The Effect of Housing Systems on the Growth, Egg production, Overall Egg Weight and Egg Quality Traits of a New Turkish Laying Hen Hybrid, Akbay

ABSTRACT

This study was conducted to determine the effects of housing systems (free-range and conventional cage) during the egg-laying phase on the growth, egg production, overall egg weight, and egg quality traits of a new Turkish laying hen hybrid, Akbay. A total of 600 (300 hens per housing system) Akbay laying hen hybrids were used in this study. At the end of the rearing cycle (17 weeks) the average live weight and cumulative feed intake for both groups were 1150.8g and 5067.52g, respectively. The live weight and cumulative feed intake at the onset of laying for both groups were 1198.42g and 5537.77g, respectively. Egg production, average daily feed intake, and average daily feed conversion ratio were significantly higher (p≤0.05) in free-range hens than in hens housed in cages. The live weight at peak production was significantly higher (p≤0.05) in hens housed in cages than in free-range hens. Significant differences (p≤0.05) in terms of internal and external egg quality traits were observed between the housing systems in this study. Generally, the free-range hens had better performance than the hens in cages. It was therefore concluded that the growth performance, egg production, overall egg weight, and egg quality traits of the new Turkish laying hen hybrid Akbay are better in the free-range production system than in convention cages; and that these hens can be housed in the free-range system without any negative effect on performance and egg quality traits.

Keywords:
Albumen and yolk quality trait; hen-housed egg production; layer chicken; production system; shell quality traits; performance

INTRODUCTION

In many underdeveloped countries, other protein sources are extremely expensive when compared to eggs, which makes egg production very important and has also been increasing the global egg production and consumption (Abdallah et al., 2022). Higher chicken egg and meat consumption rates and demand have led to the increased capacity of several commercial poultry ventures, making it a rapidly growing sector worldwide. It was reported that around 5 billion chickens are reared for eggs and meat every year (Mallick et al., 2020).

The production/ housing system is one of the major factors that affects the production, egg-laying, egg quality traits, and welfare performance of laying hens. These birds are traditionally reared either in cages or non-cage production systems. However, cages have been banned in the EU and other parts of the world. Dikmen et al. (2016) reported that the initial development of conventional cages happened in the 1930s, and they have been used in traditional egg production since the 1950s. The aim of conventional cages was to increase egg production and profits using a small area or space (Sosnowka-Czajka et al., 2010; Jones et al., 2014). However, this system has been criticized for not meeting the welfare requirement of hens (Mench et al., 2011; Kursun et al., 2024). On the other hand, free range systems are considered animal friendly, and consumers consider eggs produced in them healthier than eggs from caged hens (Miao et al., 2005). According to Dikmen et al. (2016), the free-range system was developed in the 1920s, and this system is equipped with outdoor ranging areas for behavioral exhibition (Mench et al., 2011).

The feed intake and the uniformity of the body weight of laying hens are crucial, as they affect egg production, egg-laying time, egg quality traits, and welfare of laying hens. The recommended feed intake and live weight during the rearing and egg-laying cycle are very important to ensure or maintain adequate bone development (bone ossification and mineralization) before egg-laying is initiated or continued. Although free-range systems are known to be animal welfare-friendly, authors have reported conflicting results regarding the effect of housing systems on the egg-laying, egg weight, and egg quality traits of laying hens.

Therefore, this study aimed to evaluate the effect of different housing systems (conventional cage and free-range) on the performance, egg-laying, overall egg weight and egg quality traits of a new Turkish laying hen hybrid, the Akbay.

MATERIALS AND METHODS

This research was conducted at the Research and Application Centre of Cukurova University. Its approval was granted by the Ethics Committee of Cukurova University, and all euthanasia and husbandry practices fully considered animal welfare.

Experimental Birds

The birds used in the current study were Akbay hybrids, a new Turkish laying hen hybrid registered in 2019. Like Atabey hybrids, the Akbay has a white plumage color. However, while sexing cannot be done for Atabeys at an early age, sex differentiation from an early age is possible with Akbay. Currently, Akbay hybrids have not been released to farmers for commercial production, and this work is the first paper reporting the effect of different production systems (conventional cage and free-range) on the growth, egg-laying, overall egg weight, and egg quality traits of the Akbay.

Experimental Design

A total of 600 (300 hens per housing system) Akbay laying hen hybrids were used in this study. At the rearing phase (0-18 weeks), the birds were reared in a deep litter system with no outdoor access. From 18 weeks of age till the end of production (80 weeks), the birds were either reared in conventional cages or in deep litter with outdoor access. The conventional cage had dimensions of 57x57x40 cm (length-width-height). The number of hens per cage was 4, and each hen had an adequate space of 5m². The deep litter area had the dimensions of 981 x 853 x 282 cm (length-width-height). The indoor space per bird on the deep litter was 6 hens/ m², and the outdoor ranging area had 800 m², with an adequate space of 10 m²/ bird. The birds in the deep litter with outdoor access had access to metallic perches. There was a total of 3 replicates for each production system, with 100 birds per replicate. Electric heaters were used to maintain standard housing temperature (22 ºC) during winter or cold season. The concentration of odor in the house and high temperatures during summer were regulated using automatic ventilators.

Photoperiodic Lightning during Rearing and Egg-laying Phase

The Hy-line brown lightning schedule was used in this study. From 0-3d of the rearing phase, chicks were exposed to 22 h photophase, and from 4-7d the chicks were given 21 h of light. The photophase was gradually decreased every week till 10 h of photophase were reached. From 8 weeks to 17 weeks of age, young pullets were exposed to constant 10 h of photophase. At 18 weeks of age, light stimulation was conducted by increasing the photophase by 1 h. The increment of the photophase by 1 h was continued every week till 16 h L and 8 h D were achieved. This lightning schedule (16 h L and 8 h D) was used till the end of the egg laying cycle.

Experimental Diet

The birds were fed different diets during the rearing and egg-laying phases. Feed and water were provided ad litbitum. The composition of the diets given during the rearing and egg-laying phases are presented in Table 1.

Table 1
The composition of diets fed the growing chicks from rearing until the end of egg-laying cycle.

Nutrient Composition	Chick Feed 0-3 wk	Pullet Grower Feed 4-10 wk	Pullet Developement Feed 11-16 wk	Egg Starter Feed 17-20 wk	Egg-laying Feed 21-80 wk
Metabolisable Energy Kcal/kg	2900	2800	2750	2750	2750
Crude Protein %	20	18	15.50	17.50	17
Methionine %	0.55	0.40	0.35	0.38	0.40
Lysine %	1.20	1.00	0.72	0.85	0.8
Calcium %	1.20	1.10	1.00	2.50	4.20
Available Phosphorus %	0.45	0.45	0.40	0.45	0.38
Chlorine %	0.20	0.20	0.20	0.20	0.2
Vitamin A IU	13000	13000	12000	12000	12000
Vitamin D3 IU	3000	3000	2500	2500	2500
Vitamin E mg	20	20	20	20	20
Vitamin K3 mg	2	2	2	2	2
Riboflavin mg	5	5	5	5	5
Vitamin B12 mg	0.02	0.02	0.01	0.01	0.01
Niacin mg	60	60	30	25	25
Thiamine mg	1.50	1.50	1.50	2	2
Vitamin B4 mg	3	3	3	3	3
Pantenoic Acid mg	10	10	10	10	10
Folic Acid mg	0.50	0.50	0.50	0.50	0.50
Biotin mg	0.10	0.10	0.05	0.05	0.05

Measurement of Growth Performance during The Rearing and Egg-laying Phases

The weekly body weight during the rearing (0-17 weeks), at the onset of laying (18 weeks), and peak egg-laying phases (29 weeks) were measured using an electronic balance of 0.001 g precision. The feed intake (FI) during the rearing and egg-laying phases was also measured using an electronic balance of 0.001 g precision. The formulae below were used to determine feed intake and feed conversion ratio (FCR) during the rearing and egg-laying cycles.

$Fl=\frac{totalgramsoffeedconsumedduringtheperiod}{hendaysduringtheperiod}$

$FCR=\frac{totalfeedweightofeachgroupduringtheegg-layingperiod}{totaleggweightduringtheegglayingperiod}$

Evaluation of Egg production/Laying Rate and Egg Weight

Throughout the egg-laying phase, eggs were collected daily per replicate, and recorded on a weekly basis. The eggs collected for each replicate were individually weighed using an electronic scale of 0.001 g precision. The overall egg-laying rate during the production period (18-80 weeks) was calculated using the formula below.

Overall Egg-laying Rate

$=\frac{Numberofeggslaidduringtheentireproductioncycle}{totalnumberhensinthatproductionsystemduringtheentirelayingperiod}\times 100$

Evaluation of External Egg Quality Traits

The external egg quality traits evaluated were egg weight, shape index, eggshell thickness, and breaking strength, using 30 eggs per production system.

Measurement of Eggshell Thickness Shell

For the measurement of shell thickness, the portion of each part of the shell (narrow, middle, and broad parts) was recorded with a shell thickness gauge, and the average of the 3 parts was recorded. The formula below was used to determine eggshell thickness. All the measurements were recorded in mm.

$Shellthickness=\frac{(Broad+Narrow+Middleparts)}{3}$

Measurement of Egg Breaking Strength

Egg-breaking strength was measured by placing the egg on an egg-breaking device (TA-XT Plus Brand Texture Analyzer). The egg was held until the device made physical contact with the egg. The experimenter then removed his hand from the egg while the device exerted mild pressure on the egg. Once the egg was broken, the force at which it broke was automatically recorded on a laptop connected to the egg-breaking device.

Measurement of Shape Index

The width and length of the eggs were measured using an electronic Vernier calliper. The Shape index was evaluated by dividing the egg width by its height and multiplying it by 100 percent.

$ShapeIndex=\frac{EggWidth(mm)}{Egglenght(mm)}\times 100$

Measurement of Internal Egg Quality Traits

Thirty eggs per housing system were used in the calculation of the internal egg quality traits. The parameters measured were albumen pH, albumen index, yolk index, and Haugh unit.

Measurement of Albumen Index

Eggs were broken on a thick transparent square glass. A Vernier calliper was then used to measure albumen height, length, and width. The formula below was used to determine the albumen index.

$AlbumenIndex=\frac{Albumenheight(mm)}{AverageofAlbumenwidth+Length(mm)}\times 100$

Measurement of Albumen pH

The albumen pH was determined by separating the albumen from the yolk, which was then collected into a transparent disposable cup. The pH meter was subsequently inserted in the cup until the pH value was recorded on the screen of the pH meter.

Measurement of Yolk Index

After breaking eggs on a thick transparent square glass, a Vernier calliper was used to measure the yolk height and width. The formula below was used to evaluate the yolk index.

$AlbumenIndex=\frac{Albumenheight(mm)}{AverageofAlbumenwidth+Length(mm)}\times 100$

Yolk Colour Measurement

The yolk was collected into a petri dish and then placed into a Konica Minolta Colorimeter CR-300 device to determine the yolk color values (L: brightness, a: redness, and b: yellowness).

Measurement of Haugh Unit

The Haugh unit was measured using the formula below:

Haugh unit= 100 log (Albumen Height +7.57-1.7 x Egg Weight^0.37)

Statistical Analysis

The normality assumption and variance homogeneity were respectively evaluated using the Shapiro-Wilk and the Levene tests. It was confirmed that the data met the assumption of normal distribution and their variances were homogeneous. Independent-samples-t-test analysis was then conducted to evaluate the significant difference between the two housing systems. All the statistical analysis was conducted using SPSS version 22.

RESULTS

During the rearing cycle, all the birds were reared together in a deep litter system. The live weight and cumulative feed intake at the end of the rearing cycle were 1150.80g and 5067.52g, respectively. Furthermore, the cumulative feed intake and live body weight at the onset of laying (18 weeks) were 5537.77g 1198.42g, respectively. The average live body weight, feed intake, and cumulative feed intake during the rearing cycle and at the onset of laying is shown in Table 2.

Table 2
Average body weight (g) and feed intake of Akbay laying hens during the rearing cycle (1-17 weeks) and at the onset of laying (18 weeks).

Age of hens (Weeks)	Performance Traits during Rearing Cycle and at the Onset of Laying
	Body weight (g)	Feed intake (g/week)	Cumulative feed intake (g)
1	71.27	90.46	90.46
2	114.35	107.584	198.04
3	182.78	134.959	333.00
4	257.96	169.889	502.89
5	337.30	212.244	715.13
6	444.76	262.072	977.20
7	535.26	310.604	1287.81
8	595.05	317.729	1605.54
9	675.78	346.584	1952.13
10	729.49	349.025	2301.15
11	815.78	371.923	2673.07
12	829.14	379.926	3053.00
13	946.547	407.379	3460.38
14	1019.84	413.382	3873.76
15	1069.09	418.36	4292.12
16	1126.45	432.002	4724.12
17	1150.80	343.396	5067.52
18	1198.42	470.256	5537.77

The effect of the different housing systems on the overall egg-laying rate/ hen-housed egg production, average daily feed intake, average daily feed conversion ratio, and live weight at 29 weeks of production is given in Table 3. The overall egg-laying rate and average daily feed intake were significantly (p≤0.05) higher in the free-range group than in the group reared in cages. While, the average daily feed conversion ratio was higher in the free-range hens, the live weight at 29 weeks of production was statistically higher in the group housed in cages (p≤0.05).

Table 3
The effect of housing systems on overall egg production/laying rate (%), average daily feed.

Parameters	Housing Systems		p-value
	Cage	Free-Range
Overall egg laying rate (18-80 wk)	74.95±14.20	76.99±15.82	<0.001*
Average daily feed intake (21-80 wk)	99.04±11.61	103.07±11.946	<0.001*
Avearge daily feed conversion ratio (21-80 wk)	2.25±0.36	2.24±0.32	<0.001*
Live weight at peak production (29 wk)	1421.44±19.98	1248.48±22.39	<0.001*

The effect of housing systems on weekly egg weight is shown in Table 4. The egg weight was significantly (p≤0.05) higher in the free-range group on most of the production weeks (25, 28, 29, 30, 31, 32, 33, 34, 40, 45, 46, 47, 48, 49 and 50th week of age). The group reared in cages had significantly (p≤0.05) higher egg weight at 43 weeks than those reared free-range. The egg weights in the other weeks of age were not statistically (p≥0.05) different between the two production systems.

Table 4
The effect of housing systems on weekly (20-50 weeks) and total (18-80 weeks) egg weight.

Age of hens (Weeks)	Housing Systems		p-value
	Cage	Free-Range
20	43.45±4.12	42.98±4.29	0.536
21	45.74±0.48	45.40±0.31	0.568
22	47.71±0.62	47.89±0.34	0.788
23	48.87±0.34	49.51±0.26	0.160
24	51.04±0.31	51.08±0.36	0.939
25	52.46±0.24	54.90±0.00	<0.001*
26	54.96±0.33	55.37±0.47	0.479
27	55.13±0.29	55.52±0.32	0.369
28	55.28±0.25	56.33±0.29	0.006*
29	55.57±0.29	59.92±0.39	<0.001*
30	56.23±0.34	58.18±0.36	<0.001*
31	56.92±0.34	58.44±0.30	0.001*
32	57.64±0.31	58.75±0.27	0.009*
33	58.52±0.29	59.62±0.30	0.009*
34	59.05±0.33	60.02±0.35	0.048*
35	58.88±0.32	59.40±0.32	0.264
36	58.80±0.30	58.93±0.31	0.763
37	59.29±0.29	59.67±0.31	0.368
38	59.55±0.29	60.40±0.33	0.054
39	59.71±0.30	60.09±0.30	0.378
40	59.30±0.31	60.26±0.32	0.034*
41	59.76±0.34	59.95±0.32	0.672
42	60.41±0.33	60.44±0.33	0.962
43	60.59±0.29	59.82±0.32	0.074
44	60.49±0.30	61.08±0.33	0.195
45	59.94±0.38	61.94±0.32	<0.001*
46	60.85±0.29	62.40±0.32	<0.001*
47	60.54±0.32	61.66±0.36	0.019*
48	60.06±0.30	62.47±0.32	<0.001*
49	60.25±0.31	62.18±0.36	<0.001*
50	60.84±0.33	62.19±0.34	0.005*
Total (18-80)	60.68±0.32	61.19±0.53	<0.001*

The effect of housing systems on external egg quality traits is presented in Table 5. The egg weight and shape index were statistically (p≤0.05) higher in free-range birds on the 40, 52 and 60th weeks. However, shell thickness and egg-breaking strength were significantly higher in the group housed in cages as compared to those reared free-range in the 36, 40, 48, and 68th weeks of age. No significant differences (p≥0.05) in terms of external egg-quality traits were observed in the other weeks. Futhermore, the average total of the external egg quality traits (egg weight, shape index, shell thickness, and egg breaking strenghth) did not differ significantly between the two housing systems.

Table 5
The effect of different housing systems on external egg quality traits.

Age of hens (Weeks)	Housing systems	Egg Weight (g)	Shape Index (%)	Shell Thickness (mm)	Egg Breaking Resistance (kg/cm2)
20	Free-range	50.80±2.05	75.16±2.67	374.111±19.679	0.752±1.401
	Cage	50.17±3.72	77.24±2.33	373.067±19.445	2.541±0.762
p-value		0.067	0.401	0.827	0.050
24	Free-range	55.69±3.91	75.09±2.65	362.911±24.781	2.911±1.397
	Cage	55.65±3.12	75.95±2.20	373.867±23.873	3.054±1.311
p-value		0.817	0.151	0.913	0.916
28	Free-range	56.56±1.92	75.56±2.24	372.978±21.557	3.653±0.564
	Cage	58.51±3.65	74.75±2.87	365.356±18.016	3.352±0.745
p-value		0.095	0.219	0.711	0.620
32	Free-range	58.30±5.17	74.434±1.993	367.222±22.823	2.063±0.912
	Cage	58.67±4.17	75.393±2.933	367.689±27.711	1.877±1.195
p-value		0.259	0.151	0.761	0.679
36	Free-range	58.92±3.93	75.169±1.856	378.156±19.027	2.736±1.086
	Cage	62.48±3.14	74.711±1.954	412.867±25.167	3.809±2.112
p-value		0.168	0.848	0.320	0.001
40	Free-range	60.83±3.29	74.412±2.766	364.222±41.570	1.000±0.484
	Cage	59.96±6.17	76.328±5.237	367.156±19.399	1.410±0.866
p-value		0.004	0.244	0.036	0.227
44	Free-range	61.87±4.20	75.064±2.629	363.889±33.859	2.866±1.235
	Cage	62.25±2.94	73.818±2.219	374.733±18.795	3.297±0.817
p-value		0.178	0.560	0.055	0.055
48	Free-range	64.42±3.84	73.271±4.141	387.156±33.239	1.768±1.324
	Cage	60.00±3.84	73.439±1.676	362.600±16.036	2.167±1.535
p-value		0.944	0.059	0.005	0.202
52	Free-range	59.653±4.18	74.661±2.988	343.311±19.341	1.489±1.179
	Cage	58.56±5.30	74.512±1.859	355.133±26.375	1.223±0.849
p-value		0.300	0.031	0.158	0.192
56	Free-range	61.87±3.98	74.427±3.051	373.222±18.626	1.434±0.882
	Cage	63.70±4.57	74.339±2.715	359.356±37.846	2.174±1.276
p-value		0.349	0.496	0.050	0.111
60	Free-range	61.36±3.87	72.721±2.869	322.378±31.239	2.3083±0.843
	Cage	59.05±5.54	73.225±2.260	350.667±30.616	2.5851±1.069
p-value		0.034	0.777	0.816	0.689
64	Free-range	58.14±2.97	73.382±3.306	355.022±21.675	2.197±1.210
	Cage	59.71±.54	74.805±2.631	365.467±29.113	2.430±1.038
p-value		0.574	0.519	0.552	0.700
68	Free-range	70.94±3.34	74.179±2.298	359.267±56.008	2.001±1.492
	Cage	68.71±2.89	74.387±2.245	364.333±30.608	2.381±1.474
p-value		0.462	0.714	0.012	0.651
Total (20-68)	Free-range	59.950±4.756	74.425±0.850	363.373±16.519	2.091±0.820
	Cage	59.802±4.309	74.838±1.144	368.638±15.030	2.485±0.745
p-value		0.394	0.307	0.404	0.215

The effect of housing systems on albumen pH, albumen index, yolk index, and Haugh unit is presented in Table 6. Free-range hens had higher (p≤0.05) albumen index than those housed in cages in the 20 and 44 weeks of age. However, albumen index and albumen pH were higher in hens housed in cages in the 24, 36, and 68th weeks than in those housed in the free-range system. Yolk index was significantly (p≤0.05) higher in free-range hens than in those housed in cages in weeks 20 and 28. Haugh unit was also statistically (p≤0.05) higher in free-range hens than in hens housed in cages at 20 and 44 weeks of age. The internal egg quality traits did not significantly (p≥0.05) differ between the two production systems in the other weeks. Moreover, the total average (20-68 weeks) of the yolk index, albumen index, and albumen pH did not significantly (p≥0.05) differ between the two housing systems.

Table 6
The effect of housing systems on internal egg quality traits.

Age of hens (Weeks)	Housing systems	Albumen Index (%)	Yolk Index (%)	Haugh Unit	Albumen pH
20	Free-range	10.806±2.030	46.264±4.136	89.584±5.595	8.217±0.297
	Cage	7.882±3.845	40.683±10.971	72.361±20.946	8.133±0.192
p-value		0.002	0.000	0.000	0.772
24	Free-range	8.832±0.030	42.043±3.028	85.544±7.121	8.725±0.154
	Cage	8.990±0.938	45.310±2.971	84.229±4.082	8.440±0.149
p-value		0.038	0.985	0.168	0.930
28	Free-range	11.437±1.499	44.499±2.418	93.239±4.604	8.105±0.146
	Cage	10.933±1.839	43.553±3.943	91.995±6.039	8.089±0.099
p-value		0.521	0.042	0.429	0.196
32	Free-range	8.980±1.444	44.851±2.280	86.388±5.776	8.479±0.165
	Cage	9.906±1.525	43.998±4.194	89.319±4.669	8.255±0.222
p-value		0.760	0.080	0.494	0.387
36	Free-range	9.275±1.195	44.162±2.893	85.864±5.600	8.474±0.129
	Cage	11.080±2.685	44.366±3.644	90.623±9.881	8.294±0.130
p-value		0.016	0.497	0.105	0.589
40	Free-range	10.722±1.086	41.602±2.200	93.256±3.717	8.227±0.120
	Cage	10.192±1.995	42.242±2.867	89.991±6.214	8.105±0.157
p-value		0.076	0.424	0.267	0.150
44	Free-range	10.546±1.301	40.896±2.714	115.165±2.263	7.917±0.174
	Cage	10.257±0.882	42.397±2.156	114.806±1.323	8.180±0.172
p-value		0.048	0.411	0.035	0.632
48	Free-range	9.485±1.148	41.124±2.825	88.034±4.417	8.223±0.126
	Cage	10.053±1.097	40.950±3.054	91.028±4.148	8.131±0.235
p-value		0.490	0.905	0.643	0.172
52	Free-range	7.311±2.492	37.705±1.877	81.706±7.865	8.576±0.216
	Cage	6.630±1.135	34.834±3.009	77.511±5.667	9.004±0.165
p-value		0.110	0.353	0.369	0.172
56	Free-range	10.984±2.822	40.772±3.695	91.381±10.044	7.462±1.928
	Cage	11.628±2.088	42.619±3.666	94.550±6.272	8.042±0.506
p-value		0.570	0.708	0.450	0.250
60	Free-range	9.700±1.196	40.773±2.909	88.651±5.317	8.739±0.142
	Cage	8.047±1.803	40.074±2.505	82.189±9.982	8.961±0.157
p-value		0.156	0.345	0.111	0.548
64	Free-range	9.305±1.984	39.136±1.748	86.850±10.441	8.479±0.198
	Cage	8.816±2.331	39.777±2.957	85.284±11.216	8.583±0.148
p-value		0.427	0.096	0.517	0.219
68	Free-range	9.424±2.074	40.310±2.305	80.053±10.507	8.598±0.233
	Cage	9.630±1.965	41.529±2.718	88.213±7.283	8.655±0.135
p-value		0.921	0.430	0.398	0.023
Total (20-68)	Free-range	9.754±1.120	41.857±2.443	89.670±8.604	8.325±0.357
	Cage	9.542±1.423	41.718±2.671	88.623±10.017	8.375±0.092
p-value		0.423	0.985	0.777	0.955

The effect of housing systems on yolk color traits is given in Table 7. The b (yellowness) and L (brightness) values were significantly (p≤0.05) higher in the free-range group than in those housed in cages in the 20^th and 24^th weeks, respectively. While the redness value was statistically higher (p≤0.05) in the free-range hens than in hens housed in cages on the 56^th week, hens housed in cages had the highest (p≤0.05) redness value at 68 weeks. The yolk color traits did not significantly (p≥0.05) differ between the two housing systems in the other weeks. Futhermore, the average total (20-68 weeks) of the L, a, and b values were not statistically (p≥0.05) different between the two housing systems.

Table 7
The effect of housing systems on yolk color traits.

Age of hens (Weeks)	Housing systems	L (Brightness)	a (Redness)	b (Yellowness)
20	Free-range	55.501±1.187	22.241±0.996	56.472±1.450
	Cage	54.081±1.890	20.301±1.856	52.038±3.420
p-value		0.149	0.075	0.027
24	Free-range	54.763±1.046	23.738±1.177	50.708±2.653
	Cage	53.401±1.974	23.661±1.024	53.337±5.771
p-value		0.028	0.241	0.058
28	Free-range	52.705±3.338	25.173±2.087	52.935±5.616
	Cage	53.566±1.161	25.461±0.995	53.650±3.149
p-value		0.052	0.154	0.327
32	Free-range	47.364±4.567	21.739±2.878	48.305±5.459
	Cage	43.285±5.384	19.809±3.985	39.795±6.556
p-value		0.680	0.189	0.820
36	Free-range	39.971±6.976	20.426±2.812	41.467±5.687
	Cage	44.923±5.574	21.746±3.814	41.267±9.075
p-value		0.479	0.946	0.236
40	Free-range	54.165±1.721	24.029±1.739	52.498±5.528
	Cage	53.591±2.738	22.792±1.395	54.412±7.206
p-value		0.119	0.876	0.185
44	Free-range	52.805±2.573	24.817±2.510	55.869±5.897
	Cage	53.063±2.582	25.359±1.686	53.755±5.308
p-value		0.878	0.234	0.309
48	Free-range	53.836±1.778	24.642±1.336	55.402±5.516
	Cage	52.789±1.800	23.757±2.857	51.013±5.827
p-value		0.925	0.062	0.909
52	Free-range	56.729±2.134	20.774±1.075	55.184±3.725
	Cage	56.592±2.711	20.830±2.007	55.169±7.929
p-value		0.195	0.067	0.080
56	Free-range	52.054±4.664	20.914±1.742	50.893±3.310
	Cage	52.366±4.711	17.989±4.906	49.242±4.853
p-value		0.603	0.006	0.082
60	Free-range	50.207±3.894	20.779±1.879	49.247±3.245
	Cage	51.252±3.969	20.061±2.129	48.769±6.394
p-value		0.918	0.716	0.245
64	Free-range	50.601±5.003	19.873±2.459	52.492±7.095
	Cage	50.843±5.004	20.006±2.212	54.807±6.869
p-value		0.984	0.890	0.827
68	Free-range	54.705±2.249	17.296±2.086	54.545±7.767
	Cage	55.627±2.137	18.954±1.190	56.437±4.305
p-value		0.477	0.027	0.052
Total (20-68)	Free-range	51.954±4.379	22.034±2.337	52.001±4.078
	Cage	51.952±3.822	21.594±2.412	51.053±5.184
p-value		0.999	0.641	0.609

DISCUSSION

The feed consumption and live weight during the end of the rearing cycle and at the onset of laying is very important, since it has a profound effect on egg-laying performance, and egg weight, as well as internal and external egg quality traits. In the present study, the cumulative feed intake and live weight at the end (17 weeks) of the rearing cycle were 5067.52g and 1150.80g, respectively. In other commercial laying hen hybrids (Hy-line W-80), live weight and cumulative feed intake at the end of the rearing cycle have been reported to vary between 1252-1332g and 5.725-6.342g, respectively (Hy-line W-80, 2023), which is similar to the live weight and cumulative feed intake at the end of the rearing period observed in the hybrids used in this study. Cumulative feed intake and live weight at the onset of laying (18 weeks) in the present study were 5537.77g and 1198.42g, respectively. Similar average live weights at the onset of production have been reported for Hy-line W-80 hens (approximately 1290-1380g), as well as for other Turkish laying hen hybrids (Atak, 1385g and Atabey, 1230g) (Hy-line W-80, 2023; Ankara Tavukculuk, 2015). However, a higher cumulative feed intake of 6500-6900g (Atak-S, Atak, and Atabey hens) and weight at sexual maturity between 1-18 weeks were reported in other commercial Turkish laying hen hybrids (Atak-S) as compared to the hybrid used in this study (Ankara Tavukculuk, 2015).

In the present study, the overall egg laying rate/hen-housed egg production was significantly higher in the free-range hens than in those housed in cages. In line with our findings, other authors have also reported higher hen-day egg production and hen-housed egg production in free-range hens compared to those housed in cages (Sekeroglu et al., 2010; Dikmen et al., 2016; Alig et al., 2023a). The higher hen-housed egg production in the free-range hens could be related to better gut and oviduct health due to birds scavenging for pasture plants and insects. It has been reported that grazing mixed-grass pastures could positively affect the intestinal microbiota, leading to an enhancement of growth and immune performance in hens housed in a free-range system (Zheng et al., 2021). Similarly, the supplementation of forage products regulates the intestinal microbiota by enhancing the proliferation of lactic acid bacteria, which may act as a shield against pathogens and therefore enhance the growth performance of chickens (Zheng et al., 2019a, 2019b). DiGiacomo & Leury (2019) also reported an enhanced feed conversion ratio and growth performance due to the additıon of black soldier fly larvae in hens’ diets. Detilleux et al. (2022) further explained that the inclusion of black soldier flies in poultry diets could improve microbiota gut health with subsequent improvement in performance traits. Moreover, according to Malematja et al. (2023), insects contain bioactive compounds and valuable nutrients that are known to influence the functionality and microbiota of the gut, which could subsequently impact the health and growth performance of birds. These improvements in gut health and performance traits could enhance nutrient absorption and utilization, leading to superior development of the reproductive tract and egg formation. Moreover, the component of natural light may have further enhanced follicular and oviduct development in the free-range hens, thereby enhancing egg production. Furthermore, hens in cages are known to be stressed, which has been reported as a major factor causing a reduction in egg production (Mashaly et al., 2004; Irshad et al., 2013).

Contrary to our observations, other authors (Al-Awadi et al., 1995; El-Sheikh & Ali, 2005; Yakubu et al., 2007; Singh et al., 2009; Englmaierová et al., 2014; Nayak et al., 2020; Zewde & Kebede, 2022; Alig et al., 2023c) have reported higher egg production in hens housed in cages than in free-range hens, as well as in hens housed in other non-cage production systems. Other authors have also observed no significant effects of housing systems on egg production (Küçükyılmaz et al., 2012). The differences in reports could be related to hen genotypes, age, stocking density, and the nutritional characteristics used by the various studies.

The average daily feed intake in the present study was higher in the free-range hens compared to those housed in cages. Other authors have also confirmed higher feed intake in hens reared in free-range or other non-cage production systems as compared to hens housed in cages (Al-Awadi et al., 1995; Yakubu et al., 2007; Sekeroglu et al., 2010; Küçükyılmaz et al., 2012; Dikmen et al., 2016; Alig et al., 2023a; ). Furthermore, at 50 weeks of production, higher feed intake was observed in hens housed in non-cage production systems than in those housed in cages (Singh et al., 2009). Zhao et al. (2021) also reported that feed intake between 1-42 days was higher in chickens reared in non-cage production systems as compared to those in cages. Some authors (Englmaierová et al., 2014) have also observed lower daily feed intakes in hens housed in cages than in other production systems. The higher feed intake in the free-range hens in the current study could be related to a better development of the digestive organs (Yang et al., 2014) and gut health leading to better digestion, assimilation, and utilization of feed. Again, highly productive hens require a higher calcium intake, which may cause them to eat more to meet the calcium requirements for egg production and eggshell formation. Additionally, hens housed in cages are known to be stressed, and stress is known to decrease feed intake (Kursun et al., 2024). However, other authors have reported higher feed intake in hens housed in cages (Tactacan et al., 2009; Alig et al., 2023c).

The feed conversion ratio in the present study was better in the free-range hens than in those housed in cages. Some authors have reported better feed conversion ratio in hens reared in non-cage production systems than in those housed in cages (Singh et al., 2009). The better feed conversion ratio in the free-range hens could be associated with better development of the GIT (gastrointestinal tract), due to hens having extra nutrients from forage plants and insects, which would lead to an enhancement in the digestion, absorption, and utilization of feed ingredients. It could also be possible that the free-range hens had a better composition of digestive enzymes and microbes due to feeding on insects and pasture plants, and this might have led to better overall gut health and functionality, contributing to a better feed conversion ratio. Contrary to our findings, better feed conversion ratios in hens housed in cages compared to those in free-range hens and hens reared in other non-cage housing systems have been reported (Küçükyılmaz et al., 2012; Englmaierová et al., 2014; Dikmen et al., 2016; Zhao et al., 2021; Alig et al., 2023a). Furthermore, Alig et al. (2023c) reported no significant effect of the housing system on the feed conversion ratio of laying hens.

In the current study, the live weight at peak production (29 weeks) was higher in hens reared in cages than in free-range hens. The higher live weight gain at peak production in hens housed in cages could be due to lower egg production, since laying hens are reported to deposit 3% of their body weight in eggs (Martin et al., 1998). Therefore, it was speculated that the higher productive ability of the free-range hens, especially at peak production, would increase the deposition of body weight into the eggs, leading to a reduction in overall body weight. Moreover, hens in cages do not have opportunities for exhibiting energy-requiring behaviours such as running, perching, and roosting. Therefore, most of the energy from feed is stored as fat in adipose tissue, which may contribute to the higher live weight observed in hens housed in cages in the present study. In agreement with our findings, Yang et al. (2014) also confirmed higher live weight in hens housed in cages compared to free-range hens. Similarly, Sekeroglu et al. (2010) reported that at 5% egg production, hens housed in cages had higher live weight than free-range hens. Other authors also reported conflicting results by observing higher live weight at 23, 28, and 38 weeks of age in hens housed in non-cage production systems. However, at the end of production (70 weeks), hens in cages had higher live weight than those reared in non-cage housing systems (Küçükyılmaz et al., 2012). Contrary to our findings, other authors have reported higher live weight in free-range hens and hens in other non-cage production systems than in hens housed in cages (Rahimi, 2021; Alig et al., 2023a). Furthermore, some authors also reported that while there was no significant effect of the housing systems on live weight at peak production, at 5 and 50% egg production, free-range hens had higher live weight than hens housed in cages (Dikmen et al., 2016). According to Singh et al. (2009), from 30-50 weeks of age, Lohman brown and Lohman white hybrid hens reared in non-cage production systems had higher live weight than their counterparts reared in cages.

Egg weight was significantly higher in free-range hens on most of the production weeks (25, 28, 29, 30, 31, 32, 33, 34, 38, 40, 45, 46, 47, 48, 49, and 50th) in the present study, except on the 43rd week, when the hens housed in cages had the significantly highest egg weight. It was speculated that hens in the free range system have larger reproductive organs, giving them superiority in terms of egg weight compared to hens housed in cages (Alig et al., 2023a). Moreover, the association between hens in cages and stress has been reported by Gibson et al. (1986), and stress has been reported to decrease egg weight (Mashaly et al., 2004). In agreement with the findings of the present study, higher egg weight/mass has been confirmed in free-range hens or hens housed in other non-cage production systems as compared to hens housed in cages (Küçükyılmaz et al., 2012; Englmaierová et al., 2014; Dikmen et al., 2016; Al-Ajeeli et al., 2018; Alig et al., 2023a, 2023b). Again, higher egg weight was observed in most of the production weeks (30 and 40^th weeks) in hens housed in non-cage production systems, except on the 20^th week, when hens in cages reportedly had significantly higher egg weight than those housed in non-cage housing systems (Singh et al., 2009). Contrary to our findings, some authors (Sekeroglu et al., 2010; Zewde & Kebede, 2022) reported no significant differences in terms of the egg weight of hens housed either in cages, free-range systems, or other non-cage housing systems. However, higher egg weight in hens housed in cages compared to free-range hens and those housed in non-cage housing systems has been reported by several authors (Yakubu et al., 2007; Nayak et al., 2020; Alig et al., 2023c).

With the external egg quality traits measured in the current study, egg weight as a quality trait was significantly higher in free-range hens on the 40^th and 60^th weeks of age compared to hens housed in cages. This could be due to the better development of the reproductive tract or ovary in the free-range hens. It could also be possible that the free-range hens had a higher ability to deposit large amounts of their body weight in eggs compared to the hens in cages. Shape index was higher in free-range hens than in hens housed in cages at 52 weeks of age, and this could be due to the significant increase in egg size of the free-range hens. A higher shape index has been reported in eggs from non-cage housing systems compared to eggs from cages (Küçükyılmaz et al., 2012; Englmaierová et al., 2014).

Contrary to the results of this study, a higher shape index has been reported in eggs from caged hens than from free-range hens (Sekeroglu et al., 2010; Nayak et al., 2020). However, other authors (Yang et al., 2014; Zewde & Kebede, 2022) have also reported no significant effects of the housing systems on shape index. Higher eggshell thickness were observed in both the free-range hens (48 and 56 weeks) and those housed in cages (40 and 68 weeks) in the current study. This could be a reflection of different calcium and phosphorus requirements or intake in those weeks causing a significant variation in eggshell thickness between the two groups in the respective weeks. Other studies have also observed higher eggshell thickness in eggs either from cages, free-range systems, or other non-cage production systems (Küçükyılmaz et al., 2012; Englmaierová et al., 2014; Yang et al., 2014; Rodríguez-Hernández et al., 2024; Alig et al., 2023b).

Egg breaking resistance was significantly higher in eggs from cages than in eggs from the free-range system at 36 weeks, and this is a direct consequence of the higher eggshell thickness from eggs obtained in cages in that week compared to eggs from the free-range hens. In line with our findings, higher eggshell-breaking strength in eggs from cages compared to those from free-range and other non-cage housing systems have been observed by other authors (Englmaierová et al., 2014; Stojanova et al., 2016; Al-Ajeeli et al., 2018; Rodríguez-Hernández et al., 2024). Contrary to our findings higher breaking strength in eggs from free-range systems than from cages has been reported (Yang et al., 2014; Alig et al., 2023b). However, some authors have also reported no significant effect of the housing on egg-breaking resistance (Sekeroglu et al., 2010).

The lack of significant difference in terms of the total average for all the external quality traits (egg weight, shell thickness, egg breaking resistace, and shape index) between the two housing systems could indicate acclimatization to the various housing systems and its environmental stimuli, enabling hens to have a stable developmental and production performance.

Regarding internal egg quality traits, eggs from free-range hens had the highest albumen index on the 20^th and 44^th weeks, but eggs from cages were superior on the 24^th and 36^th weeks. The albumen index is a direct reflection of albumen height, length, and width, which could have been higher in both groups in the respective weeks. Other authors have also observed higher albumen index in eggs either from cages or noncage housing systems (Englmaierová et al., 2014; Nayak et al., 2020). However, no significant effect of the housing on the albumen index was reported by some authors (Sekeroglu et al., 2010).

The yolk index was higher in eggs from free-range systems than in eggs from cages on the 20^th and 28^th weeks, which could be a direct effect of the higher yolk size from the free-range eggs. Higher yolk index in eggs from free-range and other non-cage housing systems as compared to eggs from conventional cages have been previously reported (Sekeroglu et al., 2010; Englmaierová et al., 2014). Contrary to our findings, some authors have also observed a higher yolk index in eggs from cages than in eggs from non-cage housing systems (Nayak et al., 2020; Zewde & Kebede, 2022).

The Haugh unit in the present study was higher in eggs from free-range systems than in eggs from cages at weeks 20 and 44. This is probably due to the higher egg weight and albumen dimensions observed in eggs from free-range hens. Higher Haugh units in eggs from free-range and other non-cage housing systems than in eggs from conventional cages have been reported (Sekeroglu et al., 2010; Englmaierová et al., 2014; Nayak et al., 2020; Zewde & Kebede, 2022; Rodríguez-Hernández et al., 2024). Contrary to the results of the present study, higher Haugh units in eggs from conventional cages than in eggs from free-range or other cage-free systems have also been reported (Stojanova et al., 2016; Alig et al., 2023b).

In the current study, albumen pH was higher in eggs from cages than in eggs from the free-range system at 68 weeks. Since hens in cages have been reported to have high levels of corticosterone due to stress, it is possible that those in cages at 68 weeks of age exhibited an excessive panting behavior to regulate body temperature, which might have caused severe loss of carbonic ions, leading to a severe increase in blood and egg pH (respiratory alkalosis) and a subsequent higher albumen pH. Contrary to the findings of the current study, no significant effect of the housing systems on albumen pH had been observed by some authors (Sekeroglu et al., 2010).

The lack of statistical difference for the total average yolk index, albumen index, and Haugh unit between the production systems could be related to ability of the hens to cope with the housing systems and its environmental stimuli with time, with hens being able to continue with normal growth and reproductive developments.

The brightness (L), redness (a), and yellowness (b) of the yolk color traits was higher in most of the weeks (weeks 20, 24, and 56) in eggs from the free-range system than in eggs from cages, except in the 68^th week, when eggs from cages had higher redness color than eggs from the free-range system. The superior egg yolk traits in the free-range hens could simply be a direct result of free-range hens feeding on forage plants, which are known to be a huge source of carotenoids (Mortensen & Skibsted, 2000), known for pigmentation of the yolk. Other types of carotenoids in forage plants such as xantophylls have been reported to improve egg yolk color (Marounek & Pebriansyah, 2018).

It is speculated that the lack of statistical difference for the total average brightness (L), redness (a), and yellowness (b) of the yolk color traits between the production systems could be related to the decline in egg quality traits due to aging irrespective of the housing system. It is also be possible that hens were able to adapt earlier to their various housing systems and their effect was not enough to cause signifcant differences in total L, a, and b values.

The growth performance, egg production, overall egg weight, and egg quality traits of the new Turkish laying hen hybrid Akbay were better in the free-range production system than in conventional cages. These hens can be housed in the free-range system without any negative effect on performance and egg production traits.

REFERENCES

• Abdallah N, Boga YE, Kursun K, et al. Automation in layer hen production. International Current Research on Agriculture and Food Technologies 2022;9.
• Al-Ajeeli MN, Leyva-Jimenez H, Abdaljaleel RA, et al. Evaluation of the performance of Hy-Line Brown laying hens fed soybean or soybean-free diets using cage or free-range rearing systems. Poultry Science 2018;97(3):812-9. https://doi.org/10.3382/ps/pex368
  » https://doi.org/10.3382/ps/pex368
• Al-Awadi AA, Husseini MD, Diab MF, et al. Productive performance of laying hens housed in minimal shade floor pens and laying cages under ambient conditions in hot arid regions. Livestock Production Science 1995; 41(3):263-9. https://doi.org/10.1016/0301-6226(93)E0119-D
  » https://doi.org/10.1016/0301-6226(93)E0119-D
• Alig BN, Ferket PR, Malheiros RD, et al. The effect of housing environment on commercial brown egg layer production, USDA grade and USDA size distribution. Animals 2023a;13(4):694. https://doi.org/10.3390/ani13040694
  » https://doi.org/10.3390/ani13040694
• Alig BN, Ferket PR, Malheiros RD, et al. The Effect of housing environment on egg production, USDA egg size, and USDA grade distribution of commercial white egg layers. Poultry 2023c;2(2):204-21. https://doi.org/10.3390/poultry2020017
  » https://doi.org/10.3390/poultry2020017
• Alig BN, Malheiros RD, Anderson KE. Evaluation of physical egg quality parameters of commercial brown laying hens housed in five production systems. Animals 2023b;13(4):716. https://doi.org/10.3390/ani13040716
  » https://doi.org/10.3390/ani13040716
• Ankara Tavukculuk. Gida tarim ve hayvancilik bakanligi tavukculuk arastima enstitusu mudurlugu. Yarka: Serbest Dolasan Tavuk Yumurtalari; 2015. Available from: www.arastirma.tarim.gov.tr/tavukculuk
• Detilleux J, Moula N, Dawans E, et al. A probabilistic structural equation model to evaluate links between gut microbiota and body weights of chicken fed or not fed insect larvae. Biology 2022;11(3):357. https://doi.org/10.3390/biology11030357
  » https://doi.org/10.3390/biology11030357
• Digiacomo K, Leury BJ. Insect meal;a future source of protein feed for pigs?. Animal 2019; 13(12):3022-3030. https://doi.org/10.1017/S1751731119001873
  » https://doi.org/10.1017/S1751731119001873
• Dikmen BY, Ipek A, Sahan Ü, et al. Egg production and welfare of laying hens kept in different housing systems (conventional, enriched cage, and free range). Poultry Science 2016;95(7):1564-72. https://doi.org/10.3382/ps/pew082
  » https://doi.org/10.3382/ps/pew082
• El-Sheikh TM, Ali AK. Evaluation of commercial laying hens performance in floor pens and conventional cages under south valley conditions in Egypt. Proceedings of the 3rd International Poultry Conference; 2005; Hurghada: EPSA; 2005. p.506-29
• Englmaierová M, Tumová E, Charvátová V, et al. Effects of laying hens housing system on laying performance, egg quality characteristics, and egg microbial contamination [original paper]. Czech Journal of Animal Science 2014;59(8). https://doi.org/10.17221/7585-CJAS
  » https://doi.org/10.17221/7585-CJAS
• Gibson SW, Hughes BO, Harvey S, et al. Plasma concentrations of corticosterone and thyroid hormones in laying fowls from different housing systems. British Poultry Science 1986;27(4):621-8. https://doi.org/10.1080/00071668608416921
  » https://doi.org/10.1080/00071668608416921
• Hy-Line. W-80 management guide. 2023. Available from: https://www.hyline.com/varieties/w-80
  » https://www.hyline.com/varieties/w-80
• Irshad A, Kandeepan G, Kumar S, et al. Factors influencing carcass composition of livestock;A review. Journal of Animal Production Advances 2013; 3(1). https://doi.org/10.5455/japa.20130531093231
  » https://doi.org/10.5455/japa.20130531093231
• Jones DR, Karcher DM, Abdo Z. Effect of a commercial housing system on egg quality during extended storage. Poultry Science 2014;93(5):1282-8. https://doi.org/10.3382/ps.2013-03631
  » https://doi.org/10.3382/ps.2013-03631
• Kursun K, Abdallah N, Boga YE, et al., The influence of different production systems on the welfare of a new commercial layer hen hybrid. Brazilian Journal of Poultry Science 2014;26(1): eRBCA-2023. https://doi.org/10.1590/1806-9061-2023-1868
  » https://doi.org/10.1590/1806-9061-2023-1868
• Küçükyilmaz K, Bozkurt M, Herken EN, et al. Effects of rearing systems on performance, egg characteristics and immune response in two layer hen genotype. Asian-Australasian Journal of Animal Sciences 2012;25(4):559. https://doi.org/10.5713/ajas.2011.11382
  » https://doi.org/10.5713/ajas.2011.11382
• Malematja E, Manyelo TG, Sebola NA, et al. The role of insects in promoting the health and gut status of poultry. Comparative Clinical Pathology 2023;1-13. https://doi.org/10.1007/s00580-023-03447-4
  » https://doi.org/10.1007/s00580-023-03447-4
• Mallick P, Muduli K, Biswal JN, et al. Broiler poultry feed cost optimization using linear programming technique. Journal of Operations and Strategic Planning 2020;3(1):31-57. https://doi.org/10.1177/2516600X19896
  » https://doi.org/10.1177/2516600X19896
• Marounek M, Pebriansyah A. Use of carotenoids in feed mixtures for poultry;a review. Agricultura Tropica et Subtropica 2018;51(3):107-11. https://doi.org/10.2478/ats-2018-0011
  » https://doi.org/10.2478/ats-2018-0011
• Martin AG, Franklin WM, Maffiol A. Quail: an egg and meat production system. North Fort Myers (FL): ECHO; 1998. p.1-14
• Mashaly MM, Hendricks GL, Kalama MA, et al. Effect of heat stress on production parameters and immune responses of commercial laying hens. Poultry Science 2004;83(6):889-94. https://doi.org/10.1093/ps/83.6.889
  » https://doi.org/10.1093/ps/83.6.889
• Mench JA, Sumner DA, Rosen-Molina JT. Sustainability of egg production in the United States-The policy and market context. Poultry Science 2011; 90(1):229-40. https://doi.org/10.3382/ps.2010-00844
  » https://doi.org/10.3382/ps.2010-00844
• Miao ZH, Glatz PC, Ru YJ. Free-range poultry production-A review. Asian-Australasian Journal of Animal Sciences 2005;18(1):113-32.
• Mortensen ALAN., Skibsted LH. Antioxidant activity of carotenoids in muscle foods. In: Decker EA, Faustman C, Lopez-Bote C, editors. New York: Wiley-Interscience; 2000. p.61-84.
• Nayak Y, Samantaray BP, Biswal L, et al. Effect of rearing system in production performance and egg quality characteristics of vanaraja layers (Gallus Gallus domesticus). International Journal of Modern Agriculture 2020;9(4)332-41.
• Rahimi A. The effect of housing system and photoperiod on welfare and production parameters on commercial white egg layers [dissertation]. North Carolina State University; 2022.
• Rodríguez-Hernández R, Rondón-Barragán IS, Oviedo-Rondón EO. Egg quality, yolk fatty acid profiles from laying hens housed in conventional cage and cage-free production systems in the andean tropics. Animals 2024;14(1):168. https://doi.org/10.3390/ani14010168
  » https://doi.org/10.3390/ani14010168
• Sekeroglu A, Sarica M, Demir E, et al. Effects of different housing systems on some performance traits and egg qualities of laying hens. Journal of Animal and Veterinary Advances 2010;9(12). https://doi.org/10.3923/javaa.2010.1739.1744
  » https://doi.org/10.3923/javaa.2010.1739.1744
• Singh R, Cheng KM, Silversides FG. Production performance and egg quality of four strains of laying hens kept in conventional cages and floor pens. Poultry Science 2009;88(2):256-64. https://doi.org/10.3382/ps.2008-00237
  » https://doi.org/10.3382/ps.2008-00237
• Sosnówka-Czajka E, Herbut E, Skomorucha I. Effect of different housing systems on productivity and welfare of laying hens. Annals of Animal Science 2010;10(4):349-60.
• Stojanova M, Kocevski D, Vukovic V, et al. Comparison of qualitative properties of eggs from hens reared in battery cages and free range system. International Journal of Agronomy and Agricultural Research 2016;9(6):77-83.
• Tactacan GB, Guenter W, Lewis NJ, Rodriguez-Lecompte JC, et al. Performance and welfare of laying hens in conventional and enriched cages. Poultry Science 2009;88(4):698-707. https://doi.org/10.3382/ps.2008-00369
  » https://doi.org/10.3382/ps.2008-00369
• Yakubu A, Salako AE, Ige AO. Effects of genotype and housing system on the laying performance of chickens in different seasons in the semi-humid tropics. International Journal of Poultry Science 2007;6(6):434-9. https://doi.org/10.3923/ijps.2007.434.439
  » https://doi.org/10.3923/ijps.2007.434.439
• Yang HM, Yang Z, Wang W, et al. Effects of different housing systems on visceral organs, serum biochemical proportions, immune performance and egg quality of laying hens. European Poultry Science/Archiv für Geflügelkunde 2014;78. https://doi.org/10.1399/eps.2014.48
  » https://doi.org/10.1399/eps.2014.48
• Zewde MM, Kebede E. Comparative evaluation of deep-litter and cage housing systems on egg production and quality, hematological parameters, and serum metabolites of white leghorn layers [dissertation]. Harar: Haramaya University; 2022.
• Zhao Y, Li P, Chen N, et al. Effects of housing systems and glucose oxidase on growth performance and intestinal health of Beijing you chickens. Poultry Science 2021;100(4):100943. https://doi.org/10.1016/j.psj.2020.12.040
  » https://doi.org/10.1016/j.psj.2020.12.040
• Zheng M, Mao P, Tian X, et al. Growth performance, carcass characteristics, meat and egg quality, and intestinal microbiota in Beijing-you chicken on diets with inclusion of fresh chicory forage. Italian Journal of Animal Science 2019b;18(1):1310-20. https://doi.org/10.1080/1828051X.2019.1643794
  » https://doi.org/10.1080/1828051X.2019.1643794
• Zheng M, Mao P, Tian X, et al. Effects of dietary supplementation of alfalfa meal on growth performance, carcass characteristics, meat and egg quality, and intestinal microbiota in Beijing-you chicken. Poultry Science 2019a;98(5):2250-9. https://doi.org/10.3382/ps/pey550
  » https://doi.org/10.3382/ps/pey550
• Zheng M, Mao P, Tian X, et al. Effects of grazing mixed-grass pastures on growth performance, immune responses, and intestinal microbiota in free-range Beijing-you chickens. Poultry Science 2021;100(2):1049-58. https://doi.org/10.1016/j.psj.2020.11.005
  » https://doi.org/10.1016/j.psj.2020.11.005

• Funding
  This study was supported by the Ministry of Agriculture and Forestry under the Research and Development Support Program with the project code TAGEM / 20 / AR-GE / 11.
• Data availability statement
  Data will be available upon request.
• Disclaimer/Publisher’s Note
  The published papers’ statements, opinions, and data are those of the individual author(s) and contributor(s). The editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions, or products referred to in the content.

Edited by

• Section editor:
  Tatiana Carlesso dos Santos

Data availability

Data will be available upon request.

Publication Dates

• Publication in this collection
  01 Nov 2024
• Date of issue
  2024

History

• Received
  03 Mar 2024
• Accepted
  19 July 2024