Beyond the Bowl: Understanding Amino Acid Requirements and Digestibility to Improve Protein Quality Metrics for Dog and Cat Foods.

The determination of amino acid (AA) requirements for mammals has traditionally been done through nitrogen (N) balance studies, but this technique underestimates AA requirements in adult animals. There has been a shift toward researchers using the indicator amino acid oxidation (IAAO) technique for the determination of AA requirements in humans, and recently in dogs. However, the determination of AA requirements specific to adult dogs and cats at maintenance is lacking and the current requirements outlined by the National Research Council are based on a dearth of data and are likely underreporting the requirements of indispensable AA (IAA) for the population. To ensure the physiological requirements of our cats and dogs are met, we need methods to accurately and precisely measure digestibility. In vivo methods, such as ileal cannulation, are most commonly used, however, due to ethical considerations, we are moving away from animal models and toward in vitro methods. Harmonized static digestion models have the potential to replace in vivo methods but work needs to be done to have these methods more accurately represent the gastrointestinal tract (GIT) of cats and dogs. The Digestible IAA Score (DIAAS) is one metric that can help define protein quality for individual ingredients or mixed diets that uses AA SID estimates and ideally those can be replaced with in vitro AA digestibility estimates. Finally, we need accurate and reliable laboratory AA analyses to measure the AA present in complete diets, especially those used to quantify methionine (Met) and cysteine (Cys), both often limiting AAs in cat and dog diets. Together, this will guide accurate feed formulation for our companion animals to satisfy requirements while avoiding over-supplying protein, which inevitably contributes to excess N excretion, affecting both the environment and feed sustainability.

In vitro digestibility and solubility of phosphorus of three plant-based meat analogues.

Interest in plant-based meat analogues has increased and can be expected to be applied to pet foods, which necessitates the understanding of the nutrient supply in those foods. Our primary aim was to advance our understanding of the digestive properties of sterilized plant-based meat analogues. The impact of the preparatory processing steps on the solubility of meat analogues was studied. Meat analogues were made by mixing water, salt, and wheat gluten with soy protein isolate, pea protein isolate, or faba bean concentrate. Mixed materials were processed into model meat analogues using shear cell technology. Products were canned in water or gravy and sterilized. An animal-based canned pet food was made as a reference. Products sampled at the processing steps (mixing, shearing, sterilization) were digested in vitro. Samples of digestate were taken at the gastric phase (0 and 120 min) and small intestinal phase (120, 200, 280, and 360 min) for analysis of protein hydrolysis. The extent digestion of nitrogen and dry matter was determined at the end of incubation. Total phosphorus, soluble phosphorus after acid treatment, and after acid and enzymatic treatment were determined. The degree of hydrolysis after gastric digestion was low but increased immediately in the small intestinal phase; products based on pea had the highest values (56%). Nitrogen digestibility was above 90% for all materials at each processing step, indicating that bioactive compounds were absent or inactivated in the protein isolates and concentrate. Phytate seemed to play a minor role in meat analogues, but phosphorus solubility was influenced by processing. Shearing decreased soluble phosphorus, but this effect was partly reversed by sterilization. Nutrient digestibility as well as phosphorus solubility in plant-based products was higher than or comparable with the reference pet food. These findings show that the digestive properties of the tested plant-based meat analogues do not limit the supply of amino acids and phosphorus.

How important is food structure when cats eat mice?

Feeding whole prey to felids has shown to benefit their gastrointestinal health. Whether this effect is caused by the chemical or physical nature of whole prey is unknown. Fifteen domestic cats, as a model for strict carnivores, were either fed minced mice (MM) or whole mice (WM), to determine the effect of food structure on digestibility, mean urinary excretion time (MUET) of 15N, intestinal microbial activity and fermentation products. Faeces samples were collected after feeding all cats a commercially available extruded diet (EXT) for 10 d before feeding for 19 d the MM and WM diets with faeces and urine collected from day 11 to 15. Samples for microbiota composition and determination of MUET were obtained from day 16 to 19. The physical structure of the mice diet (minced or not) did not affect large intestinal fermentation as total SCFA and branched-chain fatty acid (BCFA), and most biogenic amine (BA) concentrations were not different (P > 0·10). When changing from EXT to the mice diets, the microbial community composition shifted from a carbolytic (Prevotellaceae) to proteolytic (Fusobacteriaceae) profile and led to a reduced faecal acetic to propionic acid ratio, SCFA, total BCFA (P < 0·001), NH3 (P = 0·04), total BA (P < 0·001) and para-cresol (P = 0·08). The results of this study indicate that food structure within a whole-prey diet is less important than the overall diet type, with major shifts in microbiome and decrease in potentially harmful fermentation products when diet changes from extruded to mice. This urges for careful consideration of the consequences of prey-based diets for gut health in cats.

Brush border enzyme hydrolysis and glycaemic effects of isomaltulose compared to other saccharides in dogs.

Digestible carbohydrates differ in glycaemic response, therewith having the potential to influence metabolic conditions such as insulin resistance and diabetes mellitus. Isomaltulose has been proven to lower the glycaemic response in humans, which to date has not been studied in dogs. Therefore, the aim of the present study was to characterise the digestibility, as well as the physiological effects of isomaltulose in dogs, in comparison to other saccharides. To this end, three studies were performed. Study 1 was an in vitro study, evaluating the small intestinal hydrolysis of isomaltulose compared to other relevant carbohydrate sources. Three of these saccharides, having close and low-moderate degrees of hydrolysis by brush border enzymes, were also evaluated in vivo for their glycaemic effects by measuring plasma levels of glucose, insulin and glucagon-like peptide 1 (GLP-1) 0-180 min after administration of a single dosage after an overnight fast (i.e., isomaltulose, sucrose and maltodextrin in a 3 × 3 Latin-square design, in 9 dogs, Study 2). To understand if digestive enzymes, underlying glycaemic responses for isomaltulose and sucrose can be upregulated, we exposed dogs to these saccharides for 2 weeks and repeated the measurements after an overnight fast in 18 dogs (Study 3). Isomaltulose was hydrolysed by intestinal enzyme preparation from all three dogs, but the degrading activity was low (e.g., 3.95 ± 1.03 times lower vs. sucrose), indicating a slower rate of hydrolysis. Isomaltulose had a low glycaemic response, in line with in vitro data. In vitro hydrolysis of sucrose was comparable or even higher than maltodextrin in contrast to the more pronounced glycaemic response to maltodextrin observed in vivo. The numerically higher blood glucose response to sucrose after continuous consumption, might indicate an adaptive response. In conclusion, the current work provides valuable insights into the digestion physiology of various saccharides in dogs. Further investigations on related benefits are thus warranted.

Determining the protocol requirements of in-home dog food digestibility testing.

In-home pet food testing has the benefit of yielding data which is directly applicable to the pet population. Validated and standardised in-home test protocols need to be available, and here we investigated key protocol requirements for an in-home canine food digestibility protocol. Participants were recruited via an online survey. After meeting specific inclusion criteria, sixty dogs of various breeds and ages received, during 14 consecutive days, a relatively low and high digestible complete dry extruded food containing titanium (Ti) dioxide. Both foods were given for 7 d in a cross-over design. Owners collected faeces daily allowing daily faecal Ti concentrations and digestibility of nitrogen (N), dry matter (DM), crude ash, organic matter (OM), crude fat (Cfat), starch and gross energy (GE) to be determined. Faecal Ti and digestibility values for all nutrients were not different (P > 0·05) from the second day onwards after first consumption for both foods. One day of faecal collection yielded reliable digestibility values with additional collection days not reducing the confidence interval around the mean. Depending on the accepted margin of error, the food and the nutrient of interest, the minimal required sample size was between 9 and 43 dogs. Variation in digestibility values could in part be explained by a dog's neuter status (N, crude ash) and age (crude ash, Cfat) but not sex and body size. Future studies should focus on further identifying and controlling sources of variation to improve the in-home digestibility protocol and reduce the number of dogs required.

Digestion of bamboo compared to grass and lucerne in a small hindgut fermenting herbivore, the guinea pig (Cavia porcellus).

Bamboo is an enigmatic forage, representing a niche food for pandas and bamboo lemurs. Bamboo might not represent a suitable forage for herbivores relying on fermentative digestion, potentially due to its low fermentability. To test this hypothesis, guinea pigs (n = 36) were used as model species and fed ad libitum with one of three forages (bamboo, lucerne, or timothy grass) in a fresh or dried state, with six individuals per group, for 3 weeks. The nutrient composition and in vitro fermentation profile of bamboo displayed low fermentation potential, i.e. high lignin and silica levels together with a gas production (Hohenheim gas test) at 12 h of only 36% of that of lucerne and grass. Although silica levels were more abundant in the leftovers of (almost) all groups, guinea pigs did not select against lignin on bamboo. Dry matter (DM) intake was highest and DM digestibility lowest on the bamboo forage. Total short-chain fatty acid levels in caecal content were highest for lucerne and lowest for grass and bamboo. Bamboo-fed guinea pigs had a lower body weight gain than the grass and lucerne group. The forage hydration state did not substantially affect digestion, but dry forage led to a numerically higher total wet gut fill. Although guinea pigs increased DM intake on the bamboo diet, the negative effects on fermentation of lignin and silica in bamboo seemed overriding. For herbivores that did not evolutionary adapt, bamboo as an exclusive food resource can be considered as inadequate.

Effects of enzymatically hydrolysed poultry byproduct meal in extruded diets on serum angiotensin-converting enzyme activity and aldosterone in cats.

Several peptides found in hydrolysed poultry byproduct meal can inhibit angiotensin-converting enzyme (ACE) activity, a property that indicates potential antihypertensive and health-promoting effects. This study aimed to assess the effects of extruded diets containing enzymatically hydrolysed poultry byproduct meal (HPM) on cat serum ACE activity and aldosterone (ALD) concentration, nutrient digestibility, and faecal characteristics. On the basis of a preliminary in vitro ACE inhibitory activity assay, a commercial HPM and a commercial conventional poultry byproduct meal (CPM) were selected for further investigation. Two isoenergetic and isonitrogenous diets were formulated: CPM diet (25.7% CPM) and HPM diet (24.7% HPM). In trial 1, the effect of diet on serum ACE activity and ALD concentration was evaluated using 8 healthy cats (4 female and 4 male, 4.1 ± 0.38 kg BW) in a crossover design, with 5 d of adaptation and blood collection on d 6. In trial 2, apparent total tract digestibility and faecal characteristics were evaluated using 12 cats (6 female and 6 male, 4.0 ± 0.72 kg BW) in a completely randomised design. Serum ACE and ALD were analysed using a mixed model, with diet as the fixed effect and cat as the random effect. Data from trial 2 were subjected to analysis of variance, and means were compared by Tukey's test. In vitro ACE inhibitory activity of HPM (90.4%) was higher than that of CPM (52.0%). Cats fed the HPM diet tended to have lower serum ACE activity than those fed the CPM diet (126 versus 142 U/l, p = 0.09). Serum ALD was not influenced by diet. Diets had similar digestibility values, and faecal consistency scores tended to be higher (firmer faeces) in cats fed the CPM diet than in cats fed the HPM diet (4.6 versus 4.0, p = 0.09). Inclusion of HPM in extruded diets may reduce cat serum ACE activity and promote good faecal consistency without affecting digestibility. Further investigations are needed to explore the potential health benefits of HPM in hypertensive cats.

Aflatoxin B1 Conversion by Black Soldier Fly (Hermetia illucens) Larval Enzyme Extracts.

The larvae of the black soldier fly (Hermetia illucens L., BSFL) have received increased industrial interest as a novel protein source for food and feed. Previous research has found that insects, including BSFL, are capable of metabolically converting aflatoxin B1 (AFB1), but recovery of total AFB1 is less than 20% when accounting for its conversion to most known metabolites. The aim of this study was to examine the conversion of AFB1 by S9 extracts of BSFL reared on substrates with or without AFB1. Liver S9 of Aroclor-induced rats was used as a reference. To investigate whether cytochrome P450 enzymes are involved in the conversion of AFB1, the inhibitor piperonyl butoxide (PBO) was tested in a number of treatments. The results showed that approximately 60% of AFB1 was converted to aflatoxicol and aflatoxin P1. The remaining 40% of AFB1 was not converted. Cytochrome P450s were indeed responsible for metabolic conversion of AFB1 into AFP1, and a cytoplasmic reductase was most likely responsible for conversion of AFB1 into aflatoxicol.

Gaining insights in the nutritional metabolism of amphibians: analyzing body nutrient profiles of the African clawed frog, Xenopus laevis.

Whole bodies of Xenopus laevis (n = 19) were analysed for chemical composition and morphometrics. The nutrient profile (macronutrients, amino acids, fatty acids and minerals) was evaluated by sex; interactions among variables with body weights and lengths, and comparisons made with different species of marine and fresh water fish. Significant differences were found in morphometric measurements, water content, several minerals and fatty acids between sexes of X. laevis. Amino acid profiles differed in methionine, proline and cysteine, which could underlie different metabolic pathways in frogs when compared to fish. In addition, fatty acid profiles revealed more monounsaturated and n - 6 polyunsaturated fatty acids in frogs than in fish, more similar to values reported for terrestrial than aquatic vertebrates. Important interactions were also found between body measurements and fat, calcium, and phosphorus, as well as between essential and non-essential amino acids. The results indicate that frogs might have particular biochemical pathways for several nutrients, dependent on sex and linked to body weight, which ultimately could reflect specific nutrient needs.

Stability of creatine monohydrate and guanidinoacetic acid during manufacture (retorting and extrusion) and storage of dog foods.

The stability of creatine monohydrate (CrMH), crystallised guanidinoacetic acid (GAA-C) and granulated GAA (GAA-G) in a moist retorted and a dry extruded dog food formulation during production and storage was investigated. Commercial food mixtures were supplemented with CrMH, GAA-C or GAA-G. Uniformity after mixing and retorting or extrusion was determined based on replicate samples (moist n = 8, dry n = 10). Storage stability was evaluated at 25°C/60% relative humidity for 15 months and 40°C/75% for 6 months. Foods with CrMH were analysed for creatine (Cr) and creatinine (Crn), whereas GAA-C and GAA-G foods were analysed for GAA concentrations. Coefficients of variation (CV) for uniformity of the additives after mixing of moist and dry pet food formulations were below 15%, and the CV was lower in processed mixtures. Recoveries after retorting and extrusion were higher for GAA-G (79 and 99%) and GAA-C (89 and 86%) compared to CrMH (36 and 85%) foods. In moist CrMH food, Cr concentrations re-increased by 54% whilst Crn concentrations decreased by 39% after storage at 25°C for 15 months. With total molar Cr + Crn remaining stable throughout storage, Crn and Cr appeared to effectively interconvert. Storage of the extruded CrMH food at 25°C for 15 months resulted in a 63% decrease in Cr and a 39% increase in Crn concentration. The decrease in Cr concentration was larger at 6 months storage at 40°C compared to 15 months storage at 25°C. Both GAA-C and GAA-G moist and dry foods were stable during storage (<10% decrease). This study showed that GAA is highly stable during production and storage of moist and dry canine foods whilst CrMH is relatively unstable, particularly during storage. The latter makes it difficult to establish a guaranteed Cr content in finished moist retorted and dry extruded foods with CrMH.

Are carnivore digestive separation mechanisms revealed on structure-rich diets?: Faecal inconsistency in dogs (Canis familiaris) fed day old chicks.

Pronounced variations in faecal consistency have been described anecdotally for some carnivore species fed a structure-rich diet. Typically two faecal consistencies are distinguished, namely hard and firm versus liquid and viscous faeces. It is possible that a separation mechanism is operating in the carnivore digestive tract, as in many herbivore species. Six beagle dogs were fed two experimental diets in a cross-over design of 7 days. Test diets consisted of chunked day old chicks differing only in particle size (fine = 7.8 mm vs coarse = 13 mm) in order to vary dietary structure. Digestive retention time was measured using titanium oxide (TiO2) as marker. The total faecal output was scored for consistency and faecal fermentation profiles were evaluated through faecal short-chain fatty acid (SCFA) and ammonia (NH3) analyses. A total of 181 faecal samples were collected. Dietary particle size did not affect faecal consistency, fermentative end products nor mean retention time (MRT). However, a faecal consistency dichotomy was observed with firm faeces (score 2-2.5) and soft faeces (score 4-4.5) being the most frequently occurring consistencies in an almost alternating pattern in every single dog. Firm and soft faeces differed distinctively in fermentative profiles. Although the structure difference between diets did not affect the faecal dichotomy, feeding whole prey provoked the occurrence of the latter which raises suspicion of a digestive separation mechanism in the canine digestive tract. Further faecal characterisation is however required in order to unravel the underlying mechanism.

Retorting conditions affect palatability and physical characteristics of canned cat food.

The effects of different temperature and time conditions during retorting of canned cat food on physicochemical characteristics and palatability were examined. For this purpose, lacquer cans containing an unprocessed loaf-type commercial cat food were heated in a pressurised retorting system at three specified temperature-time profiles (113°C/232 min, 120°C/103 min and 127°C/60 min) to equal a similar lethality (F0 value = 30). Physicochemical properties (viscosity, texture, particle size, pH) were determined, and a 10 d three-bowl palatability test was performed with ten European shorthair cats. Retorting at 113°C/232 min resulted in differences in all the physical parameters examined ( particle size). Significant pH differences were observed (6·53, 6·63 and 6·66 for T113/232, 120 and 127°C, respectively). Preference ratios were 0·38, 0·31 and 0·31 for T113/232, 120 and 127°C, respectively (P = 0·067). It can be concluded that different retorting temperature-time profiles with equal F0 value significantly affect physical characteristics and tended to affect palatability of moist cat food.

Evaluation of an in vitro fibre fermentation method using feline faecal inocula: inter-individual variation.

The present study aimed to evaluate the inter-individual variability in fermentation of standard fibrous substrates by faecal inocula from ten healthy adult female cats. Substrates were citrus pectin (CP), fructo-oligosaccharides (FOS), guar gum (GG), sugar beet pulp (SBP) and wheat middlings (WM). Each substrate was incubated with faecal inoculum from each cat. Gas production was measured continuously during the 48 h incubation and SCFA and organic matter disappearance (only SBP and WM) after incubation. Out of ten cats, nine produced faeces on the days of inoculum preparation. The substrates contrasted in terms of fermentation parameters measured. The inter-individual variability was in general lower for the more simple and pure substrates (CP, FOS, GG) than for the more complex substrates containing mixtures of fibres (SBP, WM). Furthermore, for total SCFA and gas produced, inter-individual variability was lower than for proportions of butyrate and of branched-chain fatty acids and for the parameters of gas production kinetics. It is concluded that the variability in in vitro fermentation parameters is associated with the complexity of fibrous substrates. The presented data are instrumental for the calculation of number of faecal donors required for precise in vitro characterisation of the fermentability of dietary fibres. In addition, the number of faecal donors should be adjusted to the specific fermentation parameter(s) of interest.

Evaluation of an in vitro fibre fermentation method using feline faecal inocula: repeatability and reproducibility.

To gain knowledge on the precision of an in vitro method for characterisation of the fermentability of dietary fibres, this study aimed to evaluate the repeatability and reproducibility of such a method. Substrates used were citrus pectin (CP), fructo-oligosaccharides (FOS), guar gum (GG), sugar beet pulp (SBP) and wheat middlings (WM). Each substrate was incubated with faecal inoculum from five cats with three replicates for each substrate-cat combination. Gas production was measured continuously during the 48 h incubation and SCFA and organic matter disappearance (only SBP and WM) were determined after incubation. Four consecutive runs were performed. The within-run variability (repeatability) was generally lower for the more simple and pure substrates (CP, FOS, GG) than for the more complex substrates containing mixtures of fibres (SBP, WM). Replicates showed high variability, in particular for SCFA profiles and parameters of gas production kinetics. The between-run CV (reproducibility) for the measured parameters were, in general, below 10 % for CP, FOS and GG and higher values were obtained for SBP and WM. It is concluded that for precise dietary fibre characterisation, the number of replicates should be multiple and adjusted according to the variability of the parameters of interest and the complexity of fibres. The method yielded reproducible results with some variation in absolute values obtained, which may have an impact on the significance level of the differences among substrates.

Aflatoxin B1 Tolerance and Accumulation in Black Soldier Fly Larvae (Hermetia illucens) and Yellow Mealworms (Tenebrio molitor).

Crops contaminated with fungal mycotoxins such as aflatoxin B1 (AFB1) are often downgraded or removed from the food chain. This study aimed to evaluate the tolerance and accumulation of AFB1 in two insect species to determine whether they could be used to retain condemned mycotoxin contaminated crops in the food chain. First, instar black soldier fly larvae (Hermetia illucens, BSF) and yellow mealworm (Tenebrio molitor, YMW) were fed poultry feed spiked with AFB1 and formulated to contain levels of 0.01, 0.025, 0.05, 0.10, 0.25, and up to 0.5 mg/kg dry feed. Poultry feed without any additions and feed with only the solvent added served as controls. The AFB1 in the feed did not affect survival and body weight in the BSF and YMW larvae (p > 0.10), indicating a high tolerance to aflatoxin B1 in both species. Furthermore, AFB1 and aflatoxin M1 (AFM1) were below the detection limit (0.10 µg/kg) in BSF larvae, whereas the YMW had AFB1 levels that were approximately 10% of the European Union's legal limit for feed materials and excreted AFM1. It is concluded that both BSF larvae and YMW have a high AFB1 tolerance and do not accumulate AFB1.

Does canine inflammatory bowel disease influence gut microbial profile and host metabolism?

BACKGROUND: Inflammatory bowel disease (IBD) refers to a diverse group of chronic gastrointestinal diseases, and gut microbial dysbiosis has been proposed as a modulating factor in its pathogenesis. Several studies have investigated the gut microbial ecology of dogs with IBD but it is yet unclear if this microbial profile can alter the nutrient metabolism of the host. The aim of the present study was to characterize the faecal bacterial profile and functionality as well as to determine host metabolic changes in IBD dogs. Twenty-three dogs diagnosed with IBD and ten healthy control dogs were included. Dogs with IBD were given a clinical score using the canine chronic enteropathy clinical activity index (CCECAI). Faecal short-chain fatty acids (SCFA) and ammonia concentrations were measured and quantitative PCR was performed. The concentration of plasma amino acids, acylcarnitines, serum folate, cobalamin, and indoxyl sulfate was determined. RESULTS: No significant differences in the abundance of a selection of bacterial groups and fermentation metabolites were observed between the IBD and control groups. However, significant negative correlations were found between CCECAI and the faecal proportion of Lactobacillus as well as between CCECAI and total SCFA concentration. Serum folate and plasma citrulline were decreased and plasma valine was increased in IBD compared to control dogs. Increased plasma free carnitine and total acylcarnitines were observed in IBD compared with control dogs, whereas short-chain acylcarnitines (butyrylcarnitine + isobutyrylcarnitine and, methylmalonylcarnitine) to free carnitine ratios decreased. Dogs with IBD had a higher 3-hydroxyisovalerylcarnitine + isovalerylcarnitine to leucine ratio compared to control dogs. CONCLUSIONS: Canine IBD induced a wide range of changes in metabolic profile, especially for the plasma concentrations of short-chain acylcarnitines and amino acids, which could have evolved from tissue damage and alteration in host metabolism. In addition, dogs with more severe IBD were characterised by a decrease in faecal proportion of Lactobacillus.

In vitro selenium accessibility in pet foods is affected by diet composition and type.

Se bioavailability in commercial pet foods has been shown to be highly variable. The aim of the present study was to identify dietary factors associated with in vitro accessibility of Se (Se Aiv) in pet foods. Se Aiv is defined as the percentage of Se from the diet that is potentially available for absorption after in vitro digestion. Sixty-two diets (dog, n 52; cat, n 10) were in vitro enzymatically digested: fifty-four of them were commercially available (kibble, n 20; pellet, n 8; canned, n 17; raw meat, n 6; steamed meat, n 3) and eight were unprocessed (kibble, n 4; canned, n 4) from the same batch as the corresponding processed diets. The present investigation examined if Se Aiv was affected by diet type, dietary protein, methionine, cysteine, lysine and Se content, DM, organic matter and crude protein (CP) digestibility. Se Aiv differed significantly among diet types (P< 0·001). Canned and steamed meat diets had a lower Se Aiv than pelleted and raw meat diets. Se Aiv correlated positively with CP digestibility in extruded diets (kibbles, n 19; r 0·540, P =0·017) and negatively in canned diets (n 16; r - 0·611, P =0·012). Moreover, the canning process (n 4) decreased Se Aiv (P =0·001), whereas extrusion (n 4) revealed no effect on Se Aiv (P =0·297). These differences in Se Aiv between diet types warrant quantification of diet type effects on in vivo Se bioavailability.

Resistant starch diet induces change in the swine microbiome and a predominance of beneficial bacterial populations.

BACKGROUND: Dietary fibers contribute to health and physiology primarily via the fermentative actions of the host's gut microbiome. Physicochemical properties such as solubility, fermentability, viscosity, and gel-forming ability differ among fiber types and are known to affect metabolism. However, few studies have focused on how they influence the gut microbiome and how these interactions influence host health. The aim of this study is to investigate how the gut microbiome of growing pigs responds to diets containing gel-forming alginate and fermentable resistant starch and to predict important interactions and functional changes within the microbiota. RESULTS: Nine growing pigs (3-month-old), divided into three groups, were fed with either a control, alginate-, or resistant starch-containing diet (CON, ALG, or RS), and fecal samples were collected over a 12-week period. SSU (small subunit) rDNA amplicon sequencing data was annotated to assess the gut microbiome, whereas comprehensive microarray polymer profiling (CoMPP) of digested material was employed to evaluate feed degradation. Gut microbiome structure variation was greatest in pigs fed with resistant starch, where notable changes included the decrease in alpha diversity and increase in relative abundance of Lachnospiraceae- and Ruminococcus-affiliated phylotypes. Imputed function was predicted to vary significantly in pigs fed with resistant starch and to a much lesser extent with alginate; however, the key pathways involving degradation of starch and other plant polysaccharides were predicted to be unaffected. The change in relative abundance levels of basal dietary components (plant cell wall polysaccharides and proteins) over time was also consistent irrespective of diet; however, correlations between the dietary components and phylotypes varied considerably in the different diets. CONCLUSIONS: Resistant starch-containing diet exhibited the strongest structural variation compared to the alginate-containing diet. This variation gave rise to a microbiome that contains phylotypes affiliated with metabolically reputable taxonomic lineages. Despite the significant microbiome structural shifts that occurred from resistant starch-containing diet, functional redundancy is seemingly apparent with respect to the microbiome's capacity to degrade starch and other dietary polysaccharides, one of the key stages in digestion.

In vivo degradation of alginate in the presence and in the absence of resistant starch.

This study evaluated the intestinal degradability of alginate during 74 days intake in pigs as models for humans. Diets contained pregelatinized starch, retrograded starch, alginate, or a mix of retrograded starch and alginate. Faeces were collected on day 1, 3, 7, 14, 39 and 74. Clear trends in intestinal alginate degradation were observed. Up to day 39, the total tract digestibility of alginate was limited (0.52 ± 0.10), and was lower with the inclusion of retrograded starch in the diet (0.34 ± 0.02). More than 90% of the faecal alginate was insoluble in water, which may explain the low digestibility of the alginate. The digestibility of mannuronic acid (M) was 2-3 times higher than that of guluronic acid (G). The changes of G:M ratio and the relative amounts of alginate oligosaccharides between day 39 and 74 indicated that the microbiota needed more than 39 days to adapt to alginate. This study demonstrated that in-depth analyses of dietary fibres are valuable in understanding the fate of the dietary fibres in the large intestine as it was shown that degradation of a dietary fibre depends not only on the properties of the fibre itself, but also on the other dietary fibres present in the diet and the adaptation time.