Effect of housing system and housing density on performance, viability, and gastrointestinal tract growth of broiler chicks during the first 2 wk of age

Abstract

This experiment was conducted to study the effect of housing systems and housing densities on the performance and digestive tract growth of broiler chicks during the first 2 wk of age. A total of 3,600 Cobb500 day-old chicks were stocked at 4 densities (30, 60, 90, and 120 chicks/m²), and reared under 2 housing systems (conventional housing system and newly developed housing system), yielding a 2 × 4 factorial arrangement. The studied traits were performance, viability, and gastrointestinal tract development. The results indicated that housing systems and housing densities significantly (P < 0.001) affected the performance and GIT development of chicks. There were no significant interactions between housing system and housing density for body weight, body weight gain, feed intake, and feed conversion. The results also showed that the effects of housing density were age-dependent. That is, the higher the density, the lower the performance and digestive tract growth with advancing age. In conclusion, birds in the conventional system outperformed birds in the newly developed housing system, and further work is needed to improve the new housing system. To achieve the highest performance, digestive tract growth, and digesta content, a density of 30 chicks/m² is recommended for chicks up to 14-days old.

INTRODUCTION

Housing system (HS) is a crucial factor affecting bird comfort, welfare, health, and productive and reproductive efficiency (Willis et al., 2002; Chen et al., 2013; Attia et al., 2021a,b). The poultry housed either conventional or traditional systems; conventional system such as floor/deep litter system and traditional system such as battery cage and plastic net rearing (Yan et al., 2021). Several studies evaluated the effect of different housing systems on the performance and health of broilers (Swain et al., 2002; Willis et al., 2002; Vanan et al., 2014). The findings of these literatures on different rearing systems are equivocal for bird health and performance. There are numerous underlining issues for the differences. One is the effect of bedding materials on bird health and performance (Choct, 2009) and the other is coccidiosis.

Great efforts in conventional floor HS are given to control the “macroenvironment: Macrospace and time” (i.e., whole house temperature, ventilation, and humidity) which is not always possible due to huge variations of the outside environment or due to bad management and carelessness of the workers. Thus, the novelty of this paper is the use of a highly automated newly developed HS (Innovative Control System Company, Bethlehem, PA) completely isolated from the house environment to precisely biosecurity and control the microenvironment “Microspace and time” (faster and better control of critical control points). Furthermore, this new system incorporates moving 3-mm conveyer belts directly beneath the chicks for improved hygiene and manure removal once every 24 h (as opposed to a conventional system that incorporates bedding material). Furthermore, in order to provide and maintain the appropriate CCP, this system pushed air into the system via multiducts to create high air velocity with positive pressure (in contrast to conventional systems, which use negative air pressure to bring air into the house). In addition, this system has multiple tiers to contribute to the literature by brooding the greatest number of birds in the smallest area while spending the least amount of money on energy, labor, housing, and so on. If such a system proves successful, the implications are remarkable. Example, one new housing systems (1 × 25 m with 10 tiers) can produce approximately 75,000 chicks every 10 d more than enough to be placed in a broiler farm with 3 conventional houses, and can reduce manpower from 3 of 3 conventional HS to 1 in new HS. Brooded chicks in the farm or hatchery during the brooding period at a newly developed HS with microenvironment rather than macroenvironment. Furthermore, because chicks are more susceptible to diseases during this period due to an underdeveloped thermoregulatory system, digestive system, and immune system, this system is designed with high biosecurity to reduce disease transmission and pathogen spread from one pen to another and farm to farm. As a result, this study concentrated on the brooding period rather than the grown out period as the transitional environment between the hatchery environment and the farm environment. After that, birds can be transferred to more grow out houses at the age of 10 to 14 d rather than transferring them to a section of the house, when they are more evolved and less susceptible to variations in house climate and pathogen infection. Hence, this research is undertaken to test newly developed HS for broilers and explore the advantages/disadvantages in practice.

There are few, if any, recorded scientific publications on the housing density (HD) of broiler chicks raised to 14 d of age. Most of the information available in the literature is aimed at the final HD at the end of the rearing cycle. Stress can be caused by a variety of environmental factors (Gangloff and Greenberg, 2023). According to recent research, High HD is an important environmental factor and the main constraint in modern poultry production to reach their full growth potential at market age as well as livability, and intestinal health (Chegini et al., 2019; Esmaeili-Fard et al., 2022; Franco-Rosselló et al., 2022; Son et al., 2022). Broilers are typically housed in varying ranges of HD depending on the country's regulations, production system and target body weight, aiming at minimizing fixed costs and maximizing profitability (Gholami et al., 2020; Nawarathne et al., 2020). During the brooding period, farmers and researchers use various housing densities in conventional broiler farms at the entry and then expand to the entire house as the birds grow. However, the impact of these various densities has not been studied and no precise information is available. Stocking density and housing system have an impact on broiler performance up to slaughter age. However, the brooding period after hatching (10–14 d) represent 33 to 47% of the production cycle (30 d) of broiler chicks in Saudi Arabia, thus becomes more critical and important in the span of a broiler's life, posing a greater challenge to growers (Bruzual et al., 2000; Zahraa and Ghamdi, 2008). In addition, good management practices of broiler development during the brooding period is critical for improving growth performance due to the digestive system develops strongly during the brooding period, followed by skeletal and muscular growth (Cardeal et al., 2020; Kallam and Sejian, 2021). The present study, therefore, was undertaken to assess the performance and gastrointestinal tract growth of broilers chicks at various housing densities level. Moreover, to evaluate chick's performance under a newly developed housing system in comparison to conventional housing.

Materials and Methods

The study was carried out at the Rostum Poultry Farm in Riyadh, Saudi Arabia. The trial took place in Riyadh during the spring months with average temperatures ranging from 20.4°C to 33.4°C and an average relative humidity of 28%.

Birds and Husbandry

The experimental procedures were approved by the Ethics, Methodology, and Animal Welfare Studies Committee of King Saud University, Saudi Arabia (No. KSU-SE-23-17). A total 3,600 at day-old chicks (Cobb 500) were obtained from a local hatchery. On arrival, chicks weighed individual and distributed into 24 replicate pens of equal weights for each system. Each pen (1 m²) was equipped with water line and tubular plastic feeders. To obtain real results for the HD, feeder and water space were adjusted equally in both HS, thus each pen was supplemented with 2 tubular plastic poultry feeders (30 cm length × 30 cm width × 23 cm high) and 2 adjustable water nipple systems (3 nipple water drinkers) hanging inside each pen.

The birds were fed a commercial crumbled starter diet (Table S1) and were given feed and water as needed. All critical control points such as ventilation, temperature, and lighting were controlled according to breeder guidelines (Cobb, 2022) for chicks from 0 to 14 d of age.

Treatments

The experimental treatments consisted of 2 housing systems (conventional and newly developed housing systems) and 4 housing densities (30, 60, 90, and 120 chicks/m²) resulting from a 2 × 4 factorial arrangement (8 treatments; n = 6 replicates/HD in each HS). The housing density in both housing systems, particularly the new system, was chosen on a wide interval range basis to detect the best density of birds in square meter surface area in each system with the greatest birds capacity during the brooding period without negatively affecting bird growth performance.

The number of chicks was maintained in a replicate according to the relevant HD in a constant area. Therefore, at the brooding stage, the treatments 1, 2, 3, and 4 represented 30, 60, 90, and 120 birds, respectively, stocked at 1 m² in conventional housing systems; and treatments 5, 6, 7, and 8 represented 30, 60, 90, and 120 birds, respectively, stocked at 1 m² in newly developed housing systems (Innovative Control System Company). Conventional floor housing system in pens with fresh wood shavings similar to commercial settings. New housing system (multitier closed system) with moving 3-mm conveyer belts. The new system, in brief, is a closed system inside the house and is totally closed with superior biosecurity control and isolated from the environment of the house in order to control the “microenvironment” with 60 cm high for each tier as shown in Figure 1. Air was pushed into the system via multiducts to create positive pressure (opposite of conventional broiler houses that uses negative air pressure to bring air into the house) to provide and maintain the appropriate critical control point. It is also fitted with moving 3-mm conveyer belts directly underneath the chicks for hygiene and removal of manure. The conveyer belt was set to a very slow speed (less than 1 m/h) so as to clean the manure once every 24 h with minimum disturbance to the birds. Each tier of the system was equipped with temperature, humidity and CO₂ sensors in order to control the critical control point as close as possible to the bird's requirement.

Figure 1. (.

A) Illustrated newly developed housing systems (Innovative Control System Company). (B) Newly developed housing systems as faster and better control of critical control points.

Performance Measurements

Birds were weighed individually upon arrival, and performance measures of body weight, weight gain, feed intake, and feed conversion (feed: gain) ratio were determined as pen/group on d 2, 5, 8, 11, and 14 of age. Mortality was recorded daily and was summarized along experimental study.

Gastrointestinal Tract Measurements

To determine absolute and relative weight (% BW) of the full digestive tract (GIT), 12 chicks were chosen at random and slaughtered in chick kill cones on d 3, 6, 9, and 12. Bleeding was accomplished entirely through severed blood vessels, scalding was performed, the abdominal cavity was opened, and the GIT was removed from the beginning of the proventriculus to the beginning of the ileocecal junction. Absolute GIT weight (g) was determined by aseptically removing the gizzard, small intestine, and cecum and weighing them together in both full and empty cases. The following equation was used to calculate relative digestive tract weight as a percentage of chick BW: Digestive tract relative weight (GTRW; %BW) = Empty digestive tract weight (g)/Body weight (g) × 100. Digesta relative weight (DRW) of digestive tract was calculated as the percentage of chick full digestive tract weight using the following equation (Jiménez-Moreno et al., 2019): DRW (%GIT) = [(Full digestive tract weight (g) − empty digestive tract weight (g))/Full digestive tract weight (g)] × 100. Following the selection of birds for sampling, the density of the birds was maintained as a primary experimental variable by reducing the space area allocated to each slaughtered bird.

Statistical Analysis

Data were statistically analyzed using 2-way ANOVA and SAS's General Liner Models procedure (Institute, 2004). The experimental unit was a pen for performance data and sample size (n = 12 samples per treatment) for digestive data. The following model was used:

$${\gamma }_{ijk}=\mu +H{S}_i+H{D}_j+HSH{D}_{ij}+e_{ijk}$$

where ${\gamma }_{ijk}$ represents a single observation; $\mu$ denotes the experimental mean; $H{S}_i$ denotes the effect of $i$th housing system type; $H{D}_j$ denotes the impact of $j$th housing density level; housing system by housing density interaction is represented by $HSH{D}_{ij}$, while random error is represented by $e_{ijk}$. When significant, Ryan-Einot-Gabriel-Welsch multiple range (REGWQ) test (this test controls the Type I experiment wise error rate) at a 5% probability was used for comparison between means. The Kolmogorov-Smirnov test and Box plot were used to ensure the homogeneity and normality of variances across study groups. Mortality data were also transformed using the arcsine function prior to analysis; however, the reported percentages are the actual values.

RESULTS

Performance Variables

The effects of housing system and housing density, and their interactions on the performance of broiler chicks in the first 2 wk of life are shown in Tables 1 and 2. As shown in Table 1, HS and HD had a significant effect (P > 0.001) on body weight of broiler chicks at 8 and 14 d of age. No significant difference (P > 0.05) was found between HS and HD interaction on body weight of the birds. Although the initial body weight (d 0) was not significantly different, the average body weight under the conventional system (240 and 456 g at d 8 and 14, respectively) was significantly higher than under the new system (203 and 403 g at d 8 and 14, respectively). Therefore, chick body weight was significantly (P > 0.001) higher under the conventional system than under the new system on d 8 and 14.

Table 1.

Live body weight (BW; g) of broiler chicks reared at 2 different housing systems (HS) (conventional (C) and new (N)) and 4 levels of housing densities (HD) during the first 2 wk of age.

Treatment1	HS	HD (chicks/m2)	BW at d 0	BW at d 8	BW at d 14
1	C	30	48.0	245	509
2	C	60	47.8	244	478
3	C	90	47.9	238	446
4	C	120	47.9	234	389
5	N	30	48.3	206	438
6	N	60	48.3	208	426
7	N	90	48.0	202	388
8	N	120	48.1	197	362
SE±2			0.095	1.913	5.70
HS
C			47.9	240a	456a
N			48.1	203b	403b
SE±			0.047	0.956	2.85
HD
30			48.2	225a	473a
60			48.1	226a	452b
90			48.0	220b	417c
120			48.0	216c	375d
SE±			0.067	1.35	4.03
Probabilities
HS			0.051	<0.0001	<0.0001
HD			0.458	0.012	<0.0001
HS*HD			0.602	0.945	0.133

¹At the brooding period (1–14 d), treatments 1, 2, 3, and 4 represented 30, 60, 90, and 120 birds stocked at 1 m² in conventional housing systems; and treatments 5, 6, 7, and 8 represented 30, 60, 90, and 120 birds stocked at 1 m² in newly developed housing systems.

²SE, standard error. n = 6 replicates for each density in each system.

^a–dLetters within column are significantly different at P < 0.05.

Table 2.

Average daily gain, average feed intake, feed conversion ratio, and mortality rate of broiler chicks reared at 2 different housing systems (HS) (conventional (C) and new (N)) and 4 levels of housing densities (HD) during the first 2 wk of age.

Treatment1	HS	HD (chicks/m2)	Average daily gain (g/d)			Average feed intake (g/d)			Feed conversion ratio (g:g)
			0–8 d	8–14 d	0–14 d	0–8 d	8–14 d	0–14 d	0–8 d	8–14 d	0–14 d
1	C	30	24.6	44.0	32.9	24.5	59.4	34.3	1.00	1.35	1.04
2	C	60	24.5	39.1	30.8	24.0	54.7	33.3	0.98	1.40	1.08
3	C	90	23.8	34.6	28.5	23.8	49.8	31.8	1.00	1.44	1.12
4	C	120	23.3	25.8	24.3	23.3	40.2	26.8	1.00	1.56	1.10
5	N	30	19.7	38.7	27.8	20.9	53.1	30.5	1.06	1.38	1.10
6	N	60	20.0	36.3	27.0	21.3	51.2	30.3	1.07	1.41	1.13
7	N	90	19.2	31.1	24.3	21.0	45.9	27.9	1.09	1.47	1.15
8	N	120	18.7	27.4	22.4	19.6	43.3	26.3	1.05	1.58	1.17
SE ±2			0.242	0.782	0.408	0.39	1.007	0.561	0.02	0.025	0.020
HS
C			24.0a	35.9a	29.1a	23.9a	51.0a	31.6a	0.99b	1.44	1.09b
N			19.4b	33.4b	25.4b	20.7b	48.4b	28.8b	1.07a	1.46	1.14a
SE±			0.121	0.391	0.204	0.195	0.504	0.280	0.009	0.012	0.001
HD
30			22.1a	41.3a	30.4a	22.7a	56.3a	32.4a	1.03	1.36c	1.07b
60			22.2a	37.7b	28.9b	22.7a	52.9b	31.8a	1.02	1.40bc	1.10ab
90			21.5b	32.9c	26.4c	22.4a	47.8c	29.8b	1.05	1.46b	1.13a
120			21.0c	26.6d	23.4d	21.5b	41.8d	26.6c	1.03	1.57a	1.14a
SE±			0.171	0.552	0.289	0.276	0.712	0.397	0.013	0.018	0.014
Probabilities
HS			<0.0001	0.011	<0.0001	<0.0001	0.034	0.0004	0.002	0.256	0.040
HD			0.015	<0.0001	<0.0001	0.0146	<0.0001	<0.0001	0.827	0.001	0.024
HS*HD			0.947	0.066	0.133	0.696	0.053	0.238	0.893	0.993	0.897

¹Treatments 1, 2, 3, and 4 represented 30, 60, 90, and 120 birds stocked at 1 m² in conventional housing systems; and treatments 5, 6, 7, and 8 represented 30, 60, 90, and 120 birds stocked at 1 m² in newly developed housing systems.

²SE, standard error. n = 6 replicates per treatment.

^a–dLetters within column are significantly different at P < 0.05.

Housing density significantly affected body weight of broiler chicks at d 8 (P = 0.012) and 14 (P > 0.001) of the age. Chick body weight decreased significantly with increasing HD on d 8 and 14, but not on d 0. From d 8, chicks were significantly (P = 0.012) heavier (225 and 226 g, respectively) at housing densities of 30 and 60 birds/m² than at housing densities of 90 and 120 birds/m² (220 and 216 g, respectively). However, there were no significant differences in body weight between housing densities of 30 and 60 birds/m². However, birds stocked at 90 birds/m² were significantly heavier than birds stocked at 120 birds/m². Chick body weight was also significantly different (P < 0.001) on d 14 between all housing densities of 30, 60, 90, and 120 birds/m² (473, 452, 417, and 375 g, respectively). The negative effect of high housing densities of 90 and 120 birds/m² on chick body weight began on d 8. Except on d 14, no significant difference in body weight was observed between housing densities of 30 and 60 birds/m². Thus, chicks at a HD of 30 birds/m² had the highest average body weight among all housing densities. Chicks raised at a HD of 60 birds/m² were heavier than chicks raised at 90 and 120 birds/m². In addition, birds raised at 90 birds/m² were significantly heavier than birds raised at 120 birds/m². This indicates that body weight decreases with age as HD increases.

As shown in Table 2, HS and HD had a significant effect (P < 0.05) on body weight gain, feed intake, and feed conversion of broiler chicks at 0 to 8, 8 to 14, and total 0 to 14 d of age. However, feed conversion was not affected by HD during 0 to 8 d and by HS during 8 to 14 d. No significant differences (P > 0.05) were found between HS and HD interaction on body weight gain, feed intake, and feed conversion of broiler chicks during 0 to 8, 8 to 14, and 0 to 14 d of age.

Body weight gain and feed intake of chicks in the conventional system were significantly (P > 0.05) higher than those of chicks in the new system at 0 to 8, 8 to 14, and 0 to 14 d of age. Feed intake of chicks in the conventional system was also significantly (P > 0.001) higher than that of chicks in the new system. Consequently, the feed conversion ratio of chicks in the conventional system was significantly (P > 0.05) better than that of chicks in the new system at 0 to 8 and 0 to 14 d of age and numerically better at 8 to 14 d of age.

Chick body weight gain was significantly (P > 0.05) affected by HD at 0 to 8, 8 to 14, and 0 to 14 d of age. At 0 to 8 d of age, birds with housing densities of 30 and 60 birds/m² were did not differ significantly. However, they gained more weight than birds stocked at 90 and 120 birds/m². Birds stocked at 90 birds/m² gained significantly more than birds stocked at 120 birds/m². During 8 to 14 and 0 to 14 d, birds stocked at 30 birds/m² had the highest gain among the other housing densities. In addition, gains were higher for birds stocked at 60 birds/m² than for chicks raised at 90 and 120 birds/m². In addition, gains were significantly higher for birds stocked at 90 birds/m² than for birds stocked at 120 birds/m². This indicates that the average daily gain decreases with increasing HD. Although a significant difference was found between housing densities of 30 and 60 birds/m² in body weight gain during the experimental period of 0 to 14 d, the values were similar at 0 to 8 d.

Chick feed intake was significantly (P > 0.05) affected by HD at 0 to 8, 8 to 14, and 0 to 14 d of age. Birds with housing densities of 30, 60 and 90 birds/m² did not differ significantly at 0 to 8 d of age, but consumed more feed than birds with housing densities of 120 birds/m². Thus, the HD of 120 birds/m² consumed the least (21.5 g/d). As shown on d 8 to 14, feed intake also differed significantly (P < 0.001) between all housing densities of 30, 60, 90, and 120 birds/m², with the HD of 120 birds/m² resulting in the poorest (P = 0.001) feed conversion, followed by 90 birds/m², while the HD of 30 birds/m² resulted in the best feed conversion. During 0 to 14 d, feed intake of birds stocked at 30 and 60 birds/m² (32.4 and 31.8 g/d, respectively) did not differ significantly. However, they consumed more feed than birds with housing densities of 90 and 120 birds/m² (29.8 and 26.6 g/d, respectively). In addition, birds stocked at 90 birds/m² consumed significantly more feed than birds stocked at 120 birds/m². The negative effect of high HD of 90 birds/m² on chick feed consumption occurs in the second week but was not apparent in the first week, while the negative effect of high HD of 120 birds/m² on chick feed consumption occurs in both periods and throughout the study period.

During period 8 to 14, chick feed conversion was significantly (P = 0.001) affected by HD (1.36, 1.40, 1.46, and 1.57 at housing densities of 30, 60, 90, and 120 birds/m², respectively), but was similar during period 0 to 8. This difference between housing densities in the second week resulted in significant differences in feed conversion throughout the period. The birds stocked at 30 birds/m² had the lowest and better value in feed conversion during 0 to 14 d (1.07) than those stocked at 90 and 120 birds/m² (1.13 and 1.14, respectively). This could be attributed to higher body weight gain than feed intake. However, at a HD of 60 birds/m², feed conversion was between the low and high densities.

Viability Rate

Mortality was significantly affected by system (P = 0.001) at 0 to 8 d, resulting in a significant difference in system throughout the period (P = 0.0003), and by HD (P = 0.051) at 8 to 14 d, resulting in a significant difference in HD throughout the period (P = 0.034) (Table 3). However, the percentage of mortality was not affected by the system*density interaction. In the period of 0 to 8 d, the mortality rate in the new system (3.56%) was higher than the mortality rate in the conventional system (0.87%). This means that the viability (%) in the conventional system (99.13%) was higher than the viability (%) in the new system (96.44%). During the experimental period, the percentage of mortality in the new system (5.05%) was higher than the percentage of mortality in the conventional system (2.00%). On the other hand, the viability (%) in the conventional system (98.00%) was higher than the viability (%) in the new system (94.95%), indicating that the new system decreased the viability by (5.05%) during experimental period 0 to 14 d. The highest mortality rate (P = 0.051) was at HD of 120 birds/m² (2.50%) compared to the other densities during period 8 to 14, but was similar during period 0 to 8. This difference between 120 birds/m² and other housing densities during the second week resulted in significant differences in mortality rates throughout the period. Birds stocked at 120 birds/m² had the highest mortality rate (5.29%) during 0 to 14 d than the other housing densities. Therefore, the viability (%) at 120 birds/m² was 94.71%, which means that 120 birds/m² reduced the viability by (5.29%) during 0 to 14 d.

Table 3.

Mortality rate (%) of broiler chicks reared at 2 housing systems (HS) (conventional (C) and new (N)) and 4 levels of housing densities (HD) during the first 2 wk of age.

Treatment1	HS	HD (chicks/m2)	0–8 d	8–14 d	0–14 d
1	C	30	1.00	1.00	1.99
2	C	60	0.52	0.52	1.04
3	C	90	0.54	1.27	1.81
4	C	120	1.43	1.72	3.15
5	N	30	2.99	1.00	3.98
6	N	60	3.13	0.78	3.91
7	N	90	3.99	0.91	4.89
8	N	120	4.15	3.29	7.44
SE±2			0.827	0.482	0.880
HS
C			0.87b	1.13	2.00b
N			3.56a	1.49	5.05a
SE±			0.414	0.241	0.440
HD
30			1.99	1.00b	2.99b
60			1.82	0.65b	2.47b
90			2.26	1.09b	3.35b
120			2.79	2.50a	5.29a
SE±			0.585	0.341	0.623
Statistical probabilities
HS			0.001	0.647	0.0003
HD			0.525	0.051	0.034
HS*HD			0.734	0.603	0.713

¹Treatments 1, 2, 3, and 4 represented 30, 60, 90, and 120 birds stocked at 1 m² in conventional housing systems and treatments 5, 6, 7, and 8 represented 30, 60, 90, and 120 birds stocked at 1 m² in newly developed housing systems.

²SE, standard error. n = 6 replicates per treatment.

^a,bLetters within column are significantly different at P < 0.05.

Gastrointestinal Tract Growth and Digestive Contents

The effects of the rearing system, HD, and their interactions on the absolute and relative growth of the gastrointestinal tract and digestive contents of broiler chicks during the first 2 wk of age are shown in Tables 4 and 5. Compared with the new system, birds raised in the conventional system had higher (P < 0.5) absolute weights of the digestive tract of chicks on d 3, 6, 9, and 12 and digestive contents (weight, g) on d 9 and 12 (Table 4), resulting in lower (P < 0.5) relative weights of chick digestive tract on d 9 and 12 and digestive content (weight, %) on d 12 (Table 5). The difference between absolute and relative weights between systems resulted from variance between live weights of chicks in both systems.

Table 4.

Absolute weights (g) of digestive tract and digesta of broiler chicks reared at 2 different housing systems (conventional (C) and new (N)) and 4 levels of housing densities during the first 2 wk of age.

Treatment2	Housing system (HS)	Housing densities (HD) (chicks/m2)	Digestive tract weight1 (DTAW; g)				Digesta weight (g)
			D 3	D 6	D 9	D 12	D 3	D 6	D 9	D 12
1	C	30	17.5	26.3	36.2	47.6	4.88	7.55c	12.1	17.5
2	C	60	17.1	25.6	34.7	45.3	4.62	7.51c	11.5	16.3
3	C	90	17.1	26.0	38.3	39.8	4.29	8.91b	11.9	13.6
4	C	120	17.3	26.7	31.3	37.4	4.07	7.06c	9.9	12.1
5	N	30	15.2	21.6	32.3	38.7	5.23	9.90a	12.5	12.5
6	N	60	15.7	25.2	32.3	39.3	5.45	7.02c	10.4	14.2
7	N	90	14.6	22.5	31.4	36.5	5.22	7.10c	7.6	10.7
8	N	120	15.4	23.1	31.7	36.5	4.75	6.79d	8.6	9.4
SE±3			0.527	1.09	1.46	1.71	0.487	0.673	1.04	1.05
HS
C			17.2a	26.2a	35.1a	42.5a	4.46b	7.76	11.3a	14.9a
N			15.2b	23.1b	31.9b	37.8b	5.16a	7.70	9.80b	11.7b
SE±			0.264	0.547	0.730	0.857	0.244	0.336	0.521	0.524
HD
30			16.4	24.0	34.2	43.1a	5.05	8.73a	12.3a	15.0a
60			16.4	25.4	33.5	42.3a	5.03	7.27b	10.9ab	15.2a
90			15.9	24.3	34.9	38.2b	4.75	8.01ab	9.76b	12.2b
120			16.3	24.9	31.5	36.9b	4.41	6.92b	9.23b	10.8b
SE±			0.373	0.773	1.03	1.21	0.345	0.476	0.737	0.741
Statistical probabilities
HS			<0.0001	0.0002	0.003	0.0002	0.046	0.901	0.040	<0.0001
HD			0.705	0.545	0.122	0.001	0.515	0.045	0.020	<0.0001
HS*HD			0.806	0.241	0.096	0.117	0.939	0.025	0.167	0.527

¹Absolute digestive tract weight1 (DTAW; g): weight of digestive tract empty without digesta.

²n = 12 samples per treatment.

³SE, standard error.

^a–dLetters within column are significantly different at P < 0.05.

Table 5.

Gastrointestinal tract development index (relative weights of digestive tract (% BW) and digesta (% full digestive tract) of broiler chicks reared at 2 housing systems (conventional (C) and new (N)) and 4 levels of housing densities during the first 2 wk of age.

Treatment	Housing system (HS)	Housing density (HD) (chicks/m2)	Digestive tract weight1 (DTRW; %)				Digesta weight ((%)
			D 3	D 6	D 9	D 12	D 3	D 6	D 9	D 12
1	C	30	18.52	14.6	12.9	10.8	21.6	22.3	25.2	26.9
2	C	60	17.9	14.5	12.6	10.4	21.2	22.7	24.9	26.5
3	C	90	17.9	15.1	13.2	10.2	19.8	25.4	23.6	25.4
4	C	120	19.0	14.7	12.0	10.5	18.5	21.0	23.7	24.6
5	N	30	17.3	13.1	12.9	12.2	25.2	31.3	28.1	24.2
6	N	60	17.5	16.3	13.7	11.9	25.5	22.1	24.3	26.4
7	N	90	17.0	14.8	13.7	11.5	26.1	24.3	19.2	22.8
8	N	120	17.9	16.0	13.4	12.7	23.6	22.7	21.3	20.2
SE±3			0.516	0.575	0.46	0.43	2.02	2.04	2.31	1.60
HS
C			18.3	14.7	12.6b	10.5b	20.3b	22.8	24.3	25.8a
N			17.4	15.3	13.4a	12.1a	25.1a	25.1	23.2	23.4b
SE±			0.258	0.288	0.230	0.217	1.01	1.02	1.15	0.798
HD
30			17.9	14.3	12.9	11.5	23.4	26.8	26.7	25.5
60			17.7	15.4	13.1	11.1	23.3	22.4	24.6	26.4
90			17.4	15.0	13.4	10.8	23.0	24.9	21.4	24.1
120			18.4	15.3	12.7	11.6	21.0	21.9	22.5	22.4
SE±			0.365	0.407	0.325	0.308	1.43	1.45	1.63	1.13
Statistical probabilities
HS			0.015	0.128	0.018	<0.0001	0.001	0.119	0.492	0.033
HD			0.266	0.179	0.402	0.286	0.622	0.068	0.114	0.075
HS*HD			0.917	0.078	0.464	0.626	0.927	0.058	0.444	0.597

¹Digestive tract relative weight (DTRW; % BW) = Empty digestive tract weight (g)/body weight (g) × 100. Digesta relative weight (%) = [(Full digestive tract weight1 (g) − empty digestive tract weight (g)/Full digestive tract weight (g)) × 100].

²n = 12 samples per treatment.

³SE, standard error.

^a,bLetters within column are significantly different at P < 0.05.

Housing density did not affect relative digestive tract weight (%) and digestive content (%) of broiler chicks, but had a significant effect on digestive content weight (g) during the test period and on absolute digestive tract weight on d 12.

At d 6, the digesta were higher contents in the lower housing densities 30 birds/m² than other densities at d 6 than 90 and 120 birds/m² housing densities at d 9. At d 12, the birds stocked at low housing densities (30 and 60 birds/m²) were higher absolute digestive tract weight without digesta and higher digesta content than birds stocked at high housing densities (90 and 120 birds/m²). This indicated that the HD of 30 birds/m² were the best choice in improved absolute weights of digestive tract (g) followed by 60 birds/m² which more obviously at d 12.

In terms of digesta content (g), the lower HD of 30 birds/m² was higher on d 6 than the other densities, and it was higher on d 9 than the higher housing densities of 90 and 120 birds/m². On d 12, the low HD birds (30 and 60 birds/m²) had higher absolute digestive tract weight without digesta and higher digesta content than high HD birds (90 and 120 birds/m²). This indicates that the HD of 30 birds/m² was the best choice for higher absolute digestive tract weight (g), followed by 60 birds/m², which was even more evident at d 12.

DISCUSSION

This experiment was the first of its kind to evaluate newly developed housing system, while most scientific publication was done on broilers reared under free-range systems, battery cages and intensive rearing. This experiment shows that, HS had significant affected chick's performance. During experimental period, birds reared at the conventional system had more body weight gain, feed intake, and therefore heavier body weight and better feed conversion ratio compared with those reared in the new house system. So that, birds in conventional system gained and converted feed more efficiently than those in new system this may be attributed to higher air speed that pumped directly to birds in new system led to crowded birds. Despite the fact that high HD may reduce airflow at the level of the bird resulting in reduced dissipation of body heat to the air (Feddes et al., 2002; Munonye, 2022; Son et al., 2022). In addition, May et al. (2000) found that broiler chickens exposed to high air velocity consumed more feed and less water while gaining more weight and having a better feed: gain ratio. They did, however, expose the birds to high air velocity from the wall fan (macroenvironment), while here pumped air directly from wide size and few number of inlet holes, which resulted in crowded birds during the first week, which was corrected later on d 7 by increasing the number and narrowing the size of air inlet holes. However, the birds are more sensitive during the brooding period than during the rest period of the growing cycle. Thus, these findings suggest that the new system needs further improvement in order to optimize performance. This was due to some limitations of the ventilation system in that the direct airflow and it should be redesigned. According to Fiorilla et al. (2022), Ross mortality was higher and Ross growth performance was less in both free-range and industrial controlled systems, with a higher percentage in the free-range system than the industrial one. Bogosavljevic-Boskovic et al. (2012) reviewed that the lower performance and mortality of broilers in free-range systems compared to intensive rearing. The differences within the same rearing system might be due to the effect of a range of genetic and nongenetic factors.

To our knowledge, this is one of the first study of its kind on HD of chicks grown until 14 d. Most scientific publications available in the literature are with the aim of final HD in mind at the end of rearing cycle. Thus, there are little or no performance indicators available to compare our work to. But, the data clearly showed that increasing HD reduced body weight, body weight gain, and feed intake and resulted in inferior feed conversion ratio but it was an age-dependent. This outcome is in agreement with the HD impacts at market age reported by others (Goo et al., 2019; Weimer et al., 2020; Attia et al., 2021a; Jhetam et al., 2022; Wang et al., 2022; Kaya and Fidan, 2023; Shynkaruk et al., 2023). While other documented that reducing HD had no influence (Thomas et al., 2004; Zhang et al., 2011) or even had negative impacts on broilers performance (Feddes et al., 2002). Correlation between HD and feed conversion was negative and in agreement with the feed conversion reported where birds at housing densities of 30 and 60 birds/m² performed best compared with those at housing densities of 90 and 120 birds/m². The findings showed that the average feed intake during the first 2 wk of age decreased when the HD was increased. According to Nawarathne et al. (2020), the birds stockpiled at 120 birds/m² consumed the least feed of all the densities. The data showed that birds at housing densities of 30 and 60 birds/m² consumed more feed compared with those at housing densities of 90 and 120 birds/m². It could be possible that increasing the numbers of water line and/or feeder space may improve performance of the birds at high HD. Due to the high HD may inhibit physical access to feeders and water nipples (Estevez, 2007; Franco-Rosselló et al., 2022; Son et al., 2022). Thus, further work is required to test this assumption.

The body weights of birds in the company's performance guide (Cobb 500) were 208 and 459 g on d 8 and 14, respectively. Therefore, body weights at housing densities of 120, 90, 60, and 30 birds/m² were higher in this study regardless of the type of HS than in the company's performance guide by d 8. This indicates that all housing densities exceeded body weight by d 8. Also, at d 14, chicks' body weight at the HD 30 bird/m², especially in the conventional system, was higher than body weight shown in company product's manual (Cobb 500). In agreement with Nawarathne et al. (2020), who observed that a lower HD (40 birds/m²) during the brooding period can reduce density stress, improve growth performance, and increase profit from broiler production. High HD reduced broiler chicken growth and digestive function by decreasing intestinal barrier function and increasing intestinal permeability (Goo et al., 2019; Li et al., 2019).

The significant effects on bird performance with age were clearly observed between 30 and 60 birds/m², where both densities weighed and gained similarly at d 8 and varied at 14 d of age. Thus, chicks' body weight at d 8 and 14, and also the gain, feed intake and feed conversion during 0 to 8, 8 to 14, and 0 to 14 d were reduced significantly with increasing HD with advanced age. These outcomes are in agreement with others (Sekeroglu et al., 2011; Zuowei et al., 2011; Nawarathne et al., 2020).

Mortality is considered as end point of welfare and therefore the final indicator of stress (Buijs et al., 2009). The HS and HD had a significant effect on mortality. Similarly, Hall (2001) established significant effect of mortality which increased with increasing HD. In contrast to Nawarathne et al. (2020), who found that mortality percentages during the brooding period were not significantly different between the 3 HD treatments. The higher mortality rate in new system is attributed to improper ventilation (higher air speed). Unexpected, the performance and gastrointestinal development of chicks were suboptimal under a newly developed housing system in comparison to conventional brooding. The results of the current work clearly showed that critical control point in the new system need further work. The standard critical control point cannot by applied without careful and smart modification. Smarter housing systems needed in the future to bring the poultry industry to new era.

The higher the level of HD the lower the performance and lighter digestive organs weights which is expected. However further work is needed to model the influence of HD on growth performance. The long range interval between housing densities needs to be reduced to produce better models and achieve better differentiation between the levels chosen in our work.

CONCLUSIONS

In conclusion, the results indicated that, under the conditions of this study, changes in HD and HS during the brooding period influenced broiler chick performance, digestive tract development, and digesta content. Further, high HD at the brooding period resulted in lower the performance and lighter digestive tract organs for the broiler birds, while a lower HD (30 birds/m²) enhanced the growth performance, and digestive tract development. Therefore, based on these results, the recommended number of birds per square meter when reared in various housing systems up to 14 d of age, particularly in conventional system, is 30. Housing density variations of up to 60 kg/m² are acceptable if supported by adequate husbandry programs, feeding and watering equipment, lighting programs, ventilation systems, and litter materials. Although, the performance of broiler chicks was better compared with company product's manual (Cobb 500) regardless of the type of housing system. However, there is a clear need to reduce the long-term interval between housing densities in order to produce better models and redesign the ventilation of the new system, particularly airspeed.