In recent years, increasing attention has been paid to the impact of gut health on the overall well-being of dogs and cats in pet food development. In particular, prebiotic ingredients that nutritionally modulate the intestinal microbiota have gained importance as value-adding components capable of delivering multifaceted benefits, including improved digestibility, immune support, and stool quality.
This article focuses on inulin, one of the most representative prebiotic ingredients, and provides a structured overview of its mechanisms of action, research findings in dogs and cats, and key considerations for formulation design, specifically for pet food manufacturers and R&D leaders.
Basic Properties and Mechanisms of Action of Inulin
Inulin is a water-soluble dietary fiber classified as a fructan, composed of fructose units linked by β-(2→1) glycosidic bonds, with a structure similar to sucrose. Because mammalian digestive enzymes cannot efficiently hydrolyze these bonds, inulin is not digested or absorbed in the small intestine and instead reaches the large intestine intact.
Once in the colon, inulin is fermented by intestinal microorganisms, leading to the production of short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate. These SCFAs serve as an important energy source for colonic epithelial cells, while also lowering intestinal pH and suppressing the growth of pathogenic bacteria.
As a result, inulin supplementation has been associated with increases in beneficial bacterial populations such as Lactobacillus and Bifidobacterium, alongside a potential reduction in undesirable anaerobic pathogenic bacteria.
Evidence of Prebiotic Effects in Dogs and Cats
Recent studies have demonstrated improvements in gut microbiota composition and immune function following inulin supplementation.
For example, in a double-blind study involving 26 adult cats (4 years old), cats fed a diet containing 0.6% inulin for six weeks showed an increase in fecal Firmicutes and a decrease in Bacteroides. Additionally, fecal SCFA concentrations—particularly butyrate—were significantly elevated, and antibody responses following vaccination tended to rise earlier compared with the control group.
In dogs, several studies have reported increased fecal SCFA production when diets containing hydrolyzed chicory fiber (oligofructose) or inulin at inclusion levels of 0.3–0.9% were fed. The largest increase in SCFAs was observed at the 0.9% inclusion level.
In another canine study, feeding 1% inulin resulted in enhanced humoral immune responses to erythrocyte antigens, indicating improved antibody production capacity.
Collectively, these findings suggest that relatively low dietary inclusion levels of inulin may support functional improvements in gut health and immune activity in both dogs and cats.
Recommended Inclusion Levels and Risks of Over-Supplementation
At present, there is no universally established recommended intake level for inulin in dogs and cats. However, experimental studies typically employ inclusion levels ranging from approximately 0.5% to 4% of the total diet.
For instance, Jeusette and colleagues confirmed beneficial effects in adult cats at an inclusion level of 0.6%, while canine studies have reported metabolic and immunological benefits at levels as low as 0.2–1%.
Conversely, excessive intake may lead to gastrointestinal side effects such as diarrhea or flatulence due to excessive fermentation of soluble fiber. Therefore, during product development, it is advisable to start with low inclusion levels and gradually increase them, monitoring tolerance indicators such as stool quality and gastrointestinal comfort.
Notably, Grieshop and colleagues reported that diets containing 1% chicory-derived inulin combined with mannan oligosaccharides (MOS) did not induce soft stools, and fecal quality remained within acceptable ranges.
Overall, when used within appropriate formulation ranges, inulin offers meaningful benefits, whereas excessive inclusion should be avoided.
Comparison and Combination with Other Prebiotics
Inulin is frequently used in combination with other prebiotics such as fructooligosaccharides (FOS) and mannan oligosaccharides (MOS). Combining multiple prebiotic ingredients may produce synergistic effects, leading to greater improvements in gut microbiota composition and immune parameters than single-ingredient supplementation.
For example, studies using FOS + MOS blends have shown greater increases in Bifidobacterium, enhanced neutrophil activity, and reductions in blood cholesterol and phenolic metabolites compared with single-component treatments.
In trials involving chicory-derived inulin and MOS—either alone or in combination—elderly dogs exhibited increased Bifidobacterium counts and reduced Escherichia coli populations.
From a practical formulation perspective, these findings support the development of multi-component prebiotic systems, or even synbiotic designs incorporating probiotics alongside inulin.
Processing Stability and Effects on Palatability
Inulin is relatively heat-stable and remains largely intact under neutral conditions at temperatures up to approximately 100°C. Although partial hydrolysis may occur during extrusion processing (typically 120–150°C), inulin generally retains its functional properties under standard pet food manufacturing conditions.
However, degradation into fructose or glucose may occur under acidic conditions, excessive temperatures, or prolonged heating. Therefore, careful control of pH, temperature, and residence time during processing is recommended.
From a sensory standpoint, low-molecular-weight inulin exhibits mild sweetness—approximately 30–35% of sucrose—and can contribute to improved flavor and texture when included at appropriate levels. In contrast, long-chain inulin provides minimal sweetness and primarily contributes to viscosity and water-holding capacity.
Importantly, reports of reduced palatability due to inulin inclusion in dog foods are limited, suggesting that inulin can be effectively utilized as a functional ingredient without negatively impacting acceptance.
Species- and Age-Related Differences in Response
Dogs are generally considered omnivorous and tend to ferment dietary fiber more efficiently, whereas cats are obligate carnivores with comparatively limited fiber fermentation capacity.
Consistent with this, studies in cats have demonstrated increased SCFA production—particularly butyrate—following inulin supplementation, while canine studies show more variable SCFA responses depending on breed and basal diet composition.
Regarding age, most available research has focused on healthy adult dogs and cats. Data on puppies, kittens, and geriatric animals remain limited. Jeusette and colleagues explicitly noted that findings based on healthy middle-aged cats cannot be directly extrapolated to younger or older populations.
Nevertheless, studies involving senior dogs (8–11 years old) have shown increased beneficial bacteria following supplementation with chicory fiber and MOS, suggesting that gut health modulation remains feasible even in older animals.
Overall, while the fundamental mechanisms of inulin appear similar in dogs and cats, differences in response magnitude by species and age remain an important area for future research.