Impact of stocking density and feeding regimen on broilers: performance, carcass traits and bone mineralisation

Abstract

To evaluate the effects of different stocking densities (22.5, 18.75, 15, 11.25, 7.5 broilers/m²) in ad libitum (Al) and limited or pair feeding (Pf) regimens a total of 2550 Ross-308 chicks were taken. All the Pf groups were provided the same amount of feed per broiler, as determined for the Al-fed group with 22.5 broilers/m². Daily weight gain and feed intake were reduced (P≤ 0.001) as stocking density increased in the Al groups. Feed conversion ratios were worse (P≤ 0.01) in the Pf groups. Carcass yield and mortality were not affected by density or feeding method. Length (P≤ 0.001), width and bone mineral content levels (P≤ 0.05) of the tibiotarsal bone were higher in the Al groups with no effect on bone mineral density (P> 0.05). It is concluded that feed consumption was adversely affected by stocking density resulting in poor growth and bone mineralisation.

Keywords:

• broiler
• stocking density
• feeding
• performance
• carcass
• bone mineralisation

Introduction

To achieve their genetic potential for growth, broilers must be raised under optimal environmental conditions. Any deviation from optimal conditions may impair performance (Imaeda 2000; Dozier et al. 2006). High stocking density can reduce performance because of several factors such as high environmental temperature in the microclimate of the bird, inadequate air exchange, increasing ammonia level and impeded access to feed and water (Thomas et al. 2004; Muniz et al. 2006; Onbasilar et al. 2008). In addition, limited feeding programs reduce final body weight (BW) and daily weight gain, but they improve feed efficiency (Saleh et al. 2005).

Pair-feeding is a biological technique where in both experimental and control animals are fed the same amount of feed to eliminate a feed intake (FI) effect.

The present study was performed to determine the effects of stocking density on performance, carcass traits and bone mineralisation of broiler chickens. For this reason, stocking density was evaluated in ad libitum and limited or pair feeding regimens.

Materials and methods

A total of 2550 Ross-308 chicks (3 day-old) were divided into treatment groups and sub-divided into five regular replicates according to balanced live weight and gender. This study was carried out in five different stocking densities [22.5 (90 birds/pen), 18.75 (75 birds/pen), 15 (60 birds/pen), 11.25 (45 birds/pen), 7.5 (30 birds/pen) broilers/m²] fed ad libitum (Al) and four different stocking densities (18.75, 15, 11.25, 7.5 broilers/m²) fed pair feeding (Pf). The 22.5 broilers/m² group was a shared control for both the Al and Pf regimens. For this aim, feed was given ad libitum to nine treatment groups by measuring the weight on day 4 at the starting of the study, and daily FI was recorded. Starting from this date the amount of daily FI per broiler at 22.5 broilers/m² group, all of the pair feeding groups was pair fed to treatment groups at different stocking densities from 5 to 42 days. Each pen provided equal feeder space (264 cm/pen) from pan feeders and watering space (90 cm/pen) from bell drinkers. The photoperiod was 24 h/day. Mortality rate was determined at each pen. Corn-soybean based feeds were prepared according to NRC standards (NRC 1994). Nutrient compositions of the diet (crude protein, fat and ash) were determined by the method specified in AOAC (2000) and according to raw cellulose level reported by Crampton and Maynard (1983).

All of the broilers were weighed on days 4th, 21st and 42nd. FIs of the nine treatment groups were determined daily. At the end of the 42nd day, six males and six females whose live weights were close to the group average for males and females together were slaughtered and their carcass features were determined. Bone properties were detected in three male and three female broilers whose BWs were close to the group average from each group on day 42. Length and width of left tibiotarsus were measured with a digital compass. Bone mineral content (BMC) and bone mineral density (BMD) levels of the tibiotarsus were detected with Lunar DPX (Lunar Corp., Madison, WI, USA, 1997).

Data were analyzed by two-way ANOVA using the general linear model procedure SPSS Inc. (2002). For this purpose 22.5 birds/m² group was excluded from the data set (4×2 factorial design). Then, to determine the differences between the group 22.5 birds/m² and other stocking densities for the broiler on ad libitum feeding, all Pf groups were excluded firstly from the data set. The same model was performed secondly for Pf groups by excluding all Al groups. The analyses were performed by one-way ANOVA. Significant differences (P≤0.05) were further subjected to Duncan's multiple range test for separation of mean.

Results and discussion

Interpretation of data from stocking density evaluations is often difficult because of confounding effects of density and group size in different studies. However, in general, references indicate that increasing the number of birds per unit depresses growth rate and FI (Thomas et al. 2004; Muniz et al. 2006; Sahin et al. 2007). In this study, the size of pens, feeder and drinker space and location were identical in all pens. Similar to previous studies, increasing stocking density in per unit impaired growth rate and FI in Al groups. On the other hand, opposite to the previous studies and the Al groups of this study, stocking density did not affect broiler BW and WG in Pf groups, when feed consumption was constant per broiler (Table 1). These findings indicated that feed consumption had more of a significant role on higher stocking density from the other factors such as inadequate air exchange, increasing ammonia level …, etc., in the examined densities. In addition, birds in higher stocking densities of the Pf groups could reach to feeder at the maximum distance from a feeder <2 m, if feeder space was enough per bird. This distance may be important for broiler producers. Feed conversion ratio (FCR) was not significant in different stocking density group of both Al and Pf treatments. Imaeda (2000) reported that along with an increase in the number of broilers per square metre, especially in summer months elevated ammonia levels in the air caused death as a result of ammonia poisoning. It was found that broiler density per unit area did not impact mortality in this study and similar findings were confirmed in other studies (Thomas et al. 2004; Onbasilar et al. 2008). Limited feeding program using in the Pf groups reduced BW and WG during all production period compare to ad libitum fed birds. Similarly, Saleh et al. (2005) reported that lowering amount of consumption food per bird depressed the growth rate, while it improved the FCR. On the contrary, FCR was worse in the limited Pf groups in this study.

Table 1.  The influences of different stocking density (D) and feeding regimen (F) on body weight (BW), daily weight gain (WG), feed intake (FI), feed conversion ratio (FCR) and mortality in broiler chicken.

											Statistical analyses (significance)
		Ad libitum (Al) Stocking density (broilers/m^2)				Pair feeding (Pf) Stocking density (broilers/m^2)				SEM	F	D	F × D	Al&22.5	Pf&22.5
Performance traits	22.5	18.75	15	11.25	7.5	18.75	15	11.25	7.5
BW, 4/g	80	81	80	81	80	80	79	80	81	0.3	ns	ns	ns	ns	ns
BW, 21/g	628^ABc	634^bc	655^ab	649^ab	671^a	607^B	626^AB	640^A	638^A	2.65	***	***	ns	**	*
BW, 42/g	2101^c	2234^b	2287^b	2374^a	2409^a	2114	2142	2131	2097	8.50	***	***	***	***	ns
WG, 4–21/g	32.22	32.53	33.83	33.41	34.75	30.96	32.16	32.93	32.73	0.30	*	ns	ns	ns	ns
WG, 21–42/g	70.12^c	76.20^b	77.73^b	82.13^a	82.78^a	71.26	71.95	70.99	69.51	0.79	***	***	***	***	ns
FI, 4–21/kg	0.91^c	0.95^bc	0.99^ab	1.07^a	1.07^a	–	–	–	–	0.13	–	–	–	***	–
FI, 21–42/kg	2.77^c	2.87^b	3.01^a	3.07^a	3.07^a	–	–	–	–	0.42	–	–	–	***	–
FCR, 4–21/kg	1.58	1.63	1.63	1.67	1.61	1.66	1.59	1.56	1.57	0.01	ns	ns	ns	ns	ns
FCR, 21–42/kg	1.88	1.79	1.84	1.78	1.77	1.85	1.83	1.85	1.90	0.01	**	ns	ns	ns	ns
Mortality, 21/%	0.45	0.27	0.34	0.00	0.00	0.27	0.00	1.34	0.00	0.09	ns	ns	ns	ns	ns
Mortality, 42/%	1.12	1.07	1.34	0.89	0.00	1.60	1.00	1.78	0.00	0.18	ns	ns	ns	ns	ns
Note: ^ns P > 0.05, ^* P < 0.05, ^** P < 0.01, ^*** P < 0.001. SEM, standard error of mean.
^a–cMean values with different superscripts within a line differ significantly in Al&22.5.
^A,BMean values with different superscripts within a line differ significantly in Pf&22.5.

When examined carcass characteristics (Table 2), stocking density did not affect the carcass yield and other carcass features as also reported by previous studies (Feddes et al. 2002; Dozier et al. 2006). However, ad libitum feeding program increased breast meat ratio parallel to increasing BW and reduced wings, neck and back ratios. These findings were confirmed by Saleh et al. (2005). In addition, length and width of the tibiotarsal bone increased in ad libitum feeding groups due to the possible higher final BW. BMC level increased significantly parallel to size of the bone. BMD level was not affected by density or feeding regimen. The results of the present study are in concurrence with those of Talaty et al. (2009) reported that higher BW increased the bone length and area, it affected BMC level as well, but not BMD level. Lowering stocking density did not affect bone traits of both feeding regimens of the present study. Similar findings were noted by Tablante et al. (2003) and Simsek et al. (2009) stressed that stocking density increased tibial dyschondroplasia (TD) incidence relating with reducing physical activity, but not bone mineral values.

Table 2.  The influences of different stocking density and feeding regimen on carcass traits and bone mineralisation in broiler chickens.

											Statistical analyses (significance)
		Ad libitum (Al) Stocking density (broilers/m^2)				Pair feeding (Pf) Stocking density (broilers/m^2)				SEM	F	D	F × D	Al&22.5	Pf&22.5
Carcass traits	22.5	18.75	15	11.25	7.5	18.75	15	11.25	7.5
Carcass,%	71.16	70.96	71.23	72.45	70.33	69.92	71.32	70.40	71.42	0.18	ns	ns	*	ns	ns
Thighs,%	40.38^AB	41.25	42.02	41.53	40.76	39.93^B	41.76^A	41.14^A	41.35^A	0.22	ns	ns	ns	ns	*
Breast,%	31.01	30.93	31.00	32.29	31.56	31.46	29.23	30.02	30.57	0.23	*	ns	ns	ns	ns
Wings,%	12.42^a	12.32^a	12.17^a	11.58^b	12.45^a	12.57	12.51	12.31	12.39	0.06	*	*	ns	*	ns
Neck and back,%	15.01	14.15	13.52	12.98	12.92	14.77	15.03	15.20	14.41	0.16	**	ns	ns	ns	ns
Abdominal fat,%	1.20	1.35	1.29	1.61	1.41	1.30	1.47	1.33	1.28	0.02	ns	ns	ns	ns	ns
Bone traits
Tibiotarsus length (cm)	8.46	8.70	8.76	8.85	8.83	8.48	8.35	8.43	8.36	0.04	***	ns	ns	ns	ns
Tibiotarsus width (cm)	0.86	0.90	0.88	0.91	0.93	0.83	0.90	0.86	0.83	0.01	*	ns	ns	ns	ns
Tibiotarsus BMD level (g/cm^2)	0.139	0.133	0.148	0.186	0.185	0.157	0.159	0.134	0.137	0.00	ns	ns	ns	ns	ns
Tibiotarsus BMC level (g)	1.86	1.87	1.94	2.01	2.18	1.70	1.83	1.91	1.83	0.04	*	ns	ns	ns	ns
Note: ^ns P > 0.05, ^* P < 0.05, ^** P < 0.01, ^*** P < 0.001. BMD, bone mineral density; BMC, bone mineral content.
^a,bMean values with different superscripts within a line differ significantly in Al&22.5.
^A,BMean values with different superscripts within a line differ significantly in Pf&22.5.

It is noted that feed consumption is a prominent factor affecting stocking density. It might be suggested that, with an appropriate feedbox design, more products can be obtained from the unit area in higher stocking densities. Feed restriction reduces BW and daily weight gain. It deteriorates FCR and bone mineralisation.

Acknowledgements

This work was supported financially by a grant (106 O 431) from the Scientific and Technical Research Council of Turkey (TUBITAK) and we would like to thank OZNESIL Corp. that provided the opportunity to carry out this study.