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[Ital J Anim Sci vol.13:2014] [page 169]
The utilisation of prebiotics
and synbiotics in dogs
Carlo Pinna, Giacomo Biagi
Dipartimento di Scienze Mediche
Veterinarie, Università di Bologna,
Ozzano dell’Emilia (BO), Italy
Abstract
The microbiota of the large intestine plays a
fundamental role in maintaining the state of
health of the gastrointestinal tract and the host.
The use of specific dietary supplements such as
prebiotics and synbiotics might positively influ-
ence the composition and metabolism of the
intestinal microbial population. Several studies
have been conducted on the use of prebiotics in
dogs. Most studies have aimed to assess
whether using prebiotics brings about an
improvement in the canine intestinal ecosys-
tem. Moreover, the effect of prebiotics on
canine immune system has also been investi-
gated. Among the prebiotics used in the studies
present in the literature, short-chain fruc-
tooligosaccharides and oligofructose seem to be
the most effective in modulating the canine
intestinal ecosystem and improving intestinal
absorption of minerals but with little or no
effect on canine immune system. Conversely,
mannanoligosaccharides may have a positive
influence on the immune system of dogs. Some
positive effects of prebiotics on canine intestin-
al microbiota might be enhanced when these
are used in combination with one or more pro-
biotic strains (synbiotic). Clinical effects of pre-
biotics have been investigated in humans and
animal models but little evidence exists that
prebiotics may be helpful in canine diseases.
Finally, most studies on canine intestinal micro-
biota were conducted using traditional culture
methods, so that more research remains to be
done with modern molecular identification
methods to investigate the effects of prebiotic
substances. This paper presents an overview of
the scientific literature dealing with the use of
prebiotics and synbiotics in the canine species.
Introduction
The gastrointestinal microbiota is a complex
ecosystem that influences gastrointestinal
functionality and the host’s health in general.
Prebiotics are non-digestible carbohydrates that
withstand digestion and reach the colon where
they stimulate growth and/or activity of benefi-
cial microbial species. Prebiotic substances
have been the object of several studies in dogs
as they may improve the composition of canine
intestinal microbiota, reducing the presence of
pathogens and toxins. Moreover, prebiotics may
result in enhanced immune function and could
be used in the treatment of specific diseases of
dogs such as infections by intestinal pathogens,
intestinal constipation and hepatic and renal
failure.
Recently, considerable interest has arisen
towards the use of fibre and prebiotic sub-
stances in the food intended for dogs. In fact,
though the dog is recognised as an animal
with a prevalently carnivorous diet, several
studies have demonstrated that by positively
modifying the intestinal microbiota, prebiotic
substances (mainly of vegetable origin) are
capable of exerting a large influence on the
trophic and health conditions of the digestive
system and, consequently, on the animal’s gen-
eral state of wellbeing. It is the purpose of this
review to present an overview of the scientific
literature dealing with the use of prebiotics
and synbiotics in the canine species.
The intestinal microbiota
of dogs
To date, studies on the characterisation of
canine intestinal microbiota are rather scarce
and little is known about which factors may
determine variations in terms of the number
and species of bacteria present. Like in all
mammals, a dog’s gastrointestinal tract is ster-
ile at birth, but with the passing of hours it
comes to be populated by numerous bacterial
species originating from the birth canal and
the surrounding environment, as well as from
maternal milk (Buddington, 2003). At the end
of the weaning period, with the transition to a
diversified diet, the resident microbial popula-
tion undergoes a considerable change in terms
of both species and number, also showing
enormous differences between one dog and
another (Schaible and Kaufmann, 2005).
Similarly to what had already been observed
by some authors in studies aimed at character-
ising human intestinal microbiota (Langendijk
et al., 1995; Harmsen et al., 2000), Greetham et
al. (2002) and more recently Hooda et al.
(2012) highlighted the scant reliability of tra-
ditional culture methods for isolating and
identifying dog intestinal microbiota.
Thanks to more recent studies making use of
molecular identification methods (Suchodolski
et al., 2009; Middelbos et al., 2010; Handl et al.,
2011; Suchodolski, 2011; Swanson et al., 2011;
Beloshapka et al., 2013), hundreds of phylo-
types have been identified in the intestine of
the dog. The phyla Firmicutes, Bacteroidetes,
Proteobacteria, Fusobacteria and Actino -
bacteria account for over 99% of the bacterial
species harboured in the intestine of dogs.
However, the phyla Spirochaetes, Tenericutes,
Verruco-microbia, Cyanobacteria and
Chloroflexi have also been identified. In the
study by Beloshapka et al. (2013), predominant
bacterial families in adult beagles fed raw
meat-based diets included Fusobacteriaceae,
Clostridiaceae, and Bacteroidaceae and pre-
dominant genera included Fusobacterium,
Cetobacterium,Clostridium, and Bacteroides.
Moreover, the canine intestine also hosts non-
bacterial microorganisms. In their work,
Swanson et al. (2011) identified archea (about
1% of all sequencing reads), fungi (about
0.01% of all sequences) and viruses (less than
1% of all sequencing reads).
With respect to the variability of the compo-
sition of canine intestinal microbiota, consid-
erable intraspecies differences have been
observed in dogs housed under identical condi-
tions and receiving the same diet, with very
marked variations in the microbial species
residing in the large intestine compared to
those found in the small intestine. Moreover,
there are large differences between the bacte-
rial species that inhabit the different sections
of the intestine and faecal microbiota
(Suchodolski et al., 2005).
The animal’s age is one of the factors influ-
Corresponding author: Prof. Giacomo Biagi,
Dipartimento di Scienze Mediche Veterinarie,
Università di Bologna, Via Tolara di Sopra 50,
40064 Ozzano dell’Emilia (BO), Italy.
Tel. +39.051.2097379 - Fax: +39.051.2097373.
E-mail: giacomo.biagi@unibo.it
Key words: Dog, Immune system, Intestinal
microbiota, Prebiotics, Synbiotics.
Received for publication: 16 September 2013.
Accepted for publication: 28 December 2013.
This work is licensed under a Creative Commons
Attribution NonCommercial 3.0 License (CC BY-
NC 3.0).
©Copyright C. Pinna and G. Biagi, 2014
Licensee PAGEPress, Italy
Italian Journal of Animal Science 2014; 13:3107
doi:10.4081/ijas.2014.3107
Italian Journal of Animal Science 2014; volume 13:3107
REVIEW ARTICLE
Non-commercial use only
[page 170] [Ital J Anim Sci vol.13:2014]
encing the composition of faecal microbiota: in
older animals, lecithinase-positive clostridia
and bacteria belonging to the class bacilli are
found in higher concentrations than lacto-
bacilli, pepto-streptococci and bifidobacteria
(Benno and Mitsuoka, 1989; Benno et al., 1992;
Mitsuoka, 1992); furthermore, faecal microbio-
ta seems to be influenced not only by age, but
also by the dog breed (Simpson et al., 2002).
Unfortunately, studies that investigated the
effect of age on canine intestinal microbiota
were conducted using traditional culturing
techniques and no research was done using
current assays.
Main effects of intestinal
microbiota on the host’s health
Gastrointestinal microbiota is a complex
ecosystem made up of hundreds of bacterial
species, some of which are potentially patho-
genic, while others are considered good for the
host (Roberfroid et al., 1995). The beneficial
microorganisms that reside in the large intes-
tine influence gastrointestinal functionality
and the host’s health in general, in virtue of
some principal mechanisms: i) detoxification
of some toxic substances introduced through
the diet or newly formed as a result of metabol-
ic processes of the body and of intestinal
microbiota (Tomomatsu, 1994); ii) barrier
effect against the proliferation of potentially
pathogenic bacteria and their adhesion to the
intestinal mucosa, thanks to occupation of the
attack sites of these microorganisms and pro-
duction of selective antimicrobial substances
(Liévin-Le Moal and Servin, 2006); iii) uptake
of ammonia and amine used as a source of
nitrogen to support microbial protein synthe-
sis, with a consequent reduction in the intes-
tinal absorption of these undesirable sub-
stances (Howard et al., 2000); iv) interaction
with the host immune system (Round and
Mazmanian, 2009; Cerf-Bensussan and
Gaboriau-Routhiau, 2010); and v) production
of vitamins (LeBlanc et al., 2012).
The short-chain fatty acids (SCFA) that
derive from microbial fermentation of carbohy-
drates represent a source of energy that the
host can use. In particular, SCFA are used as
energy substrates by colonocytes (butyric
acid), hepatocytes (propionic acid and lactic
acid) and peripheral tissues (acetic acid;
Cummings and Englyst, 1987). It has been esti-
mated that microbial fermentations can cover
between 2 and 7% of the maintenance energy
requirements of an adult dog (Herschel et al.,
1981; Stevens and Hume, 1998). Besides creat-
ing a favourable environment for beneficial
microbial species, the pH reduction caused by
SCFA induces a shift from ammonia to ammo-
nium ions, thus preventing absorption by the
intestine (McQuaid, 2005).
Prebiotics and synbiotics
According to a recent definition, a prebiotic
is a selectively fermented ingredient that allows
specific changes, both in the composition
and/or activity in the gastrointestinal microbio-
ta that confers benefits upon host well-being
and health (Roberfroid, 2007). To be effective,
a prebiotic has to withstand digestion and
reach the colon where it selectively stimulates
the growth and/or metabolic activity of micro-
bial species that promote evident beneficial
effects for the host.
Prebiotics are non-digestible carbohydrates,
mainly oligosaccharides with a low degree of
polymerisation, obtained by extraction from
vegetable raw materials (for example, hot
water extraction of inulin from chicory, arti-
chokes, bananas and wheat and of specific
oligosaccharides from soybeans; Franck and
Bosscher, 2009), by enzymatic synthesis [for
example, the fructooligosaccharides (FOS)
produced from sucrose and galactooligosac-
charides (GOS) obtained from lactose (Fujita
et al., 1992; Spiegel et al., 1994)] or else by par-
tial enzymatic hydrolysis of oligosaccharides
and polysaccharides [for example, the hydroly-
sis of inulin to FOS and of xylan polymers to
xylooligosaccharides (XOS) under the action
of xylanase (Imaizumi et al., 1991; De Bruyn et
al., 1992)]. Main characteristics of some prebi-
otic substances are presented in Table 1.
However, fructans such as inulin (a long-chain
fructan, up to 60 units), oligofructose (OF;
fructans chains with 8 to 10 units, often
referred to as long-chain FOS) and short-chain
FOS (fructans chains with 3-5 units) have
been widely tested in companion animals
(Hernot et al., 2008) and seem to be the most
frequently used prebiotic substances in the pet
food industry. Moreover, pet food ingredients
may contain certain amounts of natural prebi-
otic substances (Van Loo et al., 1995; Campbell
Pinna and Biagi
Table 1. Main characteristics of some non-digestible oligosaccharides with prebiotic potential.
Name Chemical composition Production process dp
Inulin β(2-1) fructans with a terminal glucose Extraction from chicory root, artichokes, 11-60
bananas and wheat
Oligofructose (long-chain β(2-1) fructans Enzymatic (β-fructosidase) synthesis from sucrose 8-10
fructo-oligosaccharides) or partial enzymatic or chemical hydrolysis from inulin
Short-chain β(2-1) fructans Enzymatic (β-fructosidase) synthesis from sucrose 3-5
fructo-oligosaccharides or partial enzymatic or chemical hydrolysis from inulin
Galacto-oligosaccharides Chains of galactose with some glucose Enzymatic (β-galactosidases) synthesis 2-5
(oligogalactose) from lactose
Soybean-oligosaccharides Mainly galactose with presence of mannose, Extraction from soybeans 3-4
glucose, fructose, arabinose and xylose
Xylo-oligosaccharides β(1-4)-linked xylose Partial enzymatic (xylanases) hydrolysis of 2-10
polyxylans polymers from vegetables and fruits
Lactitol 4-O-β-D-galactopyranosyl-D-glucitol Hydrogenation of lactose 2
Lactulose Galactose and fructose Isomerisation of lactose 2
dp, degree of polymerisation.
Non-commercial use only
[Ital J Anim Sci vol.13:2014] [page 171]
et al., 1997; Hussein et al., 1998; Moshfegh et
al., 1999). The fructan content of some veg-
etable raw materials is presented in Table 2.
The combination of a prebiotic and one or
more probiotic bacterial strains is defined as a
synbiotic (Schrezenmeir and De Vrese, 2001).
The simultaneous combination of probiotic
strains and a source of prebiotic molecules
that they can metabolise might offer the
administered bacterial strains greater possibil-
ities of growing and colonising the host, thus
promoting the potential beneficial effects.
Effects of prebiotic substances
in healthy dogs
Effects on composition of intestinal
microbiota
Flickinger et al. (2003b) reviewed the
effects of inulin and OF in domesticated ani-
mals. The effects of prebiotics in dogs and
other companion animals were recently
reviewed by Swanson and Fahey (2006) and
Hernot et al. (2008). A brief summary of the
effects of prebiotics on canine intestinal
microbiota is reported in Table 3.
The effects on canine intestinal microbiota
which result from the administration of sub-
stances with prebiotic action have been stud-
ied by various authors, but with sometimes
conflicting results. For example, in a study
with adult beagles, Flickinger et al. (2003a)
found that the use of OF [fructose chains
obtained from hydrolysed inuline, degree of
polymerisation (dp) of 3 to 10] at different
doses (3, 6 and 9 g/kg of diet) linearly
Prebiotics and synbiotics in dogs
Table 2. Fructan content of some vegetable raw materials.
Vegetable Moshfegh et al. (1999) Campbell et al. (1997)
Inulin, g/100 g of as is OF, g/100 g of as is Short-chain FOS, g/100 g of DM
Artichoke, globe 4.4 0.4 2.2
Banana 0.5 0.5 0.6
Barley 0.8 0.8 1.9
Chicory root 41.6 22.9 2.1
Jerusalem artichoke 18.0 13.5 28.6
Oats -- 0.4
Onion powder 18.3 18.3 4.8
Peas -- 0.8
Potato, sweet -- 0.1
Rye -- 4.1
Wheat - 1.4
Wheat bran 2.5 2.5 4.0
OF, oligofructose; FOS, fructooligosaccharides; DM, dry matter.
Table 3. Effects of prebiotic administration on composition of canine faecal microbiota.
Reference Prebiotic used Level of Method of Lactobacilli Bifidobacteria C. perfringens Total clostridia E. coli/coliforms
inclusion, g/kg determination
Howard et al., 2000° scFOS 15 Selective media ↔↔ ND ↑↔
Strickling et al., 2000 FOS 5 ↔↔ ↔ ↔
MOS 5 Selective media ↔↔ ↓ ND ↔
XOS 5 ↔↔ ↔ ↔
Willard et al., 2000 FOS 10 Selective media ↔↔ ND ↔↔
Flickinger et al., 2003b OF 9 Selective media ↔↔ ↓ ND ND
Middelbos et al., 2007a scFOS+dried yeast 12+3 DNA analysis ↑↑↔
ND ↔
scFOS+dried yeast 9+6 ↑↑↔ ↔
Barry et al., 2009 scFOS 2 and 4 DNA analysis ↔↔ ↔ ND ↔
Inulin 2 and 4 ↔↔ ↔ ↔
Biagi et al., 2010 Lactitol 10 Selective media ↔NR ↓ND ↓
Beloshapka et al., 2012 Polydextrose 5, 10 and 15 DNA analysis ↔↔ ↓ ND ↔
scFOS, short-chain fructooligosaccharides; ND, not determined; FOS, fructooligosaccharides; MOS, mannanoligosaccharides; XOS, xylooligosaccharides; OF, oligofructose; NR, not recovered.
°Bacterial counts were conducted on intestinal digesta.
Non-commercial use only
[page 172] [Ital J Anim Sci vol.13:2014]
increased the aerobic population and reduced
C. perfringens in faeces [respectively, +0.8 and
-0.3 log10 cfu/g of faecal dry matter (DM) with
9 g/kg of OF, compared with control], without
exerting any influence on the faecal popula-
tion of lactobacilli and bifidobacteria. The lat-
ter result was also observed by Swanson et al.
(2002b) when adult dogs were fed FOS at 2 g/d.
In another study (Howard et al., 2000), the
administration of short-chain FOS (at 15 g/kg
of diet) increased aerobic population in the
distal colon of adult dogs (+1.8 log10 cfu/g of
faecal DM, compared with a diet containing
cellulose at 60 g/kg). In the study by Grieshop
et al. (2004), feeding adult dogs with chicory
(10 g/kg of diet) or mannanoligosaccharides
(MOS; 10 g/kg of diet) increased faecal bifi-
dobacteria (+0.4 and +0.5 log10 cfu/g of faecal
DM, respectively) and MOS also resulted in a
decrease of faecal E. coli concentrations.
In a study by Strickling et al. (2000), the use
of FOS (OF from chicory root), MOS (from
yeast cell wall of Saccharomyces cerevisiae) or
XOS (mainly made of xylobiose and xylotriose,
which are dimers and trimers of xylose, respec-
tively) at a dietary concentration of 5 g/kg DM
did not affect the number of faecal bifidobacte-
ria in adult dogs; compared with animals
administered FOS and XOS, those receiving the
diet supplemented with MOS showed a numer-
ical reduction in C. perfringens in the faeces (-
0.26 and -0.68 log10 cfu/g of faecal DM, respec-
tively). Although MOS are often described as
prebiotic non-digestible oligosaccharides, they
are not fermented by beneficial bacteria;
instead, MOS act by binding and removing
pathogens from the gastrointestinal tract and
stimulating the immune system (Spring et al.,
2000). In a study by Vickers et al. (2001), in
vitro fermentation of different sources of inulin
and FOS increased concentrations of SCFA,
whereas fermentation of MOS resulted in mod-
erate production of SCFA.
In another study, Barry et al. (2009) did not
observe any effect on the faecal microbiota of
dogs after administering short-chain FOS or
inulin at relatively low doses (2 and 4 g/kg of
diet). Vanhoutte et al. (2005), in contrast,
highlighted the positive role played by a combi-
nation of OF (4.5 g/d) and inulin (5.6 g/d) on
the intestinal microbiota of dogs; their find-
ings included, in particular, an increase in the
populations of streptococci; interestingly, no
bifidobacteria were detected in any of the
seven dogs that were involved in the study.
Similarly, Willard et al. (2000) reported that
bifidobacteria and lactobacilli were inconsis-
tently isolated from faeces of dogs during a
study in which FOS were used as a dietary sup-
plement at 10 g/kg of diet.
When administered to a group of adult shep-
herd dogs, lactosucrose (1.5 g/d), a bifidogenic
fibre enzymatically synthesised from D-galac-
tose, D-fructose and D-glucose, showed to be
effective in increasing bifidobacteria (+0.5
log10 cfu/g of faeces) and decreasing C. perfrin-
gens (-1.6 log10 cfu/g of faeces) in the faeces
(Terada et al., 1992).
In a recent study (Beloshapka et al., 2012),
the utilisation of polydextrose (a polysaccha-
ride synthesised by random polymerisation of
glucose and sorbitol with an average dp of 12)
at dietary concentrations of 5, 10 and 15 g/kg of
diet linearly reduced faecal concentrations of
C. perfringens in healthy adult dogs (-0.3, -0.4
and -0.8 log10 cfu/g of faecal DM with polydex-
trose at 5, 10 and 15 g/kg of diet, respectively),
without affecting the faecal concentrations of
E. coli, lactobacilli and bifidobacteria.
In a study by Biagi et al. (2010), various
fibre sources and prebiotic substances were
tested in the dog, both in vitro and in vivo.
Among the substrates used in the in vitro test,
FOS (two different sources: from partially
hydrolysed inulin from chicory with dp 3 to 7
and from chicory with dp 2 to 10), lactitol,
inulin from chicory (two sources: one with
dp>20 and the other one with dp 2 to 60), cit-
rus and apple pectins and psyllium fibre
showed to be rapidly fermentable by canine
intestinal microbiota, resulting in a reduction
in the pH of faecal inocula. Among the sub-
stances tested, lactitol had an evident positive
effect on undesirable bacterial populations, as
reflected in an in vivo reduction in the concen-
trations of coliform bacteria and C. perfringens
(-2.2 and -1.0 log10 cfu/g of faeces, respective-
ly) when lactitol was fed to adult dogs at 10
g/kg of diet for 30 d. Middelbos et al. (2010)
reported that supplementing the diet with beet
pulp had the effect of significantly increasing
the clostridia count in dog faecal specimens
(from 83 to 90% of bacteria-assigned
sequences obtained using pyrosequencing). In
the previously cited study by Biagi et al.
(2010), compared with control, beet pulp
induced an increase in the pH (+0.13) and
counts of coliforms (+0.5 log10 CFU/mL) of fae-
cal inocula. Moreover, Middelbos et al. (2010)
observed that beet pulp also induced a reduc-
tion in the concentration of bacteria belonging
to the phylum Actinobacteria (from 1.4 to 0.8%
of total sequences), which includes bifidobac-
teria, without, however, affecting the number
of bacilli, among which we find numerous bac-
terial species considered to be beneficial and
belonging to the genus Lactobacillus spp.
According to what emerged during the study
conducted by Middelbos et al. (2007a), the
dietary inclusion of two combinations of short-
chain FOS and dried yeast as a source of MOS
(12 g/kg FOS+3 g/kg yeast cell wall and 9 g/kg
FOS+6 g/kg yeast cell wall, respectively) result-
ed in an increase in the faecal populations of
bifidobacteria (+1.0 and +1.4 log10 CFU/g of
feacal DM, respectively) and lactobacilli (+0.9
log10 CFU/g of feacal DM for both treatments)
and, consequently, a lowering of the faecal pH
(-0.3 and -0.4, respectively). The authors also
highlighted a tendency toward a reduction in
the faecal counts of E. coli, hypothesising that
MOS had the ability to bind to the fimbriae of
some pathogenic bacteria, such as, precisely,
coliform bacteria and Salmonella spp., thus
preventing them from colonising the intestinal
wall. In another study with adult dogs
(Middelbos et al., 2007b), a yeast cell wall
preparation fed at different levels of inclusion
(0.5, 2.5, 4.5 and 6.5 g/kg of diet) as a source of
MOS linearly reduced faecal counts of E. coli
(-0.9 log10 CFU/g of feacal DM in dogs receiv-
ing 6.5 g/kg of yeast cell wall).
Beloshapka et al. (2013) investigated the
effect of inulin (14 g/kg of diet) or a yeast cell
wall extract (14 g/kg of diet) in adult dogs
receiving raw meat-based diets [containing
approximately per kg of diet 250 to 300 g of
crude protein (CP) and 450 to 500 g of fat].
Administration of inulin resulted in lower fae-
cal abundance of Enterobacteriaceae and
Escherichia and higher faecal lactobacilli while
the yeast cell wall extract increased faecal bifi-
dobacteria. Moreover, inulin reduced faecal
abundance of some Bacteroides and
Fusobacterium species.
Based on results from the cited studies,
despite some discrepancies, the use of prebiot-
ic substances seems to represent an efficient
way to manipulate the gastrointestinal ecosys-
tem of dogs, increasing the abundance of ben-
eficial bacteria and reducing the presence of
undesired microbes. Among the prebiotics that
have been tested, short-chain FOS and OF,
when used at concentrations higher than 10
g/kg of diet, seem to be the most effective in
modulating the canine intestinal ecosystem.
Effects on intestinal ammonia
and other bacterial catabolites
In general, limitation of carbohydrates as a
source of energy in the hindgut leads to micro-
bial proteolysis with consequent release of
toxic substances, such as ammonia and
amines (Russell et al., 1983).
Prebiotics might reduce concentrations of
ammonia in the animal intestine, as increased
fermentation leads to higher amounts of nitro-
gen converted into bacterial protein (Howard
et al., 2000). Moreover, the use of prebiotics
might reduce intestinal proteolysis and pro-
Pinna and Biagi
Non-commercial use only
[Ital J Anim Sci vol.13:2014] [page 173]
duction of putrefactive compounds by increas-
ing the number of beneficial bacteria, enhanc-
ing SCFA production and reducing luminal pH
(Terada et al., 1992). In the study by Biagi et al.
(2010), compared with control, the ammonia
concentration was lower in the inocula to
which citrus pectin was added (-23%) and
higher in those treated with gluconic acid and
inulin (+17 and 20%, respectively). In the
same study, FOS and lactitol had no effect on
ammonia concentrations. In a previous in vitro
study that used swine cecal inoculum, gluconic
acid instead brought about a reduction in the
ammonia concentration (Biagi et al., 2006).
Terada et al. (1992) reported a significant
decrease of faecal ammonia (-60%) and bad
smell of faeces in dogs receiving 1.5 g/d of lac-
tosucrose. Similarly, in the study by Flickinger
et al. (2003a), faecal ammonia concentrations
tended to be reduced by OF but concentrations
of other protein catabolites remained unaffect-
ed. In contrast, ammonia intestinal and faecal
concentrations were not influenced by diet in
the already cited studies by Strickling et al.
(2000) and Barry et al. (2009); the same result
was observed in the study by Beynen et al.
(2002) in which adult dogs received a diet sup-
plemented with OF (dp from 3 to 20) at 10 g/kg
for 30 d. Similarly, the use of FOS at 30 g/kg in
adult dogs did not reduce faecal ammonia
(Hesta et al., 2003). In the study by Swanson et
al. (2002b), the use of FOS reduced faecal con-
centrations of indole (a protein catabolite of
bacterial origin) by 1.2 mol/g of faecal DM but
faecal ammonia and biogenic amines were
unaffected. Beloshapka et al. (2012) reported
that faecal indole concentrations tended to
decrease with increasing dietary levels of poly-
dextrose but other protein catabolites (ammo-
nia, phenol and branched-chain fatty acids)
were not influenced by treatment.
Finally, Propst et al. (2003) reported that the
use of different concentrations (3, 6 and 9 g/kg
of diet) of OF or inulin in adult dogs resulted in
increased faecal ammonia and isovalerate (a
branched-chain fatty acid that derives from
protein fermentation) concentrations. In the
same study, OF also resulted in increased fae-
cal concentrations of total biogenic amines
and SCFA and reduced faecal phenols. Zentek
et al. (2002) found that the intake of MOS (1
g/kg BW/d) had the effect of lowering both the
pH (-0.3) and the ammonia concentration (-38
µmol/g of faeces) in canine faeces. The same
authors also noted that the utilisation of MOS
significantly decreased faecal unbound water
content (from 165 to 55 g/kg of faeces) and
apparent digestibility of protein, the latter
result presumably as a consequence of the
increased viscosity of the intestinal chyme.
The conflicting results that are observed
when prebiotics are fed to dogs are not easy to
explain. First, different basal diets might
cause some discrepancy: diets that are rich in
wheat, barley or oats are likely to contain sig-
nificant amounts of soluble fiber (including
short-chain fructans; Van Loo et al., 1995)
that might mask the effect of prebiotics.
Another cause of conflicting results might
reside in the type of prebiotics that are used:
in fact, within the same category, prebiotic
substances may differ based on their origin,
degree of polymerisation, etc. Obviously, the
level of dietary inclusion of prebiotics also
has an influence on their effects: in particu-
lar, FOS seem to be effective at concentra-
tions higher than 10 g/kg of diet. Moreover, in
many studies the effects of prebiotics on
intestinal microbiota were evaluated based
only on faecal analyses. This is very common
today, as most scientists try to avoid for ethi-
cal reasons any type of invasive methods of
analysis when a study is conducted with dogs.
Unfortunately, it is well known that the con-
centration of bacterial metabolites able to
cross the intestinal mucosa can vary while
digesta move along the intestine (Stevens
and Hume, 1998). Therefore, faeces might
not reflect the changes in the concentration
of ammonia, SCFA and other molecules that
the prebiotic may have induced in the colon.
Finally, another reason for discrepancies in
the effect of prebiotics might reside in the
inconsistent presence of their target bacteria
in dogs, namely bifidobacteria and lactobacil-
li. In fact, while some authors reported high
average concentrations of bifidobacteria in
the faeces of experimental dogs (Flickinger et
al., 2003a; Middelbos et al., 2007a), bifidobac-
teria were inconsistently isolated from canine
faeces in the studies by Willard et al. (2000),
Greetham et al. (2002), Apanavicius et al.
(2007), Biagi et al. (2007, 2010), Lamendella
et al. (2008). Similarly, Willard et al. (2000)
reported that lactobacilli were inconsistently
isolated from dog faeces.
In the study by Beloshapka et al. (2013),
according to 454 pyrosequencing, bifidobacteria
were not detectable and lactobacilli were pres-
ent at less than 0.05% of total sequences. In the
same study, when faecal samples were analysed
by quantitative polymerase chain reaction both
Bifidobacterium and Lactobacillus were
detectable, even if at low levels. Authors con-
cluded that bifidobacteria and lactobacilli might
be underestimated using these 16S rRNA gene-
based sequencing approaches due to the pres-
ence of several sources of bias, as already high-
lighted by other authors (Garcia-Mazcorro et al.,
2011; Handl et al., 2011).
Effects on intestinal short-chain
fatty acids
Short-chain fatty acids (acetate, propionate,
lactate and butyrate) are the main products of
carbohydrate fermentation. There is evidence
that butyric acid is the preferred fuel substrate
of the terminal ileal mucosa (Chapman et al.,
1995) and the epithelial cells of the large intes-
tine (Roediger, 1980). Moreover, these organic
acids possess antibacterial properties
(Knarreborg et al., 2002) and reduce luminal
pH thus improving animal intestinal health.
In the in vitro study by Biagi et al. (2010),
total SCFA in the inocula were increased by
lactitol (+18%), inulin from chicory (+17%),
pectins from apple (+15%), psyllium fiber
(+21%) and partially hydrolysed guar gum
(+69%). The higher SCFA concentrations lead
to significantly lower pH values of inocula.
Similarly, faecal propionic acid and total SCFA
were increased in dogs fed OF at 6 g/kg of diet
(+55 and +31%, respectively; Flickinger et al.,
2003a). These results agree with those
obtained by Propst et al. (2003), who reported
higher faecal concentrations of acetic, propi-
onic and butyric acids in dogs receiving inulin
or OF at different levels of inclusion (3, 6 and
9 g/kg of diet). Similarly, the utilisation of poly-
dextrose at 5, 10 and 15 g/kg of diet in adult
dogs resulted in lower faecal pH and higher
faecal concentrations of acetate, propionate
and total SCFA (Beloshapka et al., 2012).
Conversely, Barry et al. (2009) reported
decreased faecal concentrations of acetic acid,
propionic acid and total SCFA in dogs fed inulin
at 2 and 4 g/kg of diet. In a study by Twomey et
al. (2003), the administration of FOS at 30 or 60
g/kg of diet to dogs resulted in higher faecal lac-
tate concentrations (85, 143 and 289 mmol/kg of
faeces for control, FOS at 30 g/kg and FOS at 60
g/kg, respectively) and lower faecal pH (5.4, 5.3
and 5.0 for control, FOS at 30 g/kg and FOS at 60
g/kg, respectively).
Effects on faecal quality
It has been observed that the utilisation of
prebiotics can result in humans in increased
stool weight and decreased stool transit time
(Macfarlane et al., 2006). Prebiotics are some-
times proposed in humans as mild laxatives
despite the fact that a clear scientific evidence
of this effect is still lacking (Cummings and
Macfarlane, 2002).
Twomey et al. (2003) observed that adminis-
tration of FOS at 30 or 60 g/kg of diet to dogs
resulted in decreased faecal dry matter (DM;
327, 303 and 296 g/kg of faeces for control, FOS
at 30 g/kg and FOS at 60 g/kg of diet, respective-
ly). Conversely, several authors (Strickling et
al., 2000; Swanson et al., 2002b; Flickinger et al.,
Prebiotics and synbiotics in dogs
Non-commercial use only
[page 174] [Ital J Anim Sci vol.13:2014]
2003a; Beloshapka et al., 2012) did not observe
any effect of prebiotic administration on canine
faecal dry matter when prebiotics were admin-
istered at lower doses than those used by
Twomey et al. (2003). Based on the literature, it
seems evident that high dietary concentrations
of prebiotics may have an influence on faecal
volume and consistency. Because, in general,
pet owners expect their dogs to excrete small
and firm faeces, prebiotics should be adminis-
tered to dogs at relatively low concentrations
(less than 20 g/kg of dietary DM).
Effects on nutrient digestibility
Several authors reported that prebiotic con-
sumption by dogs resulted in lower organic
matter (OM) and CP total tract apparent
digestibility (Diez et al., 1997, 1998a, 1998b;
Zentek et al., 2002; Flickinger et al., 2003a;
Hesta et al., 2003; Propst et al., 2003;
Middelbos et al., 2007a; Beloshapka et al.,
2012). Conversely, Middelbos et al. (2007b)
reported higher ileal digestibility of OM (79.4
vs 74.5%) and CP (72.4 vs 65.3%) in dogs fed
spray-dried yeast cell wall at 6.5 g/kg of diet. In
the study by Twomey et al. (2003), total tract
apparent digestibility of protein in dogs receiv-
ing FOS at 30 or 60 g/kg of diet was unaffected.
In general, prebiotic consumption leads to
higher faecal nitrogen concentrations because
faecal bacterial mass is increased (Hesta et al.,
2003; Karr-Lilienthal et al., 2004) thus leading
to lower apparent digestibility of OM and CP. As
already mentioned, conversion of ammonia
nitrogen into bacterial protein is a positive
effect that can improve intestinal health.
Another possible effect of prebiotics is an
improved intestinal absorption of minerals. In a
study with adult dogs, Beynen et al. (2002) found
that the use of OF at 10 g/kg increased apparent
calcium (+86%) and magnesium (+67%) absorp-
tion, whereas phosphorus absorption was unaf-
fected. Similarly, the use of lactulose at 1 or 3 g/MJ
of metabolisable energy in adult dogs increased
apparent calcium (+63 and +83%, respectively)
and magnesium (+27 and +52%, respectively)
absorption in a dose-dependent manner, but not
phosphorus (Beynen et al., 2001). Results from
these two studies seem to confirm that, similarly
to what has been observed in other animal
species and humans (Scholz-Ahrens et al., 2007),
prebiotics may have a positive influence on calci-
um and magnesium intestinal absorption in dogs.
The positive effects of prebiotics on mineral
absorption have been attributed to several mech-
anisms, including increased solubility of minerals
and enterocytes proliferation because of
increased bacterial production of SCFA and
increased expression of calcium binding proteins
(Scholz-Ahrens et al., 2007).
Effects on immune system
The gastrointestinal tract is the main site of
interaction between the immune system and
microorganisms. While the immune system
plays a very important role in maintaining
homeostasis with intestinal microbiota, bacte-
ria residing in the gut influence development of
gut-associated lymphoid tissues and shape ani-
mal immunity (Round and Mazmanian, 2009).
The effects of prebiotics on immune system
of dogs and other animal species were recently
reviewed by Lomax and Calder (2009). While
the utilisation of 8.7 g/kg of diet of a combina-
tion of high fermentable fiber sources (contain-
ing a mixture beet pulp, FOS and gum arabic;
Field et al., 1999), short-chain FOS at 9.1 g/kg of
diet (Adogony et al., 2007) or inulin (30 g/kg of
diet; Verlinden et al., 2006) had only little or no
effect on canine immune system, the utilisation
of FOS in combination with MOS increased ileal
IgA concentrations (+1.5 mg/g DM; both FOS
and MOS were used at 1 g/d; Swanson et al.,
2002b). In another study (Swanson et al.,
2002c), dietary supplementation with FOS at 2
g/d plus MOS at 1 g/d increased blood lympho-
cytes and reduced blood neutrophils in adult
dogs. Conversely, in the study by Grieshop et al.
(2004), a combination of chicory (10 g/kg of
diet) and MOS (10 g/kg of diet) reduced periph-
eral blood lymphocyte concentration with no
other effect on immune system. Similarly,
Middelbos et al. (2007b) observed only limited
effects on canine immune system when a yeast
cell wall preparation was fed to adult dogs. At
present, the prebiotic effects on canine immu-
nity have not been well studied and more
research is needed. Nevertheless, based on the
cited studies, despite some discrepancies, the
utilisation of MOS seems to enhance immune
system in dogs. Conversely, based on current
knowledge, the influence of FOS and inulin on
canine immune system might be negligible.
Effects of synbiotics
in healthy dogs
Ogué-Bon et al. (2010) conducted in vitro
tests to assess the synergistic potential of some
prebiotic substrates (FOS, GOS and inulin) and
several probiotic strains (Bifidobacterium
bifidum, B. longum, Lactobacillus plantarum, L.
acidophilus and L. rhamnosus). In this study, a
specificity between bacterial strain and fer-
mentable substrate emerged clearly; for exam-
ple, GOS were rapidly used by bifidobacteria
(thanks to their ability to synthesise -galactosi-
dase), as had already been highlighted by other
authors (Gopal et al., 2001; Rada et al., 2008;
Zanoni et al., 2008). FOS, on the other hand,
were shown to be easily metabolised by all the
test strains with the exception of L. rhamnosus;
this latter finding confirms what had been pre-
viously observed by Kaplan and Hutkins (2000)
and is probably ascribable to a deficiency of the
enzyme -fructosidase in L. rhamnosus strains.
Results from the study by Ogué-Bon et al.
(2010) also indicated that the synbiotic combi-
nation GOS+B. bifidum induced greater modu-
lation of canine faecal microbiota compared
with GOS alone.
In a study by Swanson et al. (2002a), two
experiments were performed with a group of
dogs receiving for 28 d short-chain FOS (4 g/d),
a strain of Lactobacillus acidophilus (2 x 109
cfu/d) or their combination. In the second exper-
iment, compared with control, FOS supplemen-
tation increased faecal total aerobes (+0.6 log10
cfu/g of faecal DM), bifidobacteria (+0.6 log10
cfu/g of faecal DM) and lactobacilli (+0.7 log10
cfu/g of faecal DM). The combination of FOS and
L. acidophilus resulted in effects of larger entity
on the concentration of bacterial metabolites
compared to administration of either of the two
preparations alone. More specifically, the synbi-
otic was particularly effective in reducing the
faecal concentrations of ammonia (compared
with control, -5% in the second experiment) and
of some catabolites (branched-chain fatty acids;
compared with control, -8 and -22% in experi-
ment 1 and 2, respectively) deriving from pro-
tein fermentation.
Tzortzis et al. (2004b) carried out an in vitro
investigation into the effects on canine gut
microbiota of several prebiotic substances,
including a particular galactooligosaccharide
[galactosyl melibiose mixture (GMM); synthe-
sised using -galactosidase isolated from L.
reuteri], in association with L. acidophilus and
L. reuteri strains. The authors observed that all
of the various tested substrates (FOS with dp 2
to 9, GMM, melibiose and raffinose) possessed
prebiotic properties, but GMM showed a higher
increase in bifidobacteria and lactobacilli as
well as a higher decrease in clostridia com-
pared to the other prebiotics (FOS, melibiose
and raffinose). Furthermore, the increase in
the counts of bifidobacteria was highest for the
combination of GMM and L. reuteri (compared
with inoculum at start, +1.3 log10 CFU/mL).
During another in vitro study, Tzortzis et al.
(2004a) investigated the effect of various car-
bon sources on the production of extracellular
antagonistic compounds against two
Escherichia coli strains and Salmonella enteri-
ca serotype Typhimurium by three canine-
derived lactobacilli strains (L. mucosae,L. aci-
dophilus and L. reuteri). Results showed that
Pinna and Biagi
Non-commercial use only
[Ital J Anim Sci vol.13:2014] [page 175]
production of antimicrobial compounds by lac-
tobacilli strains was influenced by substrate in
a synergistic mode of action.
In another study (Garcia-Mazcorro et al.,
2011), the administration for 21 d of a com-
mercial synbiotic containing 7 different pro-
biotic species (Enterococcus faecium,
Streptococcus salivarius ssp. termophilus,
Bifidobacterium longum, Lactobacillus aci-
dophilus,L. casei ssp. rhamnosus,L. plan-
tarum and L. delbrueckii ssp. bulgaricus) and
a mixture of FOS and arabinogalactans
induced a significant increase in the concen-
trations of Enterococcus and Streptococcus
spp. (species present in the probiotic supple-
ment) in dog faeces during synbiotic admin-
istration. In the same study, none of the eval-
uated serum (cobalamin, folate, IgA, trypsin-
like immunoreactivity and pancreatic lipase
immunoreactivity) or faecal (IgA and a1-pro-
teinase inhibitor) markers of gastrointestinal
and immune function were influenced by syn-
biotic administration. The association
between commercially available probiotic
strains (Lactobacillus plantarum, two strains
of L. acidophilus, L. rhamnosus,Bifidobac -
terium longum and B. bifidum) and commer-
cially available fibre blends (rice bran, citrus
pectin and barley and maize starch) was stud-
ied by Ogué-Bon et al. (2011). The authors
observed that rice bran was capable of increas-
ing SCFA production and stimulating the
growth of probiotic strains. This finding is par-
ticularly interesting since rice bran is com-
monly used as a fibre supplement in the pet
food industry and could therefore add a prebi-
otic effect to the known dietary effects tied to
the use of this type of fibre, which include
increasing the faecal mass and providing a lax-
ative action. Finally, the authors noted that rice
bran on its own had the same effect on the fae-
cal counts of bifidobacteria and lactobacilli and
concentrations of SCFA as the various synbiot-
ic combinations, thus revealing that in this
case no synergism existed between the probi-
otic strains and fibre source used. Despite the
relatively low number of studies that have been
conducted with synbiotics in the canine
species, there is some evidence that the proper
combination of a prebiotic with one or more
probiotic strains might result in a synergistic
effect on dog intestinal microbiota.
Roles of prebiotic substances
in canine disease
One potential benefit from the utilisation of
prebiotics in humans and monogastric ani-
mals is to reduce infection by intestinal
pathogens (Callaway et al., 2008). In fact, pre-
biotics can stimulate the growth of bacteria
that compete against pathogens (Roberfroid,
2007) and also modulate activity of the
immune system (Seifert and Waltz, 2007;
Lomax and Calder, 2009).
By increasing the number of lactobacilli in
the intestine, inulin at 10 g/kg of diet could
provide positive action against Salmonella
typhimurium infections, based on what was
observed by Apanavicius et al. (2007) in exper-
imentally infected puppies. The antagonist
action of lactobacilli against Salmonella
typhimurium (de Moreno de LeBlanc et al.,
2010) is in fact well known. In the already cited
study by Apanavicius et al. (2007), inuline sup-
plementation decreased enterocyte sloughing,
an indicator of intestinal damage, and
increased acetate intestinal concentrations
whereas the utilisation of FOS at 10 g/kg of
diet resulted in decreased enterocyte slough-
ing but did not affect lactobacilli counts.
As already mentioned, the use of prebiotics
might reduce the intestinal concentrations of
ammonia and, as a consequence, the amount of
ammonia that is absorbed into circulation and
burdens liver and kidneys (Howard et al., 2000).
Dogs with hepatic failure do not metabolise
ammonia well and might not be able to convert
ammonia into urea. On the other hand, dogs
with renal functional impairment lose their
ability to excrete nitrogen wastes. For these rea-
sons, prebiotics such as lactulose (McQuaid,
2005) could be used in the treatment of dogs
with renal or liver failure to prevent uremia and
hepatic encephalopathy, respectively.
The utilisation of prebiotics can produce
some benefits in humans in the management of
constipation by increasing stool weight and
decreasing stool transit time (Macfarlane et al.,
2006); moreover, there is some evidence that
prebiotics might be helpful in the treatment of
inflammatory bowel disease in humans and ani-
mal models (Hedin et al., 2007). At present, no
studies have been done to verify these prebiotic
effects in dogs. In general, more research needs
to be done to investigate the possible role of pre-
biotics in canine disease.
Conclusions
A reading of the literature shows that by
relying on the use of prebiotic substances it
may be possible to manipulate the gastroin-
testinal ecosystem of dogs with the aim of
improving their intestinal wellbeing and
enhancing their immune function. Utilisation
of prebiotics has several beneficial effects in
the canine intestine, including improved com-
position of intestinal microbiota, reduced con-
centrations of protein catabolites and
enhanced production of SCFA. Among prebi-
otics, short-chain FOS and OF seem to be the
most effective in modulating canine intestinal
microbiota and improving intestinal absorp-
tion of minerals but with little or no effect on
canine immune system. Conversely, MOS may
have a positive influence on the immune sys-
tem of dogs but more research is needed on
this subject. Furthermore, evidence exists that
some positive effects of prebiotics in dogs
might be enhanced if these are used in combi-
nation with specific probiotic strains, in the
form of a synbiotic. Unfortunately, to date,
most studies with prebiotics in dogs were con-
ducted with healthy adult animals so that little
is known about the interaction between prebi-
otic administration and factors such as age
and health status.
Clinical effects of prebiotics have been
widely investigated in humans but, at present,
little evidence exists that prebiotics may be
helpful in canine diseases such as infections
by intestinal pathogens, intestinal constipa-
tion and hepatic and renal failure. More
research needs to be done to investigate the
possible role of prebiotics in canine disease
and possibly to link prebiotic-induced changes
in the intestinal microbiota to significant
physiological outcomes.
Finally, most studies on canine intestinal
microbiota were conducted using traditional
culture methods, so that more research
remains to be done with modern molecular
identification methods to investigate the
effects of prebiotic substances in dogs.
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