Skip to main content
NCBI home page
Journal of Animal Science logoLink to Journal of Animal Science
. 2021 Jan 29;99(2):skab028. doi: 10.1093/jas/skab028

Nutrient digestibility and fecal characteristics, microbiota, and metabolites in dogs fed human-grade foods

Sungho Do 1, Thunyaporn Phungviwatnikul 1, Maria R C de Godoy 1,2, Kelly S Swanson 1,2,3,✉
PMCID: PMC8611730  PMID: 33511410

Abstract

Human-grade (HG) pet foods are commercially available, but they have not been well studied. Our objective was to determine the apparent total tract digestibility (ATTD) of HG pet foods and evaluate their effects on fecal characteristics, microbiota, and metabolites, serum metabolites, and hematology of dogs. Twelve dogs (mean age = 5.5 ± 1.0; BW = 11.6 ± 1.6 kg) were used in a replicated 4 × 4 Latin square design (n = 12/treatment). The diets included 1) Chicken and Brown Rice Recipe (extruded; Blue Buffalo); 2) Roasted Meals Tender Chicken Recipe (fresh; Freshpet); 3) Beef and Russet Potato Recipe (HG beef; JustFoodForDogs); and 4) Chicken and White Rice Recipe (HG chicken; JustFoodForDogs). Each period consisted of 28 d, with a 6-d diet transition phase, 16 d of consuming 100% of the diet, a 5-d phase for fecal collection, and 1 d for blood collection. All data were analyzed using the Mixed Models procedure of SAS 9.4. Dogs fed the extruded diet required a higher (P < 0.05) daily food intake (dry matter basis, DMB) to maintain BW. The ATTD of dry matter (DM), organic matter (OM), energy, and acid-hydrolyzed fat (AHF) were greater (P < 0.05) in dogs fed the HG diets than those fed the fresh diet, and greater (P < 0.05) in dogs fed the fresh diet than those fed the extruded diet. Crude protein ATTD was lower (P < 0.05) for dogs fed the extruded diet than those fed all other diets. Dogs fed the extruded diet had greater (P < 0.05) fecal output (as-is; DMB) than dogs fed fresh (1.5–1.7 times greater) or HG foods (2.0–2.9 times greater). There were no differences in fecal pH, scores, and metabolites, but microbiota were affected by diet. Dogs fed HG beef had higher (P < 0.05) relative abundance of Bacteroidetes and lower (P < 0.05) relative abundance of Firmicutes than dogs fed the fresh or HG chicken diets. The Actinobacteria, Fusobacteria, Proteobacteria, and Spirochaetes phyla were unchanged (P > 0.05), but diet modified the relative abundance of nearly 20 bacterial genera. Similar to previous reports, these data demonstrate that the fecal microbiota of dogs fed HG or fresh diets is markedly different than those consuming extruded diets, likely due to ingredient, nutrient, and processing differences. Serum metabolites and hematology were not greatly affected by diet. In conclusion, the HG pet foods tested resulted in significantly reduced fecal output, were highly digestible, maintained fecal characteristics, serum chemistry, and hematology, and modified the fecal microbiota of dogs.

Keywords: canine gut microbiome, canine nutrition, nutrient digestion, pet food

Introduction

The relationship between humans and companion animals is similar to that among humans. The majority of today’s pet owners treat their animals as valued family members, coworkers, and friends (Mosteller, 2008). For instance, over 10 million dogs and cats in the United States have a birthday celebration each year, and over 20 million dogs are reported to sleep in bed with their owners. Other behaviors that are suggestive of pet humanization are that pet animals have names and many owners allow pet animals to access all rooms of their house, so they can spend much of their time with them (Sanders, 1990). Not surprisingly, the evolution of the pet–human relationship has greatly influenced the pet food industry in recent years.

There are many different factors (life stage, breed, or health status of animal; diet price; diet format; ingredient profile) that affect what owners choose to feed their pet animals. Because pets are increasingly regarded as family members, many pet food trends follow human food trends, especially those that focus on health and wellness (Sharon et al., 2018). This change in behavior by pet owners has lead to the exclusion of certain ingredients, such as animal byproducts, corn, soy, and artificial additives by some. Those ingredients are considered to be lower quality or of poor nutritional value for animals by many pet owners (Carter et al., 2014), so there has been an increased desire to purchase certain segments of pet food manufactured using organic, holistic, natural, or human-grade (HG) ingredients.

According to the Association of American Feed Control Officials (AAFCO), the use of the “human-grade” term is only acceptable when the product is manufactured following federal regulations for current good manufacturing practices for human edible foods in 21 CFR part 117 (AAFCO, 2017). To be approved, the manufacturing facility must be inspected and licensed to produce human food by appropriate authorities (local, county, or state public health authorities). Despite the challenges that have occurred in regard to facility inspection and certification, HG foods are now commercially available.

Unfortunately, little research has been performed on the HG dog food formats mentioned above. Therefore, the objective of this study was to determine the apparent total tract digestibility (ATTD) of macronutrients, fecal characteristics, microbiota, and metabolites, serum metabolites, and hematology of dogs fed extruded, fresh, and HG dog diets. We hypothesized that dogs fed HG foods would have greater ATTD and lead to lower fecal output compared with extruded and fresh diets. We also hypothesized that HG foods would have no negative effects on fecal characteristics, serum chemistry, or hematology, but lead to a reduction in fecal metabolites and altered fecal microbiota due to their higher digestibility.

Materials and Methods

All procedures were approved by the University of Illinois Institutional Animal Care and Use Committee prior to experimentation. All methods were performed in accordance with the United States Public Health Service Policy on Humane Care and Use of Laboratory Animals.

Animals and housing

Twelve healthy adult beagle dogs (mean age = 5.5 ± 1.0 yr; BW = 11.6 ± 1.6 kg) were used in a replicated 4 × 4 Latin square design (n = 12/treatment). All dogs were housed individually in pens (approximately 1.2 m wide × 2.4 m long) during the study. Dogs had free access to fresh water at all times. Dogs were provided with toys for behavioral enrichment at all times and exercised outside of their cages and socialized with each other and humans for approximately 1 h at least 3 d/wk. On the basis of the maintenance energy requirement for adult dogs (National Research Council, 2006) and information from previous feeding records, an amount of food to maintain BW was offered and intake was measured twice daily (8 am and 5 pm).

Experimental periods and diets

The experiment was composed of four 28-d periods, with each consisting of a 7-d diet transition phase, 16 d consuming 100% of the diet, a 5-d fecal collection phase, and 1 d for blood collection. The diets included 1) Life Protection Formula Chicken and Brown Rice Recipe (extruded; Blue Buffalo, Wilton, CT); 2) Roasted Meals Tender Chicken Recipe with Garden Vegetables (fresh; Freshpet, Secaucus, NJ); 3) Beef and Russet Potato (HG beef; JustFoodForDogs, Irvine, CA); 4) Chicken and White Rice (HG chicken; JustFoodForDogs, Irvine, CA). Dogs were weighed and body condition scores were assessed (9-point scale) once a week prior to the 8 am feeding. All dietary treatments were formulated to meet all AAFCO (2019) nutrient recommendations for adult dogs at maintenance or tested using AAFCO feeding trials.

Diet adaptation: dogs were adapted to the new dietary treatment at the beginning of each experimental period using the following feeding protocol:

  • Days 1–2: 75% kcal from prior dietary treatment + 25% kcal from new dietary treatment

  • Days 3–4: 50% kcal from prior dietary treatment + 50% kcal from new dietary treatment

  • Days 5–6: 25% kcal from prior dietary treatment + 75% kcal from new dietary treatment

  • Days 7–28: 100% kcal from new dietary treatment

Sample collection

During the fecal collection phase, total fecal samples were collected, weighed, and scored using the following scale: 1 = hard, dry pellets, small hard mass; 2 = hard, formed, dry stool; remains firm and soft; 3 = soft, formed, and moist stool, retains shape; 4 = soft, unformed stool, assumes shape of container; and 5 = watery, liquid that can be poured. Samples were then frozen at −20 °C until further analysis. Fresh feces (within 15 min) were collected for measurement of pH, moisture content, microbiota populations, and metabolite concentrations. Fecal pH was measured immediately using an AP10 pH meter (Denver Instrument, Bohemia, NY) equipped with a Beckman Electrode (Beckman Instruments Inc., Fullerton, CA) and then aliquots were collected. Fecal metabolites included short-chain fatty acids (SCFA) and protein fermentative products [ammonia; branched-chain fatty acids (BCFA); phenols; indoles]. Fecal aliquots (2 tubes/dog; ~2 g/tube) for analysis of phenols and indoles were frozen at −20 °C immediately after collection. One aliquot (~5 g per dog) was collected and placed in 2 N hydrochloric acid for ammonia, SCFA, and BCFA analyses. An additional aliquot was used for fresh fecal dry matter (DM) determination (2 preweighed pans/dog; 1–2 g/pan). Four aliquots of fresh feces were collected for microbiota analysis. Those samples were immediately transferred to sterile cryogenic vials (Nalgene, Rochester, NY), quickly frozen in dry ice, and stored at −80 °C until analysis.

On the last day of each period, approximately 5 mL of blood was collected via jugular or cephalic puncture. Dogs were fasted for 12 h overnight prior to blood collection, but had free access to water at all times. Samples were immediately transferred to appropriate vacutainer tubes: 1) 4.5 mL in no. 368660 BD Vacutainer Plus plastic serum tube with clot activator and gel for serum separation (Becton Dickinson, Franklin Lakes, NJ) for serum chemistry profile and 2) 0.5 mL in no. 365974 BD Microtainer Capillary blood collector with K2EDTA additive (Becton Dickinson, Franklin Lakes, NJ) for hematology.

Chemical analysis and apparent total tract macronutrient digestibility calculations

Diet subsamples were collected. The fresh, HG beef, and HG chicken diets were first lyophilized, then all diets were ground through a 2-mm screen using a Wiley Mill (model 4, Thomas Scientific, Swedesboro, NJ), with dry ice to allow for proper grinding before analysis. Total fecal samples were composited and dried at 57 °C for a week. Fecal samples were then ground through a 2-mm screen using a Wiley Mill (model 4). DM and organic matter (OM) concentrations were analyzed according to the Association of Official Analytical Chemists (AOAC, 2006; DM: method 934.01; OM: method 942.05). Fat concentrations were measured by acid hydrolysis according to the AACC (1983) followed by diethyl ether extraction (Budde, 1952). Crude protein (CP) concentration was calculated from Leco total nitrogen values (TruMac N, Leco Corporation, St. Joseph, MI; AOAC, 2006). Gross energy was measured using an oxygen bomb calorimeter (model 1261, Parr Instruments, Moline, IL). Total dietary fiber concentrations of the diet samples were determined according to Prosky et al. (1985; Methods 985.29 and 991.43). Apparent total tract macronutrient digestibility of nutrients and energy was calculated using the following equation: Digestibility (%) = [Nutrient intake (g/d) − Fecal output (g/d)]/Nutrient intake (g/d) × 100%.

Fecal metabolites

Fecal SCFA (acetate, propionate, and butyrate) and BCFA (valerate, isovalerate, and isobutyrate) concentrations were determined by gas chromatography according to Erwin et al. (1961). During analyses, a gas chromatograph (Hewlett-Packard 5890A series II, Palo Alto, CA) and a glass column (180 cm × 4 mm i.d.) packed with 10% SP-1200/1% H3PO4 on 80/100 mesh Chromosorb WAW (Supelco Inc., Bellefonte, PA) were used. Nitrogen was the carrier gas with a flow rate of 75 mL/min. Temperatures of the oven, detector, and injector were 125, 175, and 180 °C, respectively. Fecal ammonia concentrations were determined according to the method of Chaney and Marbach (1962). Fecal phenol and indole concentrations were evaluated by gas chromatography according to Flickinger et al. (2003).

Fecal DNA extraction and sequencing

Total DNA from fecal samples were extracted using Mo-Bio PowerSoil Kits (MO BIO Laboratories, Inc., Carlsbad, CA), followed by quantification of extracted DNA using a Qubit 3.0 Fluorometer (Life Technologies, Grand Island, NY). Quality of extracted DNA was assessed by electrophoresis using agarose gels (E-Gel EX Gel 1%; Invitrogen, Carlsbad, CA). DNA samples were sent to CosmosID (Rockville, MD) for metagenomic library creation and shotgun sequencing. DNA libraries were prepared using the Illumina Nextera XT library preparation kit (Illumina, San Diego, CA), with a modified protocol. Libraries were then sequenced on an Illumina HiSeq platform (2 × 150 bp).

Bioinformatics

Unassembled sequencing reads were directly analyzed by CosmosID bioinformatics platform (CosmosID Inc., Rockville, MD) described elsewhere (Hasan et al., 2014; Lax et al., 2014; Ottesen et al., 2016; Ponnusamy et al., 2016) for microbiome analysis and profiling of organism relative abundance. An average of 4.3 million reads per sample was obtained. α-Diversity was estimated using Chao1, the Shannon Index, and the Simpson Index. β-Diversity was calculated using Jaccard distance measures and presented using a principal coordinates analysis plot.

Serum chemistry and hematology

Serum chemistry profile and hematology were analyzed using a Hitachi 911 clinical chemistry analyzer (Roche Diagnostics, Indianapolis, IN) at the University of Illinois Veterinary Medicine Diagnostics Laboratory.

Statistical analyses

All data were analyzed using the Mixed Models procedure of SAS (version 9.4; SAS Institute, Cary, NC) with treatment as a fixed effect and dog and period as random effects. Differences between treatments were determined using a Fisher-protected least significant difference with a Tukey’s adjustment to control for experiment-wise error. A probability of P < 0.05 was accepted as being statistically significant.

Results

Chemical composition

The chemical composition of the diets tested is presented in Table 1. The DM content was highest in the extruded diet [91.01% dry matter basis (DMB)] followed by the fresh (41.13% DMB) and HG foods [30.61% (beef) and 31.18% (chicken) DMB]. On a DMB, the HG foods [95.65% (beef) and 93.88% (chicken)] and extruded diet (93.63%) had a similar OM content, but the fresh diet (86.38%) had a lower OM content. The acid-hydrolyzed fat (AHF), gross energy, and digestible energy were highest for the HG beef diet (37.04%, 6.58 kcal/g, and 6.24 kcal/g DMB) and lowest for the extruded diet (14.25%, 5.12 kcal/g, and 4.43 kcal/g DMB) and HG chicken diet (14.57%, 5.03 kcal/g, and 4.74 kcal/g DMB). The fresh diet had the highest CP (36.41% DMB), followed by the HG foods [29.62% (beef) and 29.53% (chicken) DMB], and was lowest in the extruded diet (26.46% DMB). In terms of dietary fiber, similarities were observed in the HG foods that contained the lowest concentrations [7.02% (beef) and 7.09% (chicken) DMB], the fresh diet had an intermediate concentration (11.63% DMB), and the extruded diet had the highest concentration (14.22% DMB).

Table 1.

Chemical composition of diets fed to healthy adult dogs

Treatment
Item Extruded1 Fresh2 HG beef3 HG chicken4
DM, % 91.01 41.13 30.61 31.18
------ DM basis ------
OM, % 93.63 86.38 95.65 93.88
Ash, % 6.37 13.62 4.35 6.12
Acid-hydrolyzed fat, % 14.25 25.54 37.04 14.57
CP, % 26.46 36.41 29.62 29.53
Total dietary fiber, % 14.22 11.63 7.02 7.09
Gross energy, kcal/g 5.12 5.40 6.58 5.03
Digestible energy, kcal/g5 4.43 4.97 6.24 4.74
Open in a new tab

1Extruded diet: deboned chicken, chicken meal, brown rice, barley, oatmeal, pea starch, flaxseed, chicken fat (preserved with mixed tocopherols), dried tomato pomace, natural flavor, peas, pea protein, salt, potassium chloride, dehydrated alfalfa meal, potatoes, dried chicory root, pea fiber, alfalfa nutrient concentrate, calcium carbonate, choline chloride, dl-methionine, preserved with mixed tocopherols, dicalcium phosphate, sweet potatoes, carrots, garlic, zinc amino acid chelate, zinc sulfate, vegetable juice for color, ferrous sulfate, vitamin E supplement, iron amino acid chelate, blueberries, cranberries, barley grass, parsley, turmeric, dried kelp, yucca schidigera extract, niacin (vitamin B3), glucosamine hydrochloride, calcium pantothenate (vitamin B5), copper sulfate, biotin (vitamin B7), L-ascorbyl-2-polyphosphate (source of vitamin C), l-lysine, l-carnitine, vitamin A supplement, copper amino acid chelate, manganese sulfate, taurine, manganese amino acid chelate, thiamine mononitrate (vitamin B1), riboflavin (vitamin B2), vitamin D3 supplement, vitamin B12 supplement, pyridoxine hydrochloride (vitamin B6), calcium iodate, dried yeast, dried Enterococcus faecium fermentation product, dried Lactobacillus acidophilus fermentation product, dried Aspergillus niger fermentation extract, dried Trichoderma longibrachiatum fermentation extract, dried Bacillus subtilis fermentation extract, folic acid (vitamin B9), sodium selenite, and oil of rosemary.

2Fresh diet: chicken, ground oats, chicken liver, rice bran, eggs, carrots, natural flavors, spinach, salt, vinegar, β-carotene, celery powder, choline chloride, vitamin E supplement, niacin, calcium pantothenate, biotin, riboflavin, thiamine mononitrate, vitamin B12 supplement, pyridoxine hydrochloride, folic acid, zinc proteinate, iron proteinate, manganese proteinate, copper proteinate, sodium selenite, and calcium iodate.

3Human-grade beef diet (HG beef): ground beef, russet potatoes, sweet potatoes, green beans, carrots, safflower oil, beef liver, green peas, apples, Icelandic premium EPA and DHA, natural calcium, phosphorus amino acid chelate, magnesium bisglycinate chelate, taurine, choline chloride, natural kelp, vitamin E, biotin, selenium amino acid chelate, manganese bisglycinate chelate, zinc oxide, vitamin D3, vitamin B1, and riboflavin.

4Human-grade chicken diet (HG chicken): chicken thigh, long grain white rice, spinach, carrots, apples, chicken gizzard, chicken liver, Icelandic premium EPA and DHA, calcium pyrophosphate, natural calcium, choline bitartrate, natural kelp, magnesium bisglycinate chelate, iron bisglycinate chelate, copper bisglycinate chelate, vitamin D3, vitamin B12, and riboflavin.

5Digestible energy measured by gross energy—fecal energy.

Food intake, fecal output, and apparent total tract macronutrient digestibility

Dogs fed the HG foods had a higher (P < 0.05) daily as-is food intake than dogs fed fresh or extruded diets (Table 2). Moreover, dogs fed the fresh diet had a higher (P < 0.05) daily as-is food intake than dogs fed the extruded diet. However, dogs fed the extruded diet had a higher (P < 0.05) daily DM food intake than dogs fed the fresh or HG foods. Moreover, dogs fed the fresh diet had a higher (P < 0.05) daily DM food intake than dogs fed the HG foods. The caloric intake (kcal/d) of dogs fed the extruded diet was greater (P < 0.05) than those fed the fresh or HG foods, and was greater (P < 0.05) for dogs fed the fresh diet or HG beef diet than those fed the HG chicken diet. Daily fecal output (as-is, DMB, kcal) was greater (P < 0.05) in dogs fed the extruded diet than dogs fed the fresh or HG foods. Similarly, dogs fed the fresh diet had a higher (P < 0.05) daily fecal output (as-is, DMB, kcal) than dogs fed the HG foods. Apparent total tract digestibility of DM, OM, and energy was greater (P < 0.05) for dogs fed the HG foods than dogs fed the extruded or fresh diets. Likewise, dogs fed the fresh diet had a higher (P < 0.05) ATTD of DM, OM, and energy than dogs fed the extruded diet. Dogs fed the HG beef diet had greater (P < 0.05) AHF ATTD than dogs fed the fresh diet. Dogs fed the fresh or HG foods had greater (P < 0.05) AHF ATTD than dogs fed the extruded diet. Dogs fed the extruded diet had a lower (P < 0.05) ATTD of CP than dogs fed the fresh or HG foods.

Table 2.

Apparent total tract macronutrient digestibility and food intake and fecal output of adult dogs fed an extruded dry kibble diet, a fresh roasted diet, or human-grade foods

Treatment1
Item Extruded Fresh HG beef HG chicken SEM P-value
Food intake
 g food/d (as-is) 188.13c 357.83b 396.67a 410.83a 14.059 <0.001
 g food/d (DM basis) 171.21a 147.19b 121.40c 128.10c 3.665 <0.001
 kcal/d 876.59a 794.85b 798.81b 644.36c 17.637 <0.001
Fecal output
 g feces/d (as-is) 95.92a 64.35b 47.72c 39.37c 3.727 <0.001
 g feces/d (DM basis) 31.85a 19.00b 11.15c 11.82c 1.393 <0.001
 kcal/d 163.09a 102.59b 73.36c 59.44c 6.866 <0.001
Digestibility
 DM, % 81.47c 87.14b 90.84a 90.71a 0.663 <0.001
 Organic matter, % 85.38c 90.52b 92.64a 93.75a 0.551 <0.001
 Acid-hydrolyzed fat, % 93.33c 96.88b 98.57a 97.49ab 0.319 <0.001
 Crude protein, % 83.39b 93.61a 92.82a 92.77a 0.664 <0.001
 Energy, % 86.53c 91.99b 94.78a 94.27a 0.539 <0.001
Open in a new tab

1Extruded dry kibble diet (extruded); fresh roasted diet (fresh); human-grade beef diet (HG beef); human-grade chicken diet (HG chicken).

a–cWithin a row, means lacking a common superscript differ (P < 0.05).

Serum chemistry profiles and hematology

Serum chemistry profiles and hematology of dogs fed all diets were within the reference range for adult dogs, with the exception of globulin (2.5 to 2.6 g/dL; reference range: 2.7 to 4.4 g/dL), Cl (103.7 to 112.8 mmol/L; reference range: 107 to 118 mmol/L), albumin to globulin ratio (1.3 to 1.4; reference range: 0.6 to 1.1), hematocrit (50.3 to 52.6%; reference range: 35 to 52%), and white blood cell count (5.4 to 5.8 × 103/µL; reference range: 6 to 17 × 103/µL; Tables 3 and 4). Of these parameters, only hematocrit was affected by diet, with dogs fed the extruded diet having a lower (P < 0.05) percentage than dogs fed HG beef. A few other metabolites and cell counts were affected by diet, but were within reference ranges so they unlikely to have a high level of physiological relevance.

Table 3.

Serum chemistry profiles for adult dogs fed an extruded dry kibble diet, a fresh roasted diet, or human-grade foods

Treatment1
Item Reference range Extruded Fresh HG beef HG chicken SEM P-value
Creatinine, mg/dL 0.5–1.5 0.67b 0.73ab 0.88a 0.83ab 0.033 0.0254
Blood urea nitrogen, mg/dL 6–30 13.08 17.50 15.08 15.17 0.844 0.1448
Total protein, g/dL 5.1–7.0 5.94 6.00 5.91 5.89 0.051 0.3081
Albumin, g/dL 2.5–3.8 3.39ab 3.43a 3.40ab 3.30b 0.031 0.0161
Globulin, g/dL 2.7–4.4 2.55 2.57 2.51 2.59 0.033 0.5448
Albumin:globulin ratio 0.6–1.1 1.33 1.36 1.37 1.29 0.018 0.1793
Ca, mg/dL 7.6–11.4 10.06 10.03 10.08 9.92 0.105 0.5555
P, mg/dL 2.7–5.2 3.99a 3.54ab 3.17b 3.48ab 0.111 0.0020
Na, mmol/L 141–152 144.17 143.92 144.83 144.42 0.191 0.3820
K, mmol/L 3.9–5.5 4.31ab 4.41a 4.45a 4.11b 0.041 0.0005
Na:K ratio 28–36 33.58b 32.83b 32.83b 35.33a 0.328 0.0009
Cl, mmol/L 107–118 110.67 111.58 112.75 103.67 2.120 0.4081
Glucose, mg/dL 68–126 89.00y 93.50xy 94.33x 89.33xy 1.395 0.0385
Alkaline phosphatase (ALP)2, U/L 7–92 32.08a 18.92b 20.08b 32.00a 1.472 <0.0001
Corticosteroid-induced ALP, U/L 0–40 5.75 3.75 4.00 4.25 0.670 0.1273
Alanine transaminase, U/L 8–65 26.33 22.50 20.42 21.75 1.942 0.6721
Gamma glutamyltransferase, U/L 0–7 3.00 2.83 3.17 3.00 0.123 0.6517
Total bilirubin, mg/dL 0.1–0.3 0.18 0.15 0.17 0.28 0.039 0.6108
Creatine phosphokinase, U/L 26–310 110.75 129.58 165.67 149.08 13.885 0.5446
Cholesterol, mg/dL 129–297 214.33b 236.50a 209.67b 197.50b 5.761 0.0001
Triglycerides, mg/dL 32–154 77.42a 56.67b 56.67b 77.33a 2.283 <0.0001
Bicarbonate, mmol/L 16–24 20.42 19.25 19.92 20.00 0.268 0.2186
Anion gap 8–25 17.33 17.50 17.08 16.50 0.267 0.4194
Open in a new tab

1Extruded dry kibble diet (extruded); fresh roasted diet (fresh); human-grade beef diet (HG beef); human-grade chicken diet (HG chicken).

2ALP, alkaline phosphatase.

a,bWithin a row, means lacking a common superscript differ (P < 0.05).

x,yWithin a row, means lacking a common superscript differ (P < 0.10).

Table 4.

Hematology of adult dogs fed an extruded dry kibble diet, a fresh roasted diet, or human-grade foods

Treatment1
Item Reference range Extruded Fresh HG beef HG chicken SEM P-value
Red blood cells, 106/µL 5.50–8.50 7.33b 7.69a 7.74a 7.52ab 0.079 0.0109
Reticulocyte count, % — 0.40 0.47 0.41 0.44 0.034 0.4198
Hemoglobin, g/dL 12.0–18.0 17.03b 17.90a 17.94a 17.48ab 0.177 0.0254
Hematocrit, % 35.0–52.0 50.28b 52.55ab 52.66a 51.46ab 0.462 0.0261
Mean cell volume, fi 58.0–76.0 68.72a 68.39ab 68.01b 68.45ab 0.215 0.0141
Mean corpuscular hemoglobin, pg 20.0–25.0 23.26 23.30 23.17 23.27 0.096 0.5846
Mean corpuscular hemoglobin, g/dL 33.0–38.6 33.87 34.07 34.08 33.96 0.079 0.3328
White blood cells, 103/µL 6.0–17.0 5.84x 5.70xy 5.38y 5.80xy 0.189 0.0748
 Neutrophils, 103/µL 3.0–11.5 4.05 3.23 3.49 4.14 0.242 0.2728
 Neutrophils, % — 67.08 57.67 61.92 70.94 3.071 0.4330
 Lymphocytes, 103/µL 1.0–4.8 1.14 1.44 1.31 1.28 0.071 0.1794
 Lymphocytes, % — 21.08y 25.30xy 25.57x 22.67xy 1.211 0.0590
 Monocytes, 103/µL 0.20–1.4 0.26xy 0.16y 0.27x 0.24xy 0.018 0.0772
 Monocytes, % — 4.55ab 2.58b 5.2a 4.11ab 0.326 0.0252
 Eosinophils, 103/µL 0.1–1.0 0.13 0.16 0.11 0.12 0.012 0.3669
 Eosinophils, % — 2.17 2.77 2.00 2.11 0.192 0.4457
 Basophils, 103/µL 0.0–2.0 0.00 0.00 0.00 0.00 0.001 0.4018
 Basophils, % — 0.02 0.15 0.06 0.00 0.027 0.2112
Open in a new tab

1Extruded dry kibble diet (extruded); fresh roasted diet (fresh); human-grade beef diet (HG beef); human-grade chicken diet (HG chicken).

a,bWithin a row, means lacking a common superscript differ (P < 0.05).

x,yWithin a row, means lacking a common superscript differ (P < 0.10).

Fecal characteristics and metabolites

The fecal characteristics, including pH, scores, DM, and metabolite concentrations (SCFA, BCFA, phenol, indole, ammonia), are presented in Table 5. Dogs fed the extruded diet had a higher fecal DM (P < 0.05) than dogs fed the fresh or HG beef diets. Dogs fed the HG chicken or fresh diets had a higher (P < 0.05) fecal DM than dogs fed the HG beef diet. Even though macronutrient ATTD were drastically different among diets, there were no differences in fecal pH, scores, or metabolite concentrations among diets (P > 0.05).

Table 5.

Fecal characteristics and metabolites of adult dogs fed an extruded dry kibble diet, a fresh roasted diet, or human-grade foods

Treatment1
Item Extruded Fresh HG beef HG chicken SEM P-value
Fecal characteristics
 pH 6.15 6.28 6.01 5.94 0.050 0.0707
 Fecal score2 2.63 2.75 2.75 2.70 0.068 0.9049
 Fresh fecal, DM % 33.21a 29.31b 23.56c 30.76ab 0.812 <0.0001
Fecal metabolites, µmol/g DM
 Acetate 280.39 294.93 321.88 281.41 15.585 0.7559
 Propionate 148.37 130.46 158.34 140.06 11.880 0.8685
 Butyrate 61.88 63.64 66.36 62.77 6.269 0.9943
 Total SCFA3 490.64 489.04 546.58 484.24 26.624 0.8175
 Isobutyrate 5.99 5.83 5.55 5.61 0.360 0.9523
 Isovalerate 7.73 8.29 7.03 7.68 0.513 0.8034
 Valerate 1.86 0.56 1.09 1.08 0.197 0.1106
 Total BCFA3 15.57 14.68 13.66 14.37 0.891 0.8676
 Phenol 0.35 0.38 0.12 0.29 0.095 0.7634
 Indole 1.05 1.14 1.09 1.29 0.131 0.9297
 Total P/I3 1.40 1.52 1.21 1.58 0.209 0.9302
 Ammonia 98.91 118.82 112.49 101.22 4.045 0.1908
Open in a new tab

1Extruded dry kibble diet (extruded); fresh roasted diet (fresh); human-grade beef diet (HG beef); human-grade chicken diet (HG chicken).

2Fecal scores: 1, hard, dry pellets; small hard mass; 2, hard formed, remains firm and soft; 3, soft, formed and moist stool, retains shape; 4, soft, unformed stool; assumes shape of container; 5, watery, liquid that can be poured.

3Total SCFA = acetate + propionate + butyrate; total BCFA = valerate + isovalerate + isobutyrate; total P/I = phenol + indole.

a–cWithin a row, means lacking a common superscript differ (P < 0.05).

Fecal microbiota

Assessment of fecal α-diversity indices (Chao 1: 56.73 ± 1.08; Simpson index: 0.78 ± 0.02; Shannon index: 3.27 ± 0.11) showed no differences (P > 0.05) among treatments. To estimate β-diversity, the Jaccard distance based on the presence or absence of bacterial species was calculated. Fecal microbial communities of dogs fed the extruded or fresh diets were relatively close to each other, whereas dogs fed the HG foods tended to drift away and be more variable among dogs (Supplementary Figure 1).

The predominant fecal phyla of all dogs were Actinobacteria (4.75% to 11.31% of total sequences), Bacteroidetes (15.26% to 43.12%), Firmicutes (38.72% to 68.69%), Proteobacteria (4.02% to 7.84%), and Fusobacteria (0.67% to 4.97%; Table 6). At the phyla level, the relative abundance of Bacteroidetes was greater (P < 0.05) in dogs fed the HG beef diet (43.12%) than dogs fed the fresh (23.09%) or HG chicken (15.26%) diets. Dogs fed the fresh (63.18%) or HG chicken (68.69%) diets had a higher (P < 0.05) relative abundance of Firmicutes than dogs fed the HG beef (38.72%). Other bacterial phyla were not affected by diet.

Table 6.

Predominant bacterial phyla and genera (% of total sequences) in the feces of adult dogs fed an extruded dry kibble diet, a fresh roasted diet, or human-grade foods

Treatment
Phyla Genera Extruded Fresh HG beef HG chicken SEM P-value
Actinobacteria 8.08 4.75 11.31 6.71 0.977 0.0626
Slackia 0.01 0.03 0.01 0.01 0.006 0.6319
Adlercreutzia 0.02ab 0.00b 0.15a 0.00b 0.022 0.0257
Bifidobacterium 4.4ab 0.26b 6.93a 2.12ab 0.953 0.0247
Collinsella 3.65 4.46 4.20 4.58 0.428 0.8343
Bacteroidetes 32.37 ab 23.09 b 43.12 a 15.26 b 3.149 0.0022
Tannerella 0.00 0.00 0.00 0.01 0.004 0.4959
Bacteroides 15.41b 18.84b 42.05a 11.38b 2.909 <0.0001
Odoribacter 0.02 0.00 0.01 0.00 0.005 0.4051
Parabacteroides 0.11 0.14 0.08 0.08 0.021 0.7759
Prevotella 16.77a 4.07b 0.92b 3.77b 1.944 0.0113
Alistipes 0.01 0.00 0.00 0.00 0.002 0.5626
Firmicutes 54.24 ab 63.17 a 38.72 b 68.69 a 3.317 0.0007
Streptococcus 3.97ab 0.07b 1.62b 18.11a 2.141 0.0071
Kandleria 0.01 0.00 0.00 0.02 0.004 0.2739
Absiella 0.01 0.49 0.78 0.12 0.150 0.1692
Undefined genus in order Clostridiales 0.16 0.47 0.45 0.20 0.077 0.3467
Terrisporobacter 0.00 0.04 0.05 0.61 0.117 0.1997
Allobaculum 1.53b 4.49a 3.93ab 1.41b 0.423 0.0053
Butyricicoccus 0.24a 0.09b 0.02b 0.03b 0.021 <0.0001
Tyzzerella 0.02 0.02 0.08 0.14 0.022 0.1065
Dorea 0.05a 0.04ab 0.01b 0.03ab 0.005 0.0114
Undefined genus in family Lachnospiraceae 7.37b 16.84a 9.24b 8.96b 1.012 0.0024
Dialister 0.23a 0.07ab 0.02b 0.10b 0.031 0.0335
Undefined genus in family Oscillospiraceae 0.00 0.01 0.00 0.00 0.002 0.4018
Lactobacillus 6.36a 4.44ab 0.11b 1.70ab 0.888 0.0315
Subdoligranulum 0.03 0.00 0.01 0.00 0.004 0.0596
Holdemanella 0.78a 0.50a 0.11b 0.06b 0.071 <0.0001
Clostridium 0.06 0.60 0.81 7.01 1.263 0.1686
Coprobacillus 0.00 0.08 0.00 0.00 0.017 0.2729
Paeniclostridium 0.00 0.00 0.00 0.02 0.004 0.4018
Megamonas 17.24 14.88 9.93 16.97 1.781 0.4384
Romboutsia 0.00 0.00 0.00 0.04 0.009 0.3498
Faecalibacterium 0.11 0.19 0.14 0.07 0.028 0.3509
Veillonella 0.62 0.00 0.00 0.00 0.155 0.4018
Candidatus Arthromitus 0.02 0.00 0.00 0.02 0.005 0.1332
Acidaminococcus 0.00 0.00 0.01 0.00 0.003 0.5145
Enterococcus 0.03 0.06 0.00 0.05 0.017 0.5704
Leuconostoc 0.00 0.01 0.02 0.00 0.004 0.2763
Catenibacterium 2.84a 0.52b 0.18b 1.26b 0.278 0.0003
Ruminococcus 0.03 0.05 0.04 0.01 0.010 0.4270
Turicibacter 0.05 0.03 0.09 0.71 0.428 0.3024
Lachnospira 0.00 0.00 0.00 0.00 0.001 0.4018
Intestinibacter 0.00 0.00 0.00 0.02 0.004 0.3176
Clostridioides 0.00 0.00 0.02 0.01 0.006 0.6580
Coprococcus 1.01b 3.10a 1.83ab 2.41ab 0.238 0.0129
Phascolarctobacterium 0.07 0.06 0.15 0.12 0.033 0.7057
Blautia 7.55ab 9.82a 4.74b 4.31b 0.657 0.0057
Staphylococcus 0.03 0.00 0.00 0.00 0.007 0.4018
Roseburia 0.00 0.00 0.02 0.01 0.005 0.3730
Undefined genus in order Clostridiales 0.00 0.00 0.00 0.01 0.002 0.1195
Erysipelatoclostridium 0.01 0.10 0.00 0.00 0.017 0.0981
Christensenella 0.30ab 0.15b 0.25ab 0.34a 0.025 0.0405
Undefined genus in family Peptostreptococcaceae 3.49 5.87 3.79 3.80 0.349 0.0556
Undefined genus in family Erysipelotrichaceae 0.01 0.06 0.22 0.01 0.051 0.3940
Proteobacteria 4.51 4.02 5.56 7.84 0.716 0.1390
Escherichia 0.10 0.42 1.66 0.77 0.244 0.0985
Citrobacter 0.00 0.00 0.00 0.00 0.001 0.4018
Anaerobiospirillum 0.76 1.28 0.46 0.62 0.286 0.3811
Pseudomonas 0.00 0.00 0.08 1.62 0.404 0.4127
Helicobacter 0.15 0.04 0.19 0.32 0.050 0.2492
Plesiomonas 0.00 0.01 0.00 0.02 0.007 0.4051
Undefined genus in order Burkholderiales 0.13ab 0.01b 0.36a 0.06ab 0.054 0.0350
Shigella 0.00 0.01 0.04 0.05 0.009 0.1396
Sutterella 3.27 2.24 2.48 4.33 0.477 0.3537
Parasutterella 0.10ab 0.00b 0.29a 0.04ab 0.044 0.0426
Fusobacteria 0.67 4.97 1.27 1.47 0.641 0.0693
Fusobacterium 0.66 4.83 1.22 1.40 0.624 0.0691
Cetobacterium 0.01 0.13 0.06 0.08 0.020 0.1516
Spirochaetes 0.04 0.00 0.02 0.02 0.009 0.4406
Brachyspira 0.04 0.00 0.02 0.02 0.009 0.4406
Open in a new tab

1Extruded dry kibble diet (extruded); fresh roasted diet (fresh); human-grade beef diet (HG beef); human-grade chicken diet (HG chicken).

2Bold text was used for bacterial phyla, while non-bold text was used for bacterial genera.

a,bWithin a row, means lacking a common superscript differ (P < 0.05).

At the genus level, the relative abundance of Adlercreutzia was greater (P < 0.05) in dogs fed the HG beef diet (0.15%) than dogs fed the fresh (0%) or HG chicken (0%) diets. The relative abundances of Bifidobacterium, Parasutterella, and an undefined genus in the Burkholderiales order were greater (P < 0.05) in dogs fed the HG beef diet (6.93%, 0.29%, and 0.36%, respectively) than dogs fed the fresh diet (0.26%, 0%, and 0.01%, respectively). The relative abundance of Bacteroides was greater (P < 0.05) in dogs fed the HG beef diet (42.05%) than dogs fed the extruded (15.41%), fresh (18.84%), or HG chicken (11.38%) diets. The relative abundances of Prevotella, Catenibacterium, and Butyricicoccus were greater (P < 0.05) in dogs fed the extruded diet (16.77%, 2.84%, and 0.24%, respectively) than dogs fed the fresh (4.07%, 0.52%, and 0.09%, respectively), HG beef (0.92%, 0.18%, and 0.92%, respectively), or HG chicken (3.77%, 1.26%, and 0.03%, respectively) diets. The relative abundance of Streptococcus was greater (P < 0.05) in dogs fed the HG chicken diet (18.11%) than dogs fed the HG beef (1.62%) or fresh (0.07%) diets. The relative abundance of Allobaculum was greater (P < 0.05) in dogs fed the fresh diet (4.49%) than dogs fed the HG chicken (1.41%) or extruded (1.53%) diets.

The relative abundances of Dorea and Lactobacillus were greater (P < 0.05) in dogs fed the extruded diet (0.05% and 6.36%) than dogs fed the HG beef diet (0.01% and 0.11%). The relative abundance of an undefined genus in the Lachnospiraceae family was greater (P < 0.05) in dogs fed the fresh diet (16.84%) than dogs fed the HG beef (9.24%), HG chicken (8.96%), or extruded (7.37%) diets. The relative abundance of Dialister was greater (P < 0.05) in dogs fed the extruded diet (0.23%) than dogs fed the HG beef (0.02%) or HG chicken (0.10%) diets. The relative abundance of Holdemanella was greater (P < 0.05) in dogs fed the extruded (0.78%) or fresh (0.50%) diets than dogs fed the HG beef (0.11%) or HG chicken (0.06%) diets. The relative abundance of Coprococcus was lower (P < 0.05) in dogs fed the extruded diet (1.01%) than dogs fed the fresh diet (3.10%). The relative abundance of Blautia was lower (P < 0.05) in dogs fed the HG beef (4.74%) or HG chicken (4.31%) diets than dogs fed the fresh diet (9.82%). Lastly, the relative abundance of Christensenella was lower (P < 0.05) in dogs fed the fresh diet (0.15%) than dogs fed the HG chicken diet (0.34%).

Discussion

The pet food industry continues to grow because of increased disposable income and the importance of companionship with animals, which can contribute to improved physical health, emotional health, and social well-being of pet owners (McConnell et al., 2011). There is not growth in all areas, however. From 2009 to 2017, several dog and cat foods were recalled for safety concerns related to deficient or high concentrations of vitamins and minerals, plastic contamination, and pathogen (Salmonella and L. monocytogenes) contamination (FDA, 2017; White et al., 2017). These and other safety concerns have motivated some consumers to search out alternatives with higher real or perceived safety and quality, including foods that limit byproducts generated from the human food system (Laflamme et al., 2008; Swanson et al., 2013). This buying behavior has resulted in rapid growth of specific pet food segments, including those being labeled as “natural,” “organic,” or “human-grade,” as well as homemade recipes. Despite their popularity in the market, many of these diets have not been well tested. Therefore, we investigated the effects of HG dog foods on ATTD, fecal characteristics, metabolites, and microbiota, serum metabolites, and hematology of adult dogs in the current study.

The chemical composition of the experimental diets in this study varied considerably due to different ingredient profiles, guaranteed analysis targets, and processing procedures. Despite their great differences, stool quality was adequate for dogs fed all diets. There are many variables that affect fecal quality, including nutrient digestibility, fiber content, DM intake, and fat tolerance (Hernot et al., 2005; Wakshlag et al., 2011). In this experiment, fecal DM differed slightly, but fecal pH and scores were not different among diets.

The digestibility of a pet food and consequent fecal output provide a measure of its quality and is important to pet owners from a waste disposal perspective. Nutrient digestibility may be affected by many factors, such as the processing procedures used to prepare the food, ingredient profile, and the physiological state of the animal. In this study, HG foods consistently had higher nutrient digestibilities than the fresh and extruded diets tested. A recent study calculated the nutrient digestibility of chicken-based ingredients differing by processing method (rendered, retorted, steamed, and raw) using the precision-fed cecectomized rooster assay (Oba et al., 2019), which has been demonstrated to accurately estimate canine ileal nutrient digestibility of ingredients or complete pet foods (Johnson et al., 1998). In Oba et al. (2019), DM and OM digestibilities of raw chicken (DM: 75.91% and OM: 80.51%), steamed chicken (DM: 76.46% and OM: 80.56%), and retorted chicken (DM: 73.49% and OM: 77.78%) were similar and much greater than that of chicken meal (DM: 60.05% and OM: 65.87%). In a separate study, Oba et al. (2020) used the cecectomized rooster assay to test six HG dog foods, including the beef- and chicken-based HG foods tested in the current study. Oba et al. (2020) reported digestibilities of DM (74.0% and 82.3%), OM (81.9% and 89.2%), AHF (87.9% and 94.6%), and GE (86.9% and 93.7%), demonstrating that these complete foods had digestibilities at the same level or higher than that of the lightly processed chicken-based ingredients.

Although the results of HG foods have not been reported until now, a few recent studies have tested fresh or raw meat diets in dogs and cats and are in agreement with the current study. Algya et al. (2018), for instance, tested an extruded dry kibble diet, two mildly cooked (fresh) diets, and a raw diet in dogs. Those researchers reported that mildly cooked and raw diets had higher CP (94.6%, 88.3%, and 92.0%), AHF (97.2%, 97.5%, and 95.8%), and energy (92.7%, 90.8%, and 90.7%) ATTD than an extruded diet (85.1%, 92.1%, and 87.4%, respectively). Similarly, Bermingham et al. (2017) reported that extruded diets had lower ATTD of DM (81.3% to 83.4%), energy (87.2% to 89.2%), crude fat (98.1% to 98.4%), and CP (79.9% to 82.8%) than raw meat diets (78.6% to 97.9%; energy: 94.3% to 98.8%; crude fat: 97.8% to 99.7%; protein: 96.7% to 99.2%). Another study conducted by Kerr et al. (2014) compared an extruded diet, a beef-based raw diet, and a cooked beef-based raw diet for cats. In that study, ATTD of DM (86.7% and 83.8%), OM (90.5% and 88.5%), CP (93.3% and 92.9%), fat (95.5% and 95.3%), and energy (91.5% and 89.8%) was greater for the raw or cooked raw diets than the extruded diet (DM: 78.2%; OM: 83.9%; CP: 81.6%; fat: 91.3%; energy: 84.7%).

The amount of fecal output may be influenced by food intake, nutrient digestibility, the chemical composition of the diet, and physiological state of the animal. Although the water-holding capacity of the dietary ingredients is a factor, greater nutrient digestibility usually results in lower fecal output. In the current study, dogs fed HG foods had two to three times lower fecal output than dogs fed the extruded diet and about 1.5 times lower fecal output than dogs fed the fresh diet. Again, our results are similar to those of a previous studies testing fresh or raw diets. In Bermingham et al. (2017), dogs fed a raw meat diet had lower fecal output (20.9 to 40.1 g DMB) than dogs fed an extruded diet (56.9 to 70.4 g DMB). In Algya et al. (2018), dogs fed fresh or raw diets consumed more food and calories than dogs fed the extruded diet, but fecal output was not affected [29.4 (extruded), 19.9 (grain-free fresh), 29.6 (raw), 28.8 (grain-containing fresh) g/d DMB].

The extremely high nutrient and energy digestibilities of HG pet foods, as demonstrated in the current study and reported by Oba et al. (2020), explain how pets may consume a lower amount of HG food and still maintain BW and excrete less waste when compared to traditional (extruded) pet foods. Even though the HG foods tested herein were highly palatable and digestible, their high moisture content and low as-is caloric content made it relatively easy to maintain BW of dogs in the study. More research is required to test for potential long-term health benefits of feeding such diets. Processing method and amount influence the nutritional value of food, something that has been demonstrated in both human and pet foods. A high level of food processing, and how it affects caloric density and nutrient quality of foods, is thought to contribute to the poor nutritional status and obesity present in an increasing number of humans in the United States, and is an important aspect of public health nutrition policy (Fernandes et al., 2019). In humans, ultra-processed diets have been shown to increase energy intake and weight gain (Hall et al., 2019). Energy intake has been reported to be higher in dogs and cats fed highly processed, extruded diets in some studies (Lund et al., 2005; Orsolya Julianna et al., 2020), but not others (Lund et al., 2006), so more research is needed to determine how diet format affects obesity in pets.

In addition to the signs of gastrointestinal health that are noticeable to pet owners, including fecal score, volume, color, and odor, the abundance and activity of the microbiota are critical to long-term health. Although the effects of diet on the canine gastrointestinal microbiome and metabolome have been well studied in recent years (Barko et al., 2018), including diets testing raw and fresh diets (Beloshapka et al., 2013; Sandri et al., 2017; Algya et al., 2018), the effects of HG foods have yet to be tested. Even though there were many differences in nutrient digestibility and fecal output in the current study, fecal metabolites were surprisingly not affected. Many factors affect the rate of SCFA production, such as the substrate source reaching the colon (carbohydrate vs. protein), gastrointestinal transit time, and the taxonomic groups and activity of the microbiota present in the colon. Fecal pH is highly correlated with SCFA and is a good indicator of SCFA production. Production of SCFA by microbial fermentation in the hindgut decreases the luminal pH, and an acidic pH prevents the growth of pathogenic species. Because SCFA serve as an important energy source for colonocytes, greater production is typically preferred as long as fecal quality is not affected (Wong et al., 2006). Even though greater SCFA production is preferred, it is often difficult to detect differences in fecal samples because these organic acids are rapidly absorbed and utilized by the colon.

Ammonia, phenols, indoles, and BCFA are putrefactive components that are produced by protein fermentation (Miner and Hazen, 1969). The fermentation of branched-chain amino acids, namely leucine, isoleucine, and valine, generate BCFA. The production of BCFA may be modified by dietary protein concentration, quality, and digestibility (Smith and Macfarlane, 1998; Aguirre et al., 2016). Ammonia is generated from the deamination of amino acids and can become toxic at high concentrations. As described by Cummings and Macfarlane (1991), fecal ammonia concentrations are decreased when carbohydrate fermentation and bacterial growth is increased in the hindgut because of the higher incorporation of nitrogen into microbial cells. In addition to BCFA and ammonia, phenols and indoles are another category of metabolic derivatives of proteolytic fermentation. Phenols and indoles are deaminated forms of aromatic amino acids, including tyrosine, phenylalanine, and tryptophan. In the current study, there were no differences in fecal ammonia, phenols, indoles, and BCFA among dietary treatments.

Gut microbiota differences are known to be affected by the host species (breed and sex of dog), diet consumed, and other environmental exposures, as well as the laboratory assays [DNA extraction procedures, type of sequencing (shotgun vs. 16S rRNA amplicons)] and databases used for microbial annotation (Deng and Swanson, 2015). When it comes to diet specifically, fecal microbial shifts may be affected by ingredient profile, nutrient concentrations and digestibility, and processing procedures. These factors influence the digestion and absorption of nutrients and affect what substrates enter the colon and are available for microbial metabolism. The gastrointestinal microbiome changes quickly in response to dietary interventions. In this study, the predominant bacterial phyla (Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria, and Fusobacteria) detected were the same as those reported in other studies (Beloshapka et al., 2011; Bermingham et al., 2017; Kim et al., 2017; Sandri et al., 2017; Algya et al., 2018). However, the relative abundances (% of total sequences) of bacteria were unique for each diet type tested. For example, the relative abundances of Actinobacteria (8.08%) and Bacteroidetes (32.37%) of dogs fed the dry extruded diet in this study were higher than those often reported in the literature, including dogs fed a commercial extruded diet (0.65% and 17.32%) by Kim et al. (2017). In addition, the relative abundance of Firmicutes (38.72%) and Fusobacteria (1.27%) in dogs fed HG beef in the current study were lower than is typically reported in dogs (60.81% and 10.95%; Sandri et al., 2017). Approximately 20 bacterial genera among these phyla and others were influenced by diet.

In pet foods, digestible carbohydrates serve as an available source of energy and glucose. Some carbohydrates, however, are not digested by the animal and serve as a source of fiber. Fiber is not a required nutrient for dogs and cats, but it is necessary for normal functionality and health of the gastrointestinal tract. The physical and chemical properties of the fiber, including solubility, fermentability, and particle size, vary with carbohydrate sources in the diet (Dhingra et al., 2012). In the current study, the primary carbohydrate sources among diets differed greatly (extruded diet: brown rice, barley, oatmeal, pea starch, dried tomato pomace, alfalfa meal, chicory root, pea fiber, sweet potatoes, carrots, dried kelp; fresh diet: ground oats, rice bran, carrots, spinach; HG beef diet: russet potatoes, sweet potatoes, green beans, carrots, green peas, apples, kelp; HG chicken diet: long grain white rice, spinach, carrots, apples, kelp).

Dogs fed the extruded diet (high fiber; low digestibility) had a greater relative abundances of fecal Prevotella and Catenibacterium than dogs fed the fresh diet (moderate fiber and digestibility) and HG foods (low fiber; high digestibility). Prevotella is a dominant genus of the Bacteroides phyla that is often increased with plant-based, high-fiber diets so this response was not surprising (Tett et al., 2019). Catenibacterium is another polysaccharide degrader and member of the Firmicutes phyla that has been shown to be increased in pigs fed oat bran (He et al., 2018) and humans consuming a diet high in plant-based foods (Garcia-Mantrana et al., 2018). Dogs fed the extruded diet also had a greater relative abundances of fecal Butyricicoccus, Dialister, and Holdemanella than dogs fed the HG foods (low fiber; high digestibility). These taxa are also known to be fiber degraders and/or SCFA producers increased in diets containing whole grains such as barley and brown rice (Martinez et al., 2013). The relative abundance of fecal Lactobacillus was greater in dogs fed the extruded diet than dogs fed the HG chicken diet. This enrichment may have been due to the L. acidophilus fermentation product it contains and/or the greater fiber content, including that coming from chicory, which has been shown to increase lactobacilli (Ivarsson et al., 2012; de Godoy et al., 2015).

An undefined genus in the Lachnospiraceae family and other genera within Lachnospiraceae (Blautia, Coprococcus, Allobaculum) were enriched in dogs fed the fresh diet. This bacterial family contains many fiber-degrading and SCFA-producing bacteria and are often enriched in humans and dogs having greater fiber intake (Di Iorio et al., 2019; Jackson and Jewell, 2020; Vacca et al., 2020). Fecal Allobaculum and Coprococcus are considered beneficial intestinal bacteria because they produce butyrate and lactate (Greetham et al., 2004). Streptococcus was highly enriched in dogs fed the HG chicken diet. This taxonomic group is known to have extensive carbohydrate fermentative capabilities, including resistant starches and dietary fibers (van den Bogert et al., 2013; Warren et al., 2018). Although the HG chicken diet was not rich in dietary fiber, it contained the greatest amount of starch, some of which may have been resistant to digestion and available for fermentation. Bifidobacterium was enriched in dogs fed the HG beef diet. Because this taxonomic group is typically associated with fiber and prebiotic consumption, this response was unexpected, but would be deemed as a beneficial shift in dogs consuming this diet.

Many studies have evaluated how different types of carbohydrates affect the microbiome composition in dogs. Dogs fed traditional fibers like beet pulp have been reported to have lower Fusobacteria and higher genera within the Firmicutes phyla (Middelbos et al., 2010). Dogs fed other fermentable fibers or prebiotics (e.g., fructooligosaccharides) typically have greater lactic-acid bacteria such as Lactobacillus spp. and Bifidobacterium spp. and lower potential pathogens such as Clostridium perfringens and Escherichia coli (Swanson et al., 2002; Flickinger et al., 2003; Middelbos et al., 2007). Although many of the shifts in microbiota are due to the enzymatic capabilities and cross-feeding among taxa, others may be due to their tolerance to a low pH caused by the production of SCFA coming from carbohydrate fermentation. Although some taxa, such as lactic-acid bacteria, are acid tolerant, many pathogens are unable to survive at a low pH.

Although the primary dietary components used to manipulate the microbiome include fibers and other nondigestible carbohydrates, protein and fat sources are also important. Protein-based ingredients differ in regard to protein quality (amino acid profile), amino acid and nitrogen concentration, protein:energy ratio, and digestibility. If not highly digestible, high protein intake increases the flow of undigested proteins into the colon, which increases the occurrence and activity of proteolytic bacteria. Even though big shifts may not always be observed in dogs fed raw meat, fresh, or HG diets—due to their high digestibility—they are often noted in extruded diets. High-protein diets have been reported to increase the abundance of Clostridium populations. Although beneficial taxa exist, many are considered intestinal pathogens (α-toxin is a major pathogenic factor; Zentek et al., 2004). Ephraim et al. (2020) reported that the relative abundances of Prevotella, Ruminococcus, Collinsella, Phascolarctobacterium, and Faecalibacterium were decreased in dogs fed a high-protein extruded diet (45.77% CP, DMB) compared with dogs fed moderate-protein (25.34% CP, DMB) or low-protein (18.99% CP, DMB) extruded diets. Other than the change to Prevotella previously mentioned, these other taxa were unchanged in the current study. It is difficult to assess whether protein content affected the microbiota of the current study, but it seems that most changes were driven by carbohydrate content and type. Other than the extruded diet, all diets were highly digestible, so little protein would be expected to reach the colon for fermentation.

Dietary fats are highly digestible and are not easily utilized by intestinal microbiota, so they are much less likely to affect the microbiome when compared with proteins and carbohydrates. Dietary fatty acids may alter the gut microbiota in a few ways, however, including increasing the flow of bile acids into the large intestine. Bile acids are potent antimicrobial factors that affect microbiota via membrane lysis and cellular damage. In addition, bile salt hydrolases, which are enzymes present in many bacterial taxa, including Lactobacillus, Clostridium, Bifidobacterium, and Enterococcus, catalyze bile acid deconjugation reactions and may affect both gastrointestinal microbiota and host metabolism (Begley et al., 2006; Tian et al., 2019). Although the feeding of a high-fat diet has been reported to decrease intestinal bacterial abundance and diversity (Turnbaugh et al., 2008), α-diversity was not affected in the current study. Past studies have also reported an enrichment in fecal Bacteroides in humans consuming high-protein, high-fat diets (David et al., 2014; Wu et al., 2011). This change seems to be in agreement with the current study, whereby a much greater relative abundance of fecal Bacteroides was present in dogs fed the HG beef diet (highest fat content) than dogs fed all other diets. Algya et al. (2018) reported a similar enrichment in fecal Bacteroides in dogs fed high-fat fresh and raw diets compared with dogs fed a low-fat extruded diet. Although this taxonomic shift is likely due to fat content, Bacteroides has a large repertoire of genes capable of breaking down and metabolizing dietary fibers (Xu and Gordon, 2003). Therefore, it is difficult to identify the driving factor for this change in the current study.

Although more research is needed to identify which dietary components are the largest drivers, the microbiota data of the current study seem to agree with previous studies testing raw and fresh diets. As has been reported in the past, our data demonstrate that the fecal microbiota of dogs fed HG or fresh diets is markedly different from those consuming extruded diets. These differences are likely due to the ingredient sources, nutrient concentrations, and processing methods used among the various diet types. Because all dogs in the current study and those in similar studies were healthy, it demonstrates the great flexibility of the canine gastrointestinal microbiota and highlights the fact that what is deemed as being “normal” for dogs is highly reliant on the diet being consumed at the time of fecal collection.

In conclusion, the diets tested in this study were well accepted and dogs remained healthy throughout the study. As expected, the HG foods had an extremely high digestibility that was higher than that of extruded and fresh diets, without any differences observed in regard to fecal characteristics (pH or score) or metabolites. Many differences in the fecal microbiota were observed among the diets, which were likely due to differences in ingredient source, nutrient concentrations, and processing methods. In line with past studies, data from this study suggest that the typical fecal microbiota of dogs fed fresh or HG diets differ from that of dogs fed extruded diets. Further research is required to evaluate the functional role of the microbiota and how they interact with HG ingredients to influence pet health.

Supplementary Material

skab028_suppl_Supplementary_Figure_1
Click here for additional data file. (273.8KB, docx)

Acknowledgment

The funding for this study was provided by JustFoodForDogs, Irvine, CA.

Glossary

Abbreviations

AHF

acid-hydrolyzed fat

ATTD

apparent total tract digestibility

BCFA

branched-chain fatty acids

CP

crude protein

DM

dry matter

DMB

dry matter basis

HG

human-grade

OM

organic matter

SCFA

short-chain fatty acids

Conflict of interest statement

The authors declare no real or perceived conflicts of interest.

Literature Cited

  1. AACC . 1983. Approved methods. 8th ed. Saint Paul (MN): American Association of Cereal Chemists. [Google Scholar]
  2. Aguirre, M., A.  Eck, M. E.  Koenen, P. H.  Savelkoul, A. E.  Budding, and K.  Venema. . 2016. Diet drives quick changes in the metabolic activity and composition of human gut microbiota in a validated in vitro gut model. Res. Microbiol. 167:114–125. doi: 10.1016/j.resmic.2015.09.006 [DOI] [PubMed] [Google Scholar]
  3. Algya, K. M., T. L.  Cross, K. N.  Leuck, M. E.  Kastner, T.  Baba, L.  Lye, M. R. C.  de Godoy, and K. S.  Swanson. . 2018. Apparent total tract macronutrient digestibility, serum chemistry, urinalysis, and fecal characteristics, metabolites and microbiota of adult dogs fed extruded, mildly cooked, and raw diets. J Anim. Sci. 96:3673683. doi: 10.1093/jas/sky235 [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Association of American Feed Control Officials (AAFCO).  2017. AAFCO human grade standards for pet products. Champaign (IL): AAFCO, Inc. [Google Scholar]
  5. Association of American Feed Control Officials (AAFCO).  2019. Official publication. Oxford (IN): AAFCO. [Google Scholar]
  6. Association of Official Analytical Chemists (AOAC).  2006. Official methods of analysis. 17th ed. Gaithersburg (MD): Association of Official Analytical Chemists. [Google Scholar]
  7. Barko, P. C., M. A.  McMichael, K. S.  Swanson, and D. A.  Williams. . 2018. The gastrointestinal microbiome: a review. J. Vet. Intern. Med. 32:9–25. doi: 10.1111/jvim.14875 [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Begley, M., C.  Hill, and C. G.  Gahan. . 2006. Bile salt hydrolase activity in probiotics. Appl. Environ. Microbiol. 72:1729–1738. doi: 10.1128/AEM.72.3.1729-1738.2006 [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Beloshapka, A. N., S. E.  Dowd, L.  Duclos, and K. S.  Swanson. . 2011. Comparison of fecal microbial communities of healthy adult dogs fed raw meat-based or extruded diets using 454 pyrosequencing. J. Anim. Sci. 89:284. doi: 10.2527/asasann.2017.228. [DOI] [PubMed] [Google Scholar]
  10. Beloshapka, A. N., S. E.  Dowd, J. S.  Suchodolski, J. M.  Steiner, L.  Duclos, and K. S.  Swanson. . 2013. Fecal microbial communities of healthy adult dogs fed raw meat-based diets with or without inulin or yeast cell wall extracts as assessed by 454 pyrosequencing. FEMS Microbiol. Ecol. 84:532–541. doi: 10.1111/1574-6941.12081. [DOI] [PubMed] [Google Scholar]
  11. Bermingham, E. N., P.  Maclean, D. G.  Thomas, N. J.  Cave, and W.  Young. . 2017. Key bacterial families (Clostridiaceae, Erysipelotrichaceae and Bacteroidaceae) are related to the digestion of protein and energy in dogs. Peerj  5:e3019. doi: 10.7717/peerj.3019 [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Budde, E. F. 1952. The determination of fat in baked biscuit type of dog foods. J. Assoc. Off. Agric. Chem. 35:799–805. doi: 10.1093/jaoac/35.3.799 [DOI] [Google Scholar]
  13. Carter, R. A., J. E.  Bauer, J. H.  Kersey, and P. R.  Buff. . 2014. Awareness and evaluation of natural pet food products in the United States. J. Am. Vet. Med. Assoc. 245:1241–1248. doi: 10.2460/javma.245.11.1241 [DOI] [PubMed] [Google Scholar]
  14. Chaney, A. L., and E. P.  Marbach. . 1962. Modified reagents for determination of urea and ammonia. Clin. Chem. 8:130–132. [PubMed] [Google Scholar]
  15. Cummings, J. H., and G. T.  Macfarlane. . 1991. The control and consequences of bacterial fermentation in the human colon. J. Appl. Bacteriol. 70:443–459. doi: 10.1111/j.1365-2672.1991.tb02739.x [DOI] [PubMed] [Google Scholar]
  16. David, L. A., C. F.  Maurice, R. N.  Carmody, D. B.  Gootenberg, J. E.  Button, B. E.  Wolfe, A. V.  Ling, A. S.  Devlin, Y.  Varma, M. A.  Fischbach, . et al.  2014. Diet rapidly and reproducibly alters the human gut microbiome. Nature  505:559–563. doi: 10.1038/nature12820 [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Deng, P., and K. S.  Swanson. . 2015. Gut microbiota of humans, dogs and cats: current knowledge and future opportunities and challenges. Br. J. Nutr. 113:S6–S17. doi: 10.1017/S0007114514002943 [DOI] [PubMed] [Google Scholar]
  18. Dhingra, D., M.  Michael, H.  Rajput, and R. T.  Patil. . 2012. Dietary fibre in foods: a review. J. Food Sci. Technol. 49:255–266. doi: 10.1007/s13197-011-0365-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. de Godoy, M. R., Y.  Mitsuhashi, L. L.  Bauer, G. C.  Fahey, Jr., P. R.  Buff, and K. S.  Swanson. . 2015. In vitro fermentation characteristics of novel fibers, coconut endosperm fiber and chicory pulp, using canine fecal inoculum. J. Anim. Sci. 93:370–376. doi: 10.2527/jas.2014-7962 [DOI] [PubMed] [Google Scholar]
  20. Di Iorio, B. R., M. T.  Rocchetti, M.  De Angelis, C.  Cosola, S.  Marzocco, L.  Di Micco, I.  di Bari, M.  Accetturo, M.  Vacca, M.  Gobbetti, . et al.  2019. Nutritional therapy modulates intestinal microbiota and reduces serum levels of total and free indoxyl sulfate and p-cresyl sulfate in chronic kidney disease (Medika study). J. Clin. Med. 8:1424. doi: 10.3390/jcm8091424 [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Ephraim, E., C. Y.  Cochrane, and D. E.  Jewell. . 2020. Varying protein levels influence metabolomics and the gut microbiome in healthy adult dogs. Toxins  12:12–517. doi: 10.3390/toxins12080517 [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Erwin, E. S., G. J.  Marco, and E. M.  Emery. . 1961. Volatile fatty acid analyses of blood and rumen fluid by gas chromatography. J. Dairy Sci. 44:1768–1771. doi: 10.3168/jds.S0022-0302(61)89956-6 [DOI] [Google Scholar]
  23. Fernandes, A. C., D. K.  Rieger, and R. P. C.  Proença. . 2019. Perspective: public health nutrition policies should focus on healthy eating, not on calorie counting, even to decrease obesity. Adv. Nutr. 10:549–556. doi: 10.1093/advances/nmz025 [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Flickinger, E. A., E. M.  Schreijen, A. R.  Patil, H. S.  Hussein, C. M.  Grieshop, N. R.  Merchen, and G. C.  Fahey, Jr. 2003. Nutrient digestibilities, microbial populations, and protein catabolites as affected by fructan supplementation of dog diets. J. Anim. Sci. 81:2008–2018. doi: 10.2527/2003.8182008x [DOI] [PubMed] [Google Scholar]
  25. Food and Drug Administration (FDA).  2017. Animal and Veterinary Recalls Archive.  http://www.fda.gov/AnimalVeterinary/SafetyHealth/RecallsWithdrawals/default.htm. Accessed November 21, 2020.
  26. Garcia-Mantrana, I., M.  Selma-Royo, C.  Alcantara, and M. C.  Collado. . 2018. Shifts on gut microbiota associated to mediterranean diet adherence and specific dietary intakes on general adult population. Front. Microbiol. 9:890. doi: 10.3389/fmicb.2018.00890 [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Greetham, H. L., G. R.  Gibson, C.  Giffard, H.  Hippe, B.  Merkhoffer, U.  Steiner, E.  Falsen, and M. D.  Collins. . 2004. Allobaculum stercoricanis gen. nov., sp. nov., isolated from canine feces. Anaerobe  10:301–307. doi: 10.1016/j.anaerobe.2004.06.004. [DOI] [PubMed] [Google Scholar]
  28. Hall, K. D., A.  Ayuketah, R.  Brychta, H.  Cai, T.  Cassimatis, K. Y.  Chen, S. T.  Chung, E.  Costa, A.  Courville, V.  Darcey, . et al.  2019. Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metab. 30:67–77. doi: 10.1016/j.cmet.2019.05.008 [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Hasan, N. A., B. A.  Young, A. T.  Minard-Smith, K.  Saeed, H.  Li, E. M.  Heizer, N. J.  McMillan, R.  Isom, A. S.  Abdullah, D. M.  Bornman, . et al.  2014. Microbial community profiling of human saliva using shotgun metagenomic sequencing. PLoS One  9:e97699. doi: 10.1371/journal.pone.0097699 [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. He, B., Y.  Bai, L.  Jiang, W.  Wang, T.  Li, P.  Liu, S.  Tao, J.  Zhao, D.  Han, and J.  Wang. . 2018. Effects of oat bran on nutrient digestibility, intestinal microbiota, and inflammatory responses in the hindgut of growing pigs. Int. J. Mol. Sci. 19:2407. doi: 10.3390/ijms19082407 [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Hernot, D., V.  Biourge, H.  Dumon, L.  Martin, R.  Sergheraert, and P.  Nguyen. . 2005. Effect of dietary fermentable to non-fermentable fiber ratio on fecal putrefactive products in dogs varying in body size. In: Proceedings: Waltham Symposium, Washington, DC.  Melton Mowbray (UK): Waltham Centre for Pet Nutrition. [Google Scholar]
  32. Ivarsson, E., H. Y.  Liu, J.  Dicksved, S.  Roos, and J. E.  Lindberg. . 2012. Impact of chicory inclusion in a cereal-based diet on digestibility, organ size and faecal microbiota in growing pigs. Animal  6:1077–1085. doi: 10.1017/S1751731111002709 [DOI] [PubMed] [Google Scholar]
  33. Jackson, M. I., and D. E.  Jewell. . 2020. Balance of saccharolysis and proteolysis underpins improvements in stool quality induced by adding a fiber bundle containing bound polyphenols to either hydrolyzed meat or grain-rich foods. Gut Microbes  10:298–320. doi: 10.1080/19490976.2018.1526580 [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Johnson, M. L., C. M.  Parsons, G. C.  Fahey, Jr., N. R.  Merchen, and C. G.  Aldrich. . 1998. Effects of species raw material source, ash content, and processing temperature on amino acid digestibility of animal by-product meals by cecectomized roosters and ileally cannulated dogs. J. Anim. Sci. 76:1112–1122. doi: 10.2527/1998.7641112x [DOI] [PubMed] [Google Scholar]
  35. Kerr, K. R., K. L.  Kappen, L. M.  Garner, P. L.  Utterback, C. M.  Parsons, and K. S.  Swanson. . 2014. Commercially available avian and mammalian whole prey diet items targeted for consumption by managed exotic and domestic pet felines: true metabolizable energy and amino acid digestibility using the precision-fed cecectomized rooster assay. J. Anim. Sci. 92:4478–4485. doi: 10.2527/jas.2013-7246 [DOI] [PubMed] [Google Scholar]
  36. Kim, J., J. U.  An, W.  Kim, S.  Lee, and S.  Cho. . 2017. Differences in the gut microbiota of dogs (Canis lupus familiaris) fed a natural diet or a commercial feed revealed by the Illumina MiSeq platform. Gut Pathog. 9:68. doi: 10.1186/s13099-017-0218-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Laflamme, D. P., S. K.  Abood, A. J.  Fascetti, L. M.  Fleeman, L. M.  Freeman, K. E.  Michel, C.  Bauer, B. L.  Kemp, J. R.  Doren, and K. N.  Willoughby. . 2008. Pet feeding practices of dog and cat owners in the United States and Australia. J. Am. Vet. Med. Assoc. 232:687–694. doi: 10.2460/javma.232.5.687 [DOI] [PubMed] [Google Scholar]
  38. Lax, S., D. P.  Smith, J.  Hampton-Marcell, S. M.  Owens, K. M.  Handley, N. M.  Scott, S. M.  Gibbons, P.  Larsen, B. D.  Shogan, S.  Weiss, . et al.  2014. Longitudinal analysis of microbial interaction between humans and the indoor environment. Science  345:1048–1052. doi: 10.1126/science.1254529 [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Lund, E. M., P. J.  Armstrong, C. A.  Kirk, and J. S.  Klausner. . 2005. Prevalence and risk factors for obesity in adult cats from private US veterinary practices. Int. J. Appl. Res. Vet. Med. 3:88–96. [Google Scholar]
  40. Lund, E. M., P. J.  Armstrong, C. A.  Kirk, and J. S.  Klausner. . 2006. Prevalence and risk factors for obesity in adult dogs from private US veterinary practices. Int. J. Appl. Res. Vet. Med. 4:177–186. [Google Scholar]
  41. Martinez, I., J. M.  Lattimer, K. L.  Hubach, J. A.  Case, J.  Yang, C. G.  Weber, J. A.  Louk, D. J.  Rose, G.  Kyureghian, D. A.  Peterson, . et al.  2013. Gut microbiome composition is linked to whole grain-induced immunological improvements. ISME J. 7:269–280. doi: 10.1038/ismej.2012.104 [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. McConnell, A. R., C.  Brown, T. M.  Shoda, L. E.  Stayton, and C. E.  Martin. . 2011. Friends with benefits: on the positive consequences of pet ownership. J. Pers. Soc. Psychol. 6:1239–1252. doi: 10.1037/a0024506 [DOI] [PubMed] [Google Scholar]
  43. Middelbos, I. S., N. D.  Fastinger, and G. C.  Fahey, Jr. 2007. Evaluation of fermentable oligosaccharides in diets fed to dogs in comparison to fiber standards. J. Anim. Sci. 85:3033–3044. doi: 10.2527/jas.2007-0080 [DOI] [PubMed] [Google Scholar]
  44. Middelbos, I. S., B. M.  Vester Boler, A.  Qu, B. A.  White, K. S.  Swanson, and G. C.  Fahey, Jr. 2010. Phylogenetic characterization of fecal microbial communities of dogs fed diets with or without supplemental dietary fiber using 454 pyrosequencing. PLoS One  5:e9768. doi: 10.1371/journal.pone.0009768 [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Miner, J. R., and T. E.  Hazen. . 1969. Ammonia and amines: components of swine-building odor. Trans. ASAE  12:772–774. doi: 10.13031/2013.38950 [DOI] [Google Scholar]
  46. Mosteller, J. 2008. Animal-companion extremes and underlying consumer themes. J. Bus. Res. 61:512–521. doi: 10.1016/j.jbusres.2007.07.004 [DOI] [Google Scholar]
  47. National Research Council.  2006. Nutrient requirements of dogs and cats. Washington (DC): National Research Council of the National Academies. [Google Scholar]
  48. Oba, P. M., P. L.  Utterback, C. M.  Parsons, M. R. C.  de Godoy, and K. S.  Swanson. . 2019. Chemical composition, true nutrient digestibility, and true metabolizable energy of chicken-based ingredients differing by processing method using the precision-fed cecectomized rooster assay. J. Anim. Sci. 97:998–1009. doi: 10.1093/jas/sky461 [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Oba, P. M., P. L.  Utterback, C. M.  Parsons, and K. S.  Swanson. . 2020. True nutrient and amino acid digestibility of dog foods made with human-grade ingredients using the precision-fed cecectomized rooster assay. Transl. Anim. Sci. 4:442–451. doi: 10.1093/tas/txz175 [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Orsolya Julianna, T., V.  Kata, J.  Vanda Katalin, and P.  Péter. . 2020. Factors affecting canine obesity seem to be independent of the economic status of the country – A survey on Hungarian companion dogs. Animals  10:1267. doi: 10.3390/ani10081267 [DOI] [PMC free article] [PubMed] [Google Scholar]
  51. Ottesen, A., P.  Ramachandran, E.  Reed, J. R.  White, N.  Hasan, P.  Subramanian, G.  Ryan, K.  Jarvis, C.  Grim, N.  Daquiqan, . et al.  2016. Enrichment dynamics of Listeria monocytogenes and the associated microbiome from naturally contaminated ice cream linked to a listeriosis outbreak. BMC Microbiol. 16:275. doi: 10.1186/s12866-016-0894-1 [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Ponnusamy, D., E. V. Kozlova, J. Sha, T. E. Erova, S. R. Azar, E. C. Fitts, M. L. Kirtley, B. L. Tiner, J. A. Andersson, C. J. Grim, et al. 2016. Cross-talk among flesh-eating Aeromonas hydrophila strains in mixed infection leading to necrotizing fasciitis. Proc. Natl. Acad. Sci. 113:722–727. doi: 10.1073/pnas.1523817113 [DOI] [PMC free article] [PubMed] [Google Scholar]
  53. Prosky, L., N. G.  Asp, I.  Furda, J. W.  DeVries, T. F.  Schweizer, and B. F.  Harland. . 1985. Determination of total dietary fiber in foods and food products: collaborative study. J. Assoc. Off. Anal. Chem. 68:677–679. [PubMed] [Google Scholar]
  54. Sanders, C. R. 1990. The animal other self: self-definition, social identify and companion animals. Adv. Consum. Res. 17:662–668. [Google Scholar]
  55. Sandri, M., S.  Dal Monego, G.  Conte, S.  Sgorlon, and B.  Stefanon. . 2017. Raw meat based diet influences faecal microbiome and end products of fermentation in healthy dogs. BMC Vet. Res. 13:65. doi: 10.1186/s12917-017-0981-z [DOI] [PMC free article] [PubMed] [Google Scholar]
  56. Sharon, L. F., T.  Suzanne, and S.  Madeleine. . 2018. Pet humanisation: what is it and does it influence purchasing behaviour. Dairy Vet. Sci. J. 5:555659. doi: 10.19080/JDVS.2018.05.555659 [DOI] [Google Scholar]
  57. Smith, E., and G.  Macfarlane. . 1998. Enumeration of amino acid fermenting bacteria in the human large intestine: effects of pH and starch on peptide metabolism and dissimilation of amino acids. FEMS Microbiol. Ecol. 25:355–368. doi: 10.1016/S0168-6496(98)00004-X [DOI] [Google Scholar]
  58. Swanson, K. S., C. M.  Grieshop, E. A.  Flickinger, L. L.  Bauer, J.  Chow, B. W.  Wolf, K. A.  Garleb, and G. C.  Fahey, Jr. 2002. Fructooligosaccharides and Lactobacillus acidophilus modify gut microbial populations, total tract nutrient digestibilities and fecal protein catabolite concentrations in healthy adult dogs. J. Nutr. 132:3721–3731. doi: 10.1093/jn/132.12.3721 [DOI] [PubMed] [Google Scholar]
  59. Swanson, K. S., R. A.  Carter, T. P.  Yount, J.  Aretz, and P. R.  Buff. . 2013. Nutritional sustainability of pet foods. Adv. Nutr. 4:141–150. doi: 10.3945/an.112.003335 [DOI] [PMC free article] [PubMed] [Google Scholar]
  60. Tett, A., K. D.  Huang, F.  Asnicar, H.  Fehlner-Peach, E.  Pasolli, N.  Karcher, F.  Armanini, P.  Manghi, K.  Bonham, M.  Zolfo, . et al.  2019. The Prevotella copri complex comprises four distinct clades underrepresented in westernized populations. Cell Host Microbe  26:666–679.e7. doi: 10.1016/j.chom.2019.08.018 [DOI] [PMC free article] [PubMed] [Google Scholar]
  61. Tian, Y., J.  Cai, W.  Gui, R. G.  Nichols, I.  Koo, J.  Zhang, M.  Anitha, and A. D.  Patterson. . 2019. Berberine directly affects the gut microbiota to promote intestinal farnesoid × receptor activation. Drug Metab. Dispos. 47:86–93. doi: 10.1124/dmd.118.083691 [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Turnbaugh, P. J., F.  Bäckhed, L.  Fulton, and J. I.  Gordon. . 2008. Diet-induced obesity is linked to marked but reversible alterations in the mouse distal gut microbiome. Cell Host Microbe  3:213–223. doi: 10.1016/j.chom.2008.02.015. [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. van den Bogert, B., O.  Erkus, J.  Boekhorst, M.  de Goffau, E. J.  Smid, E. G.  Zoetendal, and M.  Kleerebezem. . 2013. Diversity of human small intestinal Streptococcus and Veillonella populations. FEMS Microbiol. Ecol. 85:376–388. doi: 10.1111/1574-6941.12127 [DOI] [PubMed] [Google Scholar]
  64. Vacca, M., G.  Celano, F. M.  Calabrese, P.  Portincasa, M.  Gobbetti, and M.  De Angelis. . 2020. The controversial role of human gut Lachnospiraceae. Microorganisms  8:573. doi: 10.3390/microorganisms8040573 [DOI] [PMC free article] [PubMed] [Google Scholar]
  65. Wakshlag, J. J., K. W.  Simpson, A. M.  Struble, and S. E.  Dowd. . 2011. Negative fecal characteristics are associated with pH and fecal flora alterations during dietary change in dogs. Intern. J. Appl. Res. Vet. Med. 9:278–283. [Google Scholar]
  66. White, B. L., B. L.  Johnson, R.  Morgan, and R. G.  Shields. . 2017. Changes in the food safety landscape of pet foods in the United States. In: Ricke, S., G. Atungula, C. Rainwater, and S. H. Park, editors. Food and feed safety systems and analysis. London, UK: Academic Press; p. 3–23. doi: 10.1016/B978-0-12-811835-1.00001-4 [DOI] [Google Scholar]
  67. Wong, J. M., R.  de Souza, C. W.  Kendall, A.  Emam, and D. J.  Jenkins. . 2006. Colonic health: fermentation and short chain fatty acids. J. Clin. Gastroenterol. 40:235–243. doi: 10.1097/00004836-200603000-00015 [DOI] [PubMed] [Google Scholar]
  68. Wu, G. D., J.  Chen, C.  Hoffmann, K.  Bittinger, Y. Y.  Chen, S. A.  Keilbaugh, M.  Bewtra, D.  Knights, W. A.  Walters, R.  Knight, . et al.  2011. Linking long-term dietary patterns with gut microbial enterotypes. Science  334:105–108. doi: 10.1126/science.1208344 [DOI] [PMC free article] [PubMed] [Google Scholar]
  69. Xu, J., and J. I.  Gordon. . 2003. Honor thy symbionts. Proc. Natl. Acad. Sci. USA  100:10452–10459. doi: 10.1073/pnas.1734063100 [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. Zentek, J., S.  Fricke, M.  Hewicker-Trautwein, B.  Ehinger, G.  Amtsberg, and C.  Baums. . 2004. Dietary protein source and manufacturing processes affect macronutrient digestibility, fecal consistency, and presence of fecal Clostridium perfringens in adult dogs. J. Nutr. 134:2158S–2161S. doi: 10.1093/jn/134.8.2158S [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

skab028_suppl_Supplementary_Figure_1
Click here for additional data file. (273.8KB, docx)

Articles from Journal of Animal Science are provided here courtesy of Oxford University Press

RESOURCES