Effect of Dietary Fiber and Genetic Strain on the Performance and Energy Balance of Broiler Chickens

The experiment was conducted to evaluate the effect of dietary fiber on the performance and energy balance of broiler chickens of a fast-growing strain (Cobb500) and a slow-growing strain (Label Rokens during the period of 1 one to 42 days of used In total, 360 male broilers (240 fast-grorain and 120 slow-grtrain)were, housed in collective cages. A completely randomized experimental dewith in a 3x2 factorial arrangement was applied, consisting of three groups of birds (slow-growing – SG; fast-growing fed ad libitum – FGAL; and fast-growing pair-fed with SG broilers – FGPF) and two iso-protein dis (a 3100 kcal ME/kg low-fiber diet and a 2800 kcal ME/kg high-fiber dietHwith containing 14% wheat bran and 4% oat hulls). Dietary fiber level did not affect feed intake (FI); however, it resulted in lower weight gain (WG) and worse feed conversion ratio (FCR) (p ≤ 0.001) in birds fed the HFD diet due to its lower energy content. The FGPF group presented higher WG than SG and better FCR (p ≤ 0.001), indicating that fast-growing birds present better performance than SG broilers, even under restricted feed intake. The SG group retained more energy relative to body weight (p ≤ 0.001), which is associated to higher body fat retention in this strain (p ≤ 0.001). The slow-growing strain did not present better use of high-fiber diet than fast-growing strain as expected.


INTRODUCTION
The inclusion of alternative feed ingredients in poultry feeds as a consequence of the increasing use of corn and soybeans in biofuel production has increased dietary fiber (DF) levels in non-ruminants diets.
Dietary fiber is traditionally considered a diet diluent and often, an antinutritional factor (Rougière et al., 2010).However, moderate amounts of fiber may promote organ development, enzyme production, and nutrient digestibility in poultry.Some of these effects result from better gizzard function, with an increase in the gastroduodenal reflux that promotes the contact between nutrients and digestive enzymes (Mateo et al., 2012;Gonzalez-Alvarado et al., 2008;Jimenez-Moreno et al., 2009).
Commercial broiler strains have been selected for high growth rate and high feed efficiency based on the use of highly digestible diets with no metabolizable energy (ME) limitations.This selection promoted changes in digestive tract form and functions that may have impaired the utilization of low-digestibility diets (Shires et al., 1987).On the other hand, slow-growing genetic strains were not submitted to the same selection pressure; these birds are usually reared under alternative poultry production systems, and may be better adapted to lower quality diets.In Brazil, slow-growing Label Rouge strains have been widely used in alternative broiler production systems (Dourado et al., 2009).
The objective of this study was to compare performance and energy balance responses between a commercial fast-growing broiler strain and a slowgrowing strain fed diets containing two different fiber levels.

MATERIAL AND METHODS
In total, 360 male broilers, out of which 240 were of a fast-growing commercial strain (Cobb) and 120 of a slow-growing strain (Label Rouge), were housed in 36 battery cages with 10 birds each, in a environmentallycontrolled room with 24 h of light per day, from one to 42 days of age.
During the first four experimental days, all birds were fed a single pre-starter feed ad libitum.From day 5, two iso-protein diets were fed: a low-fiber diet (LFD), based on corn and soybean meal, with 3100 kcal ME/ kg; or a high-fiber diet (HFD), based on the LFD, to which 14% wheat bran and 4% oat hulls were added, containing 2800 kcal ME/kg, which corresponded to an increase of 7.7% in neutral detergent fiber.The LFD and the pre-starter diet were formulated to contain the nutritional levels recommended by Rostagno et al. (2011).A single experimental diet was fed during the entire period to each treatment group to allow comparing diet digestibility among different bird ages (Table 1).
The diets were fed to three different groups of 120 each: slow-growing Label Rouge birds fed ad libitum (SG), Cobb500 birds fed ad libitum (FGAL), and Cobb500 birds pair-fed with Label Rouge birds (FGPF).This last group was housed one day after the Label Rouge birds in order to receive the same amount of feed consumed by the Label group in the previous day to evaluate digestibility at the same feed intake level.Pair feeding was performed according to diet type, i.e., FGPF birds were fed once a day with the same amount of feed consumed by Label fed LFD or Label fed HFD during the previous day.
A completely randomized experimental design in a 3x2 factorial arrangement, with six treatments of six replicates each, was applied.
The following responses were evaluated: feed intake (FI), weight gain (WG), and feed conversion ratio (FCR) during the periods of 1 to 7, 1 to 21, 21 to 42, and 1 to 42 days.
Energy balance and protein and fat retention were evaluated using the comparative slaughter method, where one bird with average body weight per replicate was sacrificed at the beginning and at the end of the experiment.Carcass and feather samples were collected and submitted to laboratory analysis.The following parameters were calculated: total ME intake (MEI), total gross energy retention (GER), and total heat production (HP), calculated as the difference between MEI and GER, all expressed in kcal; ME intake per live weight (MEI/LW), energy retention per live weight (ER/LW), and heat production per live weight (HP/ LW), expressed in kcal/kg relative to final live weight; percentage of metabolizable energy retention (MER); crude protein retention per live weight (CPR/LW), and crude fat retention per live weight (CFR/LW), expressed in g/kg, also relative to final live weight.
Carcass dry matter, ashes, and crude protein contents were determined according to the methods of the AOAC (1995).Carcass gross energy was determined using an isoperibolic calorimeter (IKA WERKE, model C2000).
Responses were submitted to analysis of variance using the statistical software package Statgraphics

Performance
There was no significant interaction (p>0.05) between fiber level and bird group (Table 2).However, during all evaluated periods, birds fed the HFD presented lower WG (p ≤ 0.01) and worse FCR (p ≤ 0.001).
FI was not influenced by the diet, except for the period of 1 to 7 days, when the broilers fed the HFD had lower FI (p ≤ 0.05).This result may be partially explained by the low magnitude of the evaluated values (106 g for LFD and 101 g for HFD).Also, because birds may had adapted to the pre-starter diet supplied up do day 4, the coarseness of the HFD probably caused this temporary lower feed intake.
The analysis of the total experimental period (1 to 42 days) confirms that FI was not affected by dietary fiber level, and that the HFD adversely affected WG and FCR (p ≤ 0.001), independently of bird strain.The study of Shires et al. (1987) showed that broilers fed 6.3% higher FDA grew significantly slower.On the other hand, the observations of Rezaei & Rajati (2010) with broilers and of Van Krimpen et al. (2009) with layers that diets with diluted energy promoted higher FI was not confirmed in the present study.This demonstrates that birds were close to the limit of their intake capacity.Similarly, studying modern broilers strains, Raber et al. (2009) stressed the lack of an expected control of feed intake, whereas Nielse et al. (2011), working with broiler breeders, suggested that high-fiber diets may reduce hunger, thereby decreasing feed intake.
The FGAL group presented higher FI and WG (p ≤ 0.001) than the other groups during all evaluated periods.The feed conversion ratio of the FGAL group was better as compared to Label Rouge birds in all evaluated periods (p ≤ 0.001), except between 21 and 42 days of age, when no significant differences were detected among treatments.
Fast-growing pair fed broilers presented better FCR and higher WG as compared to SG birds (p ≤ 0.001) during the period of 1 to 7 days because birds were not pair-fed during the first four experimental days.FI was no longer significantly different between these two groups during the remaining periods.From 1 to 21 days of age, WG of the SG group was not significantly different from FGPF; however, their FCR was worse (p ≤ 0.001).During the period of 21 to 42 days, FGPF birds gained more weight (p ≤ 0.001) than SG birds, and presented better FCR than the other two groups (p ≤ 0.001).For the total experimental period the same trend was observed.This response may be related to a physiological adaptation to feed restriction after 21 days of age.In the present study, fast-growing Cobb broilers were superior to slow-growing Label Rouge in all performance responses, including at the same feed intake level.
Table 2 -Individual performance response of slow-growing and fast-growing broilers divided in three groups (SG, FGAL, FGPF) during the periods of 1 to 7, 1 to 21, 21 to 42 e 1 to 42 days of age fed diets with two fiber levels.

Energy balance and protein and fat retention
There was no significant interaction between fiber level and bird group for energy-balance responses (Table 3).The birds fed the LFD presented higher ME availability, producing more body fat, with higher efficiency of ingested ME utilization.Heat production relative to live weight was higher in birds fed HFD (p ≤ 0.05), possibly due to their slower growth rate, which increases heat production associated to maintenance, and perhaps due to the higher microbial activity in the ceca as a function of the higher dietary fiber level.Total heat production, crude protein retention, and energy intake relative to live weight (MEI/LW) were not influenced by treatments.The latter result may be explained by the fact that the birds fed the HFD presented lower WG, and consequently, lower final LW.
Due to the lower heat production/live weight, higher dietary ME, and lack of FI difference, the birds fed the LFD retained more relative and total energy (ER/ LW and MER), resulting in higher carcass fat retention (CFR/LW).Conversely, Warpechowski (2005) observed compensatory ME intake in broilers fed high-fiber diets, with consequent similar heat production and energy intake between diets with different fiber levels.

Table 1 -
Composition of the experimental diets on fresh matter basis (FM).

Table 3 -
Energy balance and protein and fat retention of slow-growing and fast-growing broilers divided into three groups (SG, FGAL, FGPF) and fed diets with two fiber levels during the period of 1 to 42 days of age.