In the wild, feral cats typically eat small mammals, reptiles, birds and insects. It is often not possible to mimic natural feeding behaviours of feral cats. Extruded diets have been the traditional alternative fed to domestic cats. Commercial chicken-based extruded diets (EXT) have complex diet formulations, including protein, fat, carbohydrate, fibre, vitamin and mineral ingredients. Association of American Feed Control Officials (AAFCO)( 1 ) recommend minimum concentrations of 26 % crude protein (DM basis) and 9 % fat DM basis. If these minimum concentrations are targeted by formulators, commercial feline EXT may contain up to 50–55 % carbohydrates. Plantinga et al. ( Reference Plantinga, Bosch and Hendriks 2 ) estimated the diet of feral cats expressed on a DM basis would contain 63 % crude protein (CP), 23 % fat and 2·8 % nitrogen-free extract (i.e. digestible carbohydrate).
Given their carnivorous nature, it has been hypothesised that the protein:carbohydrate ratio of feline diets is important for feline health (i.e. obesity, feline diabetes and gut microbiota)( Reference Bermingham, Kittelmann and Henderson 3 – Reference Verbrugghe, Janssens and Meininger 6 ). As lower bacterial diversity and great shifts in commensal bacteria are often present in inflammatory bowel diseases, it suggests that a balanced gut microbiota is important for maintaining host health( Reference Abecia, Hoyles and Khoo 7 – Reference Janeczko, Atwater and Bogel 9 ). Several studies have examined the impact of dietary alterations on faecal microbial populations in cats( Reference Bermingham, Kittelmann and Henderson 3 – Reference Hooda, Vester Boler and Kerr 5 , Reference Barry, Middelbos and Vester Boler 10 – Reference Kerr, Dowd and Swanson 13 ); however, very few have examined the microbial population of cats fed a ‘wild-type’ diet( Reference Desai, Musil and Carr 12 , Reference Kerr, Dowd and Swanson 13 ). Commercially available whole prey may be more similar to the feral cat diet. For example, commercially available 1–3-d-old chicks (CHI) are approximately 72–76 % CP, 16–20 % fat and <5 % nitrogen-free extract( Reference Kerr, Morris and Burke 14 , Reference Kerr 15 ). Previous studies have shown that extruded and whole-prey diets differ in digestibility as well as macronutrient composition( Reference Kerr, Morris and Burke 14 – Reference Vester, Burke and Dikeman 17 ), and this may alter the fermentable substrates that are available to the gastrointestinal microbiota for fermentation( Reference Depauw, Bosch and Hesta 18 , Reference Depauw, Hesta and Whitehouse 19 ). The objective of the present study was to compare the faecal microbiota of cats fed an EXT chicken-based diet to those fed commercially available whole CHI.
Experimental methods
Study design
The animal protocol was approved by the University of Illinois Animal Care and Use Committee. Faecal samples were collected from neutered male domestic cats (mean age = 5·7 years; body condition score 4·5–5·5 of 9). A completely randomised design was utilised to test the impacts of two dietary treatments (Table 1): (1) EXT (n 3 cats; P & G Petcare); and (2) raw CHI (n 5 cats; Rodent Pro). The raw chicks were frozen (−20°C) upon arrival, and thawed in the refrigerator for 24 h prior to feeding. Fresh water was available ad libitum. A computer was used to randomly allot cats to treatment. Cats were adapted to diets for 10 d, prior to fresh faecal collection (<15 min from defection). Faecal samples were stored at −80°C until DNA extraction.
Table 1. Chemical composition of CHI and an EXT fed to domestic cats*
* CHI, 1–3-d-old chicks (Rodent Pro); EXT, extruded chicken-based diet (P & G Petcare).
†Ingredient composition of EXT as reported by manufacturer: chicken, chicken by-product meal, maize meal, maize grits, dried beet pulp, poultry by-product meal, natural flavour, dried egg product, brewers dried yeast, sodium bisulphate, potassium chloride, fructooligosaccharides, animal fat (preserved with mixed tocopherols, a source of vitamin E), fish oil (preserved with mixed tocopherols, a source of vitamin E), DL-methionine, choline chloride, calcium carbonate, vitamins (vitamin E supplement, niacin, ascorbic acid, vitamin A acetate, calcium pantothenate, biotin, thiamine mononitrate (source of vitamin B1), pyridoxine hydrochloride (source of vitamin B6), vitamin B12 supplement, riboflavin supplement (source of vitamin B2), inositol, vitamin D3 supplement and folic acid), taurine, minerals (zinc oxide, manganese sulphate, copper sulphate, potassium iodide and cobalt carbonate) and rosemary extract.
Sample analysis
Faecal bacterial DNA was isolated according to procedures described previously( Reference McInnes and Cutting 20 ) using the MO BIO PowerSoil™ Kit (MO BIO Laboratories). Amplification of a 600 bp sequence of the V4–V6 variable regions of the 16S rRNA gene was done using barcoded primers as previously described( Reference Cephas, Kim and Mathai 21 ). PCR amplicons were further purified utilising AMPure XP beads (Beckman-Coulter Inc.). Amplicons were combined in equimolar ratios to create a DNA pool that was used for pyrosequencing. DNA quality of amplicon pools was assessed before pyrosequencing using a 2100 Bioanalyzer (Agilent Technologies). Pyrosequencing was performed at the W. M. Keck Center for Biotechnology at the University of Illinois utilising a 454 Genome Sequencer and FLX titanium reagents (Roche Applied Science).
Data analysis
High-quality (quality value >25) sequence data derived from the sequencing process was processed using a proprietary analysis pipeline (www.mrdnalab.com) and as described previously( Reference Swanson, Dowd and Suchodolski 22 ).
Statistical analysis
Sequence percentages at each taxonomic level were analysed using the Mixed models procedure of SAS (version 9.3; SAS Institute). The fixed effect of diet was tested. Means were separated for treatments using a Fisher-protected least significant difference with Tukey's adjustment. Results are reported as least-squares means with P ≤ 0·05 defined as significant and P ≤ 0·10 as trends for treatment effects.
Results
Regardless of dietary treatment, Firmicutes (62–88 % of all sequences) was the predominant bacterial phylum in cat faeces (data not shown). Fusobacteria (0·2–17 % of all sequences), Proteobacteria (2–16 % of all sequences), Actinobaceria (1·4–18 % of all sequences), Tenericutes (1·4–9 % of all sequences) and Bacteroidetes (0–3 % of all sequences) also were predominant phyla present (data not shown). The proportion of Bacteroidetes was greater (P = 0·03) in faeces of cats fed EXT (1·6 % of all sequences) than those fed CHI (0·2 % of all sequences; data not shown).
Proportions of genera, however, depended on dietary treatment (Table 2). The predominant genera in faeces of cats fed CHI were Clostridium (11–25 % of sequences), Blautia (4–19 % of sequences), unidentified Lachnospiraceae (14–16 % of sequences), Peptococcus (7–13 % of sequences), Fusobacterium (4–13 % of sequences), Ruminococcus (2–9 % of sequences) and Collinsella (2–8 % of sequences). The predominant genera in faeces of cats fed EXT were Megamonas (2–28 % of sequences), Megasphaera (0·01–26 % of sequences), Blautia (10–16 % of sequences), Collinsella (1–16 % of sequences), Lactobacillus (0·2–14 % of sequences), Clostridium (8–12 % of sequences) and unidentified Lachnospiraceae (4–7 % of sequences).
Table 2. Predominant bacterial genera (expressed as percentage of sequences) in faeces of domestic cats fed CHI (n 5) or EXT (n 3)*
* CHI, 1–3-d-old chicks (My Pet Carnivore); EXT, extruded chicken-based diet (P&G Petcare).
†ND, not detected.
Four genera were present in a majority of samples (n 5) for cats fed CHI (Holdemania (three of five; 0–0·5 % of sequences), Escherichia (four of five; 0–0·2 % of sequences), Marvinbyantia (five of five; 0·01–0·1 % of sequences) and Acetanaerobacterium (three of five; 0–0·02 % of sequences)), but were not detected in the samples for cats fed EXT (data not shown). Five genera were present in a majority of samples (n 3) for cats fed EXT (Megasphaera (three of three; 0·01–26 % of sequences), Lactobacillus (three of three; 0·2–14 % of sequences), Prevotella (three of three; 0·1–2·6 % of sequences), Subdoligranulum (two of three; 0–1·4 % of sequences) and Bifidobacterium (two of three; 0–0·8 % of sequences), but were not detected in the samples for cats fed CHI (data not shown). Cats fed CHI had greater (P < 0·05) Psuedobutyrivibrio, unidentified Lachnospiraceae and Peptococcus populations and tended to have greater (P < 0·10) Slackia, Allobaculum, Eubacterium, Oscillibacter and unidentified Ruminococcaceae populations. In contrast, cats fed CHI had lower (P < 0·05) Faecalibacterium and Succinivibrio populations and tended to have lower (P < 0·10) Phascolarctobacterium, Megamonas and unidentified Coriobacteriaceae populations.
Discussion
We identified a significant shift in the faecal bacteria of cats fed CHI v. EXT. As these diets contained ingredient and nutrient differences, differences in proportions of bacterial populations can only be attributed to the treatments as a whole. To our knowledge, most of the studies investigating the effects of diet on bacterial composition utilising next-generation sequencing in cats have examined the effects of commercial dry( Reference Hooda, Vester Boler and Kerr 5 , Reference Barry, Middelbos and Vester Boler 10 , Reference Tun, Brar and Khin 11 ) and canned diets( Reference Bermingham, Kittelmann and Henderson 3 , Reference Bermingham, Young and Kittelmann 4 ). Only preliminary data for the differences in bacterial composition between a raw meat and kibbled diets fed to dogs have been reported( Reference Beloshapka, Dowd and Duclos 23 , Reference Beloshapka, Dowd and Suchodolski 24 ). No data have been reported for a whole-prey diet type in either cats or dogs; however, in a companion paper, we also present the microbial populations of cats fed whole and ground chicks and the effects of clinically confirmed symptomatic salmonellosis( Reference Kerr, Dowd and Swanson 13 ).
Bermingham et al. ( Reference Bermingham, Young and Kittelmann 4 ) reported increased faecal proportions of Lactobacillus (32 v. 0·1 % of sequences) and Megasphaera (23 v. <0·1 % of sequences) in the faecal microbiota of cats fed a commercial dry diet (i.e. lower protein, higher nitrogen-free extract; CP = 33 %, DM basis; fat = 11 %, DM basis) compared with those maintained on a commercial wet diet (i.e. higher protein, lower nitrogen-free extract; CP = 42 %, DM basis; fat = 42 %, DM basis). Hooda et al. ( Reference Hooda, Vester Boler and Kerr 5 ) reported increased faecal proportions of Megasphaera (18–33 v. <0·1–0·1 % of sequences), Subdoligranulum (2–6 v. 0·1–0·3 % of sequences) and Bifidobacterium (12–21 v. < 0·1–0·1 % of sequences) in kittens fed a moderate protein-moderate carbohydrate diet (CP = 34 %, DM basis; fat = 19 %, DM basis) compared with those fed a high-protein, low-carbohydrate diet (CP = 53 %, DM basis; fat = 24 %, DM basis). Beloshapka et al. ( Reference Beloshapka, Dowd and Duclos 23 ) reported increased faecal proportions of Faecalibacterium (10 v. 0·3 % of sequences), Lactobacillus (9 v. < 0·1 % of sequences) and Prevotella (9 v. 0·2 % sequences) for dogs fed an EXT compared with raw-meat-based diets. Although these studies also reported other differences not observed herein, those listed here are similar to our data, and indicated that the protein:carbohydrate ratio may impact these genera. However, both Bermingham et al. ( Reference Bermingham, Young and Kittelmann 4 ) and Hooda et al. ( Reference Hooda, Vester Boler and Kerr 5 ) reported decreased faecal proportions of Faecalibacterium (<0·1 v. 0·5 % of sequence, and 0·1–2 v. 5–7 % of sequences, respectively) for the lower-protein v. higher-protein diet, which are contrary to our results and those reported by Beloshapka et al. ( Reference Beloshapka, Dowd and Duclos 23 ).
Another aspect of diet that can impact microbial populations is dietary fibre. Although it has been recognised that animal tissues provide substrate for fermentation (i.e. animal fibre( Reference Depauw, Bosch and Hesta 18 , Reference Depauw, Hesta and Whitehouse 19 )), their role in gut health has not been fully elucidated, and little is known about their impacts on microbial populations. The EXT diet tested herein included multiple ingredients that would contribute to the dietary fibre fraction, including beet pulp and fructooligosaccharides, which likely contributed to the differences in microbial populations. Lactobacillus, Bifidobacterium and Faecalibacterium species are generally considered beneficial bacteria and are often targeted with dietary fibre and prebiotic inclusions. Middelbos et al. ( Reference Middelbos, Vester Boler and Qu 25 ) reported increased faecal proportions of Faecalibacterium (30 v. 9 % of sequences) in dogs fed a diet containing 7·5 % beet pulp fibre (total dietary fibre = 4·5 %, DM basis) compared with 0 % supplemental fibre (total dietary fibre = 1·4 %, DM basis). Fructooligosaccharides are rapidly fermented and serve as a source of soluble, prebiotic fibre( Reference Barry, Wojcicki and Middelbos 26 , Reference Barry, Wojcicki and Bauer 27 ). Several studies in cats and dogs have reported that fructooligosaccharides exert a prebiotic effect in the colon, stimulating the growth of Bifidobacterium spp., Lactobacillus spp. or both( Reference Barry, Middelbos and Vester Boler 10 , Reference Sparkes, Papasouliotis and Sunvold 28 ). These studies are consistent with the results reported herein.
The present study had limitations, including our sampling protocol, number of animals and the nature of the diets tested. First, baseline samples were not collected before dietary treatments were administered. Thus, while differences due to diet were identified, we were unable to identify microbiome shifts from baseline. Second, given the low number of animals studied, our statistical power was low and our ability to translate the data to larger cat populations was limited. Finally, because the diets were greatly different in terms of nutrient composition and physical form, microbiome differences could not be attributed to any single factor or nutrient, but only the entire diet as a whole.
To conclude, there is growing evidence that the proportions of gastrointestinal microbes are altered in some disease states, including cancer, gastrointestinal diseases and metabolic diseases( Reference Ley, Turnbaugh and Klein 29 – Reference Turnbaugh, Backhed and Fulton 31 ). Given the potential of diet to modulate microbial populations, diet therapies may play a role in their treatment. However, it is unclear if this dysbiosis is causative or symptomatic of these disease states. Additionally, there is little data available regarding microbial populations, dysbiosis and disease states for cats( Reference Inness, McCartey and Khoo 8 , Reference Kerr, Dowd and Swanson 13 ). The present study has highlighted some interesting differences in gastrointestinal microbes of cats eating extruded v. raw diets. More research is needed, however, to determine the long-term impacts of the alterations in the proportions of faecal microbial populations and the health of domestic cats.
Acknowledgements
The authors have no conflicts of interest to declare. This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. In regards to authorship, K. R. K. and K. S. S. contributed to formulation of research, study design and study execution. K. R. K. and S. E. D. contributed to data analysis. K. R. K. and K. S. S. contributed to manuscript writing. As stated in the Experimental Methods section, the animal protocol for this experiment was approved by the University of Illinois Animal Care and Use Committee.
This paper was published as part of the WALTHAM International Nutritional Sciences Symposium Proceedings 2013, publication of which was supported by an unrestricted educational grant from Mars Incorporated. The papers included in these proceedings were invited by the Guest Editor and have undergone the standard journal formal review process. They may be cited.
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