© The Authors, 2026, Published by the Universidad del Zulia*Corresponding author: arzourne@gmail.com
Keywords:
Laying phase
Egg quality
PCA
Correlation
Age-related variation and multivariate analysis of internal and external egg quality traits in
ISA Brown hens
Variación relacionada con la edad y análisis multivariado de las características de calidad interna y
externa del huevo en gallinas ISA Brown
Variação relacionada à idade e análise multivariada de características internas e externas de qualidade
dos ovos em galinhas ISA Brown
Douaa Amireche
Nedjoua Arzour-Lakehal*
Asma Nour El Houda Belagoune
Rev. Fac. Agron. (LUZ). 2026, 43(1): e264303
ISSN 2477-9407
DOI: https://doi.org/10.47280/RevFacAgron(LUZ).v43.n1.III
Animal production
Associate editor: Dra. Rosa Razz
University of Zulia, Faculty of Agronomy
Bolivarian Republic of Venezuela
PADESCA Research Laboratory, University of Constantine
1, Institute of Veterinary Sciences El-Khroub, Constantine,
Algeria.
Received: 09-09-2025
Accepted: 28-11-2025
Published: 28-12-2025
Abstract
This study evaluated age-related variations in internal and
external egg quality traits in ISA Brown hens raised under semi-arid
Algerian conditions. Hens were assessed at two production stages:
5,977 at peak lay (25-30 weeks) and 5,430 at late lay (75-80 weeks).
A total of 360 eggs were collected (180 per stage), at a rate of 30
eggs per week, randomly selected at the beginning of each week.
Egg weight, shell thickness, shape index, yolk and albumen indices,
Haugh units, and yolk color were measured. A one-way analysis
of variance (ANOVA) was used to detect age-related dierences,
Pearson correlation to examine interrelationships among traits,
and principal component analysis (PCA) to identify general age-
related patterns. Signicant dierences were observed between the
two laying stages. Peak-lay eggs showed superior internal quality,
particularly in albumen height and Haugh units, whereas late-lay
eggs exhibited greater mass but reduced albumen integrity. Shell
thickness and yolk shape remained relatively stable. Correlation
analysis revealed stronger trait associations during peak lay, which
weakened with advancing age. PCA showed contrasting age-related
trends between egg size and internal quality: egg size increased
with age, whereas internal quality declined, while shell- and yolk-
related traits remained relatively constant. The ndings of this study
apply to hens up to 80 weeks of age. Further studies covering longer
production cycles are recommended to determine whether these
patterns persist beyond this period.
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2026, 43(1): e264303 January-March. ISSN 2477-9409.
2-6 |
Resumen
Este estudio evaluó las variaciones relacionadas con la edad en los
parámetros internos y externos de la calidad del huevo en gallinas ISA
Brown, criadas en condiciones semiáridas de Argelia. Las gallinas
fueron evaluadas en dos etapas de producción: 5.977 en el pico de
puesta (25-30 semanas) y 5.430 en la fase nal (75-80 semanas).
Se recolectaron 360 huevos en total (180 por etapa), a razón de 30
huevos por semana, seleccionados al azar al inicio de cada semana.
Se midieron el peso del huevo, el grosor de la cáscara, el índice de
forma, los índices de yema y albúmina, las unidades Haugh y el color
de la yema. Se utilizó un análisis de varianza de una vía (ANOVA)
para detectar diferencias relacionadas con la edad, la correlación de
Pearson para examinar las interrelaciones entre los rasgos y un análisis
de componentes principales (ACP) para identicar patrones generales
asociados con la edad. Se observaron diferencias signicativas entre
las dos etapas de puesta. Los huevos del pico de puesta mostraron
una mejor calidad interna, especialmente en la altura de la albúmina y
unidades Haugh, mientras que, los huevos de la fase nal presentaron
mayor masa pero menor integridad de albúmina. El grosor de la
cáscara y la forma de la yema se mantuvieron relativamente estables.
El análisis de correlación reveló asociaciones más fuertes entre los
rasgos durante el pico de puesta, las cuales se debilitaron con el avance
de la edad. El ACP mostró tendencias contrastantes relacionadas con
la edad entre el tamaño del huevo y la calidad interna: el tamaño
del huevo aumentó con la edad, mientras que la calidad interna
disminuyó, mientras que los rasgos relacionados con la cáscara y la
yema permanecieron relativamente constantes. Los resultados de éste
estudio son aplicables a gallinas de hasta 80 semanas de edad. Se
recomiendan estudios adicionales que abarquen ciclos de producción
más prolongados paraedeterminar si estos patrones se mantienen más
allá de este período.
Palabras clave: fase de puesta, calidad del huevo, ACP, correlación
Resumo
Este estudo avaliou variações relacionadas à idade nos parâmetros
internos e externos da qualidade dos ovos de galinhas ISA Brown
criadas em condições semiáridas na Argélia. As aves foram avaliadas
em duas etapas produtivas: 5.977 no pico de postura (25-30 semanas)
e 5.430 na fase nal (75-80 semanas). Um total de 360 ovos foi
coletado (180 por etapa), à razão de 30 ovos por semana, selecionados
ao acaso no início de cada semana. Foram medidos o peso do ovo,
a espessura da casca, o índice de forma, os índices de gema e
albúmen, a unidade Haugh e a coloração da gema. Utilizou-se uma
análise de variância de uma via (ANOVA) para detectar diferenças
relacionadas à idade, correlação de Pearson para examinar inter-
relações entre os traços e análise de componentes principais (PCA)
para identicar padrões gerais associados à idade. Foram observadas
diferenças signicativas entre as duas etapas de postura. Os ovos do
pico apresentaram melhor qualidade interna, especialmente na altura
do albúmen e na unidades Haugh, enquanto os ovos da fase nal
apresentaram maior massa, porém menor integridade do albúmen. A
espessura da casca e o formato da gema permaneceram relativamente
estáveis. A análise de correlação revelou associações mais fortes entre
os traços durante o pico de postura, que enfraqueceram com o avanço
da idade. A PCA mostrou tendências contrastantes relacionadas à
idade entre o tamanho do ovo e a qualidade interna: o tamanho do
ovo aumentou com a idade, enquanto a qualidade interna diminuiu,
enquanto os traços relacionados à casca e à gema permaneceram
relativamente constantes. Os resultados deste estudo são aplicáveis
a galinhas até 80 semanas de idade. Estudos adicionais que incluam
ciclos produtivos mais longos são recomendados para vericar se
esses padrões persistem além desse período.
Palavras-chave: fase de postura, qualidade dos ovos, PCA,
correlação.
Introduction
The poultry sector plays a vital role in the national economy and
global food security by eciently supplying aordable and high-
quality animal protein to meet rising consumer demand. Among its
products, eggs stand out for their rich nutritional prole, providing
highly digestible proteins, balanced amino acids, and essential
vitamins and minerals. Their easy storage, transport, and aordability
make eggs a dietary staple across diverse populations. Accordingly,
egg quality is a critical factor inuencing market value, transport and
packaging, and consumer satisfaction (Ulbad and Andre, 2024).
Egg quality is typically assessed through both external
characteristics, such as shell strength, thickness, weight, and shape
index, and internal traits, including albumen and yolk weight and
height, Haugh unit, and yolk color. These traits are interconnected
and inuenced by numerous factors, including genetics, diet, housing,
environmental conditions, and particularly hen’s age (Zita et al.,
2009; Silversides and Scott, 2001; Duman et al., 2016).
As commercial production systems evolve, laying cycles have
been gradually extended from the traditional 72 weeks to 80 weeks
or beyond (Liu et al., 2018). This shift has prompted renewed interest
in maintaining egg quality throughout prolonged production cycles
(Arulnathan et al., 2024; Molnár et al., 2016) However, age-related
changes—such as increased egg size, decline in albumen freshness, and
reduced shell quality pose challenges for sustainability and economic
eciency (Şekeroğlu et al., 2024; Biesiada-Drzazga et al., 2022).
Isa Brown hens, a leading commercial layer strain, exhibit
notable changes in egg quality as they age. Eggs produced at peak lay
typically display optimal internal traits, whereas those laid later tend
to be heavier but may exhibit diminished freshness and shell integrity
(Kraus and Zita, 2019; Kim et al., 2014). Despite these known trends,
egg quality dynamics and interaction between internal and external
factors throughout the laying phases under local conditions remain
poorly documented.
This study aimed to evaluate age-related variation in internal
and external egg quality traits in ISA Brown hens and to examine
the relationships among traits using correlation analysis and principal
component analysis (PCA).
Material and methods
Study location and housing conditions
The study was conducted at the government experimental farm
of Baaraouia, Constantine, Algeria. Laying hens were housed in
conventional cages, with four birds per cage, ensuring sucient space
per animal. Environmental conditions were maintained at 21-24 °C,
with a 16-hour light and 8-hour dark photoperiod. The ock was
managed under strict sanitary protocols, including routine cleaning,
medication schedules, and vaccination programs. Hens had ad libitum
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Amireche et al. Rev. Fac. Agron. (LUZ). 2026, 43(1): e264303
3-6 |
that shell deposition continued, but it was insucient to match the
higher metabolic demand of larger eggs, a common phenomenon in
extended laying cycles. Contrary to several reports of age-related
thinning (Duman et al., 2016), shell thickness remained remarkably
consistent (0.39 vs. 0.38 mm; p= 0.49), supporting observations by
Roberts et al. (2013), that shell deposition may stabilize in older
layers under optimized conditions. Arulnathan et al. (2024) reported
a value above 0.3 mm in all reviewed studies, which supports shell
thickness quality resilience among extended lay cycles.
Table 1. External and internal egg quality traits (Mean ± SD) of
ISA Brown hens at Peak (25–30 weeks) and late (75–80
weeks) production phase.
Trait
25-30 W
Mean ± SD
75-80 W
Mean ± SD
P value
Egg weight (g) 60.39 ± 4.01 64.19 ± 5.72 <0.001
Egg length mm 55.49 ± 1,66 58.67 ± 2.68 <0.001
Egg width mm 43.78 ± 1.47 44.41 ± 1.81 <0.001
Egg surf area cm
2
77.63 ± 4.39 83.54 ± 6.39 <0.001
Shape Index (%) 78.94 ± 2.71 75.79 ± 3.27 <0.001
Shell weight 6.05 ± 0.52 6.20 ± 0.67 0.02
Shell Ratio (%) 10.04 ± 0.74 9.69 ± 1.05 <0.001
Shell thickness 0.39 ± 0.04 0.38 ± 0.06 0.49
Yolk weight 13.98 ± 1.09 17.01 ± 2.18 <0.001
Yolk height 14.45 ± 1.05 15.42 ±1.06 <0.001
Yolk ratio 23.20 ± 1.7 26.6 ± 3.4 <0.001
Yolk index 38.09 ± 3.02 37.91 ± 3.63 0.612
Yolk colour 9.39 ± 1.02 7.78±0.83 <0.001
Albumen weight 40.34 ± 3.34 40.98 ± 5.13 0.165
Albumen height 9.26 ± 1.65 7.22 ± 1.6 <0.001
Albumen ratio 66.75 ± 1.86 63.70 ± 3.74 <0.001
Albumen index 12.50 ± 2.9 8.49 ± 2.62 <0.001
Haugh unit 95.18 ± 7.99 82.72 ± 10.52 <0.001
Album/yolk ratio 2.89 ± 0.29 2.44 ± 0.42 0.065
Yolk-related traits increased with age, as both yolk weight and yolk
height rose signicantly (p<0.001), while the yolk index remained
stable and the yolk ratio increased (Şekeroğlu et al., 2024; Roberts et
al., 2013; Kraus and Zita, 2019), indicating that yolk morphology is
preserved despite volumetric changes. However, yolk color declined
(p<0.001), possibly due to reduced carotenoid dietary or absorption
in aging hens (Abanikannda and Leigh, 2012; Marzec et al., 2018).
In contrast, albumen quality declined. Albumen height, index,
and ratio all decreased (p<0.001), though albumen weight remained
unchanged. The Haugh unit dropped from 95.18 to 82.72 (p<0.001),
conrming internal degradation with age (Roberts et al., 2013).
Nonetheless, values remained above the commercial acceptability
suggesting maintained quality under controlled conditions.
Phenotypic correlations of external and internal traits
Phenotypic correlations during peak production phase (25-30
weeks)
Internally, yolk weight was positively correlated with yolk height
and yolk ratio (p<0.001), indicating that heavier yolks were more
voluminous and elevated. A low correlation was reported between
yolk weight and albumen weight (r = 0.236, p<0.01), while albumen
access to clean water and were fed a commercial diet (120 g.hen
-1
.
day
-1
) throughout the laying period until culling at 80 weeks of age.
The diet used throughout the laying period was analysed.
Between 25 and 30 weeks of age, hens received a diet containing
2914.7 kcal.kg
-1
of metabolizable energy, 16.3 % of crude protein,
4.00 % of calcium, and of 0.42 % phosphorus. During the late laying
phase (75 to 80 weeks of age), the diet contained 2793.8 kcal.kg
-1
of
metabolizable energy, 14.35 % of crude protein, 3.5 % of calcium,
and 0.36 % of phosphorus.
Egg Collection and Sampling
A total of 360 eggs were collected across the two laying stages
(180 eggs per stage). Each week, 30 eggs were sampled. The ock
consisted of 6,000 ISA Brown hens, of which 5,977 were in peak lay
(25-30 weeks) and 5,430 were in late lay (75-80 weeks). The poultry
house comprised ve battery rows; each week, an equal number of
eggs were randomly selected from dierent positions within each
row, all eggs were individually numbered, weighed, and analysed on
the day of the collection to assess both internal and external traits.
Egg quality measurements and calculations
Egg weight, shell weight, and yolk weight were measured using a
precision digital scale. Albumen weight was calculated by subtracting
yolk and shell weights from total egg weight. Morphometric parameters
including yolk height and diameter, albumen height, egg width and
length, and shell thickness (at the equator, blunt, and pointed ends)
were recorded with a digital caliper. Yolk color was assessed using the
DSM Roche Yolk Color Fan, measurement were used in equations to
calculate the egg quality traits following established studies (Şekeroğlu
et al., 2024; Biesiada-Drzazga et al., 2022).
• Shape Index (%) = (Egg Width / Egg Length) x100
• Yolk Index = Yolk Height / Yolk Diameter
• Albumen index= (albumen height/ (albumen length
+albumen width /2)) x 100
• Yolk (albumen) Ratio (%) = (Yolk (albumen) Weight / Egg
Weight) x100
• Yolk/Albumen Ratio = Yolk Weight / Albumen Weight
• Haugh Units = 100 × log (AH + 7.57 − 1.7 x EW^0.37),
where AH = albumen height (mm), EW = egg weight (g)
Statistical Analysis
Data analysis was performed using PASW Statistics 18 (SPSS Inc,
2010), t test and Pearson’s correlation coecients were computed to
assess trait distributions and interrelationships. Multivariate structure
was explored with Principal Component Analysis (PCA) to explore
internal and external egg quality relationships across laying phases.
Results and discussion
External and internal egg quality traits: Age-related changes
The descriptive statistics of egg quality traits (Table 1)
demonstrated a progressive increase in egg weight across the
production cycle, rising from 60.39 g at peak to 64.19 g at 80 weeks
(p<0.001), consistent with previous reports (Roberts et al., 2013;
ISA Brown, 2016), and accompanied by a corresponding rise in egg
surface area due to greater egg length and width, in agreement with
(Abanikannda and Leigh, 2012). Conversely, the shape index declined
from 78.94 % to 75.79 % (p<0.001), indicating more elongated eggs
consistent with Abanikannda and Leigh (2012). While the values
remained commercially acceptable, this trend may aect packaging
and handling eciency (Duman et al., 2016). Shell weight increased
slightly (p = 0.02), but the shell ratio decreased (p<0.001), suggesting
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2026, 43(1): e264303 January-March. ISSN 2477-9409.
4-6 |
weight showed a positive relationship with yolk height (p<0.05),
reinforcing its association with overall egg mass, in agreement
with Olawumi and Ogunlade (2007). Albumen ratio was negatively
correlated with yolk ratio and weight and positively with albumen
weight (p<0.001), this inverse volumetric relation is consistent with
the result of Vekić et al. (2022).
Externally, egg weight was moderately associated with shell
weight (r = 0.540), in line with Rotimi et al. (2022) and Adeoye et
al. (2022). Shell weight also correlated with shell ratio (r = 0.674),
but correlation of shell ratio declined with egg weight (r = –0.256),
indicating thinner shells in larger eggs—an issue noted in commercial
ocks (Mitrović et al., 2010). Shell thickness was positively
correlated with shell weight and ratio (r = 0.284 and 0.305), but not
with egg weight (r = 0.025), suggesting independent regulation of
shell deposition, in accordance with Ukwu et al. (2017). Shape index
was not signicantly correlated with other traits, consistent with Vekić
et al. (2022) rearming its role as an independent morphological
descriptor.
Across internal–external relationships, egg weight strongly
predicted albumen weight (r = 0.891), while its association with yolk
weight was moderate (r = 0.494), conrming ndings of Olawumi and
Ogunlade (2007), and Vekić et al. (2022). Albumen ratio increased
with egg weight, indicating albumen dominance in larger eggs.
Freshness traits like albumen index and Haugh unit were weakly
linked to shell characteristics, consistent with Vekić et al. (2022), and
showing their independence (Table 2).
Phenotypic correlations during late production phase (75-80
weeks)
During late lay, yolk weight maintained a strong positive
correlation with yolk ratio (r = 0.762, p<0.001) and strong negative
correlation with albumen ratio (r = –0.668). A weak but signicant
negative association with Haugh unit (r = –0.158, p<0.05) suggests
that greater yolk mass may compromise albumen freshness in older
hens. Still, yolk height remained positively correlated with yolk weight
(r = 0.239) and albumen weight (r = 0.337), indicating preserved
coordination among internal traits. Albumen weight showed a negative
correlation with yolk ratio (r = –0.680), consistent with internal
balancing mechanisms observed previously (Inca et al., 2020).
Table 2. Pearson correlation coecients among egg quality traits at peak.
Traits YR AW AR HU YH EW SI SW SR ST
YW .617*** .236** -.483*** .054 .517*** .494** .077 .119 -.183* .060
YR -.609*** -.917*** .010 .214** -.406** -.107 .265** .009 -.031
AW .693*** .050 .245*** .891** .217** .477** -.360** .053
AR .050 -.145 .434** .116 .027 -.375** -.044
HU .104 .073 .071 -.217** -.132 -.152*
YH .278** .108 .065 -.276** -.138
EW .125 .540*** -.256*** .025
SI .073 -.034** .028
SW .674*** .284***
SR .305***
* p<0.05, ** p<0.01, *** p<0.001. Abbreviations: YW = yolk weight, YR = yolk ratio, AW = albumen weight, AR = albumen ratio, HU = Haugh unit, YH = yolk height, EW = egg weight, SI
= shape index, SW = shell weight, SR = shell ratio, ST = shell thickness.
Among external traits, egg weight retained its positive correlation
with shell weight (r = 0.431), though weaker than at peak lay (r = 0.540).
Notably, the negative correlation between egg weight and shell ratio
strengthened in late lay (r = –0.387 vs. –0.256), suggesting increased
shell insuciency with age consistent with Padhi et al. (2013). The
strong link between shell weight and shell ratio (r = 0.662) persisted,
while shell thickness remained only weakly related to other traits and
shape index continued to show no signicant correlations, conrming
its limited predictive value.
Internal–external trait relationships showed that egg weight
remained a strong predictor of albumen weight (r = 0.908), but its
correlation with yolk weight declined markedly with age (r = 0.209
vs. 0.494 at peak), reecting a shift toward albumen dominance in
older eggs. This was supported by a slightly higher
iinverse correlation
between yolk ratio and egg weight (r = –0.422 vs. –0.406), and a
slightly higher positive correlation between egg weight and albumen
ratio (r = 0.477 vs. 0.434), these moderate but consistent shifts align
with the patterns reported by Padhi et al. (2013) and Inca et al. (2020).
In contrast to peak lay, freshness indicators such as Haugh unit and
albumen index exhibited no meaningful correlations with shell or egg size
traits, conrming their physiological independence in older hens (Table 3).
In summary, egg weight remains a reliable, non-invasive predictor
of albumen content across ages, but its links to yolk traits weaken with
hen age and other internal traits remain poorly correlated with external
features, requiring direct measurement.
Principal Component Analysis (PCA)
A principal component analysis was performed to explore the
multidimensional relationships among internal and external egg quality
traits across both laying phases. Six components were extracted, with
the rst two accounting for the majority of the variance.
The rst component (FAC1), explaining 32.40 % of the total
variance, was strongly correlated with internal egg quality parameters,
including albumen index, Haugh unit and albumen height. During the
peak egg laying phase (25-30 weeks), FAC1 scores were consistently
positive, peaking at 25 weeks, indicating high albumen properties.
On the other hand, at the end of the egg-laying cycle (75-80 weeks),
these scores became negative, with a minimum observed at 77 weeks,
reecting a gradual deterioration of internal characteristics. This agrees
with Sarica et al. (2012), also Udeh et al. (2021) highlighted albumen
traits as key indicators, though they focused on genetic dierences.
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Amireche et al. Rev. Fac. Agron. (LUZ). 2026, 43(1): e264303
5-6 |
Table 3. Pearson correlation coecients among egg quality traits at late phase.
Traits YR AW AR HU YH EW SI SW SR ST
YW .762*** -.057 -.668*** -.158* .239** .209** .026 .100 -.065 .100
YR -.680*** -.961*** -.155* -.047 -.422** -.038 -.213** .147* .113
AW .753*** .071 .337*** .908** .088 .335** -.428** -.108
AR .169* .107 .477** .054 .062 -.354** -.165**
HU -.060 -.072 .119 -.153* -.087 -.004
YH .417** .114 .122 -.228** -.201**
EW .110 .431*** -.387*** -.041
SI .005 -.087 .016
SW .662*** .226**
SR .268***
* p < .05, ** p < .01, *** p < .001. Abbreviations: YW = yolk weight, YR = yolk ratio, AW = albumen weight, AR = albumen ratio, HU = Haugh unit, YH = yolk height, EW = egg weight, SI
= shape index, SW = shell weight, SR = shell ratio, ST = shell thickness.
The second component (FAC2), representing 24.10 % of the
variance, was mainly associated with egg size and weight, with high
correlations for albumen weight and total egg weight. Unlike FAC1,
FAC2 scores remained relatively stable across most weeks, but showed
a marked increase at 80 weeks, reecting the larger egg size produced
by hens at the end of the laying cycle. This opposite evolution between
FAC1 and FAC2 highlights an important physiological compromise:
while the eggs become larger with age, their
iinternal characteristics
degrade (Table 4) (Sirri et al., 2018; Lee et al., 2013).
FAC3 explained 10.44 % of the variance and was mainly associated
with secondary internal quality traits such as albumen height, Haugh
unit, and albumen index (Roberts et al., 2013). However, it did not
show a clear age-related pattern.
FAC4 explained 9.89 % of the variance, related to shell weight
and thickness, showed limited age-related variation, suggesting
stable shell quality, likely due to adequate calcium nutrition.
FAC5, accounting for 6.85 % of the variance, associated with yolk
morphology, also remained consistent, aligning with Inca et al.
(2020) (Table 4).
The weekly distribution of PCA scores (Table 5) on Components
1 and 2 as illustrated in Figure 1, separates the two laying phases:
peak-lay eggs (weeks 25-30) cluster in the upper right quadrant,
indicating high internal freshness and structural integrity. In contrast,
late-lay eggs (weeks 75-80) are more dispersed, with negative scores
on Component 1 and increasing values on Component 2, reecting
reduced freshness and increased egg mass. These visual patterns
reinforce the physiological trade-o observed with age and conrm
the multidimensional nature of egg quality dynamics.
Table 4. Component matrix of egg quality traits from PCA.
Trait FAC1 FAC2 FAC3 FAC4 FAC5 FAC6
Egg weight -.376 .821 -.006 .026 -.090 .160
Egg surface area -.621 .574 .118 .151 -.251 -.148
Shape index .463 .071 .194 .193 .240 .782
Yolk weight -.859 .045 .346 -.047 -.124 .189
Yolk ratio -.750 -.495 .397 -.071 -.081 .113
Shell weight -.276 .329 -.091 .810 .137 -.082
Shell ratio .038 -.383 -.090 .827 .223 -.233
Shell thickness -.070 -.128 -.142 .529 -.036 .094
Haugh unit .734 .079 .558 .108 -.223 -.130
Yolk colour .670 .006 .236 .059 -.068 .035
Albumen index .740 .116 .526 .115 -.138 -.164
Albumen weight .034 .931 -.177 -.057 -.063 .106
Albumen ratio .706 .580 -.355 -.163 .015 -.043
Egg length -.696 .431 .011 .037 -.303 -.420
Egg width -.334 .622 .238 .266 -.100 .385
Yolk height -.480 .427 .381 -.188 .542 -.097
Yolk index .002 .364 .336 -.118 .749 -.291
Alb/yolk ratio .738 .518 -.399 .016 .034 -.063
Albumen height .698 .197 .587 .108 -.213 -.139
Table 5. Weekly mean scores for FAC1 and FAC2 across laying period.
Week 25 26 27 28 29 30 75 76 77 78 79 80
FAC1 1.35 .82 .86 .64 .43 .56 -.59 -.90 -1.19 -.91 -.49 -.57
FAC2 -.18 -.23 -.07 -.04 -.03 .15 -.29 .11 .06 -.04 .03 .52
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2026, 43(1): e264303 January-March. ISSN 2477-9409.
6-6 |
Figure 1. Weekly mean scores on principal components 1 and 2.
Conclusion
This study conrms the viability of ISA Brown hens to maintain
acceptable egg quality up to 80 weeks under Algerian conditions.
Despite declines in freshness-related traits with age, structural
integrity remained stable, suggesting physiological adaptability. The
weakening of inter-trait correlation in late lay suggests a decoupling
of structural and compositional integration, reinforcing the need
for direct measurement of freshness and internal quality indicators
beyond surface parameters. Collectively, the results conrm that
Isa Brown hens can remain productive with acceptable egg quality
beyond conventional culling thresholds. Extending laying cycles
under controlled environmental and nutritional conditions is feasible
and may contribute to more sustainable poultry production in semi-
arid regions. Future research should therefore integrate performance,
welfare, and cost-benet analyses beyond 80 weeks to guide long-
term data-driven strategies for the poultry industry.
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W25
W26
W27
W28
W29
W30
W75
W76
W77
W78
W79
W80
-0,4
-0,3
-0,2
-0,1
0
0,1
0,2
0,3
0,4
0,5
0,6
-1,5 -1 -0,5 0 0,5 1 1,5
principal component 2 (FAC2)
principal component 1 (FAC1)
peak
late