Sex differences modulating serotonergic polymorphisms implicated in the mechanistic pathways of risk for depression and related disorders.

Despite consistent observations of sex differences in depression and related emotional disorders, we do not yet know how these sex differences modulate the effects of genetic polymorphisms implicated in risk for these disorders. This Mini-Review focuses on genetic polymorphisms of the serotonergic system to illustrate how sex differences might modulate the neurobiological pathways involved in the development of depression. We consider the interacting role of environmental factors such as early-life stress. Given limited current knowledge about this topic, we highlight methodological considerations, challenges, and guidelines for future research. © 2016 Wiley Periodicals, Inc.

Apparent total tract nutrient digestibility and metabolizable energy estimation in commercial fresh and extruded dry kibble dog foods.

Commercial fresh cooked foods have started gaining popularity among American dog owners in recent years. However, nutrient digestibility and the estimation of metabolizable energy (ME) of commercial fresh dog foods remain inadequately understood, even though both measures are critical to provide the intended calories for the target animal. In this preliminary study, different cohorts of normal-weight dogs were fed one of five test diets of comparable macronutrient composition: a chicken-based extruded dry kibble diet (n = 12), and chicken- (n = 12), beef- (n = 6), pork- (n = 6), or turkey-based fresh food (n = 6) for 10 d. Daily food intake and fecal characteristics were recorded, and fecal samples were collected for nutrient analysis. Despite comparable dry matter (DM) and caloric intakes between the two chicken-based diets, the fresh diet led to lower defecation frequency (1.2 ± 0.2 vs. 1.7 ± 0.5 times/d, adjusted P < 0.001), lower fecal DM (24 ± 8 vs. 47 ± 10 g/d, adjusted P < 0.001), and lower fecal calories (92 ± 31 vs. 189 ± 43 kcal/d, adjusted P < 0.001) than the kibble diet. The apparent total tract digestibility of DM, protein, fat, nitrogen-free extract, and calories of the kibble diet were all significantly lower than any of the fresh diets (adjusted P < 0.001 for all). Measured ME per food DM in all of the fresh diets, except the pork-based recipe, was significantly higher than that of the kibble diet (adjusted P < 0.001 for all). For the kibble diet, the modified Atwater calculation underestimated the ME and the NRC 2006 calculation was the most accurate predictor of ME. The standard Atwater calculation performed best for the two fresh diets that had the highest fat content (chicken, beef) and the NRC 2006 calculation performed best for the fresh diet that had the highest protein content (pork). ME of the turkey-based diet was equally overestimated and underestimated with the standard Atwater and NRC 2006 methods, respectively. We propose that commercial and home-prepared fresh diets should be assessed using standard Atwater factors as commonly done in human nutrition, or preferably for commercial products, by direct measurement in conforming feeding trials.

Heterogeneity of gut microbial responses in healthy household dogs transitioning from an extruded to a mildly cooked diet.

BACKGROUND: The gut microbiota (GM) is associated with canine health and can be impacted by diet. Dog owners in the U.S. have increasingly shown an interest in feeding their dogs a mildly cooked (MC) diet. However, its impact on canine GM and health remains largely unknown. METHODS: Healthy household dogs were tracked upon switching from various brands of extruded to MC diets for four weeks. A health assessment was completed and stool samples were collected by each owner before (day 0) and after the diet transition (day 28). Shotgun metagenomic sequencing was performed at both time points to characterize the GM. RESULTS: Dogs completed the study by either completing the health assessments (n = 31) or providing stool samples at both time points (n = 28). All owners reported either better or no change in overall health at the end of the study (61% and 39%, respectively), and none reported worse overall health. Defecation frequency was also reported to be lower (58%) or about the same (35%). Principal coordinate (PCo) analysis showed a significant shift (p = 0.004) in the ß-diversity of the GM upon diet transition (34.2% and 10.3% explained by the first two axes). The abundances of 70 species increased after the diet change (adjusted p < 0.05), 67% and 24% of which belonged to the Lactobacillales and the Enterobacterales orders respectively. The abundances of 28 species decreased (adjusted p < 0.05), 46%, 18%, and 11% of which belonged to the Clostridiales, Bacillales, and Bacteroidales orders, respectively. Lower Lactobacillales and Enterobacterales, and higher Bacteroidales at baseline were associated with a greater shift along the PCo1 axis. Protein content of the baseline diet was correlated with the shift along the PCo1 axis (ρ = 0.67, p = 0.006). CONCLUSION: Owners reported either improvement or no change in health in dogs transitioning from extruded kibble to MC diets for 4 weeks, but this report of health perception requires further exploration in a controlled trial. Diet change also led to a significant shift in the GM profile of healthy dogs. The magnitude of shift was associated with baseline GM and dietary protein, and warrants further examination of individualized responses and personalized nutrition in companion dogs. These results also support future investigation of the impact of a MC diet on health maintenance given its increasing popularity.

The microbiota of healthy dogs demonstrates individualized responses to synbiotic supplementation in a randomized controlled trial.

BACKGROUND: Probiotics have been demonstrated to ameliorate clinical signs of gastrointestinal diseases in dogs in various studies. However, the effect of probiotics in a healthy population, as well as factors contributing individualized responses, remain largely unknown. This trial examined gut microbiota (GM) and health outcomes in household dogs after synbiotic (SN) supplementation containing probiotics and inulin (a prebiotic). Healthy dogs were randomized to receive SN (50 mg/d inulin and 20 billion total CFU/d of L. reuteri, P. acidilactici, E. faecium, L. acidophilus, B. animalis, L. fermentum, L. rhamnosus) or placebo (PL) for 4 weeks. Owners completed a health survey and collected stool samples for GM profiling (shotgun metagenomic sequencing) at baseline and week 4 in both groups, and at week 6 in the SN group. RESULTS: A significant shift (p < 0.001) in ß-diversity was observed in the SN (n = 24), but not PL group (n = 19), at week 4 relative to baseline. Forty-five bacterial species, 43 (96%) of which were Lactobacillales, showed an increase in the relative abundances (≥2 fold change, adjusted p < 0.05) in the SN group at week 4. E. coli also decreased at week 4 in the SN group (2.8-fold, adjusted p < 0.01). The altered taxa largely returned to baseline at week 6. The degree of changes in ß-diversity was associated with GM at baseline. Specifically, dogs with higher Proteobacteria and lower Lactobacillales responded more robustly to supplementation in terms of the change in ß-diversity. Dogs fed SN tended to have lower diarrhea incidence (0% vs 16%, p = 0.08). CONCLUSIONS: SN supplement had a short-term impact on the gut microbiota in healthy household dogs as characterized by shotgun metagenomic sequencing. Findings warrant further investigation with longer duration and populations at risk of gastrointestinal diseases. The magnitude of response to the supplement was associated with microbial profile at baseline. To our knowledge, this is the first study documenting such association and may provide a basis for personalized nutrition in companion dogs.