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METABOLISM AND NUTRITION |
Departamento de Producción Animal, Universidad Politécnica de Madrid, 28040 Madrid, Spain
3 Corresponding author: gonzalo.gmateos{at}upm.es
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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0.01). Heat processing had little effect on relative weight (RW) of the digestive organs. An interaction between cereal and HP of the cereal was detected for the gizzard and the liver; HP of corn reduced RW of the gizzard and increased that of the liver, but no effect was observed with HP of rice. The RW of the proventriculus was increased by SH inclusion (P 0.05), whereas the RW of the gizzard was increased by OH inclusion (P 0.001). Also, SH inclusion increased gizzard digesta (P 0.01) and moisture (P 0.001) content. Dietary treatment did not affect relative length (cm/kg of empty BW) of the intestines. Feeding rice tended to increase gizzard digesta pH (P = 0.081) but reduced that of the intestines (P 0.001). Neither HP of the cereal nor hull inclusion affected pH of the digestive tract. We conclude that the RW of the proventriculus and gizzard is reduced by feeding rice and increased by hull inclusion. Dietary treatment had little effect on the weight and relative length of the intestines. Chicks might require a minimal amount of fiber in the diet to stimulate the development of the upper gastrointestinal tract.
Key Words: fiber • rice • heat processing • gastrointestinal tract • chick
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The use of rice in substitution of corn improves nutrient digestibility and productive performance in piglets (Mateos et al., 2006, 2007). However, the information available on the use of rice in broiler diets is scarce. Rice grain is rich in highly digestible starch and low in nonstarch polysaccharides content (Vicente et al., 2008). Therefore, the inclusion of rice increases energy but reduces the fiber content of the diet, which might compromise GIT health in young birds. Heat processing of the cereal is a common practice in piglet feeding to improve nutrient digestibility and productive performance (Medel et al., 2004). Moritz et al. (2005) observed that chicks fed extruded corn had better feed intake and BW gain than chicks fed raw corn, and Plavnik and Sklan (1995) reported that extrusion or expansion of wheat and barley increased the AMEn of mash diets in 18- to 21-d-old broilers. Also, García et al. (2008) found that micronization or expanded barley improved feed intake and BW gain from 1 to 7 d of age but had little effect on nutrient digestibility and growth at 28 d of age. However, the influence of HP of the cereal on the development of the GIT has not been studied in detail. González-Alvarado et al. (2007) did not observe any significant effect of steam cooking of corn or rice on the size of the different organs of the GIT, and Gracia et al. (2003) observed that steam cooking of barley increased the relative weight (RW) of the liver but had no effect on pancreas and small intestine (SI).
It is widely accepted that a reduction in the crude fiber content of the diet increases nutrient digestibility in broilers (Carré, 2004). However, when crude fiber is reduced, the size and the content of the gizzard and the development of the GIT are affected (Riddell, 1976; Jørgensen et al., 1996; Hetland et al., 2005). In fact, Hetland et al. (2003) observed that the inclusion of fiber in the diet improved starch and ether extract digestibility, probably through stimulating gizzard activity, increasing the refluxes of the digesta from duodenum to the gizzard, and improving 
-amylase and bile acid secretion. However, there is no comparative information on the influence of fiber sources differing in chemical and physical characteristics on the development and pH of the GIT. The aim of this trial was to evaluate the inclusion of different sources of fiber in diets based on rice or corn, either raw or HP, on the development of the digestive organs and digesta pH in broilers from 1 to 22 d of age.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Two batches of yellow corn and polished broken rice (Japonica variety; 80% Senia and 20% Tainato cultivars) were obtained from a commercial supplier (Esasa, Valladolid, Spain) and split into 2 portions. The first portion of corn was hammer-milled (2.5-mm screen, Model DFZC-635, Bühler AG, Uzwil, Switzerland) and used as such in the manufacturing of the diet. The second portion of corn was ground, steam-cooked (Model AK38–1, Amandus Kahl, Reinbek, Germany) for 60 min at 104 ± 3°C, flaked through riffled rolls, cooled and dried (125°C for 10 min), ground (2.5-mm screen, Model DFZC-635, Bühler AG), and used to make the feed. Similar procedures were used for rice, but in this case, the second portion was cooked for 45 min at 90 ± 3°C. Oat hulls (OH) and soy hulls (SH) were obtained from the same commercial supplier, ground through a hammer mill (2-mm screen, Model Z-I, Retsch, Stuttgart, Germany), and included as such in the corresponding experimental diets. The composition of the cereals and fiber sources tested are shown in Table 1
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). In the corresponding experimental diets, 3% OH or SH was included at the expenses (wt/ wt) of sepiolite. The composition and mean particle size (MPS) of the experimental diets is shown in Table 3.
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All experimental procedures used in this research were approved by the Animal Ethics Committee of the University of Madrid and were in compliance with the Spanish guidelines for the care and use of animals in research (Boletín Oficial Estado, 2005).
One-day-old straight-run broiler chicks (Cobb 500) with an initial BW of 39.3 ± 3.12 g were obtained from a commercial hatchery (Cobb España, Alcalá de Henares, Madrid, Spain) and allocated in a windowless, environmentally controlled room. A total of 432 chicks were distributed at random into 36 groups (3 groups per each dietary treatment). The 12 chicks within each replicate were housed in battery cages of 1 x 0.9 m2 (Avícola Grau, Madrid, Spain) provided with wire flooring and equipped with 2 drinker cups and a 1-m linear feeder. Room temperature was kept at 33°C during the first 3 d of the trial and then was reduced gradually according to age until reaching 24°C at 21 d. The chicks were kept on a 23 h/d light program and had free access to mash feed and water throughout the trial. The trial was conducted as a completely randomized design with 12 dietary treatments arranged factorially with 2 cereals (corn and rice), 2 HP of the cereal (raw and steam-cooked), and 3 fiber sources (none, 3% OH, and 3% SH). All diets were fed in mash form.
Analytical Evaluation of Ingredients and Feeds
Particle distribution and MPS of ground cereals, hulls, and diets were determined in triplicate according to the methodology recommended by American Society of Agriculture Engineers (1995). Briefly, 3 subsamples (100 g) were sieved using a Filtra 200 shaker (Filtra S.A., Barcelona, Spain) provided with 7 sieves ranging from 2,500 to 40 µm.
The water-holding capacity (WHC) of the fiber sources and diets were determined as indicated by Giger-Reverdin (2000) with modifications. Briefly, 3 subsamples (1 g) were left to soak for 16 to 24 h with excess distilled water (100 mL) and then filtered on a fritted glass crucible (porosity 2). The wet sample was weighed after letting the water drain for 10 min. The WHC was calculated as the quantity of water retained in the sample and expressed as liters per kilogram of DM.
Ingredients and feeds were analyzed in triplicate for moisture by the oven-drying method (930.15), total ash by muffle furnace (942.05), nitrogen by the Dumas method (968.06) using LECO equipment (Model FP-528, Leco Corporation, St. Joseph, MI), and ether extract by Soxhlet fat analysis after 3 N HCl acid hydrolysis (920.39) as described by Association of Official Analytical Chemists International (2000). Starch content of ingredients was measured by the -amylase glucosidase method (996.11) as described by Association of Official Analytical Chemists International (2000). Gross energy was measured with an adiabatic bomb calorimeter (Model 356, Parr Instrument Company, Moline, IL), and neutral detergent fiber and acid detergent fiber were determined sequentially as described by Van Soest et al. (1991) and expressed on an ash-free basis.
Digestive Organ Measurements and pH of Digesta
At the beginning of the trial, 13 chicks were randomly selected from a total of 445 birds, weighed individually, and killed by cervical dislocation. In addition, at 5, 9, 15, and 22 d of age, 2 birds per cage were randomly selected, weighed, and killed. The digestive tract with contents of all these birds was removed aseptically and weighed. Then, the proventriculus, gizzard, duodenum, jejunum, ileum, ceca, liver, and pancreas were excised, cleaned, dried with desiccant paper, and measured. The weight of the empty organs was expressed relative to live BW, whereas the weight of the fresh digesta content of each organ was expressed relative to full organ weight. The lengths of the duodenum, jejunum, ileum, and ceca were determined and expressed relative to empty BW (RL) at same ages. Moisture content of the gizzard was determined by oven-drying at 60°C for 72 h in all the birds. The Koilin membrane of the gizzard of all the chicks killed at 22 d of age was cleaned, dried with desiccant paper, and weighed, and the weight was expressed relative to the empty gizzard weight. Also, the digesta contents of the gizzard, jejunum, and ileum of 2 birds per replicate were collected at this age, homogenized in a 50-mL beaker, and used to measure the pH of each segment of the GIT in duplicate samples using a digital pH meter (Model 507, Crison Instruments S. A., Barcelona, Spain). The average pH obtained in these 2 birds was used for further analyses. Finally, the moisture content of the jejunum digesta was also determined at this age.
Statistical Analysis
All data sets were analyzed for normal distribution using the NORMAL option of the UNIVARIATE procedure and for homogeneity of variances for treatment means through the Levene’s test using the HOVTEST option of the GLM procedure of SAS (SAS Institute, 1990). Data of BW were analyzed as a completely randomized design using the GLM procedure of SAS (SAS Institute, 1990). All the other data were analyzed as a completely randomized design using the MIXED procedure of SAS (Littell et al., 1996). The effects of type of cereal, HP of the cereal, fiber inclusion, and their interactions were studied. Preplanned orthogonal comparisons were used to determine the effects of hull inclusion (none vs. 3% hulls) and type of hulls (OH vs. SH). The results in tables are reported as least squares means. The experimental unit was the cage for all traits studied. All differences were considered significant at P 0.05. Polynomial orthogonal contrasts were performed to study the linear and quadratic evolution of RW, RL, and fresh contents of the organs and the moisture content of the gizzard digesta with age. In addition, the RW of the Koilin membrane of the gizzard, the moisture content of the jejunum digesta, and the pH of the digesta of the gizzard, jejunum, and ileum at 22 d of age were analyzed using the GLM of SAS software (SAS Institute, 1990).
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RESULTS |
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). Consequently, MPS was smaller for the rice than for the corn diets (482 vs. 537 µm; Table 3). The inclusion of hulls increased MPS of the diets (515 and 527 vs. 488 µm for OH, SH, and control diets, respectively). The MPS ranged from 586 µm for the diet based on HP corn with 3% OH to 456 µm for the diet based on HP rice without hulls. The WHC was similar for corn and rice (1.97 vs. 1.92 L/kg of DM) and was greater for HP corn than for raw corn (2.79 vs. 1.92 L/kg of DM). However, no differences were detected between raw and HP rice. Consequently, WHC was greater for the diets based on HP corn (2.73 vs. 2.24 L/kg of DM for HP and raw corn diets, respectively), but no differences were observed for the diets based on rice. Effect of Age
The RW of all the organs and segments of the GIT was affected by age (Figure 1). The RW of the digestive tract and proventriculus were maximal from 1 to 5 d of age and then declined with age. In general, the RW of the SI was maximal from d 5 to 9 and then decreased until d 22. The RW of the gizzard and ceca declined with age throughout the study. The maximal RW of the liver and pancreas was observed between d 5 and 9. The relative fresh digesta content (% full organ) of the gizzard was little affected by age from d 1 to 15, but it was reduced by 7.1% from d 15 to 22 (Figure 2). Digesta content was greatest at d 22 for the duodenum (65.7%), jejunum (57.2%), and ileum (57.0%) and at d 9 for the ceca (56.1%; Figure 2). The RL of the duodenum, ileum, and ceca decreased with age, and the decline was more pronounced at early ages (P 0.05; Figure 3). In contrast, the RL of the jejunum increased from d 1 to 5 and then decreased until d 22.
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Type of cereal had no effect on BW of chicks at any age (Table 4). Chicks fed corn had smaller empty BW (79.0 vs. 79.9% BW; P 0.01), larger digestive tracts (15.7 vs. 15.0%; P 0.01), and heavier proventriculi (0.81 vs. 0.76%; P 0.01), gizzards (3.28 vs. 2.84%; P 0.001), and pancreas (0.42 vs. 0.40%; P 0.01) than chicks fed rice (Tables 5, 6, and 7). Type of cereal had little effect on the RW of the distal part of the GIT (Tables 7 and 8) and the liver (Table 9). In addition, digesta (35.1 vs. 28.9%; P 0.001) and moisture (66.1 vs. 64.1%; P 0.05) content of the gizzard were greater in chicks fed corn than in chicks fed rice (Table 10). Fresh digesta content of the jejunum was not affected by the cereal, but moisture was greater in chicks fed corn than in chicks fed rice (P 0.05; Table 11). Also, ileum and ceca contents were greater for chicks fed corn than for chicks fed rice (54.3 vs. 49.3% for ileum and 51.9 vs. 45.6% for ceca; P 0.01; Table 12). The RL of the different segments of the GIT were not affected by the cereal of the diet (Tables 13 and 14). Chicks fed corn had greater jejunum and ileum pH (P 0.001) and tended to have lower gizzard pH than chicks fed rice (P = 0.081; Table 15).
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The BW of chicks was not affected by HP of the cereal (Table 4). Heat processing of the cereal had little effect on the development of the different organs and segments of the GIT. Some interactions were observed between type of cereal and HP of the cereal; the proventriculus was smaller in chicks fed raw rice than in chicks fed HP rice (P 0.05), but no effect was detected in chicks fed corn. In addition, the RW of the gizzard was reduced (P 0.05) and the moisture content of its digesta was increased (P 0.01) when corn was HP, but no effects were observed with HP of rice (Tables 6 and 10). Also, the RW of the liver increased with HP of corn (3.82 vs. 4.39%), but no effect was observed with HP of rice (P 0.001; Table 9).
Effect of Fiber
The BW of chicks was not affected by the inclusion of fiber in the diet (Table 4). The inclusion of a fiber source in the diet affected the RW of the proventriculus and the gizzard in different ways but had no effect on the distal part of the GIT (Tables 6, 7, and 8). The proventriculi were heavier in chicks fed SH than in chicks fed OH or the control diet (0.82 vs. 0.78 and 0.76%; P 0.05). In contrast, chicks fed SH or the control diet had lighter gizzards than chicks fed OH (2.96 and 2.85 vs. 3.37%; P 0.001). The RW of the Koilin membrane was smaller in chicks fed OH than in chicks fed SH or the control diet (12.21 vs. 16.83 and 16.16 g/ kg of empty gizzard; P 0.001), but the absolute weight was similar (1.87 vs. 1.94 vs. 1.74 g for OH, SH, and the control diet, respectively). Gizzard digesta content (% full gizzard) was greater with SH than with OH or the control diet (35.3 vs. 31.5 and 29.4%; P 0.01), but no effects were observed in digesta content in the other segments of the GIT (Tables 10, 11, and 12). Digesta moisture content in the gizzard was greater with the SH- than with the remaining diets (67.7 vs. 62.7 and 64.9 for SH, OH, and the control diet, respectively; P 0.001). Hull inclusion reduced digesta moisture content in the jejunum (80.8 vs. 79.7%; P 0.05; Table 11). An interaction between type of cereal and fiber inclusion was detected; fresh digesta content of the gizzard was increased when hulls were added to the rice diet but not when added to the corn diet (P 0.001). In addition, SH increased the moisture content of the digesta (P 0.05) in chicks fed rice, but no effect was observed in chicks fed corn. Also, digesta content of the gizzard decreased markedly with age in chicks fed raw rice without hulls but not in chicks fed raw rice with hulls (P 0.01).
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DISCUSSION |
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With the exception of the RW of the gizzard and the SI, the age at which the RW and RL of the different organs and segments of the GIT reached the maximal value agrees with previous reports (Nitsan et al., 1991; Nir et al., 1993; Sell, 1996; Gracia et al., 2003). The RW of the gizzard was decreased from hatching until d 22, in agreement with data of Ravindran et al. (2006). In contrast, Dror et al. (1977), Nitsan et al. (1991), and Gracia et al. (2003) reported maximal RW at 3 to 4 d of age. Opposite to these observations, Sell et al. (1991) observed that the RW of the gizzard of turkeys increased rapidly from 0 to 4 d posthatching and then remained relatively constant until 8 d of age, and Uni et al. (1999) found that the RW of the gizzard was constant from hatching to 12 d. The SI reached a maximal RW between 5 and 9 d and then declined rapidly with age, which agrees with reports of Sell (Sell et al.,1991; Sell, 1996) and Sklan (2001). In contrast, Gracia et al. (2003), Cuervo et al. (2002), and Ravindran et al. (2006) found that the maximal RW of the SI was obtained from 8 to 14 d of age. The RL of all the segments of the GIT decreased with age, which agrees with data of Santos et al. (2006) and Ravindran et al. (2006). Ravindran et al. (2006) suggested that the chick increases the intestinal mass with age to compensate for the decline in RL, thereby maintaining the supply of nutrients to demanding tissues.
Effect of Cereal
Chicks fed corn had heavier digestive tracts, proventriculi, gizzards, and pancreas than chicks fed rice. Consequently, empty BW was heavier for chicks fed rice than for chicks fed corn. The heavier GIT found for chicks fed corn is consistent with the greater fiber content and MPS of these diets. Rao et al. (2000) found that hens fed corn had heavier gizzards than hens fed rice, and Nir et al. (1995) observed that the RW of the digestive tract and the proventriculus increased when the MPS of the diet was increased. Moreover, these authors reported that chicks fed finely ground feeds had smaller gizzards with lower digesta contents than chicks fed coarsely ground feeds, in agreement with our results. Coarse particles and fibrous constituents of the diet tend to remain longer in the gizzard, increasing the mechanical stimulation of this organ (Hetland and Svihus, 2001).
Gizzard pH was reduced in chicks fed corn, although the differences with respect to chick fed rice were not significant. González-Alvarado et al. (2007) observed that gizzard pH was lower in broilers fed corn than in broilers fed rice. Duke (1986) indicated that the presence of feed in the gizzard induces the secretion of HCl in the proventriculus via mechanoreceptors. Opposite to the observation in the gizzard, the pH in the jejunum and in the ileum was lower for chicks fed rice than for chicks fed corn. Gizzard digesta content was less in chicks fed rice than in chicks fed corn, a finding that is consistent with the greater fiber and fat content and greater MPS of the corn diets (Mateos and Sell, 1980; González-Alvarado et al., 2007). Hetland and Svihus (2001) indicated that gizzard digesta content was increased when the fiber content of the diet increased. Nir et al. (1994) observed that chicks fed coarsely ground diets had lower gizzard pH than chicks fed finely ground diets, an effect that was consistent with their heavier gizzards. Type of cereal did not affect the RW and RL of any segments of the distal GIT, except for ileum weight that was increased with rice.
Effect of HP
Heat processing did not affect the RW of the pancreas or the RW and RL of the different segments of the GIT. It was observed that HP increased the RW of the liver in chicks fed corn but not in chicks fed rice. Gracia et al. (2003) reported that steam cooking increased liver weight in chicks fed barley but that the effects disappeared when the diet was supplemented with enzymes. The reason for this observation is unknown, but HP solubilizes the fiber portion of the barley diet, increasing intestinal viscosity. An increase in viscosity might have stimulated bile acid production and increased liver weight, but no effects could be noticeable when the diet was supplemented with enzymes. In addition, HP might have released the lipids contained within the cells of the corn grain, which in turn might have resulted in an increase in bile acid production and in liver weight. The moisture content of the digesta of the gizzard increased with HP of corn, but no effects were observed with rice, a finding that is consistent with the WHC of the 2 cereals. Corn starch is rich in amorphous regions, whereas rice starch is more crystalline in nature (Tester et al., 2004). When heat is applied to the cereal, the amorphous regions of starch are expanded during swelling, and consequently, the WHC and the MPS of the starch increase (French, 1973). However, HP breaks rapidly, and, without expansion, the crystalline starch and therefore MPS is reduced and WHC is not modified at a high extent (Svihus et al., 2005). Therefore, HP increased more the WHC of corn than of rice, and, consequently, HP increased gizzard digesta moisture content more in the corn than in the rice diets.
Effect of Fiber
The inclusion of fiber in the diet affected the RW of the proventriculus and the gizzard, as well as gizzard digesta content, in different ways. These results agree with Riddell (1976) and Hetland and Svihus (2001), who observed proventricular hypertrophy and poor development of the gizzard in chicks fed low-fiber diets and that the inclusion of fiber in these diets increases gizzard weight. Fiber sources differ in properties such as particle size, cation exchange capacity, and WHC. Consequently, the influence of a fiber source on transit time of the digesta and on the development of the GIT varies according to its chemical composition and physical characteristics (Bach Knudsen, 2001). A fiber source with a high WHC will increase the bulk of gizzard digesta and, therefore, gizzard size (Svihus et al., 2002). In the current trial, the RW of the proventriculus, gizzard digesta content, and moisture content of the gizzard were greater in chicks fed SH than in chicks fed OH, a finding that is consistent with the greater WHC of SH. The greater WHC of SH, probably because of its greater solubility (Van Soest, 1985), results in a bulkier chyme and in a reduction in the passage rate of the digesta from the proventriculus and gizzard to the SI. The RW of the Koilin layer (% empty gizzard) was lower for chicks fed OH than for chicks fed SH or the control diet, but the absolute weight was similar. The inclusion of OH in the diet increased in greater proportion the weight of the muscular layers of the gizzard than the surface of the inner layer covering of gizzard. Consequently, the proportion of the Koilin layer per unit of gizzard weight was reduced with OH inclusion.
After grinding, insoluble fiber sources, especially those rich in lignin, have a greater proportion of large particles than more soluble sources. Feed particles are retained in the gizzard until a certain minimal critical size is reached (Hetland et al., 2002; Svihus et al., 2002), and therefore, lignified fiber sources, such as OH, are retained longer in the gizzard than nonlignified sources such as SH. As a result, gizzard development and activity should be greater with OH than with SH diets, an observation that is consistent with the results of the current research. The effects of hull inclusion on the RW of the gizzard and on its digesta and moisture content were more pronounced in the rice than in the corn diet, an observation that is consistent with the greater fiber content, WHC, and MPS of the corn diets. Hetland et al. (2005) demonstrated that when 10% OH was added to a rice diet, gizzard content was increased. They also observed that the effects of fiber on gizzard development were more pronounced with coarsely ground OH than with finely ground OH. In fact, Hetland et al. (2003) found that fiber concentration was greater in the gizzard digesta than in the original diet, indicating that OH were retained longer in the gizzard than the remaining components of the diet. This finding suggests that the passage of the chyme through the gizzard is faster when the diet is low in fiber.
It is concluded that the maximal growth of all the organs and segments of the GIT is reached before d 9. The inclusion of hulls and the substitution of rice by corn stimulated the development of the upper part of the digestive tract but had little effect on the development of the distal part. Heat processing of the cereal has little effect on the development of the different organs and segments of the GIT, except for liver that was increased in the diet based on rice. A minimal amount of fiber in the diet is required to stimulate the development of the upper part of the GIT and for optimal functioning of the gizzard in young broilers.
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FOOTNOTES |
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2 Current address: Universidad Autónoma de Tlaxcala, Av. Universidad 1, Tlaxcala, C. P. 9000, México
Received for publication February 13, 2008. Accepted for publication May 17, 2008.
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