Use of Dietary Fiber in Broilers
Published on: 2/15/2014
Author/s : Encarnación Jiménez-Moreno1* and Gonzalo G. Mateos2 (1Department of
Animal and Avian Sciences, Universidad de Maryland, College Park, Maryland,
2Department of Animal Production, University Polytechnic of Madrid, Madrid,
Spain)
11-02-2017
1.
Generalities
Gastrointestinal
infections with pathogenic bacteria y the subsequent clinical expression of
disease occur frequently in young animals under current intensive production
systems. Infections are responsible growth rates and consequently cause
economic losses in animal production. Antibiotics modify the microflora of the
gastrointestinal tract (GIT) and are the main available tool to prevent and
treat digestive illness. The inclusion of antibiotics at low levels intro the
feed for an extended period of time was a common practice in the poultry
industry to control digestive disorders and proved to provide economic benefits
to the broiler industry (Castanon, 2007). However, the indiscriminate use of
in-feed growth promoters of antibiotic origin may result in selection for the
survival o resistant bacterial species or strains. In addition, genes encoding
for resistance to antibiotics also can be transferred to formally susceptible
bacteria, posing a threat to both animal and human health. Consequently, the
European Union (EU-27) banned the marketing of antibiotics as in-feed growth
promoters. On the other hand, the use of animal proteins such as meat and bone
meal are also banned in poultry feeds. Moreover, the use of fish meal and other
animal protein sources is reduced to minimum because of cost and further
legislative restriction. Consequently, the feeds currently produced by the
European integrated poultry Industry are based exclusively on vegetable
feedstuffs without any growth promoter of antibiotic origin. Under these
circumstances, necrotic enteritis and related problems are frequently reported
under field conditions. Therefore, producers are forced to introduce
modifications in the diets to reduce the incidence of enteric diseases (Mateos
et al., 2002). The manipulation of the ingredient composition and nutrient
content of the diet together with changes in feed manufacture, technology
together with management practices in the field, may improve health status of the
GIT. Feeding highly digestible ingredients, enzyme supplementation, heat
processing of the cereal and inclusion of moderate amounts of fiber in the diet
have been some of the alternatives proposed to improve nutrient digestibility
and growth performance in the absence of growth promoters (Mateos et al., 2002;
González-Alvarado et al., 2007, 2008). Dietary fiber (DF) is a component of the
diet that affects the development of the GIT and may modify the characteristics
of the intestinal contents that promote the balanced growth of the native
microbiota (Montagne et al., 2003; Mateos et al., 2012).
2.
Dietary Fiber in Poultry
Tradicionally, DF has been considered an anti-nutritional factor
and a diluent in non-ruminant diets. Also, many nutritionists have considered
that the requirements of broiler for crude fiber (CF) are low and recommended
to reduce its content in diets for broiler chick to less than 3.0-4.0%,
depending on the age (Swennen et al., 2010). Janssen and Carré (1985) indicated
that fibrous components of the food had negative effects on growth performance
of the broiler chicks. In fact, these authors reported a strong negative
correlation between CF of the diet and protein and ether extract digestibility.
Also, Sklan et al. (2003) observed that increasing the CF content of the diet
from 3 to 9% reduced growth performance and impaired nutrient retention in
turkeys. However, in last years, the influence of CF content in the poultry
diet on voluntary feed intake and digestibility of nutrients is subject to
debate. Recent studies have defined in detail the beneficial effects of the
fiber on growth performance and its influence on 1) the satiety and animal
welfare, 2) gut health including non-specific colitis and other enteric
disturbances, 3) changes in the intestinal microflora and 4) gizzard activity
and motility of the TGI. Consequently, fiber fraction is not considered as
anti-nutritional component o the diet. In fact, it has proposed that the
inclusion of moderate amount of fiber in diets for broilers may have positive
effects on gizzard activity improving the mixing of the digesta and motility of
the GIT, gut health preventing the adhesion of certain pathogen bacterial
population to the epithelial mucosa, and growth performance of non-ruminant
animals (Mateos et al., 2002; Montagne et al., 2003; Mateos et al., 2012).
Under practical conditions, the response of these variables to the
incorporation of fiber in the diet depends on a great extent on the nutritional
technologies and management techniques used, including type of housing (cage
vs. floor pens), composition and physical structure of the basal diet (i.e.
type of cereal), type and level of inclusion of fiber, feed form (mash vs.
pellet or crumbles), health status (i.e. conditions of hygiene and incidence of
diseases and digestive disorders), and age of the bird.
The controversy of the effects of the fiber on the broiler
productivity might be because of the term of “dietary fiber” that is not
clearly defined. Originally the main method used for analysis of fiber in
feedstuffs was the CF, a method that is still widely accepted by the feed
industry. Other methods provided are neutral detergent fiber, acid detergent
fiber and lignin. All these analytical methods are more satisfactory
alternative for defining and characterizing the fiber content of the
ingredients. The term “dietary fiber” is, in most recent animal nutrition,
defined as “edible parts of plants or analogous carbohydrates that are
resistant to digestion and absorption in the human small intestine, with
complete or partial fermentation in the large intestine” (AACC, 2001). Dietary
fiber is predominantly found in plant cell walls and includes polysaccharides
(resistant starch and soluble and insoluble nonstarch polysaccharides),
oligosaccharides, lignin, and associated plant substances.
It is
common to characterize DF based on its solubility in water. The soluble fiber
corresponds to water extractable polysaccharides that precipitate in alcohol or
acetone solutions, and includes among others β-glucans from barley and oats,
arabinoxylans from wheat and rye, pectins from fruits and beet pulp and
galactomanans from legumes. In contrast, insoluble fiber is composed of
cellulose and hemicelluloses, and certain amounts of pectin substances, protein
bound to the fiber and lignin. Dietary fiber exhibits a range of physical
properties that act in concert with the chemical properties to determine the
physiological effects in animals. Differences in structure, solubility, water
holding capacity, viscosity, bulk and other physicochemical properties of
fibrous ingredients may affect in different ways the structure of the digesta
and passage rate through GIT (Fahey et al., 1992). Consequently, feed intake,
development and epithelial morphology of the GIT, GIT motility, digestive
juices secretion and nutrient digestion and absorption may vary depending on
the source of fiber (Montagne et al., 2003; Svihus, 2011; Mateos et al., 2012).
On the other hand, chemical composition and fermentative capability as well as
the grade of lignification of the source of fiber may affect growth and
distribution of the species and the total population of the resident microflora
in the GIT.
3.
Dietary Fiber, Passage Rate and Development of the Gastrointestinal Tract
The effects of fiber inclusion on the transit time of the
digesta and the development of the digestive organs vary depending on the physicochemical
properties and level of fiber added (Bach Knudsen, 2001). In this respect,
insoluble fibers such as that contained in oat hulls reduces length of the
small intestine (González-Alvarado et al., 2007), stimulates gizzard activity
and increases its contents (Jiménez-Moreno et al., 2009a; Hetland and Svihus,
2001) and decreases intestinal transit time which might indicate an improvement
of the functioning of the GIT. A faster passage rate by feeding insoluble fiber
may be related with the lack of physical structure such as microcrystalline
cellulose (Cao et al., 1998) or fine grinding of the fiber (Hetland and Svihus,
2001). Coarse fiber particles are retained for a longer time in the gizzard
than fine fiber particles. An accumulation of coarse fiber particles stimulates
grinding activity of the gizzard, allowing for a better regulation of feed flow
to the intestines and higher secretion of digestive juices.
Chicks adapt to fiber-rich diets by increasing the volume and
weight of their digestive tract (Håkansson et al., 1978, González-Alvarado et
al., 2008). The effect of the fiber on gutfill depends on type and level of
inclusion of fiber and the segment of the GIT considered. An increase in the
dietary fiber intake increases the amount of gutfill causing a physical
distension of the walls of the digestive tract and a concomitant increase in
size and gut capacity (Jørgensen et al., 1996; Jiménez-Moreno et al., 2009a,
2013a,b). An increase in size of the digestive organs might be indicative of a
hypertrophy of gut tissues (Jørgensen et al., 1996). A hypertrophy of visceral
organs such as the GIT makes precise higher energy expenditure than those
associated to carcass yield (Anugwa et al., 1989). Also, the lack of fiber in
the diet may cause a dilation and poor development of the walls of the
proventriculus and gizzard (Svihus et al., 2011) that might affect theirs
functionality. Damaged proventriculi are enlarged, swollen and filled with
fluid and feed and often rupture during routine evisceration causing
contamination of the carcass and important economic losses (Huff et al., 2001).
On the hand, the inclusion of structural DF increases the size and holding
capacity of the gizzard (Svihus, 2011; Jiménez-Moreno et al., 2013b). The
gizzard is responsible for a complete grinding of feed and a well regulated
feed flow as well as whole GIT motility. Duke (1992), Hetland et al. (2003) and
Sacranie et al. (2012) have indicated that atrophy of the gizzard reduces the
reflux of chyme from the intestines, impairing the digestive processes and
reducing performance. In contrast, welldeveloped proventriculi and gizzards
increase HCl secretion and intestinal refluxes that serve to reexpose the
digesta to pepsin, facilitating the mixing of the feed with endogenous enzymes.
The magnitude of effects of the inclusion of the fiber on
physiology and development of the digestive organs depends not only on the
nature and particle size of the fiber source (Jiménez-Moreno et al., 2010) but
the level of fiber (Jiménez-Moreno et al., 2011a; 2013b). Jiménez-Moreno et al
(2013b) reported that the effects of fiber inclusion on the enlargement of GIT
were more evident with sugar beet pulp than with oat hulls, a finding that
could be related to the higher pectin content of sugar beet pulp. Soluble fiber
particles such as those from sugar beet pulp, retain high amounts of water and
swell when pass through GIT, increasing the bulk of the digesta and causing
physical distension of the walls of the digestive tract and a concomitant
increase in size. Jiménez-Moreno et al. (2009a) observed that chyme with a high
pectin content may produce greater dilatation of the proventriculus increasing
in size and its contents. The coarse fiber particles are selectively retained
in the gizzard that ensures a complete grinding and a well-regulated feed flow
and secretion of digestive juices. Jiménez-Moreno et al. (2010) reported that
the inclusion of 3% of sugar beet pulp or oat hulls but not microcrystalline
cellulose, increased gizzard weight in broilers fed similar type of diets.
Cellulose inclusion resulted in similar relative size and digesta content of
the gizzard than those of the control diet. Cellulose is a highly insoluble
fiber source with a very a low particle size, water holding capacity, and swelling
water capacity. Because of its lack of physical structure, cellulose particles
did not accumulate and stimulate gizzard functioning. Consequently, cellulose
inclusion did not produce any increase in size of digestive organs or to reduce
gizzard pH. Oat hulls have high lignin content and therefore, oat hulls
containing diets are more resistant to grinding than sugar beet pulp.
Consequently, oat hulls particles could be retained for a longer time in
agreement with the higher dry matter contents observed in the gizzard. An
accumulation of oat hull particles stimulates the grinding activity of the
gizzard, allowing for a better development of the muscular layers and causing
an increase in organ size (González-Alvarado et al., 2008). Pectins from sugar
beet pulp by its high solubility, water holding and swelling capacities,
increased the bulk of the digesta which in turn might produce a physical
dilation of the proventriculus walls and a concomitant increase in organ size.
In addition, as swollen sugar beet pulp particles increased in size, they were
retained for longer in the gizzard. Consequently, gizzard digesta content and
size were increased and gizzard pH reduced in birds fed the sugar beet pulp
diet. In a latter study, Jiménez-Moreno et al. (2011a) reported in 36 dold
broilers reared in floor pens that the inclusion of 5% of oat hulls or sugar
beet pulp increased the gizzard weight and its contents and reduced gizzard pH
(Table 1). Also, these authors reported that the neutral and acid detergent
fiber and lignin contents (based on dry matter) of the gizzard were higher in
oat hulls containing- than in sugar beet pulp containing diets indicating that
oat hulls particles were retained for a longer time that sugar beet pulp
particles which in turn might lead to an increase in hydrochloric secretions
from the proventriculus. Jiménez-Moreno et al. (2011b) reported an increased
gizzard weight when pea hulls were increased up to 7.5% to a low fiber diet.
However, gizzard pH was reduced with the inclusion of 2.5% of pea hulls but no
further changes were observed with further pea hulls increases (Figure 1.a) in
consistent with higher dry matter contents in this organ (Figure 1.b).
Grinding of fibrous ingredients might modify the native
structure of the fiber and in consequence, the physicochemical properties of
the digesta, the passage rate and development of GIT (Amerah et al., 2007;
Jiménez-Moreno et al., 2010). Coarsely ground oat hulls increase feed passage
as compared to finely ground oat hulls (Hetland and Svihus, 2001). Stimulating
effect of coarse insoluble on gizzard function, in particular more frequent and
powerful contractions and the subsequent intraluminal pressure changes that
they induce, leads to an increase in the occurrence of gastric refluxes (Hetland
et al., 2003; Sacranie et al., 2012) improving nutrient digestibility. In
contrast, fine ground fiber may impair gizzard function, reducing nutrient
digestibility. In this respect, Jiménez-Moreno et al. (2010) studied the
effects of type and particle size of dietary fiber on digestive traits and
growth performance of broilers from 1 to 21 d of age. The control diet
contained 3% sepiolite and had 1.54% CF. The other diets substituted (wt/wt)
the sepiolite of the control diet by microcrystalline cellulose or by oat hulls
or sugar beet pulp ground through a 0.5 or 2.0-mm screen. These authors
observed that broiler fed fine oat hulls diet exhibited similar gizzard weight
and pH suggesting that fine oat hulls particles were retained and partly
induced the same response in agreement with findings of Sacranie et al. (2012).
Contrary, broilers fed fine sugar beet pulp diet had lighter gizzards but
higher contents indicating that grinding of sugar beet pulp resulted in a loss
of mechanical abrasion of the gizzard walls. When these two fiber sources were
finely ground, the sugar beet pulp lost its physical structure where the oat
hulls maintained it.
The grade of lignification and elasticity y/or resistance to
grinding of insoluble fiber sources might affect also, digestive
characteristics and growth performance of broilers. Jiménez-Moreno et al.
(unpublished data; Table 2) reported that diluting a control diet with
increases of oat hulls, sunflower hulls or rice hulls (0 to 5%) increased
gizzard weight and reduced gizzard pH; effects that were more evident for oat
hulls than for rice hulls being sunflower hulls in intermediate position. Oat
hulls particles are fusiform, more elastic and resistant to grinding whereas
rice hulls and sunflower hulls particles are rectangular, more stiffness, and
poorly resistant to breakage by pressure in aqueous medium. Therefore, it is
expected that oat hulls particles will be retained in the gizzard for a longer
time resulting in a higher mechanical abrasion of the gizzard walls and organ
size. Contrary, rice hulls have high silica contents that caused an erosion of
the Koilin layer of the gizzard when broilers ate high amounts of these hulls
for a long term.
Pelleting reduces feed particle size and modifies the structure
of the feed that affect digestive characteristics and growth performance of
broilers. Pelleting may modify the functional properties (viscosity, binding,
resistance) of the fiber fraction (Thomas et al., 1998) and in consequence, the
response of broilers to fiber inclusion. In this respect, Jiménez-Moreno et al.
(unpublished data) indicated that diluting broiler diets with increases of
level of inclusion of insoluble fiber (0 to 5%) increased gizzard weight; an
effect that was more evident in mash than in pelleted diets and in oat hulls
containing- than in sunflower or rice hulls containing diets (Figure 2).
Probably, the structure and functional properties of insoluble fiber may be
altered after pelleting.
Changes in pH of the GIT, especially in the upper part may
favors enzymatic activity and prevent the pathogen growth in the distal part of
the GIT. Digesta pH of the GIT is related with the digesta content retained in
the organ. A reduced proventriculus pH has been observed when a soluble fiber
such as sugar beet pulp has been included in the diet (Jiménez-Moreno et al.,
2009b,c, Jiménez-Moreno et al., 2013b). The proventriculus is characterized by
having very distensible walls, fast rate of feed passage and limited storage
capacity (Moran, 1982). Sugar beet pulp particles swell to retain water, which
could increase its capacity favouring the passage of the feed from the
proventriculus to the gizzard. The inclusion of structural fiber reduces
gizzard pH that could be associated with the increased digesta contents
(Jiménez-Moreno et al., 2009b,c, Sacranie et al., 2012, Jiménez-Moreno et al.,
2013b). The reduction of gizzard pH by the inclusion of fiber probably results
from higher HCl secretion from proventriculus, a consequence of the longer
retention time of the digesta in the gizzard. Very little scientific literature
exists that examines the effects of increasing the fiber content of the diet on
intestinal digesta in birds. Jiménez-Moreno et al. (2009c) evaluated the
changes of pH through GIT when 3% coarse oat hulls or sugar beet pulp or
microcrystalline cellulose were added to a low fiber diet for broilers. These
authors observed that the inclusion of fiber did not affect pH of the duodenum
in contrast to the findings in the upper part of the GIT. Differences in pH
observed among fiber sources in the upper part disappeared in this segment,
suggesting that bile salts secretion was higher in chicks fed the oat hulls and
sugar beet pulp diets than in chicks fed the cellulose and the control diets
without fiber added (Figure 3). Digesta pH decreased from the duodenum to the
ileum, a reduction that it was more pronounced with the cellulose than with the
sugar beet pulp diet. However, in the ceca, the pH was reduced by sugar beet
pulp probably because of the fiber of sugar beet pulp may be fermented by the
resident anaerobic microflora of the ceca.
The
effect of fiber on epithelial morphology and cell turnover is variable and
depends on the physicochemical characteristics of the DF, their level of
inclusion, the duration of ingestion, age, and the site in the intestinal tract
(van der Klis and A. van Voorst, 1993; Iji et al., 2001). Villus height to
crypt depth ratio is a useful criterion for estimating the absorptive capacity
of the small intestine (Montagne et al., 2003). A high villus height to crypt
depth ratio is indicative of better function and maturity of the intestinal
mucosa. Jiménez-Moreno et al. (2011a) reported the highest villus height to
crypt depth ratio was observed with dietary pea hulls of 2.5% and that an increase
to 7.5% of pea hulls impaired it. In a second study of these same authors
(Jiménez-Moreno et al., 2013b) observed that diluting a control diet with
increases of sugar beet pulp but not of oat hulls (0 to 7.5%) reduced villus
height and crypth depth and tended to reduce villus height to crypt depth ratio
of 12 d-old broilers (Table 3). Sarikhan et al. (2010) and Rezaei et al. (2011)
observed that the inclusion of 0.25 to 0.75% of a micronized insoluble fiber
constituted mostly by cellulose, increased villus height to crypt depth ratio
in the ileum of 42 d-old broilers. An excess of DF, as reported by
Jiménez-Moreno et al. (2011a, 2013b) when 7.5% of pea hulls or sugar beet pulp,
were added to the diet, could have increased the abrasion of the mucosal surface
of the small intestine shorting the villus and increasing mucus output. As a
result, it reduced the absorptive villus surface and hindered nutrient
retention.
4.
Dietary fiber and digestive process
Tradicionally,
fiber represents the indigestible component in poultry diets because do not
digest cellulose. Janssen and Carré (1985) reported a strong negative
correlation between CF content of the diet and protein and fat digestibility in
broilers and concluded that low CF diets improve poultry performance. However,
recent studies indicate that the inclusion of moderate amount of fiber might
benefit digestive physiology (González-Alvarado et al., 2008; Jiménez-Moreno et
al., 2011a, 2013a). In fact, Hetland et al. (2003) reported that the inclusion
of 10% insoluble fiber in the diet increased the ileal digestibility of starch
and stimulate gizzard activity. Recently, González-Alvarado et al. (2007)
demonstrated that the inclusion of 3% of oat hulls or soy hulls improved
nutrient digestibility and AMEn at
18 d of age; an effect that was more evident in diets based on rice than in
those based on corn. Diets rich in structural fiber remain in the upper GIT
longer and might be digested more completely because of increased
gastrointestinal refluxes (Sacranie et al., 2012) and hydrochloric acid
secretion (Jiménez-Moreno et al., 2010) and other digestive enzymes. Hetland et
al. (2003) observed that the inclusion of oat hulls increased amylase activity
and bile salt concentration in the chyme of broilers improving ileal starch
digestibility (Table 4). The inclusion of structural fiber such as oat hulls,
in the diet prolongs the exposure time of food to both the mechanical and
chemical components of digestion and reduces the time available for microbial
fermentation in the small intestine.
Differences
in the physicochemical properties of fibrous ingredients such as solubility,
water holding capacity, viscosity, bulk, fermentability and ability to bind
bile acids, might affect in different ways the development of the GIT and the
digestibility of nutrients in non-ruminants animals (Montagne et al., 2003).
Coarse feed particles, such as oat hulls, retain longer in the upper part of
the GIT stimulating the gizzard activity and increasing hydrochloric acid
secretion. A low gizzard pH improves pepsin activity and nitrogen retention,
and increases the solubility of the inorganic fraction of the feed (Guinotte et
al., 1995) which in turn might favor its absorption. Hetland and Svihus (2001)
found that apparent ileal digestibility of starch increased when oat hulls were
included in the diet but that those of nitrogen, fat, and ash were not
modified. Jiménez-Moreno et al. (2009b) reported that the inclusion of a
moderate amount (3%) of sugar beet pulp to low fiber diet impaired the ileal
digestibility of dry matter, organic matter, protein, and energy as well as AMEn as compared with the inclusion of 3%
of oat hulls (Table 5). Sugar beet pulp has high content in pectin, and its
particles have high water holding and swelling capacities that might be
retained for longer in the GIT. An increase in chyme accumulation in the GIT
with sugar beet pulp inclusion might result from an increase of the digesta
viscosity (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, soluble fiber sources may increase the thickness of the unstirred
water layers of the mucosa reducing nutrient dispersion and impairing
absorption (Johnson and Gee, 1981).
The
magnitude of the response of poultry to the inclusion of fiber in the diet
might vary not only with the type of fiber but with the level of inclusion.
Jiménez-Moreno et al. (2011b) reported that ileal crude protein and starch
digestibility increased with increasing level of pea hulls, showing maximum
values with pea hulls level between 2.5 and 5% (Table 6). Also, in a recent
study, Jiménez-Moreno et al. (2013a) observed that diluting a control diet with
increases of oat hulls in the diet but not of sugar beet pulp (0 to 7.5%),
improved the ileal crude protein digestibility and starch. Similar results were
observed by Pettersson and Razdan (1993) who found that the inclusion of 9.2% in
the diet had no effect on crude protein digestibility. Rogel et al. (1987)
reported in broilers that starch digestibility of raw potato increased as the
level of oat hulls in the diet increased from 0 to 12%. Similarly, Amerah et
al. (2009) observed a 9% increase in starch digestibility when the diet was
diluted with 6% wood shavings but not when diluted with the same amount of
microcrystalline cellulose. Jiménez-Moreno et al. (unpublished data) observed
increases in AMEn of
diets as the level of inclusion of oat hulls or sunflower hulls but not of rice
hulls, increased from 2.5 to 5% in the diet. High DF diets might increase mucus
output resulting in an increase in the ileal flow of nitrogen. Also, high DF
diets enhance abrasion in the small intestine of birds increasing endogenous
cell losses to the lumen. As a result, ileal digestibility of crude protein may
be reduced.
Bile
acid secretion might be the limiting step in fat digestion in young chicks and
DF might increase bile acids secretion and facilitate the emulsification of the
released dietary lipids. In fact, Hetland et al. (2003) reported that diluting
by 10% a control diet with oat hulls increased the amount of bile acids present
in the small intestine of broilers. An increase in bile acid concentration in
the gizzard of birds suggests stronger gastroduodenal refluxes which might help
to improve nutrient utilization. Jiménez- Moreno et al. (2009b) reported that
the inclusion of 3% of oat hulls or sugar beet pulp in the diet increased ether
extract digestibility in 21-d-old broilers, an improvement that was more
evident with yellow grease, a saturated fat source, than with soy oil, a more
unsaturated fat source. An increase in bile salts production with DF might
improve more the digestibility of saturated supplemental fats because in young
chicks saturated fats relies more on biliary salts presence for emulsion and
micelle formation.
5.
Dietary Fiber, Feed Intake and Growth Performance
Diets high in fiber usually contain a low energy density that
may decrease feed intake and feed conversion ratio in broilers. However,
different authors demonstrated that the inclusion of moderate amounts of
insoluble DF does not affect voluntary feed intake in broilers (Jiménez-Moreno
et al., 2010; Sacranie et al., 2012). In fact, González-Alvarado et al. (2007)
studied the effects of the inclusion of 3% oat hulls or soy hull into a control
diet based on corn that contained 2.5% CF or a control diet based on rice that
contained 1.5% CF. From 1 to 4 d of age, the inclusion of hulls reduced feed
intake but not had effect on body weight gain (BWG) indicating broilers fed the
hull-containing diets wasted more feed that those fed the control diet. In the
period from 1 to 21 d, the feed intake and BWG were increased and feed conversion
ratio (FCR) improved by the inclusion of both fiber sources. Jiménez-Moreno et
al. (2011a) studied the effects of diluting a broiler diet with increased
levels of pea hulls (0 to 7.5%) on growth, energy efficiency and nutrient
digestibility (Table 6) of broilers from 1 to 18 d of age. The inclusion of up
to 5% pea hull improved most performance traits studied, as well as nutrient
digestibility. When 7.5% pea hull was added to the diet, the benefits
disappeared but still most traits were similar to those of the control diet.
Probably, level and type of DF as well as age of the bird, modifies the
response of broilers with respect to feed intake. For example,
González-Alvarado et al. (2010) reported that the inclusion in the diet of 3%
of sugar beet pulp, a source of soluble DF, reduced feed intake from 25 to 42 d
of age as compared with a diet containing 3% of oat hulls (Table 7). However,
no negative effects of sugar beet pulp inclusion were observed during the first
10 d of life. Sugar beet pulp has high pectin content and pectins are
characterized by their high water holding capacity and swelling capacity
(Serena and Bach Knudsen, 2007). A wetter and bulkier digesta, as occurs when
sugar beet pulp is included in the diet, causes physical distension of the GIT
which might affect the physiological mechanisms that regulate feed intake
(Denbow, 1994). In this respect, Pettersson and Razdan (1993) observed that
feed intake in 18 d-old chicks was reduced when the level of sugar beet pulp of
the diet was increased from 2.3 to 9.2%. Also, Shakouri et al. (2006) observed
that the inclusion of 3.0% of either carboxymetil-cellulose or a highly
methylated citrus pectin reduced feed intake. Probably, lower feed intake may
be attributed to an increase in digesta viscosity and a longer retention time
of the digesta in the GIT.
Feed
form affects organ development and growth performance of broilers. Pelleting
reduced feed particle size and modified feed structure and thus, pelleting of
the diet might modify the response of broilers to fiber inclusion.
Jiménez-Moreno et al. (unpublished data) studied the effects of diluting a low
fiber diet (1.6 CF and 3.7% NDF) based on rice-soy protein concentrate-lard
with 0, 2.5, and 5% of 3 fiber sources (OH, rice hulls, and sunflower hulls) on
performance of broilers kept on cages fed mash or pelleted diets from 0 to 21 d
of age. Pelleting improved feed intake, body weight gain and feed conversion
ratio (Table 2). The inclusion up to 5% of rice hulls but not of oat hulls and
sunflower hulls reduced AMEn of
the diet at 21 d of age; an effect that was more evident in pelleted than in
mash diets (data not shown). Probably, the ingestion of high silica from rice
hulls in pelleted diet may explain the differences observed among fiber sources.
Modern broilers have a high capacity for feed consumption and they might accept
higher dilutions of the diet. The pellet is rapidly dissolved in the upper part
of the GIT after consumption; feed particles will not usually be retained in
the gizzard reducing in size and in functioning. The lack of a properly
functioning gizzard is related with a feed overconsumption. A well-functioning
gizzard may hinder feed overconsumption simply because of the physical
constraints in gizzard volume combined with limitations to feed passage from
the gizzard to duodenum. Moreover, previous research indicate that bird eat
litter to compensate for lack of structure in the diet (Hetland et al., 2005).
Therefore, it is recommended the inclusion of a moderate amount of structural
DF to broiler diets to avoid a overconsumption, without hindering growth of the
birds.
6.
Dietary fiber and Microflora
Biochemical
conditions in the digesta, as a result of feed composition or physiological
responses from the host affect substrate availability and concentration and
thus microbial product formation. The degree of solubility, the fermentative
capability and viscosity are 3 key physicochemical properties of fiber fraction
to modulate the growth and distribution of the species and the total population
of the resident microflora in the GIT. Soluble fiber is highly fermentable that
may alter microbial activities increasing toxin production and enhancing
enteric disease (Bach Knudsen et al., 1991). An increase in the viscosity of
lumen contents from soluble fiber not only decreases laminar flow and
convective efficiency of villi for nutrient absorption, but gas exchange
between wall and digesta also lessens. A lower partial pressure for oxygen with
increased concentrations of nutrients can enhance development of transient
microbes, particularly anaerobes. The inclusion of high methylated citruc
pectin could change the intestinal microbial population and increased the
microbial activity in the ileum especially those of Enterococci,
Bacteroidaceae, Clostridia, and E. Coli and total counts of anaerobic bacteria
in the small intestine (Shakouri et al., 2006). Jørgensen et al. (1996)
observed an increased amount of short-chain fatty acids (mainly lactic acid and
acetic acid) and H2 excretion
as result of a higher degradation of FD (pea fiber, wheat bran or oat bran)
from microbial fermentation. Contrary, insoluble fiber is poorly fermentable
and increases fecal bulk in poultry. Therefore, the effects of insoluble fiber
effects on the composition and quantity of the microflora might be relatively
insignificant. However, the inclusion of an insoluble fiber sources, such as
OH, in the diet, improved gizzard functionality and reduce gizzard pH and might
activate mechanically mucosa surface, increasing GIT motility and reducing the
chances of bacteria, such as Clostridium perfringens adhering to the mucosa surface in the
distal part of the GIT. Jiménez-Moreno et al (2011b) observed that diluting a
control diet with 5% of oat hulls but not with sugar beet pulp, reduced the
count of Clostridium perfringens and Enterobacteriae (Table 8) in consistent with a higher
amount of fibrous particles retained in the gizzard (Table 1). Therefore, an
improved functionality of the gizzard, low gizzard pH and a more rapid passage
rate from the inclusion of insoluble FD, is considered to potentially have a
beneficial effect on gut health through the sterilizing properties and lower
time available for microbial fermentation in the small intestine.
The
effect of DF on the erosion of mucus and recovery of mucins in ileal digesta
seems to depend on their physical properties, including solubility. The
inclusion of insoluble DF has a more abrasive action, scraping mucin from the
mucosa as they pass through the digestive tract. Soluble DF due to its high
water holding capacity, the particles swell and enhance action on the small
intestine of birds increasing mucus output resulting in an increase flow of
crude mucus in the lumen (Montagne et al., 2003). The modification of the
composition of the mucins following DF ingestion probably leads to modification
of the composition of commensal bacteria fixed on the mucus layer, which in
turn might alter the competition between commensal and pathogen bacteria. The
inclusion of DF that leads to more acid mucins such as insoluble fiber, appears
to increase the potential of mucus to resist attack by bacterial enzymes, which
favours the elimination of pathogens. Kalmendal et al. (2011) reported that the
inclusion in the diet of high levels of sunflower meal, an insoluble source of
DF, was associated with significant decreases in colony counts of Clostridium
spp. Moreover, a shortening of the villi from soluble fiber
ingestion reduces to area of mucins in the crypts of the small intestine
indicating that the birds fed with soluble fiber might be more susceptible to
pathogenic bacteria.
7.
Conclusions
The
inclusion of moderate amount of structural fiber in diets low in fiber
stimulates gizzard activity and improves nutrient retention and growth performance
of young broilers. The effects of inclusion of DF on physiology and development
of GIT, passage rate, microbial growth, nutrient digestibility and growth
performance differ depending on the composition of the basal diet, feed form,
type and level of DF, and age of the bird. The inclusion of up to 3% coarse
insoluble fiber source such as oat hulls, to conventional diets stimulates the
development of the GIT and improves nutrient digestibility and growth
performance. Under commercial conditions, birds require a minimum and a maximum
amount of fiber in the diet for optimal performance. Therefore, diets for
broilers should be formulated with a minimum and a maximum level of DF.
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This paper was presented at the
6th annual meeting AECACEM, Querétaro, México, February 2013
