Dietary Fish Oil and Medium Chain Triglycerides Together Modulate Feline Gut Microbiome Function but not Composition
Authors: Jackson Matthew Irick , Jewell Dennis E. 
Published: April 2020

ObjectivesWe previously reported that dietary combination of fish oil (FO) and medium chain triglycerides (MCT) decreases blood levels of feline gut microbial metabolites (postbiotics). The objective of the current study was to assess the effect of these oils in combination on the composition of the feline fecal microbiome as well as fecal levels of microbial postbiotics.MethodsRandomized crossover design with two groups, Control group (CON, n = 15) which contained no added dietary MCT or FO versus Test group (FO/MCT, n = 16) whose food contained 0.4% n3‐eicosapentaenoate and 0.3% n3‐docosahexaenoate from FO as well as 3.6% caprylate and 2.7% caprate from MCT. Cats were fed for 6 weeks and group or individually housed in environments promoting social interaction, having access to natural light that varied with season and opportunity to exercise. Health was confirmed through clinical indices. Collections were under IACUC approved protocols. Cats were fed to maintain healthy body weight. Serum and fecal samples were assessed for gut microbiome postbiotics by LC‐MS. Composition of fecal gut microbiome was assessed by sequencing of the V3‐V4 region of 16S ribosomal DNA. Univariate paired t‐tests were performed on log‐transformed serum and fecal metabolites as well as Aitchison‐transformed microbiome counts at the genera level. Significance was set at alpha = 0.05 with FDR correction.ResultsThe results showed that FO/MCT intervention decreased circulating microbial‐derived indole and phenolic postbiotics in serum as well as feces; both unconjugated and host‐sulfated postbiotics were reduced. Dietary FO/MCT also induced a broad reduction in fecal endocannabinoid immune modulators that may be produced by gut microbes; stearoyl‐, palmitoyl‐, oleoyl‐, docosahexaenoyl‐ and arachidonoyl‐ ethanolamides were decreased. Unexpectedly, fecal microbiome composition at the genera level was not markedly different when FO/MCT was consumed, even though fecal microbial postbiotics were broadly decreased. There was no effect of diet order in the crossover design, indicating that the effect of FO/MCT to reduce serum and fecal postbiotics was reversible.ConclusionsSince microbial postbiotics were decreased in feces, the proxy for colonic site of postbiotic production, the effect of FO/MCT did not appear to stem from an effect on host absorption of postbiotics into serum. As well, it is not likely that FO/MCT decreased host conjugation of postbiotics since both sulfated and non‐sulfated postbiotic forms were reduced. The effect on serum postbiotics appears to be a general phenomenon, as both the feline subjects and sources of oils were different from our previously reported study which did not examine feces. Since relative abundances of microbial genera were largely not impacted by diet, it would appear that FO/MCT intervention in cats alters microbial function without modulating microbial populations per se. In summary, the combination of dietary FO/MCT may provide an effective means to reversibly reduce production of postbiotics by gut microbes.Support or Funding InformationHill’s Pet Nutrition, Inc. Topeka, Kansas, USA