Pet Nutrition
Sources and chemistry
Beta-glucans in the aleurone layer of cereal
grains have linear, bended structures.
Th eir 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.
Th e 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). 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
microfl ora (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 off ered, 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. Th e eff ects 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.
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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. Th e
altered cytokine profi le may protect against
infl ammation.
Dietary
beta-glucans
act
as
immunomodulator only if quantity and
structure are eff ective 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
specifi c for pure β-(1,3) backbone structures
(17).
Immune indicators
Oral administration of purifi ed 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 quantifi ed as leukocyte
percentages with internalized polystyrene
beads. Serum levels of specifi c antibodies
against the antigens served as measure of
the adaptive immune system.
Th e equivalent of 0.08% purifi ed beta-
glucans in dry food stimulated phagocytosis
by 43% and induced a 3.36-fold increase
in specifi c antibodies. Th ese mean eff ects
concern 3 to 10 weeks post-antigen injection
and four studies (10, 18-22).
Infl ammatory diseases
In double-blinded, placebo-controlled trials,
lasting 8 weeks, dogs with osteoarthritis (n
= 23/group) or atopic dermatitis (n = 15 or
Creature Companion | February - March 2019 • Vol. XII • Issue 2 • Noida
16) received dry food without or with 0.08%
of a purifi ed 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 infl ammatory bowel disease, feeding
dry food without or with 0.05% purifi ed
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.
List of references is available on request from
the author ([email protected])
* Dr Anton C Beynen writes this exclusive
column on dog and cat nutrition every month.
He is affi liated with Vobra Special Petfoods.