Pet Nutrition
Fructo-oligosaccharides
Within FOS, a subgroup of the fructans,
the degree of polymerization ranges
from 2-60 for the inulins and from
2-10 for oligofructose/short-chain FOS
preparations. Inulins, which have an
α(1-2)-linked glucose end unit, are
extracted from chicory root. FOS with
shorter chains is made by enzymatic
hydrolysis of inulin or fructosylation of
sucrose, yielding products without/with or
with terminal glucose, respectively (1).
FOS is a plant storage carbohydrate. Chicory
root contains 15-20 percent inulin and
5-10 percent oligofructose (1). Wheat and
barley may hold 1-4 and 0.5-1 percent FOS
(2). As the fructose molecules in FOS have
β(2-1) linkages, they cannot be hydrolysed
by canine pancreatic α-amylase. Ingested
FOS is broken down and fermented by
colonic bacteria. FOS is efficiently converted
into short-chain fatty acids by canine feces
as microbial inoculum (3-5).
Fecal bacteria
A 1994 paper concluded that FOS feeding
changed the bacterial composition in
duodenal/proximal jejunal fluid of dogs with
intestinal bacterial overgrowth (6), but the
control and test animals were incomparable.
Even so, the results were interpreted as
indicative of a positive health response
(7), inspiring further research.
Taken together, the results of 7-11 trials
show that adding 0.6 percent FOS to
dry food doubled and tripled the fecal
numbers of desirable Bifidiobacterium and
Lactobacillus, while lowering the viable
cell counts of the undesirable Clostridia
perfringens and Escherichia coli by about
20 percent (8-17).
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Food digestion
Mixing inulin into dogs’ food, at 7 percent
of dietary dry matter, increased wet feces
quantity by 46 percent and reduced apparent
protein digestibility by 2.6 percent units
(18). The extra feces contained 89 percent
moisture, pointing to an osmotic effect
of colonic solutes generated by enhanced
bacterial activity. Inulin acts as microbial
substrate (3-5), thereby expanding fecal,
bacterial mass, including protein (19). The
latter explains, at least partly, that inulin
lowered apparent protein digestion (18).
Averaged over five trials, 0.48 percent added
FOS in dry food raised the apparent ileal
digestibilities of dry matter and protein by
3.2 and 4.0 percent units. In contrast, for
11 trials, 1.0 percent FOS decreased mean
apparent fecal digestibilities of dry matter
and protein by 0.9 and 1.4 percent units
(8, 10, 12, 14, 15, 17, 20, 21). Within trials
(14, 17, 20), the dose-response relationships
were erratic.
For 12/13 trials, mean wet stool production,
either expressed as g/day or g/100 g dry
matter intake, was unaltered by 1.2 percent
added FOS in the diet, while dry matter
content and pH of feces were unaffected
(35.9 versus 35.4 percent) and slightly
decreased (from 6.5 to 6.4) (9, 10, 12-15,
17, 20-23). Clearly, the impact of FOS on
apparent digestion and colonic bacteria
hardly altered fecal characteristics.
Creature Companion | July 2019 • Vol. XII • Issue 7 • Noida
Immunity and fermentative products
In dogs fed diets with various FOS
preparations, indicators of the immune
response and bacterial degradation of
intestinal proteins were measured, which
produced inconsistent outcomes. FOS
feeding raised immunoglobulin A in
serum and ileal content (10, 21) or had
no effect (15-17, 21), while the amount in
feces was increased (21) or decreased (10,
21). FOS also unsystematically influenced
fecal concentrations of isovalerate, indole,
putrescine and hydrogen sulfide (10, 12, 14,
16, 17, 20, 22, 24).
Salmonella challenge
Puppies were fed dry food without or with
1 percent added short-chain FOS or inulin
(25). After 14 days, half of them received an
oral dose of Salmonella enterica. One and two
days later, the infection-induced decrease in
food intake was reduced by inulin only. The
increase in body temperature was lessened
by both FOS preparations. In rats, dietary
FOS inhibited colonization, but stimulated
translocation of salmonella (26, 27).
* List of references is available on request from
the author (beynen@freeler.nl)