Hatching Characteristics and Growth Performance of Eggs with Different Egg Shapes

This study was carried out to identify the effect of the egg shape index on the hatchability, performance, and carcass yield of Japanese quails (Coturnix coturnix Japonica). Eggs were incubated in three groups, according to three different egg shape index (SI) values (Group SI-I: 70.00-73.85%, Group SI-II: 73.86-77.71% and Group SI-III: 77.7281.57%). Unhatched eggs weight loss (HEWL) was correlated with the egg shape index groups (SI-I: 18.51%, SI-II: 13.34% and SI-III: 13.96%; p<0.01), but not with the initial unhatched egg weight (HIEW), hatched egg weight (HEW), or eggshell weight of unhatched eggs (HSW) (p>0.05). The live weight of female and male chicks hatched from SII, SI-II, and SI-III egg shape index groups were compared at weeks 4 (female/male: 249.12/237.77, 244.69/236.35, and 241.52/229.72 g, respectively) and 5 (female/male:304.89/272.42, 295.76/274.34, and 285.42/271.29 g, respectively), and the results showed that females were heavier than males (p<0.05; p<0.01; p<0.001, respectively).The effect of egg shape index on slaughter weight (p<0.05), left leg weight (p<0.05), liver weight (p<0.01) and liver rate (p<0.01) was significant. Females were heavier at slaughter than males in the egg shape index groups SI-I (p<0.05), SI-II (p<0.05), and SI-III (p>0.05) (female/male: 296.87/283.80, 287.95/278.00 and 283.86/278.10 g, respectively). Males presented higher carcass yield in SI-I (p>0.05), SI-II (p<0.01) and SI-III (p<0.05) (female/male: 74.40/75.92, 74.50/76.44 and 74.80/76.42%) groups than females. Egg shape index had no effect on initial egg weight (IEW), shell blunt end weight (SBW), chick weight, shank length, growth performance or carcass traits, but egg shape indexwas correlated with egg length, egg width, and hatchability of fertile eggs (p<0.05).


INTRODUCTION
Several studies have been conducted to investigate the effect of egg quality characteristics on hatching results (Salad Uddin et al., 1994;Narushin et al., 2002;Ghodsi et al., 2010;Lotfi et al., 2011;King'ori, 2011;Peruzzi et al., 2012;Dudusola, 2013).Several characteristics, including egg weight, eggshell thickness, eggshell pore characteristics, egg shape index, and the consistency of the egg content bear importance for embryonic development and the achievement of satisfactory hatching results.Eggs presenting average physical characteristics are able to meet most of the embryo requirements throughout its development (Narushin & Romanov, 2002).
Egg shape depends on the anatomical structure of the hen, particularly of the oviduct, internal organ distribution, and shape of the pelvic bones (King'ori, 2012).The egg shape index is the ratio between maximum egg width with maximum egg length (Narushin & Romanov, 2002), and represents a numeric value of egg shape.
Many researchers (Farooq et al., 2001;Harun et al., 2001;Narushin & Romanov, 2002;King'ori, 2011) have suggested that the hatching performance achieved when normal-shaped eggs are laid is greater than that achieved with abnormally-shaped eggs.This is attributed to the change in the axial location of the embryo in normal-shaped eggs during the advanced stages of embryonic development (Ainsworth et al., 2010).In chicken eggs, on day 14 of the incubation period, the head of the embryo moves towards the blunt end of the egg and the embryo acquires a position parallel to the egg axis.
The average egg shape index values of Japanese quail eggs (Coturnix coturnix japonica) were determined by Gonzalez (1995) as 78.12%, by Esen & Ozcelik (2002) as 80%, by Ozcelik, (2002) as 79.57%, by Aktan (2004) as 78.28%, by Sezer (2007)  The present study aimed at evaluating the effects of egg shape index on hatching parameters, growth performance, and carcass characteristics of Japanese quails.

Assessment of Hatching Parameters
Eggs were collected during a three-day-period on a private farm.After transference to the incubation unit, the eggs were examined macroscopically.By means of visual inspection, cracked and broken eggs were excluded from the study material.A total of 512 eggs were obtained from 16-wk-old Japanese quails (Coturnix coturnix japonica), which reached 95% egg production.
The hatching eggs were individually numbered and weighed using a precision scale with an accuracy of 0.01 g.Egg length and width were measured using a caliper, and used for the calculation of the egg shape index (SI = width/length x 100), according to Panda (1996).Eggs were classified according to egg shape index values, and the class interval of the data was determined as described below.
Class interval = [(highest value-lowest value) / desired number of classes] Using the class interval calculated according to the formula given above, eggs were allocated into three groups according to their egg shape index values, namely Group SI-I (egg shape index: 70.00-73.85%),Group SI-II (egg shape index: 73.86-77.71%),and Group SI-III (egg shape index: 77.72-81.57%).
The numbers of eggs placed into the setter from Groups SI-I, SI-II, and SI-III were 148, 252, and 112, respectively.After egg shape index determination, eggs from each treatment group were placed randomly into trays in triple layers.Temperature and relative humidity (RH) were set at 37.5 o C and 55-60%, respectively, during the first 15 days of the incubation period and at 37.2 o C and 65-70%, respectively, during the hatching period.Prior to transference to the hatcher, all eggs belonging to each egg shape index group were labeled and placed on hatching trays.
The eggs that did not hatch at the end of the incubation period were broken out for macroscopic inspection to determine early embryonic mortality (between days 0-7 of the incubation period), intermediate embryonic mortality (between days 8-14 of the incubation period), or late embryonic mortality (between days 15-17 of the incubation period and at time of pipping) (Taha, 2011).Hatching results were calculated according to the formulae given below.
Fertility rate (FR,%) = (number of fertile eggs / number of set eggs) x 100 Hatchability of set eggs (HR,%) = (number of hatched chicks / number of set eggs) x 100 Hatchability of fertile eggs (HRF%) = (number of hatched chicks / number of fertile eggs) x 100 Rate of early embryonic mortality (EEM, %) = (number of early embryonic mortalities/ total number of fertile eggs) x 100

Hatching Characteristics and Growth Performance of Eggs with Different Egg Shapes
Rate of middle embryonic mortality (MEM,%) = (number of mid-embryonic mortalities / total number of fertile eggs) x 100 Rate of late embryonic mortality (LEM,%) = (number of late embryonic mortalities / total number of fertile eggs) x 100

Growth Performance
After hatching, each chick that hatched in all egg shape index groups was identified using a wing bands, weighed, and the right and left shank lengths were measured.Growth performance was determined using 70, 71, and 66 chicks from Groups SI-I (70.00-73.85%),SI-II (73.86-77.71%)and SI-III (77.72-81.57%),respectively, distributed in four replicates each.
The quails were fed a commercial broiler grower feed containing 22% crude protein and 3000 kcal energy/kg for five weeks.Feed and water were provided ad libitum.Quails were individually weighed, using a precision balance with 0.01 g accuracy on a weekly basis for the determination of weekly body weight.Quails were sexed at three weeks of age, according to the appearance of the breast feathers (feather sexing).
At the end of the five weeks of the rearing period, 32 birds per group (16 males and 16 females), totaling 96 birds, were sacrificed to determine carcass weight (with and without internal organs), as well as breast, right and left legs, heart, liver, empty gizzard, and intestine weights.These data were used to calculate the following parameters, according to the formulae given below.

Data Assessment and Statistical Analysis
Hatching parameter data of the egg shape index groups were analyzed using the Chi-square test.Data pertaining to all of the other hatching characteristics investigated were analyzed by one-way analysis of variance (ANOVA).Duncan's multiple comparison test was used to compare means.Within each group, carcass data of male and female animals were analyzed using the t-test.Statistical analyses were performed using the SPSS software package (Version 12).

Hatching Parameters
Egg weight, length and width mean values are presented in Table 1.The egg length and egg width differences among egg shape index groups were statistically significant (p<0.001).Initial egg weights were not different among between the egg shape index groups.
The parameters of the eggs that did not hatch at the end of the incubation period are summarized in Table 2. Egg weight was not statistically different (p<0.05)among the egg shape index groups.Egg weight loss during the incubation period was greater in Group SI-I (18.51%) than the other groups (p<0.01).Hatched eggs and chick parameter results are presented in Table 3, according to the egg shape index groups.Chick hatching weight and shank length, and egg and eggshell weights were not different among the egg shape index groups (p>0.05).The effects of egg shape index on hatching parameters are presented in Table 4.The egg shape index affected the hatchability of fertile eggs (p<0.01),hatchability rate (p<0.01), and early embryonic mortality rate (p<0.05),but had no effect on intermediate and late embryonic mortality (p> 0.05).

Growth Performance
The growth performance results of males and females are shown in Table 5, according to the egg shape index groups.The effect of the egg shape index on weekly growth performance was not significant (p>0.05).
Shank length, hatching weight, and body weight of males and females, according toegg shape index groups, are summarized in Table 6.

Hatching Characteristics and Growth Performance of Eggs with Different Egg Shapes
The body weight difference between females and males was not statistically different during the first three weeks in any of the egg shape index groups; however, in weeks 4 and 5, females were significantly heavier than males (p>0.05,p<0.01, p<0.001).
The results of the statistical analysis of slaughter weight and carcass traits are given in Table 7.
Slaughter weight, left leg weight, liver weight and liver percentage were significantly different among the egg shape index groups (p<0.05,p<0.01).
Table 6 -Shank length, hatching weight, and body weight of male and female Japanese quails during weeks 1-5 according to the egg shape index groups.The slaughter and carcass trait differences observed between males and females in the different egg shape index groups are presented in Table 8.In Groups SI-I and SI-II, the slaughter, liver, gizzard, and intestine weights of the females were significantly higher compared with males (p<0.05,p<0.01, p<0.001).In Group SI-III, only the gizzard and intestine weights were significantly higher in females compared with males Hatching Characteristics and Growth Performance of Eggs with Different Egg Shapes (p<0.01).Although carcass yield was not different between males and females in Group SI-I (p>0.05), the differences between sexes was statistically significant in Groups SI-II and SI-III (p<0.05).

DISCUSSION
In the present study, no effect of the egg shape index was detected on several parameters, including hatching weight, chick shank length and eggshell weight.This result is consistent with previous research reporting that the egg shape index does not affect hatchling weight (Saatci et al., 2005;Yilmaz & Caglayan, 2008;Lotfi et al., 2011).
However, the results demonstrated that egg shape index influences both hatchability and carcass yield, in contrast to previous research suggesting that the egg shape index does not affect hatchability (Baspinar et al., 1997;Kul & Seker, 2004;Turkyilmaz et al., 2005;Sari et al., 2010;Lotfi et al., 2011;Taha, 2011).Furthermore, the results showing that egg shape index affects early embryonic death rate do not agree with previous studies suggesting that egg shape index does not have any effect on this parameter (Copur et al., 2010;Sari et al., 2010).These differences may be attributed to different classifications of egg shape indices used among studies.In the present study, the hatchability of fertile eggs was lower in Group SI-I, in comparison with the other egg shape index groups, due to higher early embryonic death.This is attributed to the 18.51% egg weight loss observed during the incubation period, which is above the optimal egg weight loss.The egg weight loss rates in groups SI-II and SI-III were 13.34% and 13.96%, respectively, and were close to the optimal rate.
The effect of the egg shape index on the growth performance of Japanese quails during the fiveweek rearing period was not statistically significant.This result was in agreement with previous research (Copur et al., 2010).In the present study, within each egg shape index group, males and females presented significantly different body weights, as measured during the rearing period.
Relative to slaughter weight and carcass traits, only the left leg and liver weights were different among the egg shape index groups (p<0.05,p<0.01).The egg shape index did not have any effect on either carcass weight or on the other carcass parameters investigated.The lack of an effect of the egg shape index on leg length and on slaughter and carcass weights may be interpreted as a consequence of the lack of effect on hatchling weight.

CONCLUSION
Egg shape index affects the hatchability of set eggs, hatchability of fertile eggs, and early embryonic mortality.There is no influence of egg shape index on embryonic mortalities (middle and late), chick weight, and body weight during weeks.

Table 2 -
Parameters of the unhatched eggs according to egg shape index.

Table 3 -
Hatched egg and chick parameter results according to egg shape index groups.

Table 4 -
The effect of egg shape index on hatching parameters (%).
a, b: means followed by different superscripts in the same column are statistically different (p<0.05;p<0.01);FR: fertility rate, HRF: hatchability rate of fertile eggs, HR: hatchability of set eggs, EEM: early embryonic mortality rate, IEM: intermediate embryonic mortality rate, LEM: late embryonic mortality rate.

Table 5 -
Effects of egg shape index on body weight during weeks 1-5.
Slaughter weight and carcass traits of Japanese quails according to egg shape index groups (n=32).Differences between the mean values shown with different superscripts in the same column are statistically significant (p<0.05,p<0.01).

Table 8 -
Carcass traits of Japanese quails according to sex and egg shape index groups.