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Creature Companion 2019; February: 40, 42.
Anton C. Beynen
Beta-glucans in dog food
Beta-glucans are water-soluble plant fibers, comprising chains of up to 2000 glucose units in so-
called beta form. Glucose is a simple sugar, existing in solution as mixture of alpha and beta rings.
The glucose building blocks of beta-glucans are joined by one of three linkage types. Beta-glucan
constructions can differ as to linkage pattern, spatial structure and functionality. Cellulose is a
water-insoluble beta-glucan with only one linkage type; this plant fiber is not discussed here.
Corn, rice, barley, wheat and oat contain different amounts of similarly linked beta-glucans.
Another type of beta-glucans is found in baker’s yeast. The five cereal grains and yeast are
commonly used as petfood ingredient. Dog-food labels rarely highlight the beta-glucans in whole
cereals and yeast. In contrast, added concentrates of beta-glucans, isolated from the outer layer of
baker’s yeast, are reputed to strengthen dog’s immune system.
Free beta-glucans are recognized by immune cells in the intestinal wall. As a result, certain
specialized cells may more efficiently capture and disarm harmful bacteria and viruses, while
others produce more offensive antibodies. Such immunostimulation has been shown in dogs
challenged with foreign substances (antigens), while ingesting purified beta-glucans derived from
yeast or oyster mushroom. The amount ingested was equivalent to 0.08 % in dry food. Similar diet
intervention also relieved symptoms in dogs with inflammation in joints, skin or bowel.
In dogs, food with added, purified beta-glucans can stimulate the immune response elicited by
antigens. The risk, if any, of overstimulation is unknown. There is no evidence that extra intake of
beta-glucans, as purified additives, prevents development of diseases in dogs. Nevertheless, beta-
glucans did ameliorate inflammatory diseases.
Sources and chemistry
Beta-glucans in the aleurone layer of cereal grains have linear, bended structures. Their cellulose-like
fragments, generally consisting of three or four of glucose units with β-(1, 4) bonds, are interrupted
by a single β-(1, 3) linkage. Beta-glucans from yeast (Saccharomyces cerevisiae) comprise β-(1, 3)-
linked glucose residues with small numbers of β-(1, 6)-linked branches.
The approximate levels of total beta-glucans in cereal grains are as follows: corn, 1.0%; rice, 0.7%;
barley, 3.8%; wheat, 0.8%; oat, 3.7% (1-5, Note 1). Dried spent brewer’s yeast has about 11% total
beta-glucans (6-9). Yeast preparations marketed as immune stimulator contain some 60% beta-
1,3/1,6-glucans (6, 10). Dry food with 50% of a grain species holds 0.35 to 1.9% cereal beta-glucans.
Food with 1% dried brewer’s yeast or a derivative, contains 0.1 or 0.6% yeast beta-glucans.
Macronutrient digestibility
Beta-glucans are resistant to the dogs’ digestive enzymes, but are degraded by the colonic bacteria.
Barley beta-glucans were moderately fermented by dog fecal microflora (11, 12). High intakes of
beta-glucans may raise ileal digesta viscosity, thereby impairing digestion. In dogs dosed with oat-
derived beta-glucans at a rate of 1% of the dry food offered, apparent digestibility of dry matter was
reduced by 4.6 %units, while fecal mass grew larger and loosened up (13).
In dogs, apparent digestion of protein in dehulled barley was 3.5 %units lower than that for wheat
(14, 15). Replacement of 35% wheat in dry food by barley decreased protein digestibility by 7 %units
and made stools more loose and moist. The effects were partly counteracted by spraying a mixture
of beta-glucanase, xylanase and amylase onto the diet (16). Clearly, the diet contrasts in the
digestibility trials (14-16) involved more than barley beta-glucans only.
Immunomodulatory concept
Various intestinal, innate immune cells have so-called pattern recognition receptors (PRRs) that may
bind diet-derived beta-glucans, just as they do with beta-1,3-glucans in cell walls of certain
pathogenic yeasts, fungi and bacteria. Receptor binding signals phagocytosis and pathogen
degradation by the leukocytes of the innate immune system. Leukocytes also release cytokines and
antigens that stimulate antibody production by the adaptive immune system. The altered cytokine
profile may protect against inflammation.
Dietary beta-glucans act as immunomodulator only if quantity and structure are effective on their
arrival at the intestinal, innate immune cells. Beta-glucans of higher purity are active, unlike beta-
glucans embedded in (partially digested) food ingredients. PPRs are highly specific for pure β-(1, 3)
backbone structures (17).
Immune indicators
Oral administration of purified beta-glucans from yeast or oyster mushroom enhanced antigen-
induced immune responses. Dogs were injected with ovalbumin (10, 18) or vaccinated against rabies
plus parvovirus (19-21) and bordetella (22). In-vitro phagocytosis, as index of the innate immune
system, was quantified as leukocyte percentages with internalized polystyrene beads. Serum levels
of specific antibodies against the antigens served as measure of the adaptive immune system.
The equivalent of 0.08% purified beta-glucans in dry food stimulated phagocytosis by 43% and
induced a 3.36-fold increase in specific antibodies. These mean effects concern 3 to 10 weeks post-
antigen injection and four studies (10, 18-22, Note 2).
Inflammatory diseases
In double-blinded, placebo-controlled trials, lasting 8 weeks, dogs with osteoarthritis (n = 23/group)
or atopic dermatitis (n = 15 or 16) received dry food without or with 0.08% of a purified yeast beta-
glucan preparation (23, 24). Beta-glucan treatment improved owner-assessed severity scores of
arthritis and atopy by 79 and 63%. In dogs (n = 7) with inflammatory bowel disease, feeding dry food
without or with 0.05% purified yeast beta-glucan for six weeks changed the clinical index (scale 0-18)
from 5.8 to 7.1 or 6.0 to 0.9 (25). Reproducibility is unknown for each trial.
Note 1
Analysed amounts (g/100 g) of total water-soluble beta-glucans
in cereal grains and dried yeast
Ref
Corn
Rice
Barley
Wheat
Oat
Yeast*
1
5.1
5
2
0.6
2
2.9
2
0.7
2
2.1
2
3
3.4
2
4
1.0
2
3.6
1
0.8
1
4.1
1
5
0.9
0.7
3.9
0.8
4.8
6
17.0
7
8.5
8
11.0
9
8.0
Mean^
1.0
0.7
3.8
0.8
3.7
11.1
^Overall mean. *Spent dried yeast (Saccharomyces cerevisiae)
Within references, beta-glucan levels are means for the number of cereal varieties as indicated by
superscripts. Means for two husked and dehusked barley varieties were 5.0 and 4.8% (1). Reference
5 gives lowest and highest values for an undisclosed number of cereal species; the means are
presented here. The article (5) also displays various literature values.
Yeast beta-glucan was calculated as residual fraction (6), measured enzymatically as beta-1,3/1,6-
glucan (7, 9) or analysed in cell walls by polysaccharide hydrolysis followed by high performance
anion-exchange chromatography (8).
Note 2
Impact of orally administered beta-glucans on immune responses in antigen-treated dogs. The innate
and adaptive responses are represented by in-vitro phagocytosis of leukocytes and serum levels of
antigen-specific antibodies; beta-glucan effects are expressed as multiplier of the corresponding
control values
Ref
Betaglucan*
Anti
-
gen+
n
Day
Innate
response √
Adaptive
response $
Prep
Diet%
Phagocytosis
Antibody
level
10, 18
1
0.10
1
a
5
28
1.29
1
1.19
2
8.75
4
,,
2
0.17
2
,,
,,
,,
1.69
1
1.71
2
5.13
4
19, 20
3
0.02
3
b
24
56
1.
02
3
2.67
5
1.87
6
21
4
0.01
4
c
15
56
1.70
3
1.25
5
2.61
6
22
5
0.08
5
d
5
28
1.21
7
Mean
0.08
1.43
3.36
All studies had a parallel design with equal number of dogs (n) per treatment. Day refers to the
moment of blood sampling or to the means of days 42, 56 and 70 (20) or 21, 28 and 35 (22).
*Betaglucan preparation: 1,2, Saccharomyces cerevisiae fraction containing 77 or 56% beta-glucans;
3, fraction from oyster mushroom (Pleurotus ostereatus) in syrup form (Plerasan V; Pleuran,
Bratislava) containing 10 mg beta-1,3/1,6-glucans per ml (26); 4, fraction from oyster mushroom in
syrup form (VET-P-IM; Pleuran, Bratislava) containing 10 mg beta-1,3/1,6-glucans per ml; 5, tablets
(MacroGard, Biorigin, São Paulo) each containing 100 mg beta-1,3/1,6-glucan from Saccharomyces
cerevisiae.
*Betaglucan, diet%: 1,2oral doses were 15 or 25 mg/kg body weight per day. At an intake of 15 g dry
food/kg body weight per day, the dietary concentrations would be 100 and 167 mg/100 g; 3dogs
aged 4 months received 2 ml Plerasan V/5 kg body weight per day; the equivalent dietary
concentration would be 18 mg/100 g for a dry food intake of 22.5 g/kg body weight per day; 4beta-
1,3/1,6-glucan was administered to 6-weeks old dogs at a dose of 4 mg/kg body weight per day,
which would be 13 mg/100 g for dry food intake at 30 g/kg body weight per day; 5Female Beagles
were given orally 150 mg beta-1,3/1,6-glucan per day. For an assumed body weight of 12 kg and dry
food intake of 15 g/kg body weight per day, the dietary equivalent is 83 mg beta-glucans/100 g.
+ Antigen: a, ovalbumin, injected subcutaneously on Days 7 and 21; b, polyvalent vaccine, including
canine parvovirus, was administered on Days 1 and 14 and rabies vaccine on Day 28; c, polyvalent
vaccine, including canine parvovirus type 2, was injected on Days 0, 21 and 42; on Day 42, the dogs
were vaccinated against rabies virus also; d, on Days 14 and 28, dogs were vaccinated
subcutaneously with inactivated Bordetella bronchiseptica and parainfluenza virus type 2.
√ Innate immune response: in-vitro phagocytosis of 2-hydroxyethyl metacrylate by monocytes1,
neutrophils2 and total leukocytes3, expressed as percentage of positive cells.
$ Adaptive immune response: 4 level of serum antibodies against ovalbumin; 5level of antibodies
against rabies; 6level of antibodies against canine parvovirus; 7serum level of Bordetella specific
immunoglobulin M.
Note 3
Indicators of the innate immune response other than phagocytosis have also been measured. A
study presented in the table of Note 2 (10, 18) found that oral administration of two preparations of
yeast beta-glucans raised the serum levels of interleukin 2 by multiplier factors as huge as 185 and
111. In another study (19, 20), ingestion of oyster-mushroom beta-glucans did not affect
chemotactic activity of polymorphonuclears and the mitogen-induced blastogenic response of blood
lymphocytes, the multiplier factors being 1.04 each. As indicator of the adaptive immune response,
the antigen-induced level of serum total immunoglobulin G was left unchanged after oral intake of
yeast beta-glucans; the multiplier factor was 1.00 (22).
Oral yeast beta-glucans did not affect the serum levels of total immunoglobulins A and M in dogs
unchallenged with antigen; the multiplier factors were 0.95 and 1.02 (22). Unchallenged dogs, aged
6-12 months, received capsules (Imuneks, Mustafa Nevzat Drug Company, Turkey) containing 10 mg
beta-1,3/1,6-glucan from Saccharomyces cerevisiae (27, 28). The beta-glucans were administered at
a dose of 3 mg/kg body weight per day, which is equivalent to 13 mg/100 dry food, or 0.01%. After
14 days, blood cells and serum immunoglobulins were quantified in control and glucan-fed dogs
(n=4/group). Feeding yeast beta-glucans did neither influence the counts of blood neutrophils and
lymphocytes nor the serum levels of immunoglobulins A, M and G. The multiplier factors were 1.01,
0.95, 1.02, 1.18 and 1.07. For monocyte counts, the factor was 0.69.
Note 4
As described above, oral administration of purified beta-glucans from yeast (Saccharomyces
cerevisiae) and oyster mushroom (Pleurotus ostereatus) have been demonstrated to influence the
antigen-challenged immune system of dogs (10, 18-22). In one study with mice, both the feeding of
purified yeast and barley glucans had immunomodulatory activity (29). Other mouse experiments
showed immune stimulation by ingested purified beta-glucans from oat (30) or a plant pathogenic
fungus (Sclerotinia sclerotiorum) (31). Intravenously injected beta-glucans from shiitake mushroom
(Lentinula edodes) also affected the immune system in mice (32).
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