Single-cell protein from Paecilomyces variotii in dog diets: digestibility, palatability and fecal microbiota
Inclusion of 4–8% single-cell protein (SCP) from P. variotii in extruded diets linearly reduces apparent macronutrient digestibility in a dose-dependent manner but favorably shifts fecal microbiota and fermentative metabolites without impairing palatability.
| Population | Healthy adult Beagle dogs (n=15 in Exp. I; n=16 in Exp. II; n=12 in Exp. III) |
|---|---|
| Intervention | Extruded diets containing 4%, 8%, 12%, or 16% SCP from P. variotii |
| Comparator | Control diet without SCP (0%) |
| Outcome | Apparent total tract digestibility of diet dry matter; Metabolizable energy of the diet; Diet palatability; Fecal short-chain fatty acids (propionate, butyrate, total SCFA); Fecal branched-chain fatty acids (isobutyrate, total BCFA); Fecal microbiota alpha-diversity; Fecal abundance of taxa of interest (Lactobacillus, Butyricicoccus, Enterococcus, Enterocloster) |
Summary of findings
| Outcome | Effect | 95% CI | Certainty | Clinical relevance | Notes |
|---|---|---|---|---|---|
| Apparent total tract digestibility of diet dry matter | linear decrease with SCP inclusion 0-16%, p<0.05; in the effect size or 95% CI reported | — | Low | — | 1 studies |
| Metabolizable energy of the diet | linear decrease with SCP inclusion 0-16%, p<0.05; in the effect size or 95% CI reported | — | Low | — | 1 studies |
| Diet palatability | no significant difference between 0% vs 4%, 0% vs 8%, 4% vs 16% SCP; in the effect size or 95% CI reported | — | Low | — | 1 studies |
| Fecal short-chain fatty acids (propionate, butyrate, total SCFA) | quadratic effect with SCP inclusion, p<0.05; in the effect size or 95% CI reported | — | Low | — | 1 studies |
| Fecal branched-chain fatty acids (isobutyrate, total BCFA) | linear increase with SCP inclusion, p<0.05; in the effect size or 95% CI reported | — | Low | — | 1 studies |
| Fecal microbiota alpha-diversity | increase at 8% SCP vs 0%, p<0.05; in the effect size or 95% CI reported | — | Low | — | 1 studies |
| Fecal abundance of taxa of interest (Lactobacillus, Butyricicoccus, Enterococcus, Enterocloster) | higher Lactobacillus and Butyricicoccus, lower Enterococcus and Enterocloster at 8% vs 0% SCP, p<0.05; in the effect size or 95% CI reported | — | Low | — | 1 studies |
Context
The pet food industry is pursuing alternative protein sources with lower environmental footprints. SCP from filamentous fungi offers high substrate conversion efficiency and season-independent production. Data on digestibility, safety, and intestinal effects in dogs remain scarce.
What the study showed
SCP ATTD values were: DM 64.3%, CP 83.9%, AHEE 78.3%, and ME 3843.3 kcal/kg. ATTD of DM, OM, gross energy, and ME of complete diets decreased linearly as SCP inclusion increased from 0 to 16% (p<0.05); no 95% CI was reported. Quadratic effects were found for fecal propionate, butyrate, and total SCFA; linear increases were observed for isobutyrate and total BCFA (p<0.05). At 8% SCP, alpha-diversity increased (p<0.05) with higher Lactobacillus and Butyricicoccus and lower Enterococcus and Enterocloster versus 0% (p<0.05).
How it was done
Three independent experiments: Exp. I — randomized block design with 15 Beagles, 5 diets (0–16% SCP), 2 periods of 21 days (n=6/treatment); Exp. II — palatability test with 16 dogs comparing diet pairs; Exp. III — substitution method (80:20) with 12 Beagles to estimate isolated SCP digestibility and ME. No formal sample size calculation was described.
Effect magnitude
Linear decrease in diet ATTD of DM and ME with increasing SCP, but no standardized effect size or 95% CI was reported. Microbial effects were restricted to 4% vs. 0% and 8% vs. 0% comparisons, with no absolute magnitude data for taxonomic abundances.
Risk of bias
Small sample (n=6/treatment in Exp. I) without reported power calculation — risk of type II error for microbial outcomes. No risk-of-bias tool was applied (RoB 2 not applicable; absence of blinding and funder conflict of interest — FS Fueling Sustainability — raise performance and reporting bias risk). Metabolites and microbiota assessed by fecal samples only, without intestinal biopsies. The 21-day duration is insufficient to assess chronic effects.
What this study does NOT prove
This study does not prove clinical benefit for intestinal health or causality between SCP and functional microbial modulation. Results are not generalizable to dogs with gastrointestinal disease, non-Beagle breeds, or wet diets.
In clinical practice
SCP from P. variotii is technically feasible as an ingredient in canine diets at up to 8% without palatability loss. Clinicians should note that diet digestibility decreases linearly with inclusion, potentially requiring energy formulation adjustment. Microbiota effects are preliminary and insufficient to support therapeutic claims.
Limitations
Small sample (n=6/treatment in Exp. I) without reported power calculation — risk of type II error for microbial outcomes. No risk-of-bias tool was applied (RoB 2 not applicable; absence of blinding and funder conflict of interest — FS Fueling Sustainability — raise performance and reporting bias risk). Metabolites and microbiota assessed by fecal samples only, without intestinal biopsies. The 21-day duration is insufficient to assess chronic effects.
What is still missing
Long-term studies (≥6 months) in diverse canine populations, with intestinal health assessment via histology and systemic biomarkers, are needed to establish safety and efficacy under clinical conditions.
Technical appendix
Version history
- 1.0 · 2026-06-27 — Auto-generated under Evidence Standard v1.0