Abstract
General background: Egg traits are crucial indicators in poultry science due to their relevance to hatchability, chick survival, and consumer preferences. Specific background: While various factors influence egg quality, the impact of sexual maturity timing on external egg characteristics in Japanese quail remains underexplored. Knowledge gap: Limited studies have investigated how variations in the onset age of sexual maturity directly affect measurable external egg traits. Aims: This study aimed to assess the effects of early and late sexual maturity on external egg quality in Japanese quail. Results: Using 682 eggs categorized into four sexual maturity classes, we found that the age of sexual maturity significantly influenced egg weight, length, surface area, and volume, while body weight, egg breadth, and shape index remained unaffected. Novelty: The findings establish that earlier sexual maturity is associated with larger eggs, highlighting physiological advantages during early reproductive phases. Implications: These results offer insights for breeding strategies aiming to enhance egg production and quality by selecting optimal maturity ages, thus improving both economic outcomes and biological efficiency in quail production systems.
Highlight :
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The age of sexual maturity significantly affects egg weight, length, surface area, and volume in Japanese quail.
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Delayed maturity results in lower egg mass and size, indicating suboptimal reproductive performance.
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Strong correlations between egg surface area and volume highlight key structural traits for selection programs.
Keywords : Sexual Maturity, Japanese Quail, Egg Traits, Egg Quality, External Characteristics
Introduction
Bird eggs were used before several decades as a model for embryonic development [1], and disease infection [2], because of the importance several attempts were used to understand the yolk, and albumin characteristics in birds [3]. The qualitative characteristics of eggs are affected by several factors, which make the egg suitable for study or not. Therefore, the qualitative characteristics of the egg are divided into external and internal characteristics, which both were studied faithfully by several researchers [4, 5, 6, 7]. The external traits are two (Length, and breadth), which are important to find some related traits equation such as egg shape index (ESI), volume (EV), and egg surface area (ESA) [8, 9]. These traits affected directly on many phenomena like: egg hatchability [10], chick survivor [11], consumer desire [12]. Egg dimensions affected by several traits that play important role, such as hen age [13, 14], oviposition time [15], egg production chain [16], genetic background [17, 18, 19], and nutrition [20, 21].
Due to the development that has arisen in the poultry industry over the past years, the age of sexual maturity of hens has decreased significantly; our study is focus on the affected of the age of sexual maturity on the external egg traits in the Japanese quail.
Materials and Method
The study was conducted in the poultry farm of the Department of Animal Production - College of Agriculture - University of Kirkuk, for the period in (2/4/2023 – 30/7/2023). Six hundred and eighty-two females were used in this experiment at the age of 30 days. When sexual maturity began, the birds were divided into four classes according to the age of first egg production, as follows: the first class from (40-49) days, the second class from (50-59), the third class from (60-69), the fourth class more than 60 days. The females were raised in vertical batteries, as each cage contained one female to facilitate the attribution of the egg to the quail hen. The quail hen was fed on a diet containing 24% protein and 2900 kcal digestible energy. As for water, it was provided freely. When the female reached the ovulation stage, the first egg was weighed with an electronic balance with a sensitivity of (0.01) g. Then the egg dimensions, represented by length and elongation, were taken using an electronic digital caliper vernier with a sensitivity of (0.01). Then the equations below were used to calculate the (ESI), (EV), and (ESA).
Figure 1.
General linear model (GLM) within SPSS program [22] was used to find the effect of age of sexual maturity on the studied traits, and Duncan [23] multiple range test was used to find the differences among the means of the traits.
Result and Discussion
Table 1 presents the descriptive statistics mean values with standard errors (Mean ± S.E.) and coefficients of variation (CV%) of BW, EW, EL, and EB, categorized by four classes of age at sexual maturity. The age at which Japanese quail reached sexual maturity did not significantly affect their body weight (P > 0.05), as indicated by the consistent body weights across all classes. The overall mean body weight was 192.48 ± 0.67 g with a CV of 9.03%. Although class 1, 2, and 3 exhibited slightly varying means (192.96, 192.69, and 189.78 g, respectively), the differences were not statistically significant (P > 0.05), and class 4 showed a relatively lower mean of 182.14 g, with the highest variation (CV = 11.79%). This indicates that, in terms of body mass, early or delayed onset of sexual maturity may not substantially impact growth performance. Conversely, the age of sexual maturity had a statistically significant effect (P < 0.05) on egg weight. Quail that matured earlier (classes 1 to 3) laid heavier eggs compared to those maturing later (class 4). The first egg weight was highest in class 3 (8.62 g), followed by class 2 (8.39 g) and class 1 (8.22 g), while class 4 had significantly lighter eggs (7.20 g). The overall mean egg weight was 8.34 ± 0.05 g with a CV of 15.41%, reflecting notable variability particularly in class 3 (CV = 17.79%). These findings suggest that delayed maturity might be associated with physiological limitations affecting initial egg mass, possibly due to hormonal and reproductive organ development timing. Egg length was also significantly influenced (P < 0.01) by the age at sexual maturity. The longest eggs were recorded in class 3 (29.65 mm), followed by class 2 (29.30 mm) and class 1 (28.95 mm), while class 4 exhibited the shortest eggs (28.67 mm). These differences highlight a potential association between age-related ovarian maturation and structural egg formation. The overall mean egg length was 29.20 ± 0.06 mm with a low CV of 5.29%, suggesting relatively uniform length traits across groups, except for class 4, which showed slightly greater variability (CV = 6.28%). Regarding egg breadth, no statistically significant differences (P > 0.05) were observed among the four age groups. The average egg breadth was 23.24 ± 0.04 mm with a low CV of 4.08%. This suggests that while egg length and weight are sensitive to the age of maturity, egg breadth remains relatively stable across different maturity classes. Our study agreed with the finding of [24], Furthermore, [25] found that the transcriptional modifications of genes linked to fat metabolism and yolk precursor production were directly impacted by age-related hormone shifts. We verify that FSH regulates E2, an activator that causes hepatocytes to undergo functional and histological alterations via the ER-α pathway.
Traits | BW | EW | EL | EB | ||||
---|---|---|---|---|---|---|---|---|
Mean±S.E | CV | Mean±S.E. | CV | Mean±S.E. | CV | Mean±S.E. | CV | |
Overall mean | 192.48±0.67 | 9.03 | 8.34±0.05 | 15.41 | 29.20±0.06 | 5.29 | 23.24±0.04 | 4.08 |
1 =(40 – 49) | 192.96±1.25 a | 9.72 | 8.22±0.08 a | 14.35 | 28.95±0.10 ab | 5.02 | 23.09±0.05 a | 3.38 |
2 =(50 – 59) | 192.69±0.82 a | 8.53 | 8.39±0.07 a | 15.56 | 29.30±0.08 ab | 5.30 | 23.29±0.05 a | 4.32 |
3 =(60 - 69) | 189.78±2.63 a | 9.30 | 8.62±0.23 a | 17.79 | 29.65±0.25 a | 5.75 | 23.51±0.15 a | 4.30 |
4 =(60 <) | 182.14±8.12 a | 11.79 | 7.20±0.31 b | 11.22 | 28.67±0.68 b | 6.28 | 23.02±0.49 a | 5.61 |
Sig. | N.S. | * | ** | N.S. |
Means that haven’t a common letter within each column differ significantly (P<0.05)
Table 2 illustrates the descriptive analysis of egg shape index (ESI), egg surface area (ESA), and egg volume (EV). No significant differences (P>0.05) were found in the egg shape index across the four classes, which implies that the relative proportions of egg length to breadth remain consistent regardless of the maturity age. The overall ESI was 79.68 ± 0.15 with a CV of 4.94%. The ESI ranged narrowly from 79.43 to 80.75, suggesting a genetic or physiological stability of egg shape regardless of maturity onset. Significant differences (P < 0.01) were observed in egg surface area among the age groups. Class 3 had the highest ESA (2109.69 mm²), while class 4 had the lowest (2003.74 mm²). Intermediate values were observed for classes 1 and 2. These variations may be linked to enhanced follicular development and shell gland function in birds maturing at optimal periods. The overall ESA was 2054.31 ± 6.05 mm² with a moderate CV of 7.70%. Egg volume exhibited the highest variability among all traits (overall CV = 11.09%), with class 3 again recording the highest value (9278.77 mm³), and class 4 the lowest (8632.07 mm³). These significant differences (P < 0.001) further reinforce that early to mid sexual maturity yields better volumetric egg characteristics compared to delayed maturation. Given the role of yolk deposition and shell secretion in determining volume, hormonal cues at sexual onset might play a major role. Our results align with [26], who postulated that sexual maturity timing directly impacts egg formation parameters, and that equations incorporating maturity age can predict traits like egg shape index throughout the early laying period. Our study agreed with [26], who suggest that an equation including the age at sexual maturity and the age at laying egg could be used to predict the egg shape index, which was influenced by the age at sexual maturity and stayed somewhat constant during the first stage of the laying period.
Traits | ESI | ESA | EV | |||
---|---|---|---|---|---|---|
Mean±S.E. | CV | Mean±S.E. | CV | Mean±S.E. | CV | |
Overall mean | 79.68±0.15 | 4.94 | 2054.31±6.05 | 7.70 | 8921.14±37.90 | 11.09 |
1 =(40 – 49) | 79.91±0.25 a | 4.79 | 2023.91±9.19 ab | 6.84 | 8726.08±56.46 ab | 9.75 |
2 =(50 – 59) | 79.56±0.20 a | 5.09 | 2066.13±8.03 ab | 7.81 | 8996.10±50.43 ab | 11.25 |
3 =(60 - 69) | 79.43±0.51 a | 4.34 | 2109.69±27.73 a | 8.82 | 9278.77±177.14 a | 12.81 |
4 =(60 <) | 80.75±1.29 a | 4.22 | 2003.74±83.66 b | 11.05 | 8632.07±537.53 b | 16.48 |
Sig. | N.S. | ** | *** |
Means that haven’t a common letter within each column differ significantly (P<0.05)
The Pearson correlation coefficients for the analyzed traits are provided in Table 3. The correlations ranged from weak negative (-0.267) to very strong positive (0.991), reflecting varying degrees of association between traits. Age of sexual maturity (ASM) showed no significant correlation with BW, EW, or ESI (-0.074, 0.057, and -0.045, respectively), indicating that these traits are relatively independent of maturity timing. However, ASM showed significant but weak positive correlations with EL (0.114), EB (0.105), ESA (0.132), and EV (0.136), suggesting that delayed maturity slightly increases egg dimensions and volume. A moderate positive correlation (0.255, P < 0.001) was found between BW and EW, indicating that heavier birds tend to lay heavier eggs. Strong positive correlations were observed between EW and EL (0.588), EB (0.427), ESA (0.597), and EV (0.582), confirming the interdependency among egg traits. Egg length and breadth were positively correlated (r = 0.505), reflecting structural consistency in egg formation. Interestingly, ESI exhibited a strong negative correlation with EL (-0.672), a moderate positive correlation with EB (0.281), and a moderate negative correlation with ESA (-0.244) and EV (-0.122), revealing that more elongated eggs (higher length relative to breadth) yield lower ESI and may be linked to decreased surface area and volume. The strongest correlation (0.991, P < 0.001) was observed between ESA and EV, as both traits are derived from a combination of EL and EB. This tight association emphasizes the functional relevance of surface-to-volume ratios in egg physiology and possibly in hatchability and gas exchange efficiency during incubation. These results are consistent with previous findings [27], who reported similar relationships among external and internal egg traits in white quail. Understanding these correlations is crucial for improving selection programs, predicting reproductive efficiency, and optimizing breeding strategies for enhanced production. Our findings agreed with [27], Some trace minerals, notably selenium and zinc, are vital for maintaining animal health. They play key roles in hormonal and enzymatic regulation, enhance antioxidant defense mechanisms, and support metabolic and immune system functions. However, their biological effects are dose-dependent, as they may exhibit synergistic or antagonistic interactions that can lead to either beneficial or toxic outcomes [28,29], who study the correlations between the external and internal traits by using white quail, and found it is useful for understanding the production, improving the hatchability, and fertility characteristics, moreover understanding the correlations among the traits.
Traits | ASM | BW | EW | EL | EB | ESI | ESA | EV |
---|---|---|---|---|---|---|---|---|
ASM | 1 | |||||||
BW | - 0.074 NS | 1 | ||||||
EW | 0.057 NS | 0.255 *** | 1 | |||||
EL | 0.114 ** | 0.052 NS | 0.588 *** | 1 | ||||
EB | 0.105 ** | 0.106 ** | 0.427 *** | 0.505 *** | 1 | |||
ESI | -0.045 NS | 0.034 NS | - 0.267 *** | - 0.672 *** | 0.281 *** | 1 | ||
ESA | 0.132 ** | 0.097 * | 0.597 *** | 0.875 *** | 0.857 *** | - 0.244 *** | 1 | |
EV | 0.136 *** | 0.111 ** | 0.582 *** | 0.806 *** | 0.912 *** | - 0.122 ** | 0.991 *** | 1 |
Means that haven’t a common letter within each column differ significantly (P<0.05)
Conclusion
It can be concluded that the age of sexual maturity effected on the external egg traits (weight, length, surface area, and volume), and its correlated significantly with (egg length, breadth, surface area, and volume). These finding also will be useful for increase production of big eggs, by choosing suitable age of sexual maturity.
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