). The IWK strain had significantly higher egg the egg weight were measured and analyzed for
weight (53.89 ± 0.43 g) when measured from other two comparison. The IWK strain had higher yolk, albumen
strains and control population. The three strains in the and shell weights as expected on the ground that it had
present study were obtained from different sources and higher egg weight, while percent weights varied in the
with different selection criteria. Similar differences trend. Similar observations [10,15] were reported in
were reported by earlier authors in White Leghorns White Leghorns, while higher percent shell weights
[6-11]. Egg weight ranged from 50.01 ± 0.48 to 53.89 ± [12,18-20] were observed in native / backyard poultry.
0.43 g, which is in agreement with the published This suggests that the shells of White Leghorns
reports [8,11-13]. Haugh unit, a measure of albumen contribute lesser proportion to the egg weight when
quality was in the range of 65.38 ± 0.92 in IWK to compared to native / backyard poultry. In the present
80.98±1.01 in IWI strain, which is in accordance with study, the shell thickness ranged from 0.336 ± 0.003 in
the published reports [6,8-11]. Higher haugh unit IWH to 0.376 ± 0.003 mm in IWI strain, which is
values than those observed in the present study were comparable to many reports in literature [7,8,10,14].
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doi:10.5455/vetworld.2013.263-266
Table-1. Least squares means for egg quality traits in White Leghorns
Trait IWH ( IWI IWK Control
b b a b
Egg weight (g) 50.01 ± 0.48 50.66 ± 0.47 53.89± 0.43 50.48 ± 0.42
b a c b
Haugh unit 72.99 ± 1.03 80.98 ± 1.01 65.38 ± 0.92 74.85 ± 0.92
b a b b
Yolk Index 0.343 ± 0.00 0.35 ± 0.00 0.341 ± 0.00 0.34 ± 0.00
b a c b
Albumen Index 0.072 ± 0.00 0.09± 0.00 0.056 ± 0.00 0.08 ± 0.00
c b a b
Yolk weight(g) 14.16 ± 0.13 14.70± 0.13 15.58 ± 0.12 14.84 ± 0.12
b a a a
Percent Yolk weight 28.28 ± 0.24 29.17 ± 0.23 29.15 ± 0.25 29.56 ± 0.24
b b a b
Albumen Weight (g) 31.53 ± 0.43 31.19 ± 0.43 33.18 ± 0.39 30.92 ± 0.39
a b b b
Percent albumen weight 62.96 ± 0.30 61.31 ± 0.31 61.24 ± 0.30 61.10 ± 0.28
c b a b
Shell weight(g) 4.32 ± 0.05 4.77± 0.05 5.12 ± 0.05 4.72 ± 0.05
c ab a b
Percent Shell weight 8.76± 0.09 9.53± 0.08 9.61± 0.10 9.34 ± 0.09
c a b b
Shell Thickness (mm) 0.336± 0.00 0.376 ± 0.00 0.362 ± 0.00 0.365 ± 0.00
Mean) (Mean) (Mean) (Mean)
Means with different superscripts in each row differ significantly
Table-2. Heritability and correlation coefficients for egg quality traits in different strains of White Leghorns
EW HU YI AI YW AW SW ST
IWH Strain
EW 0.226 ± 0.028 -0.181 ± 0.156 0.803 ± 0.270 0.234 ± 0.110 -0.670 ± 0.153 0.814 ± 0.285 -0.744 ± 0.148 0.345 ± 0.183
HU -0.203 0.272 ± 0.174 0.471 ± 0.121 0.912 ± 0.316 0.670 ± 0.153 -0.835 ± 0.348 -0.744 ± 0.148 -0.778 ± 0.263
YI -0.135 0.195 0.107 ± 0.074 0.816 ± 0.135 0.612 ± 0.162 0.587 ± 0.112 # -0.143 ± 0.109
AI -0.154 0.914 0.205 0.121 ± 0.062 0.831 ± 0.297 -0.529 ± 0.233 0.335 ± 0.240 #
YW 0.768 -0.302 -0.203 -0.278 0.322 ± 0.371 0.448 ± 0.128 -0.816 ± 0.132 #
AW 0.964 -0.135 -0.079 -0.077 0.581 0.214 ± 0.222 0.694 ± 0.498 -0.624 ± 0.124
SW 0.531 -0.187 -0.211 -0.209 0.528 0.388 0.186 ± 0.080 0.354 ± 0.128
ST -0.229 -0.008 -0.097 -0.062 -0.035 -0.301 0.128 0.419 ± 0.193
IWI Strain
EW 0.180 ± 0.122 0.411 ± 0.248 0.919 ± 0.547 0.329 ± 0.124 0.592 ± 0.231 0.741 ± 0.126 0.481 ± 0.216 -0.263 ± 0.178
HU 0.549 0.322 ± 0.224 0.585 ± 0.202 0.909 ± 0.301 0.341 ± 0.131 0.874 ± 0.126 0.741 ± 0.123 0.681 ± 0.220
YI 0.068 0.009 0.211 ± 0.113 0.785 ± 0.108 0.709 ± 0.301 0.417 ± 0.118 0.176 ± 0.102 0.244 ± 0.116
AI 0.406 0.883 0.011 0.146 ± 0.027 0.754 ± 0.289 0.429 ± 0.101 -0.836 ± 0.689 0.176 ± 0.102
YW 0.611 0.485 0.012 0.239 0.245 ± 0.209 0.254 ± 0.109 -0.969 ± 0.942 -0.136 ± 0.020
AW 0.892 0.398 0.073 0.346 0.238 0.218 ± 0.236 0.237 ± 0.151 -0.258 ± 0.321
SW 0.294 0.280 0.023 0.203 0.346 -0.034 0.161 ± 0.079 0.336 ± 0.162
ST 0.580 0.501 0.037 0.326 0.648 0.312 0.501 0.351 ± 0.193
IWK Strain
EW 0.255 ± 0.067 0.330 ± 0.138 -0.456 ± 0.155 0.437 ± 0.386 0.591 ± 0.079 0.998 ± 0.001 -0.477 ± 0.180 0.313 ± 0.259
HU -0.005 0.299 ± 0.250 0.290 ± 0.073 0.375 ± 0.096 0.437 ± 0.386 0.998 ± 0.001 # 0.818 ± 0.152
YI -0.064 0.027 # 0.711 ± 0.088 0.752 ± 0.124 0.512 ± 0.314 # #
AI -0.155 0.726 0.447 # -0.045 ± 0.123 -0.404 ± 0.027 # -0.474 ± 0.463
YW 0.023 0.195 0.077 0.165 0.277 ± 0.101 0.013 ± 0.598 -0.324 ± 0.127 -0.667 ± 0.412
AW 0.965 -0.045 -0.074 -0.184 -0.225 0.124 ± 0.036 0.038 ± 0.102 -0.334 ± 0.118
SW 0.054 -0.004 -0.050 -0.019 0.403 -0.128 0.202 ± 0.177 0.318 ± 0.122
ST 0.111 0.031 -0.183 -0.052 0.016 0.053 0.542 0.270 ± 0.129
Control Strain
EW 0.293 ± 0.022 0.298 ± 0.170 0.660 ± 0.418 0.394 ± 0.191 0.339 ± 0.131 0.856 ± 0.101 0.556 ± 0.101 -0.718 ± 0.128
HU 0.132 0.217 ± 0.177 0.298 ± 0.101 0.450 ± 0.214 0.339 ± 0.182 0.839 ± 0.111 0.801 ± 0.447 0.616 ± 0.124
YI 0.154 0.486 0.237 ± 0.186 0.821 ± 0.134 0.650 ± 0.210 0.539 ± 0.106 0.239 ± 0.107 0.201 ± 0.142
AI 0.031 0.842 0.521 0.171 ± 0.136 0.241 ± 0.132 -0.285 ± 0.265 0.512 ± 0.125 0.218 ± 0.110
YW 0.578 -0.279 -0.074 -0.307 0.192 ± 0.136 0.131 ± 0.102 0.828 ± 0.119 #
AW 0.953 0.279 0.219 0.164 0.323 0.219 ± 0.202 0.147 ± 0.134 0.245 ± 0.108
SW 0.546 -0.161 -0.036 -0.159 0.001 0.418 # 0.352 ± 0.223
ST 0.137 -0.032 -0.018 -0.054 0.096 0.116 0.137 0.304 ± 0.301
Heritability estimates are on diagonals; Genetic correlations are in above diagonals and phenotypic correlations are in below diagonals

The reports of higher shell thickness values [13, 15, 16, percent yolk weight and percent albumen weight were
21] in backyard / other poultry could be due to their also reported [23]. The genetic correlation of albumen
higher percentage contribution to egg weight. weight with shell weight was positive in all strains
while it was negative with shell thickness except in
Heritability Estimates: Egg weight was found to be control population. The phenotypic correlation between
moderately heritable as the heritability ranged from these traits was varied. Shell weight was positively
0.180 ± 0.122 to 0.293 ± 0.022, similar to the earlier correlated with shell thickness in all the populations at
reports [6,7,10] in White Leghorns. The heritability genetic, phenotypic and environmental levels. This
estimate of haugh unit ranged from 0.217 ± 0.177 to indicates that genetic or environmental factors
0.322 ± 0.224 across the populations studied, which is affecting shell weight would bring about simultaneous
in agreement with the observations of different earlier change in shell thickness, since both of them constitute
authors [7,8,10,11]. The heritability estimates of the shell strength. High positive genetic and phenotypic
albumen and yolk indices in some populations could correlations (0.792 and 0.610, respectively) between
not be obtained probably because of small population shell percent and shell thickness were also reported
size. Yolk index and albumen index were found to be [23].
low to moderately heritable. Reviewed literature had Conclusion
varied results ranging from 0.01 [17] to 0.70 [7]. The
heritability estimate of yolk weight and albumen Significant genetic group differences were
weight were in the range of 0.097 to 0.721 and 0.124 to observed for various egg quality traits studied. The
0.250, respectively. Available literature on these estimates heritability estimates for different egg quality traits
is very scanty except one report of similar heritability were low to moderate. The association among egg
estimates for these traits [10]. The heritability quality traits was positive in general. Further studies
estimates of shell weight and shell thickness were are required in finding out the association of external
found to be low to highly heritable which ranged from and internal egg quality parameters so as to take
0.161 to 0.419 across different strains, indicating that appropriate breeding plans for producing customer
selection could be applied for the improvement of shell friendly quality eggs.
quality. These findings corroborate with the previous
reports [7, 10,17]. Authors’ contribution
SD, GPM and RC designed and implemented the study.
Correlations: The genetic and phenotypic correlations SD, GPM recorded and analysed the data. SD drafted
of egg weight with egg quality traits were mostly the manuscript. SD, GPM, MM and RC revised the
positive and moderate to high in magnitude while they manuscript. All authors read and approved the final
varied with shell quality parameters. Similar positive manuscript.
correlations of egg weight with other egg quality traits
in White Leghorns were reported [17,23]. As haugh Acknowledgements
unit is a measure of albumen height corrected for egg The first author is thankful to the Sri Venkateswara
weight, the high genetic (0.375 to 0.912) and phenotypic Veterinary University for permitting the study and to
correlations (0.726 to 0.914) with albumen index are the officials and staff of the Project Directorate on
not surprising. The correlations of haugh unit with Poultry, Hyderabad for providing facilities during the
other traits were also positive and moderate to high in study.
magnitude. These findings are in agreement with the
report of very high (0.895) genetic correlation with Competing interests
albumen index and varied correlations with other traits Authors declare that they have no competing interest.
[23]. The genetic correlations of Yolk index with
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