METABOLISM AND NUTRITION Effect of dietary fiber and fat on performance and digestive traits of broilers from one to twenty-one days of age1 E. Jiménez-Moreno, J. M. González-Alvarado,2 A. González-Serrano, R. Lázaro, and G. G. Mateos3 Departamento de Producción Animal, Universidad Politécnica de Madrid, 28040, Madrid, Spain ABSTRACT The influence of fiber source and dietary fat level on digestive traits and productive performance was studied in broilers from 1 to 21 d of age. There were 6 treatments arranged factorially with 3 sources of fiber (none; 3% oat hulls, OH; and 3% sugar beet pulp, SBP) and 2 fat sources (5% soybean oil, SO; and 5% yellow grease, YG). Each treatment was replicated 6 times and the experimental unit was a cage with 18 broilers. Fiber inclusion improved BW gain (P ≤ 0.05) and feed:gain ratio (P ≤ 0.001) and increased total tract apparent retention (TTAR) of all nutrients measured (P ≤ 0.001). The increases observed in TTAR of nitrogen and ether extract and on AMEn of the diet were more pronounced with OH than with SBP. The increases in
nutrient digestibility with OH inclusion were higher at excreta than at ileal level and in fact, SBP inclusion reduced the apparent ileal digestibility of most nutrients. The relative weight (%) of the gizzard was increased (P ≤ 0.001) and the pH of its contents was reduced (P ≤ 0.001) when additional fiber was included in the diet. The TTAR of nutrients was higher for the SO than for the YG diets (P ≤ 0.001). Also, the increases in ether extract digestibility (P ≤ 0.05) and AMEn (P ≤ 0.05) of the diet with fiber inclusion were more pronounced with the YG than with the SO. Therefore, the inclusion of moderate amounts of fiber in the diet might improve performance and nutrient digestibility in young chicks, especially when saturated fats are used.
Key words: oat hull, sugar beet pulp, fat, broiler performance, digestive trait 2009 Poultry Science 88:2562–2574 doi:10.3382/ps.2009-00179
INTRODUCTION Broiler performance at 42 d is closely related to the BW at 7 d of age (Lilburn, 1998), and BW at 7 d depends primarily on feed intake. Several feeding strategies have been proposed to improve feed intake and the development of the gastrointestinal tract (GIT) in posthatch chicks, including the use of highly digestible ingredients such as rice (González-Alvarado et al., 2007) and soy protein concentrates (Drew et al., 2004; Valencia et al., 2009), the inclusion of enzymes and other feed additives (Bedford, 2000; Mateos et al., 2002; Lázaro et al., 2003b), and heat processing of the cereal portion of the diet (Gracia et al., 2003; García et al., 2008). In most cases, the implementation of these strategies requires the use of ingredients with high energy and protein content and consequently, most diets for
©2009 Poultry Science Association Inc. Received April 7, 2009. Accepted August 23, 2009. 1 Supported by funding through Project AGL2008-03506, Ministerio de Ciencia e Innovación, Madrid, Spain. 2 Current address: Universidad Autónoma de Tlaxcala, Av. Universidad 1, Tlaxcala, CP 90000, México. 3 Corresponding author:
[email protected]
newly hatched chicks are low in crude fiber (CF). However, recent research conducted in broilers has shown that low-fiber diets are detrimental for the development of the GIT (González-Alvarado et al., 2008) and that low-fiber diets increase the incidence of enteric disorders (Montagne et al., 2003). The inclusion of fat is a common practice in modern broiler production to increase the energy content of the diet. In addition, dietary fat reduced passage rate of the digesta through the GIT, allowing for better nutrient utilization (Mateos and Sell, 1980, 1982; Latshaw, 2008). However, bile acid secretion (Krögdahl and Sell, 1989) and pancreatic lipase activity (Noy and Sklan, 1995) are low at hatch and consequently, fat digestibility is compromised in young broilers. Therefore, factors that improve gut maturity and increase bile acid secretion and enzyme activity should favor digestibility and absorption of fats in young broilers, and such an increase should be more pronounced with saturated than with unsaturated fats because saturated fats are less polar and have more difficulties for micelle formation (Krögdahl, 1985). The hypothesis of this study was that fiber would stimulate the development of the GIT and thus, the inclusion of fiber in diets low in fiber would increase the digestibility of dietary components, especially that of saturated fats.
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MATERIALS AND METHODS Husbandry and Experimental Design All procedures used in this research were approved by the Animal Ethics Committee of the Universidad Politécnica de Madrid and were in compliance with the Spanish guidelines for the care and use of animals in research (Boletín Oficial del Estado, 2005). A total of 648 one-day-old Cobb-500 male chicks with an initial BW of 39.3 ± 3.12 g was obtained from a commercial hatchery (Cobb España, Alcalá de Henares, Spain), allocated in a windowless, environmentally controlled room, and randomly placed in groups of 18 in 36 battery cages (1 m × 0.9 m; Avícola Grau, Madrid, Spain). Chicks were divided into 6 blocks by weight and diets were randomly assigned to cages within each block. The cages were provided with wire flooring and were equipped with 2 drinker cups and 1 linear feeder. Room temperature was maintained at 33°C during the first 3 d of life and then was reduced gradually according to age until reaching 24°C at 21 d. Chicks received a 23 h/d of light program and had free access to feed in mash form and water throughout the trial. The trial was conducted as a completely randomized block design with 6 diets arranged factorially with 3 fiber sources (control; 3% oat hulls, OH; and 3% sugar beet pulp, SBP) and 2 fat sources (5% soy oil, SO; and 5% yellow grease, YG).
Ingredients and Diets A batch of polished broken rice (Oryza sativa L., Japonica variety; 75% Senia and 25% Tainato cultivars) was obtained from a commercial supplier (Esasa, Valladolid, Spain), ground through a hammer mill fitted with a 2.5-mm screen, and used in the manufacturing of the feeds. The OH (Biessa, Burgos, Spain) and the SBP (Azucarera Ebro S.L., Valladolid, Spain)
used were ground through a hammer mill (model Z-I, Retsch, Stuttgart, Germany) fitted with a 2-mm screen and included as such in the corresponding experimental diets. The OH was a by-product of the food industry and contained by analysis 10.1% starch and 61.1% neutral detergent fiber. The chemical composition of the sepiolite (a complex magnesium silicate clay) and fiber sources used is shown in Table 1. The SO and the YG were obtained from local suppliers and contained 53.9 and 21.2% linoleic acid, respectively. The control diets were based on rice and soy protein concentrate and contained 5% SO or YG and 3% sepiolite (Table 2). The OH and SBP were included in the experimental diets (wt/wt) at the expenses of sepiolite. Therefore, the inclusion of the fiber sources increased the CF content of the diets (Table 3). In addition, celite, an acid-washed diatomaceous earth (Celite Corporation, Lompoc, CA), was added at 2% to all diets as an additional acid-insoluble ash source. The diets were formulated according to tables of nutrient composition of ingredients of Fundación Española Desarrollo Nutrición Animal (2003) and met or exceed the nutritional recommendations of Fundación Española Desarrollo Nutrición Animal (2008) for broilers.
Laboratory Analyses Ingredients, diets, excreta, and ileal digesta were analyzed in triplicate for moisture by the oven-drying method (930.15), total ash by a muffle furnace (942.05), and nitrogen by the Dumas method (968.06) using a Leco analyzer (model FP-528, Leco Corporation, St. Joseph, MI) as described by AOAC International (2000). Gross energy of all samples was measured with an adiabatic bomb calorimeter (model 356, Parr Instrument Company, Moline, IL) and acid insoluble ash was analyzed using the technique described by Van Keulen and Young (1977) with modifications (González-Alvarado et al., 2007). Briefly, diets, excreta, and ileal samples were
Table 1. Nutritional composition (%, as-fed basis unless stated otherwise), geometric mean diameter (GMD ± GSD, µm), water-holding capacity (WHC, L/kg of DM), and swelling capacity (SWC, mL/ kg of DM) of sepiolite, oat hulls, and sugar beet pulp Item1 Chemical analyses (%) DM Total ash CP Ether extract Starch Crude fiber Neutral detergent fiber Acid detergent fiber Gross energy (kcal/kg) Physical properties GMD ± GSD3 (µm) WHC ± SD (L/kg of DM) SWC ± SD (mL/kg of DM) 1
Sepiolite2 89.1 87.6 — — — — — — — 65 ± 1.9 3.40 ± 0.22 0.56 ± 0.09
Analyzed in triplicate samples. Sepiolite is a complex magnesium silicate clay. 3 Log normal SD. 2
Oat hulls
Sugar beet pulp
91.2 4.6 5.8 2.2 10.1 22.3 61.1 29.2 4,067
91.6 5.2 8.4 1.5 0.0 15.8 37.2 23.4 3,766
462 ± 2.1 4.93 ± 0.40 2.62 ± 0.49
696 ± 2.0 7.90 ± 0.39 4.47 ± 0.19
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ether extract (EE) of fiber sources, diets, and excreta was analyzed by Soxhlet fat analysis after 3 N HCl acid hydrolysis (method 4.b) as described by Boletín Oficial del Estado (1995). Neutral and acid detergent fiber of fiber sources and diets were determined sequentially as described by Van Soest et al. (1991) and expressed on an ash-free basis. Starch content of fiber sources, diets, and ileal contents were measured by the α-amylase glucosidase method (996.11) and CF of the fiber sources and diets by sequential extraction with diluted acid and alkali (962.09; AOAC International, 2000). The fat sources were analyzed for moisture (method 9.a), insoluble impurities (method 25), and unsaponifiable material (method 22.b) content. The oleic acid index, which measures the amount of KOH in milligrams needed for neutralizing the free fatty acids present in 100 mg of the fat sample (method 10.a; Boletín Oficial del Estado, 1977), was also determined. In addition, the fatty acid profile (%) of the experimental fats was analyzed as indicated by Grobas et al. (2001). Particle size distribution and geometric mean diameter (GMD) of sepiolite, fiber sources, and diets were determined in triplicate according to the methodology recommended by the American Society of Agricultural Engineers (1995). The water-holding capacity (WHC) of the sepiolite and fiber sources was determined as indicated by Giger-Reverdin (2000) with modifications (González-Alvarado et al., 2008). Briefly, 3 subsamples (1 g of DM) of sepiolite, fiber sources, and diets were left to soak for 16 to 24 h in excess of distilled water
Table 2. Composition of the experimental diets Ingredient
Amount (%, as-fed basis)
Broken rice Soy protein concentrate, 53% CP Fish meal, 72% CP Fat1 Sepiolite2 l-Lys-HCl, 78% dl-Met, 99% Limestone Dicalcium phosphate Sodium chloride Celite3 Vitamin and mineral premix4
57.76 22.00 7.00 5.00 3.00 0.02 0.19 0.85 1.75 0.23 2.00 0.20
1
The fat used was soybean oil or yellow grease, according to treatment. 2 Sepiolite, a complex magnesium silicate clay, was substituted (wt/wt) by either oat hulls or sugar beet pulp in the corresponding experimental diets. 3 Acid-washed diatomaceous earth (Celite Corporation, Lompoc, CA). 4 Provided the following (per kg of diet): vitamin A (trans-retinyl acetate), 10,000 IU; vitamin D3 (cholecalciferol), 2,000 IU; vitamin E (allrac-tocopherol acetate), 20 IU; vitamin K (bisulfate menadione complex), 3 mg; riboflavin, 5 mg; pantothenic acid (d-Ca pantothenate), 10 mg; nicotinic acid, 30 mg; pyridoxine (pyridoxine·HCl), 3 mg; thiamin (thiamin-mononitrate), 1 mg; vitamin B12 (cyanocobalamin), 12 μg; dbiotin, 0.15 mg; choline (choline chloride), 300 mg; folic acid, 0.5 mg; Se (Na2SeO3), 0.1 mg; I (KI), 2.0 mg; Cu (CuSO4·5H2O), 10 mg; Fe (FeSO4·7H2O), 30 mg; Zn (ZnO), 100 mg; Mn (MnSO4·H2O), 100 mg; ethoxyquin, 110 mg.
analyzed sequentially for DM, ash, and acid-insoluble ash using the same beaker, and ashing was performed at 600°C for 12 h rather than at 450°C for 6 h. The
Table 3. Chemical composition (%, as-fed basis unless stated otherwise), geometric mean diameter (GMD ± GSD, µm), and waterholding capacity (WHC, L/kg of DM) of the soy oil (SO) and yellow grease (YG) diets SO Item Calculated analysis2 (%) AMEn (kcal/kg) Crude fiber Neutral detergent fiber Digestible Lys Digestible Met Digestible Met + Cys Digestible Thr Digestible Trp Ca Available P Determined analysis3 Gross energy (kcal/kg) DM CP Starch Ether extract Total ash Neutral detergent fiber Acid detergent fiber Physical properties GMD ± GSD4 (µm) WHC ± SD (L/kg of DM) 1
Sepiolite1
Oat hulls
YG Sugar beet pulp
Oat hulls
Sugar beet pulp
3,148 1.5 3.55 1.16 0.56 0.84 0.75 0.22 1.00 0.45
3,160 2.4 5.60 1.16 0.56 0.84 0.75 0.22 1.00 0.45
3,175 2.1 4.83 1.16 0.56 0.84 0.75 0.22 1.02 0.45
3,098 1.5 3.55 1.16 0.56 0.84 0.75 0.22 1.00 0.45
3,110 2.4 5.60 1.16 0.56 0.84 0.75 0.22 1.00 0.45
3,125 2.1 4.83 1.16 0.56 0.84 0.75 0.22 1.02 0.45
3,957 90.1 20.0 37.4 6.9 9.3 5.2 1.4
4,066 90.1 21.3 38.8 7.0 7.6 6.1 1.9
4,055 90.2 20.9 35.9 7.2 7.7 5.6 1.6
3,930 89.8 20.3 40.2 6.8 9.3 5.7 1.4
4,067 89.9 20.8 38.4 7.0 7.6 7.1 2.3
4,064 89.8 20.9 37.1 6.9 7.6 6.6 2.1
591 ± 1.8 2.51 ± 0.14
743 ± 1.7 2.65 ± 0.08
724 ± 1.7 2.59 ± 0.12
628 ± 1.7 2.23 ± 0.06
742 ± 1.7 2.47 ± 0.11
682 ± 1.7 2.34 ± 0.18
Sepiolite is a complex magnesium silicate clay. According to Fundación Española Desarrollo Nutrición Animal (2003). 3 Analyzed in triplicate samples. 4 Log normal SD. 2
Sepiolite
FIBER AND FAT SOURCES IN BROILER DIETS
(100 mL). Samples were filtered on a fritted glass crucible (porosity 2) and the walls of the beaker were carefully rinsed. The wet sample was weighed after letting the water drain for 10 min, and the WHC was calculated as the amount of water retained and expressed as liters per kilogram of DM. Swelling capacity (SWC) of the sepiolite and fiber sources was determined according to the standard procedure recommended by the pharmaceutical industry (Valencia and Roman, 2006). Briefly, 3 subsamples (2 g of DM) of each material were hydrated in 10 mL of distilled water in a calibrated cylinder (25 mL) at room temperature. Samples were dispersed by gentle stirring for 5 min and left undisturbed at room temperature for 18 to 24 h. After equilibration, the bed volume was recorded and expressed as volume (mL) per gram of DM of the original sample.
Performance Body weight and feed consumption of birds were determined by cage at 1, 5, 15, and 21 d of age, and BW gain (BWG), ADFI, and feed:gain were determined from these data by period and cumulatively. Feed wastage was recorded daily by replicate. Birds that died during the experiment were weighed, and their estimated feed consumption was included in calculations of feed:gain.
Organ Development and pH of the Digesta At 5 and 15 d of age, 4 birds per cage were randomly selected, weighed individually, and killed by asphyxiation with CO2. The digestive tract with contents (from the end of the crop to the cloaca) was removed aseptically, and the proventriculus, gizzard, and ceca were excised, cleaned, dried with desiccant paper, and weighed. The fresh digesta contents of the gizzard and ceca were measured at both ages, whereas that of the proventriculus was determined only at 15 d of age. In addition, the digesta contents of the proventriculus and gizzard were collected at both ages and homogenized in a 50-mL beaker. A subsample of 1 g of digesta was suspended in 10 mL of deionized water and stirred for 5 min, and the pH was measured in duplicate samples using a digital pH meter (model 507, Crison Instruments S.A., Barcelona, Spain). The average pH obtained from the 4 birds of each cage slaughtered at each age was used for statistical analyses. In addition, the weight of the digestive tract with contents and the liver was measured at 15 d of age but not at 5 d of age. The weight of the empty organs was expressed relative to live BW (%), whereas the weight of the fresh digesta content was expressed relative to full organ weight.
Total Tract Apparent Retention and Apparent Ileal Digestibility At 5 and 15 d of age, representative samples of excreta produced during the previous 48 h were collected by
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replicate, homogenized, dried in an oven (60°C for 72 h), and ground with a hammer mill (model Z-I, Retsch, Stuttgart, Germany) fitted with a 1-mm screen. At the same ages, the ileal digesta contents of the 4 birds per replicate used for the organ development study were collected by gently squeezing the content into plastic containers, pooled, frozen at −20°C, and freeze-dried. Dried ileal digesta samples were ground using a pestle and mortar to pass through a 0.5-mm screen and were stored in airtight containers at room temperature until chemical analyses. The total tract apparent retention (TTAR) and the apparent ileal digestibility (AID) of DM, organic matter (OM), soluble ash, and nitrogen and the AMEn of the diets were estimated by the indigestible marker method using 2 N HCl insoluble ash as an indicator (Lázaro et al., 2003a). In addition, the TTAR of EE and the AID of starch and gross energy were also determined.
Statistical Analysis Performance data were analyzed as a completely randomized block design and the effects of fiber inclusion, type of fat, and their interaction were studied. Results in tables are reported as means. The experimental unit was the cage for all traits, and differences were considered significant at P ≤ 0.05. When the effects were significant, Tukey’s test was used to make pairwise comparisons between sample means. For nutrient retention and digestive traits data, with the exception of digesta content of the proventriculus that was determined only at 15 d of age, age was included as a third factor. Data on relative weight of the empty BW, digestive tract, and liver and of proventriculus content were analyzed by the GLM procedure of SAS (SAS Institute, 1990). For those digestive traits measured at 2 ages and for the TTAR and AID of nutrients, data were analyzed using the MIXED procedure of SAS (Littell et al., 1996).
RESULTS The determined chemical analysis of sepiolite, OH, SBP, and diets were close to expected values. The gross energy content of SO and YG was 9,430 and 9,420 kcal/kg, respectively. The moisture, impurities, and unsaponifiable materials content was 1.6 and 4.0%, and the oleic acid index was 1.7 and 2.5% for SO and YG, respectively. The fatty acid profile (%) of the experimental fats was 13.1 and 18.1 for C16:0, 1.4 and 9.1 for C18:0, 23.8 and 44.3 for C18:1 (n-9), 53.9 and 21.2 for C18:2 (n-6), and 6.8 and 0.4 for C18:3 (n-3) for SO and YG, respectively. The data on physical properties of sepiolite, OH, and SBP and of the experimental diets are shown in Tables 1 and 3, respectively. The GMD was greater for SBP than for OH and for both fiber sources greater than for sepiolite (696 and 462 vs. 65 µm, respectively). Consequently, the GMD of the diets increased with fiber in-
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clusion. The WHC and SWC were higher for SBP than for sepiolite with values for OH being intermediate.
Performance Mortality was low (3%) and not related to treatment (data not shown). Most of the mortality (>80%) occurred during the first week of life. No interactions between fiber and fat source were observed for any trait and therefore, only main effects are presented (Table 4). Effect of Fiber. Fiber inclusion consistently increased BWG and improved feed:gain of broilers. From 1 to 5 d of age, BWG was higher for broilers fed the fiber-containing diets than for broilers fed the control diets (P ≤ 0.001). In addition, BWG was higher for broilers fed OH than for broilers fed SBP. From 5 to 15 d and from 15 to 21 d of age, fiber inclusion improved feed:gain (P ≤ 0.001) as compared with the control diet. Consequently, at the end of the experiment, the inclusion of additional fiber improved feed:gain (P ≤ 0.001). In addition, the inclusion of OH increased BWG from 1 to 21 d of age as compared with the control diet (P ≤ 0.05) with the inclusion of SBP being intermediate. Effect of Fat. Fat source had little effect on productive performance of broilers. The only effect observed was for BWG from 1 to 21 d of age that was higher for broilers fed YG than for those fed SO (P ≤ 0.05).
Organ Development and pH of the Digesta Effect of Fiber. Fiber inclusion affected the relative weight of most organs and segments of the GIT, but the effects varied according to the source of fiber test-
ed. The inclusion of fiber increased the relative weight of the digestive tract (P ≤ 0.001) and the effects were more noticeable with SBP than with OH (Table 5). However, liver weight was not affected by fiber inclusion. The inclusion of SBP increased the relative weight of the proventriculus (P ≤ 0.001) and the ceca (P ≤ 0.001) as compared with the inclusion of OH or the control diet (Table 6). Oat hulls inclusion increased gizzard weight (P ≤ 0.01) as compared with the control diet but did not affect the relative weights of the proventriculus or the ceca. Fiber inclusion reduced the relative fresh content of the proventriculus (P ≤ 0.01) and increased that of the gizzard (P ≤ 0.001) but had no effects on the content of the ceca (Table 7). The effects of fiber inclusion on the fresh content of the proventriculus and gizzard were more evident with SBP than with OH. Fiber inclusion affected the pH of the proventriculus and gizzard (Table 8). The inclusion of SBP reduced the pH of the proventriculus with respect to OH inclusion (P ≤ 0.05), with the pH of the control diet being intermediate (Table 8). On the other hand, both fiber sources reduced the pH of the gizzard (P ≤ 0.001). Effect of Fat. Type of fat had little effect on the development and pH of the organs studied. The only effects observed were for the proventriculus that was heavier (P ≤ 0.01) and for the ceca that was lighter (P ≤ 0.05) with SO- than with YG-containing diets. Effect of Age. The relative weight of the proventriculus, gizzard, and ceca decreased with age (P ≤ 0.001). An interaction between age and type of fiber was observed for proventriculus weight, with fiber effects being greater at 5 d than at 15 d of age. Also, the relative fresh content of the gizzard decreased with age in
Table 4. Influence of fiber inclusion (fiber) and type of fat (fat) on growth performance of broilers 1 to 5 d Treatment
df
Fiber Control OH2 SBP3 SEM4 Fat Soybean oil Yellow grease SEM5 Effects6 Fiber Fat a–c
2 1
5 to 15 d
15 to 21 d
BWG1 (g/d)
ADFI (g/d)
Feed:gain
BWG (g/d)
ADFI (g/d)
Feed:gain
BWG (g/d)
ADFI (g/d)
13.2c 14.2a 13.7b 0.14
14.7 14.5 14.7 0.36
1.117 1.028 1.075 0.0288
30.1 31.1 31.0 0.51
40.6 39.9 39.9 0.69
1.350a 1.286b 1.288b 0.0096
47.9b 52.3a 50.6ab 1.04
70.5 72.4 71.2 1.68
13.6 13.8 0.11
14.7 14.6 0.33
1.086 1.060 0.0234
30.2 31.2 0.42
39.6 40.8 0.56
69.8 73.0 1.37
*** NS
NS NS
NS NS
NS NS
1.310 49.1 1.306 51.4 0.0079 0.85 Probability *** * NS NS
NS NS
Means within a main effect not sharing a common superscript differ (P ≤ 0.05). BW gain. 2 Oat hulls. 3 Sugar beet pulp. 4 n = 12. 5 n = 18. 6 Remaining interactions and remaining contrasts were not significant. *P ≤ 0.05; ***P ≤ 0.001. 1
NS NS
1 to 21 d BWG (g/d)
ADFI (g/d) Feed:gain
1.472a 1.386b 1.402b 0.0206
31.2b 33.1a 32.5ab 0.49
43.0 43.2 42.9 0.77
1.380a 1.304b 1.317b 0.0082
1.419 1.421 0.0115
31.7b 32.9a 0.40
42.3 43.7 0.63
1.336 1.332 0.0067
* *
NS NS
Feed: gain
*** NS
*** NS
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FIBER AND FAT SOURCES IN BROILER DIETS Table 5. Influence of fiber inclusion (fiber), type of fat (fat), and age on the relative weight (% of BW) of empty BW, digestive tract, and liver of broilers at 15 d of age Treatment
df
Fiber Control OH3 SBP4 SEM5 Fat Soybean oil Yellow grease SEM6 Effects7
Empty BW1 (% of BW)
Digestive tract2 (% of BW)
83.7a 83.1a 82.4b 0.26
11.9c 12.9b 13.8a 0.22
83.1 83.0 0.21
Fiber Fat
2 1
Liver (% of BW) 3.14 3.13 3.15 0.060
12.9 12.9 0.18 Probability *** NS
** NS
3.09 3.18 0.049 NS NS
a–c
Means within a column and main effect not sharing a common superscript differ (P ≤ 0.05). Body weight without the digestive tract and its contents. 2 From the end of the crop to cloaca with contents. 3 Oat hulls. 4 Sugar beet pulp. 5 n = 12. 6 n = 18. 7 The interaction between fiber and fat was not significant. **P ≤ 0.01; ***P ≤ 0.001. 1
birds fed the control diet but not in birds fed the fibercontaining diets (P ≤ 0.001). On the other hand, ceca digesta content increased with age, irrespective of type of diet (P ≤ 0.01). Digesta pH of the proventriculus decreased (P ≤ 0.001) and that of the gizzard increased (P ≤ 0.001) as the bird aged. An interaction between
age and fiber inclusion was observed for the digesta pH in both organs (P ≤ 0.01). For the proventriculus, the inclusion of SBP reduced digesta pH at 15 d of age but not at 5 d of age. In the gizzard, fiber inclusion reduced digesta pH at both ages, but the effects were more pronounced at 15 d than at 5 d of age.
Table 6. Influence of fiber inclusion (fiber), type of fat (fat), and age on the relative weight (% of BW) of proventriculus, gizzard, and ceca of broilers Proventriculus (% of BW) Treatment
df
Fiber Control OH1 SBP2 SEM3 Fat Soybean oil Yellow grease SEM4 Age SEM5 Effects6 Fiber Fat Age Fiber × age a–c
15 d
Average
5d
15 d
Average
5d
15 d
Average
0.88 0.92 1.03
0.55 0.56 0.61
0.71b 0.74b 0.82a 0.011
3.21 4.17 3.88
1.40 2.25 1.92
2.31c 3.21a 2.90b 0.032
0.57 0.56 0.61
0.44 0.41 0.49
0.51b 0.48b 0.55a 0.013
0.60 0.55
0.78a 0.74b 0.009
3.79 3.73
1.87 1.84
2.83 2.78 0.026
0.56 0.60
0.44 0.46
0.50b 0.53a 0.011
0.94
0.015
0.012 0.009
0.57
*** ** *** *
3.76
0.045
0.037
1.86
0.026 Probability *** NS *** NS
Means within a column and main effect not sharing a common superscript differ (P ≤ 0.05). Oat hulls. 2 Sugar beet pulp. 3 n = 12 for the mean within each day and n = 24 for the mean value for 5 and 15 d. 4 n = 18 for the mean within each day and n = 36 for the mean value for 5 and 15 d. 5 n = 36. 6 Remaining interactions and remaining contrasts were not significant. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. 1
Ceca (% of BW)
5d
0.96 0.93
2 1 1 2
Gizzard (% of BW)
0.58
0.018
0.015 0.011
0.45
*** * *** NS
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Table 7. Influence of fiber inclusion (fiber), type of fat (fat), and age on fresh content (% full segment) of the gastrointestinal tract of broilers Proventriculus (% full segment) Treatment
df
Fiber Control OH1 SBP2 SEM3 Fat Soybean oil Yellow grease SEM4 Age SEM5 Effects6 Fiber Fat Age Fiber × age
2 1 1 2
Gizzard (% full segment)
Ceca (% full segment)
15 d
5d
15 d
Average
5d
15 d
Average
13.9a 6.6b 11.0a 1.21
30.0 36.5 42.9
24.2 35.2 44.6
27.1c 35.9b 43.8a 0.61
54.6 49.8 51.9
57.8 56.6 57.2
56.2 53.2 54.6 1.26
9.9 11.0 0.99 — —
36.6 36.4
35.5 33.8
36.1 35.1 0.50
54.1 50.1
59.1 55.3
56.6a 52.7b 1.03
36.5
0.85
0.69 0.49
34.1
52.1
1.91
1.56 1.10
57.2
Probability *** NS * ***
** NS — —
NS * ** NS
a–c
Means within a column and main effect not sharing a common superscript differ (P ≤ 0.05). Oat hulls. 2 Sugar beet pulp. 3 n = 12 for the mean within each day and n = 24 for the mean value for 5 and 15 d. 4 n = 18 for the mean within each day and n = 36 for the mean value for 5 and 15 d. 5 n = 36. 6 Remaining interactions and remaining contrasts were not significant (P > 0.05). *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. 1
TTAR and AID of Dietary Components
OH inclusion with respect to the control diet (Tables 9 and 10). The inclusion of SBP also improved TTAR of DM, soluble ash, EE, and AMEn of the diet, but that of OM and nitrogen was not affected. The AID of DM
Effect of Fiber. The TTAR of all nutrients and the AMEn content of the diet increased (P ≤ 0.001) with
Table 8. Influence of fiber inclusion (fiber), type of fat (fat), and age on digesta pH of proventriculus and gizzard of broilers Proventriculus (pH) Treatment
df
Fiber Control OH1 SBP2 SEM3 Fat Soybean oil Yellow grease SEM4 Age SEM5 Effects6 Fiber Fat Age Fiber × age a,b
Gizzard (pH)
5d
15 d
Average
5d
15 d
Average
5.26 5.47 5.37
5.12 5.19 4.78
5.24ab 5.33a 5.08b 0.071
3.59 2.91 2.89
4.78 3.83 3.64
4.18a 3.37b 3.26b 0.054
5.08 5.05
5.20 5.23 0.058
3.13 3.13
4.01 4.15
3.57 3.64 0.044
5.32 5.41 5.37
0.089
0.073 0.051
5.07
3.13
0.065
0.053 0.038
Probability 2 1 1 2
* NS *** **
Means within a main effect not sharing a common superscript differ (P ≤ 0.05). Oat hulls. 2 Sugar beet pulp. 3 n = 12 for the mean within each day and n = 24 for the mean value for 5 and 15 d. 4 n = 18 for the mean within each day and n = 36 for the mean value for 5 and 15 d. 5 n = 36. 6 Remaining interactions and remaining contrasts were not significant. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. 1
4.08
*** NS *** ***
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FIBER AND FAT SOURCES IN BROILER DIETS
(P ≤ 0.001), OM (P ≤ 0.001), nitrogen (P ≤ 0.05), soluble ash (P ≤ 0.001), and energy (P ≤ 0.05) were higher for the OH than for the SBP diet (Tables 11 and 12). The values of AID of DM and nitrogen obtained for the control diet were intermediate between those of the OH- and SBP-containing diets. In general, the beneficial effects of OH inclusion on nutrient digestibility were lower for AID than for TTAR. In fact, most of the beneficial effects of fiber inclusion on digestibility disappeared at the ileal level. Effect of Fat. The TTAR of all nutrients, except soluble ash, were higher for the SO- than for the YGcontaining diets (P ≤ 0.001). An interaction between fat source and fiber inclusion was observed for soluble ash (P ≤ 0.05), EE (P ≤ 0.05), and for the AMEn of the diet (P ≤ 0.01). For EE and AMEn, the TTAR increased with fiber inclusion, but the effects were higher for the YG- than for the SO-containing diets. For example, the increase in EE digestibility observed with fiber inclusion was 4.2% for the YG-containing diet but only 2.1% for the SO-containing diets. As observed for TTAR, the AID of DM, OM, starch (P ≤ 0.001), and energy of the diet (P ≤ 0.001) were higher for the SO than for the YG diets. Effect of Age. The TTAR of all nutrients, except soluble ash and EE, increased (P ≤ 0.001) with age (Tables 9 and 10). The AID of OM (P ≤ 0.05) and starch (P ≤ 0.001) also increased with age, but that of nitrogen (P ≤ 0.05) and soluble ash (P ≤ 0.001) decreased. An interaction between age and source of fat was detected for the TTAR of EE (P ≤ 0.01) and AMEn of the diet
(P ≤ 0.01), and for the AID of DM (P ≤ 0.05), OM (P ≤ 0.01), starch (P ≤ 0.001), and energy (P ≤ 0.05); the increase in digestibility observed with age was higher for the YG- than for the SO-containing diets. Also, the reduction of AID of soluble ash observed with age was higher for the diets that included additional fiber than for the control diets (P ≤ 0.001).
DISCUSSION Performance The inclusion of 3% of either OH or SBP improved BWG and feed:gain from 1 to 21 d of age, indicating that young broilers require a minimal amount of fiber in the diet to maximize growth performance. This finding is consistent with data of González-Alvarado et al. (2007), who observed, using similar types of diets, that the inclusion of 3% OH or soy hulls improved significantly BWG by 5.4% and feed:gain by 2.6%. Similarly, Mateos et al. (2006) demonstrated that the inclusion of up to 4% OH in diets based on rice increased performance in weaned piglets and Pettersson and Razdan (1993) observed that the inclusion of 2.3% SBP to a corn-soybean meal diet improved broiler performance from 1 to 21 d of age. Contrary to these findings, Janssen and Carré (1985) in broilers and Sklan et al. (2003) in turkeys indicated that an increase in the fiber content of the diet reduced performance. Differences in the type and level of fiber used and the health status of the experimental animals might explain the distinct ef-
Table 9. Influence of fiber inclusion (fiber), type of fat (fat), and age on total tract apparent retention of DM, organic matter, and nitrogen (%) of the diet in broilers DM (%) Treatment
df
Fiber Control OH1 SBP2 SEM3 Fat Soybean oil Yellow grease SEM4 Age SEM5 Effects6 Fiber Fat Age Fiber × age a–c
2 1 1 2
Organic matter (%)
Nitrogen (%)
5d
15 d
Average
5d
15 d
Average
5d
15 d
Average
75.8 79.5 77.6 0.25
77.9 80.5 79.2 0.22
76.9c 80.0a 78.4b 0.17
81.6 83.1 81.2 0.24
83.7 84.3 83.0 0.21
82.6b 83.7a 82.1b 0.16
65.5 70.0 67.6 0.46
68.5 70.9 68.6 0.52
67.0b 70.4a 68.1b 0.39
78.6 76.7 0.21 77.6 0.15
79.8 78.6 0.18 79.2 0.13
79.2a 77.7b 0.14
82.9 81.0 0.20 82.0 0.14
84.2 83.1 0.17 83.7 0.12 Probability *** *** *** NS
83.6a 82.0b 0.13
68.8 66.6 0.37 67.7 0.26
70.3 68.3 0.43 69.3 0.30
69.6a 67.5b 0.32
*** *** *** NS
Means values within a column and main effect not sharing a common superscript differ (P ≤ 0.05). Oat hulls. 2 Sugar beet pulp. 3 n = 12 for the mean within each day and n = 24 for average value for 5 and 15 d. 4 n = 18 for the mean within each day and n = 36 for average value for 5 and 15 d. 5 n = 36. 6 Remaining interactions and remaining contrasts were not significant. *P ≤ 0.05; ***P ≤ 0.001. 1
*** *** *** *
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Jiménez-Moreno et al.
Table 10. Influence of fiber inclusion (fiber), type of fat (fat), and age on total tract apparent retention of soluble ash, ether extract (%), and AMEn content of the diets (kcal/kg) in broilers Soluble ash (%) Treatment
df
Fiber Control OH1 SBP2 SEM3 Fat Vegetable oil Yellow grease SEM4 Age SEM5 Soybean oil + None + 3% OH + 3% SBP Yellow grease + None + 3% OH + 3% SBP SEM6 Effects7 Fiber Fat Age Fiber × age Fat × age Fat × fiber
2 1 1 2 1 2
Ether extract (%)
AMEn (kcal/kg)
5d
15 d
Average
5d
15 d
Average
5d
15 d
Average
36.2 55.9 53.5 1.00
39.4 53.4 52.9 0.64
37.8b 54.7a 53.2a 0.68
86.0 90.3 88.8 0.42
87.7 89.5 89.1 0.32
86.8c 89.9a 89.0b 0.28
3,081 3,228 3,216 9
3,136 3,251 3,204 7
3,109c 3,240a 3,183b 6
49.4 47.7 0.86 48.5 0.57
49.0 48.2 0.52 48.6 0.37
49.2 47.9 0.55
91.4 85.4 0.34 88.4 0.24
90.9 86.3 0.26 88.8 0.18
91.1a 86.0b 0.23
3,203 3,112 8 3,157 5
3,224 3,171 6 3,197 4
3,213a 3,141b 5
35.9 59.0 53.2
39.5 54.5 53.0
37.7c 56.7a 53.1b
89.9 93.0 91.3
90.0 91.5 91.3
89.9b 92.2a 91.3a
3,145 3,268 3,195
3,173 3,269 3,228
3,159c 3,269a 3,212b
36.5 52.9 53.8 1.50
39.4 52.3 52.7 0.91
37.9c 52.6b 53.3b 0.96
82.1 87.7 86.3 0.60
85.4 87.6 86.9 0.45 Probability *** *** NS ** ** *
83.6d 87.6c 86.6c 0.40
3,017 3,188 3,129 13
3,100 3,233 3,180 10
3,059d 3,211b 3,154c 9
*** NS NS *** NS *
*** *** *** NS ** *
a–d
Means within a column and main effects not sharing a common superscript differ (P ≤ 0.05). Oat hulls. 2 Sugar beet pulp. 3 n = 12 for the mean within each day and n = 24 for average value for 5 and 15 d. 4 n = 18 for the mean within each day and n = 36 for average value for 5 and 15 d. 5 n = 36. 6 n = 6 for the mean within each day and n = 12 for average value for 5 and 15 d. 7 Remaining interactions and remaining contrasts were not significant. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. 1
fects observed by these authors. For example, the control diet used by Sklan et al. (2003) contained 3% CF, whereas in the current research, the diet had only 1.5% CF. Thus, a higher effect of fiber inclusion should be expected in the current trial because of the low fiber content of the control diet. Also, the trial of Sklan et al. (2003) was conducted on floor pens, where the birds had free access to additional fiber from the litter, reducing the need for dietary fiber. In this respect, Hetland et al. (2005) observed that birds had an appetite for fiber and that when the diet did not provide a minimal amount of this nutrient, the consumption of litter increased. Type of fat had little effect on broiler performance. The only difference observed was for BWG from 1 to 21 d of age that was greater for broilers fed YG than for broilers fed SO. This observation disagrees with most published studies that have reported similar or lower BWG in birds fed saturated fats than in birds fed more unsaturated fats (Thacker et al., 1994; Zollitsch et al., 1997; Madrazo et al., 2002). However, Pesti et al. (2002) reported that broilers fed a diet with 6% SO had lower BWG from 18 to 39 d of age than chicks fed
the same diet with 6% YG. Recently, Firman et al. (2008) compared the performance of broilers fed 1 of 7 different types of fats at 3% of inclusion from 1 to 49 d of age. They found that broilers fed the SO diet had lower BWG at 35 and 49 d of age than broilers fed the YG diet. These results indicate that in addition to fatty acid profile, other factors, probably related to the nonnutritive fraction of the supplemental fat, affect broiler growth. Yellow grease results from the mixture of fats and oils from different industries and consequently, the quality of the final product is very variable. The YG used in the current research was a high-quality fat with 21.2% linoleic acid and very low free fatty acid content, which might have eliminated the expected advantage of SO over YG on BWG of broilers.
Organ Measurements and pH of the Digesta In general, the inclusion of fiber increased the relative weight of the different segments of the GIT, but the effects varied with the type of fiber and the segment of the GIT considered. Jiménez-Moreno et al. (2009)
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FIBER AND FAT SOURCES IN BROILER DIETS
Table 11. Influence of fiber inclusion (fiber), type of fat (fat), and age on the apparent digestibility of DM, organic matter, and nitrogen (%) of the diets in broilers DM (%) Treatment
df
Fiber Control OH1 SBP2 SEM3 Fat Soybean oil Yellow grease SEM4 Age SEM5 Effects6 Fiber Fat Age Fat × age
Organic matter (%)
Nitrogen (%)
5d
15 d
Average
5d
15 d
Average
5d
15 d
Average
72.8 74.7 73.0 0.29
74.4 75.3 72.7 0.65
73.6ab 75.0a 72.8b 0.37
77.3 77.4 75.7 0.31
79.3 78.5 75.9 0.67
78.3a 78.0a 75.8b 0.47
74.2 77.7 74.2 1.17
73.6 75.0 71.3 1.28
73.9ab 76.3a 72.7b 1.00
75.0 72.0 0.24 73.5 0.17
74.6 73.6 0.53 74.3 0.37
74.8a 72.9b 0.37
78.4 75.2 0.26 76.8 0.18
78.3 77.5 0.55 77.9 0.39 Probability *** *** * **
78.4a 76.5b 0.38
75.6 75.1 0.95 75.4 0.67
72.8 73.7 1.05 73.3 0.74
74.2 74.4 0.81
2 1 1 1
*** *** NS *
* NS * NS
a,b
Means within a main effect not sharing a common superscript differ (P ≤ 0.05). Oat hulls. 2 Sugar beet pulp. 3 n = 12 for the mean within each day and n = 24 for the mean value for 5 and 15 d. 4 n = 18 for the mean within each day and n = 36 for the mean value for 5 and 15 d. 5 n = 36. 6 Remaining interactions and remaining contrasts were not significant. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. 1
also observed that the inclusion of 3% OH or SBP increased gizzard weight in broilers fed similar type of diets. The lignin content of OH is high and therefore,
OH-containing diets will be more resistant to grinding than the control diets. Consequently, OH will slow down the passing of digesta from the gizzard to the
Table 12. Influence of fiber inclusion (fiber), type of fat (fat), and age on apparent ileal digestibility of soluble ash and starch (%), and energy (kcal/kg) of the diets in broilers Soluble ash (%) Treatment
df
Fiber Control OH1 SBP2 SEM3 Fat Soybean oil Yellow grease SEM4 Age SEM5 Effects6 Fiber Fat Age Fiber × age Fat × age a–c
2 1 1 2 1
Starch (%)
Energy (kcal/kg)
5d
15 d
Average
5d
15 d
Average
5d
15 d
Average
48.5 62.8 59.7 0.88
48.1 55.6 51.7 1.17
48.3c 59.2a 55.7b 0.80
95.9 96.3 95.7 0.52
97.2 98.0 96.9 0.36
96.6 97.1 96.3 0.35
2,897 2,969 2,942 12
2,979 3,004 2,922 28
2,938b 2,987a 2,932b 16
57.1 56.9 0.72 57.0 0.51
52.4 51.2 0.95 51.8 0.67
54.8 54.1 0.65
97.3 94.5 0.42 96.0 0.30
97.5 97.4a 97.3 95.9b 0.29 0.29 97.4 0.21 Probability NS *** *** NS ***
2,998 2,874 10 2,936 7
2,986 2,951 25 2,968 16
2,992a 2,913b 13
*** NS *** *** NS
Means within a column and main effect not sharing a common superscript differ (P ≤ 0.05). Oat hulls. 2 Sugar beet pulp. 3 n = 12 for the mean within each day and n = 24 for the mean value for 5 and 15 d. 4 n = 18 for the mean within each day and n = 36 for the mean value for 5 and 15 d. 5 n = 36. 6 Remaining interactions and remaining contrasts were not significant. *P ≤ 0.05; ***P ≤ 0.001. 1
* *** NS NS *
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Jiménez-Moreno et al.
small intestine because coarse particles are retained for longer in this organ than fine particles (Svihus et al., 2002). González-Alvarado et al. (2008) suggested that the increase in gizzard size observed in broilers fed 3% OH with respect to broilers fed the control diet resulted from the greater development of the muscular layers, a finding that is consistent with the increase in gizzard weight observed in the current experiment. On the other hand, SBP has a high pectin content and consequently, SBP inclusion will increase the solubility, WHC, and SWC of the diet. Because of these properties, the inclusion of SBP in the diet will increase the bulk of the digesta, which in turn might produce physical dilation of the proventriculus walls and a concomitant increase in organ size. In addition, as they swell, SBP particles increase in size and consequently, they will be retained for longer in the gizzard. Consequently, the pH of the gizzard will be lower and its digesta content and size will be higher in birds fed the SBP-containing diets than in control birds. In the current trial, gizzard weight increased to a greater extent with OH than with SBP inclusion, probably because of the greater resistance to grinding of OH. Contrary to this finding, the relative weight of the ceca was higher with the SBP than with the OH diet, an observation that is consistent with the lower lignin and higher pectin content of the SBP. Differences in chemical characteristics of the 2 fiber sources might explain the higher fermentation capability of SBP by the resident microflora (Carabaño et al., 1997). There is no apparent explanation for the higher relative weight of the proventriculus and ceca observed in broilers fed the SO diet with respect to broilers fed the YG diet. In fact, Zollitsch et al. (1997) did not observe any effect on gizzard weight when 3.5% YG was substituted by SO in 43-d-old broilers. In all cases, the differences in organ weights observed were small and of little practical interest. The relative weight of the proventriculus, gizzard, and ceca decreased from 5 d to 15 d of age, an observation that is consistent with data reported by Ravindran et al. (2006) and González-Alvarado et al. (2008). Also, the pH value of the digesta of the proventriculus was reduced and that of the gizzard increased with age, in agreement with data of González-Alvarado et al. (2007) and of Rynsburger and Classen (2007). The diameter of the orifice of exit from the gizzard to the duodenum is smaller at 5 d than at 15 d of age, and consequently, the percentage of coarse particles retained in the gizzard will be reduced with age. As a result, and consistent with our data, the relative digesta content of the gizzard will be lower and the gizzard pH will be higher as the bird ages.
TTAR and AID of Dietary Components Traditionally, it has been accepted that dietary fiber reduced nutrient digestibility and AMEn in poultry feeds (Jørgensen et al., 1996). However, in the current
research, an increase in dietary fiber increased TTAR of most nutrients, an increase that was more evident with OH than with SBP. González-Alvarado et al. (2007) also observed that the TTAR of all nutrients increased when 3% of either OH or soy hulls were included in the diet in 18-d-old broilers. Coarse feed particles, such as those provided by the fiber sources used, remain longer in the upper part of the GIT, stimulating gizzard activity (Hetland et al., 2005) and increasing the production of HCl (Duke, 1986). A low gizzard pH improves pepsin activity and nitrogen retention and increases the solubility of the mineral fraction of the feed (Guinotte et al., 1995), which in turn might favor its absorption. Moreover, a well-developed gizzard might increase the refluxes of feed from the duodenum to the gizzard, facilitating the mixing of digesta with enzymes and improving nutrient utilization (Gabriel et al., 2003). In addition, Hetland et al. (2003) found that OH inclusion increased the concentration of the bile acids in the chyme of broilers, which might increase fat digestibility in young chicks. The beneficial effects of OH inclusion on nutrient digestibility were reduced for the starch fraction, and even disappeared for DM, OM, and nitrogen when the digestibility was expressed on ileal bases. Probably, the abrasive effect of OH on the intestinal mucosa increased endogenous cell losses, reducing ileal nitrogen digestibility. Hetland and Svihus (2001) found that the AID of starch increased when OH was included in the diet but that those of nitrogen, fat, and ash were not modified. In the current trial, the AID of DM, OM, nitrogen, and energy was lower with SBP than with OH inclusion. Moreover, the inclusion of SBP reduced AID of OM with respect to that of the control diet. A reduction in the AID of OM was also observed in broilers by Pettersson and Razdan (1993) when the level of SBP of diet was increased from 2.3 to 9.2%. Similarly, Green (1988) in adult cockerels and Gómez-Conde et al. (2007) in rabbits also have found that dietary SBP reduced ileal nitrogen digestibility. In the current trial, the weight of the digestive tract with contents was higher for the SBP than for the OH diet, which indicates that SBP-containing diets were retained for longer in the GIT. An increase in chyme accumulation in the GIT with SBP inclusion might result from an increase of the digesta viscosity as has been demonstrated in rats by Chang (1983) and in humans by Sandhu et al. (1987). As a result, the accumulation of viscous material in the GIT might interfere with the diffusion of nutrients through the mucosal surface slowing down nutrient absorption (Forman and Schneeman, 1980). In addition, the inclusion of SBP, but not OH, in the diet increases the thickness of the unstirred water layers of the mucosa reducing nutrient dispersion and impairing absorption (Johnson and Gee, 1981). On the other hand, the reduction of AID of nitrogen with age might have been caused by the higher feed intake and consequently higher nitrogen endogenous losses at 15 d of age (Ravindran and Hendriks, 2004).
FIBER AND FAT SOURCES IN BROILER DIETS
In general, the TTAR of dietary components was higher for diets based on SO than for diets based on YG, in accordance with data of Ketels and DeGroote (1989). Soy oil is primarily composed of unsaturated fatty acids, which are easier to digest than saturated fatty acids, especially in young birds. Birds younger than 2 wk secrete limited amounts of bile acids (Garrett and Young, 1975; Krögdahl, 1985), which might impair fat digestibility, especially with saturated fats. Hence, the lack of sufficient production of bile salts in chicks may account for the lower EE digestibility observed in broilers fed YG than in broilers fed SO. Hetland et al. (2003) found that the inclusion of additional fiber in the diet increased the concentration of bile acids in the chyme of broilers. Therefore, fiber inclusion should improve EE digestibility more in diets based on YG than in those based on SO. In addition, Malagelada et al. (1973) indicated that nonemulsified lipids, such as those originating from saturated fats, might interfere with the solubilization and absorption of other nutrients such as nitrogen, reducing its utilization. Moreover, an increase in EE digestibility, as observed with SO inclusion, will improve the TTAR of DM, OM, and the AMEn of the diet, in accordance with our findings. It is concluded that the inclusion of additional fiber, especially OH, in the diet improves gizzard development and nutrient retention. The inclusion of SBP impairs ileal DM, nitrogen, and energy digestibility as compared with the inclusion of OH. The inclusion of fiber improves more the TTAR of EE and AMEn of the diet in birds fed saturated fats than in birds fed less saturated fats. Therefore, young broilers might require a minimal amount of fiber in the diet to maximize performance.
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