Effect of substrate and feed antibiotics on in vitro production of volatile fatty acids and methane in caecal contents of chickens

Connecting gut microbiomes and short chain fatty acids with the serotonergic system and behavior in Gallus gallus and other avian species

The chicken gastrointestinal tract has a diverse microbial community. There is increasing evidence for how this gut microbiome affects specific molecular pathways and the overall physiology, nervous system and behavior of the chicken host organism due to a growing number of studies investigating conditions such as host diet, antibiotics, probiotics, and germ-free and germ-reduced models. Systems-level investigations have revealed a network of microbiome-related interactions between the gut and state of health and behavior in chickens and other animals. While some microbial symbionts are crucial for maintaining stability and normal host physiology, there can also be dysbiosis, disruptions to nutrient flow, and other outcomes of dysregulation and disease. Likewise, alteration of the gut microbiome is found for chickens exhibiting differences in feather pecking (FP) behavior and this alteration is suspected to be responsible for behavioral change. In chickens and other organisms, serotonin is a chief neuromodulator that links gut microbes to the host brain as microbes modulate the serotonin secreted by the host's own intestinal enterochromaffin cells which can stimulate the central nervous system via the vagus nerve. A substantial part of the serotonergic network is conserved across birds and mammals. Broader investigations of multiple species and subsequent cross-comparisons may help to explore general functionality of this ancient system and its increasingly apparent central role in the gut-brain axis of vertebrates. Dysfunctional behavioral phenotypes from the serotonergic system moreover occur in both birds and mammals with, for example, FP in chickens and depression in humans. Recent studies of the intestine as a major site of serotonin synthesis have been identifying routes by which gut microbial metabolites regulate the chicken serotonergic system. This review in particular highlights the influence of gut microbial metabolite short chain fatty acids (SCFAs) on the serotonergic system. The role of SCFAs in physiological and brain disorders may be considerable because of their ability to cross intestinal as well as the blood-brain barriers, leading to influences on the serotonergic system via binding to receptors and epigenetic modulations. Examinations of these mechanisms may translate into a more general understanding of serotonergic system development within chickens and other avians.

The role of feed enzymes in maintaining poultry intestinal health

Gut health or intestinal health is frequently discussed without any clear definition as to its meaning. It is suggested that this should be defined as intestinal integrity and functionality as both are a pre-requisite for the health of the intestine itself and the host. The health of the intestine is dependent upon a successful evolution of the absorptive capacity of the intestine, which in turn is influenced by the co-evolution of the intestinal immune systems and the microbiota. Nutrient supply plays a significant role in this process and from the perspective of the microbiota this changes with age as the intestines and upper gastrointestinal tract (GIT) microbiota become more effective in nutrient removal. Feed enzymes play a significant role in this process. Phytases can improve digestion of minerals, amino acids and energy and as a result reduce the availability of nutrients in the lower intestines for the microbiota. Protease can have a similar effect with amino acid supply. Non-starch polysaccharidases (NSPases) have a unique role in that they not only improve diet digestibility from the hosts perspective, thus limiting nutrient supply to the microbiota, but they also release soluble fragments of fibre from the insoluble matrix and/or depolymerize high molecular weight viscous fibre fractions in to smaller, more fermentable carbohydrate fractions. This results in a more favourable balance between fermentable carbohydrate to protein supply, a ratio which is deemed critical to maintaining good intestinal health. The dynamic nature of this complex evolution needs greater consideration if antibiotic free production is to succeed. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The Spatial and Temporal Characterization of Gut Microbiota in Broilers

The gut microbiota of chickens plays an important role in host physiology. However, the colonization and prevalence of gut microbiota have not been well-characterized. Here, we performed 16S rRNA gene sequencing on the duodenal, cecal and fecal microbiota of broilers at 1, 7, 21, and 35 days of age and characterized the dynamic succession of microbiota across the intestinal tract. Our results showed that Firmicutes was the most abundant phylum detected in each gut site at various ages, while the microbial diversity and composition varied among the duodenum, cecum, and feces at different ages. The microbial diversity and complexity of the cecal microbiota increased with age, gradually achieving stability at 21 days of age. As a specific genus in the cecum, Clostridium_sensu_stricto_1 accounted for 83.50% of the total abundance at 1 day of age, but its relative abundance diminished with age. Regarding the feces, the highest alpha diversity was observed at 1 day of age, significantly separated from the alpha diversity of other ages. In addition, no significant differences were observed in the alpha diversity of duodenal samples among 7, 21, and 35 days of age. The predominant bacterium, Lactobacillus, was relatively low (0.68–6.04%) in the intestinal tract of 1-day-old chicks, whereas its abundance increased substantially at 7 days of age and was higher in the duodenum and feces. Escherichia-Shigella, another predominant bacterium in the chicken intestinal tract, was also found to be highly abundant in fecal samples, and the age-associated dynamic trend coincided with that of Lactobacillus. In addition, several genera, including Blautia, Ruminiclostridium_5, Ruminococcaceae_UCG-014, and [Ruminococcus]_torques_group, which are related to the production of short-chain fatty acids, were identified as biomarker bacteria of the cecum after 21 days of age. These findings shed direct light on the temporal and spatial dynamics of intestinal microbiota and provide new opportunities for the improvement of poultry health and production.

Community composition of cecal microbiota in commercial yellow broilers with high and low feed efficiencies

The cecal microbiota plays important roles in host food digestion and nutrient absorption, which may in part affect feed efficiency (FE). To investigate the composition and functional differences of cecal microbiota between high (n = 30) and low (n = 29) feed conversion ratio (FCR; metric for FE) groups, we performed 16S rRNA gene sequencing and predicted the metagenome function using Phylogenetic Investigation of Communities by Reconstruction of Unobserved Species in yellow broilers. The results showed that the 2 groups had the same prominent microbes but with differing abundance. Firmicutes, Bacteroidetes, and Actinobacteria were 3 prominent bacterial phyla in the cecal microbial community. Although there were no differences in microbial diversity, compositional differences related to FCR were found via linear discriminant analysis (LDA) effect size; the genus Bacteroides had a significantly higher abundance (LDA >2) in the high FE (HFE) group than in the low FE group. Furthermore, genus Bacteroides had a negative FCR-associated correlation (P < 0.05). Oscillospira was positively correlated with Bacteroides in both groups, whereas Dorea was negatively correlated with Bacteroides in the HFE group. Predictive functional analysis revealed that metabolic pathways such as “starch and sucrose metabolism,” “phenylalanine, tyrosine and tryptophan biosynthesis,” and “carbohydrate metabolism” were significantly enriched in the HFE group. The relatively subtle differences in FE-associated cecal microbiota composition suggest a possible link between cecal microbiota and FE. Moreover, Bacteroides may potentially be used as biomarkers for FE to improve growth performance in yellow broilers.

Review: Methanogens and methane production in the digestive systems of nonruminant farm animals

The greenhouse gases (GHGs) derived from agriculture include carbon dioxide, nitrous oxide, and methane (CH₄). Of these GHGs, CH₄, in particular, constitutes a major component of the GHG emitted by the agricultural sector. Along with environmental concerns, CH₄ emission also leads to losses in gross energy intake with economic implications. While ruminants are considered the main source of CH₄ from agriculture, nonruminant animals also contribute substantially, and the CH₄ emission intensity of nonruminants remains comparable to that of ruminants. Means of mitigating CH₄ emissions from enteric fermentation have therefore been sought. Methane is produced by methanogens-archaeal microorganisms that inhabit the digestive tracts of animals and participate in fermentation processes. As the diversity of methanogen communities is thought to be responsible for the differences in CH₄ production among nonruminant animals, it is necessary to investigate the archaeal composition of specific animal species. Methanogens play an important role in energy metabolism and adipose tissue deposition in animals. Higher abundances of methanogens, along with their higher diversity, have been reported to contribute to lean phenotype in pigs. In particular, a greater abundance of Methanosphaera spp. and early dominance of Methanobrevibacter smithii have been reported to correlate with lower body fat formation in pigs. Besides the contribution of methanogens to the metabolic phenotype of their hosts, CH₄ release reduces the productivity that could be achieved through other hydrogen (H₂) disposal pathways. Enhanced participation of acetogenesis in H₂ disposal, leading to acetate formation, could be a more favorable direction for animal production and the environment. Better knowledge and understanding of the archaeal communities of the gastrointestinal tract (GIT), including their metabolism and interactions with other microorganisms, would thus allow the development of new strategies for inhibiting methanogens and shifting toward acetogenesis. There are a variety of approaches to inhibiting methanogens and mitigating methanogenesis in ruminants, which can find an application for nonruminants, such as nutritional changes through supplementation with biologically active compounds and management changes. We summarize the available reports and provide a comprehensive review of methanogens living in the GIT of various nonruminants, such as swine, horses, donkeys, rabbits, and poultry. This review will help in a better understanding of the populations and diversity of methanogens and the implications of their presence in nonruminant animals.

Effects of Raw and Fermented Rapeseed Cake on Growth Performance, Methane Production, and Breast Meat Fatty Acid Composition in Broiler Chickens

The study was conducted to evaluate the effects of partial replacement of soybean meal (SBM) by 15% raw or fermented rapeseed cake (RRC or FRC) to broilers' diets on growth performance, nutrient utilization, methane emission, and breast muscle fatty acid (FA) composition. A total of 420 one-day-old female Ros 308 broilers were used in three independent experiments (300 birds in the first experiment and 60 in the second and third experiments). In each trial, three treatments were set up: a control group (without rapeseed), and diets replaced soybean meal with 15% addition of RRC or FRC. Birds fed the FRC diet experienced no effect (p > 0.05) on performance or nutrients utilization. Methane emission and total methanogen population in the ceca was decreased (p < 0.05) with the FRC diet. The concentrations of n-3 and n-6 FAs in the breast tissue of fourteen-day-old birds were not affected (p > 0.05) by FRC. However, the n-6/n-3 ratio in the breast muscle of 28-day-old birds was reduced (p < 0.001). In conclusion, the replacement of SBM by FRC in the broiler diets did not show any unfavorable effects on performance or nutrient utilization. Furthermore, the breast meat FA profile was improved, methanogen counts significantly decreased, and methane emission was limited.

Methane emissions of geese (Anser anser) and turkeys (Meleagris gallopavo) fed pelleted lucerne

In contrast to mammalian herbivores, birds are generally perceived to produce little methane (CH₄) during digestion, and accounting for poultry in greenhouse gas inventories is considered unnecessary. We measured CH₄ emissions in six domestic geese (Anser anser, 5.0 ± 0.9 kg) and six domestic turkeys (Meleagris gallopavo, 6.3 ± 0.6 kg) kept on a diet of lucerne pellets only, using open-circuit chamber respirometry. Measurements of oxygen consumption were similar to previously published values in these species. Absolute CH₄ emissions per day were lower in geese (0.58 ± 0.10 L) than in turkeys (1.48 ± 0.16 L) and represented 0.4 ± 0.2 and 0.6 ± 0.1% of gross energy intake, respectively. These results confirm previous findings on the presence of methanogenes in the digestive tract of poultry species, and in vitro measurements performed on poultry caecal contents. In relation to mammalian herbivores in terms of absolute CH₄ emissions, CH₄ yield per dry matter or gross energy intake, or the CH₄:CO₂ ratio, the lucerne-fed geese and turkeys had comparatively low values. The emission of CH₄ in spite of the very short digesta retention times and low fibre digestibility, as measured in the same animals, gives rise to the hypothesis that that in some birds, caecal fermentation and the associated CH₄ production may be related to the microbial digestion of uric acid. The hypothesis that CH₄ emissions in poultry may depend not only on dietary fibre but also on dietary digestible protein (that is excreted as uric acid in urine and retrogradely transported from the cloaca into the caeca) remains to be tested.

Effects of dietary Enteromorpha powder supplementation on productive performance, egg quality, and antioxidant performance during the late laying period in Zi geese

This study investigated the effects of dietary Enteromorpha powder supplementation on the productive performance, egg quality, and antioxidant performance of Zi geese during the late laying period. Three hundred twelve Zi geese (1 yr old) were randomly allocated into 2 cohorts to form a control group and an experimental group (with each cohort including 6 replicates and 21 female geese and 5 male geese in each replicate). The control group was fed a basal diet, and the experimental group was fed a diet containing 3% Enteromorpha powder. The data showed that Enteromorpha powder supplementation significantly improved egg production, laying rate, average daily egg weight (P < 0.01), and egg yolk color (P < 0.05). Supplementation decreased the ADFI and feed conversion rate (P < 0.01). Compared with the control group, glutathione peroxidase (GSH-Px) activity was significantly higher in serum and ovary tissue (P < 0.05), but GSH-Px activity was lower in liver tissue (P < 0.01). Malondialdehyde was reduced in liver and ovary tissue (P < 0.05) in the Enteromorpha powder supplementation group. Meanwhile, the expression of the CAT gene was significantly upregulated in the liver (P < 0.01) in the Enteromorpha group. These results indicate that dietary Enteromorpha powder supplementation improved productive performance and reduced the level of lipid peroxidation in Zi geese during the late laying period.

Evaluation of bee venom as a novel feed additive in fast-growing broilers

1. The present study was designed to evaluate purified bee venom (BV) as an alternative to antibiotics in broiler chickens. The experimental treatment diets were formulated by adding BV into a maize-soybean meal-based diet to give 0, 10, 50, 100, and 500 μg BV per kg of diet. 2. Dietary BV quadratically improved (P < 0.05) feed conversion ratio and increased body weight gain at 1-21 d as level in diet increased. Higher BV levels lowered relative weight of spleen (linear and quadratic, P < 0.05), bursa of Fabricius (quadratic, P < 0.05), and liver (linear and quadratic, P < 0.05) at 21 d of age. Relative breast meat yields were increased quadratically at 21 d and linearly at 35 d with supplementation levels. Dietary BV increased (linear and quadratic, P < 0.05) lightness (L*) value for meat at 21 d, decreased (linear, P < 0.05) ileal villus height and narrowed (quadratic, P < 0.05) width. 3. Dietary BV inclusion linearly increased the concentration of secretory immunoglobulin A (sIgA) on ileal mucosa at 21 d and decreased (quadratic, P < 0.05) nitric oxide contents in serum samples at 21 d and 35 d. Total short-chain fatty acids (SCFA) in caecal digesta were reduced with increasing venom in diets at 21 d of age. None of the serum parameters except for creatinine was affected by dietary BV. 4. It was concluded that dietary BV exhibited wide range of in vivo biological properties in broiler chickens and could be incorporated into feed to promote growth and animal health.

The effects of dietary non-starch polysaccharides on Ascaridia galli infection in grower layers

This study examined whether Ascaridia galli infection can be controlled by dietary non-starch polysaccharides (NSP) in chickens. One-day-old chicks were fed either a basal diet (CON) or CON plus insoluble NSP (I-NSP), or CON plus soluble NSP (S-NSP) for 11 weeks. Three weeks later, birds from half of each feeding group were inoculated with 250 embryonated eggs of A. galli, and slaughtered 8 weeks post-infection to determine worm counts. Both NSP diets, particularly S-NSP, increased prevalence of infection (P<0·05) and worm burden (roughly +50%) of the birds (P<0·001). A. galli infection caused a less efficient (P=0·013) feed utilization for body weight gain (BWG) resulting in lower body weights (P<0·001) irrespective of type of diet consumed. NSP-fed birds, particularly those on I-NSP, consumed more (+8%) feed per unit BWG and showed retarded (P<0·001) BW development compared to CON-fed birds. Intracaecal pH was lowered by S-NSP (P<0·05). Both NSP diets increased the volatile fatty acids pool size in caeca (P<0·001) with S-NSP exerting a greater effect (+46%) than I-NSP (+24%). It is concluded that both NSPs supplemented diets alter gastrointestinal environment in favour of the nematode establishment, and thus have no potential for controlling A. galli infection in chickens.

Effects of dietary inulin on the intestinal short chain fatty acids and microbial ecology in broiler chickens as revealed by denaturing gradient gel electrophoresis

Inulin can stimulate the growth of the intestinal bacteria as well as alter the ratio among various short chain fatty acids (SCFA) produced. In the present study, we analyzed the effect of dietary inulin on the intestinal bacterial community as determined by denaturing gradient gel electrophoresis analysis of universal 16S rDNA after amplication with PCR and SCFA profile. Broilers were fed a diet primarily composed of corn-soybean meal or same diet with 1% inulin for 42 d. The relative weight of digesta-filled ceca of the inulin-fed group was higher (P<0.01) than in the control group. Amongst SCFA, only acetate could be detected in the jejunal digesta, which tended to be higher (P=0.09) in inulin-fed group compared with the control group. Inulin did not affect the total concentration of SCFA in the cecal digesta. The relative proportion of n-butyrate was elevated (P=0.05) with a concomitant decrease in the concentration of n-valerate (P<0.05) in the inulin-fed group compared with the control group. Dietary inulin did not affect the number of PCR-denaturing gradient gel electrophoresis bands nor their diversity in the jejunal and cecal digesta. Intragroup similarities were not different between the groups, nor were any differences between intra-and intergroup similarities in the jejunal and cecal samples. In conclusion, inulin altered the cecal microbial metabolic activity without any major impact on the composition of intestinal bacterial communities as measured by the present techniques.

Comparison of in vitro fermentation and molecular microbial profiles of high-fiber feed substrates incubated with chicken cecal inocula

High fiber and nonstarch polysaccharide-based poultry diets have received more interest recently for retaining or promoting beneficial gastrointestinal microbial populations. The objective of this study was to investigate and compare the in vitro potential fermentability of high-fiber feed substrates (HFFS) by laying hen cecal microflora. Feed sources examined included soybean meal, soybean hull, beet pulp, wheat middlings, ground sorghum, cottonseed meal, 100% alfalfa meal, 90% alfalfa + 10% commercial layer ration, 80% alfalfa + 20% commercial layer ration, and 70% alfalfa + 30% commercial layer ration. Cecal contents and HFFS were incubated anaerobically in serum tubes at 39 degrees C for 24 h. Samples from 2 trials were analyzed at 0 and 24 h for short-chain fatty acids (SCFA). Short-chain fatty acids in samples at 0 h were subtracted from 24-h samples to determine the net production of SCFA. In both trials involving HFFS incubations with cecal inocula, acetate production was highest followed by propionate and butyrate whereas isobutyrate and isovalerate production were in trace amounts. In trial 2, detectable valerate production appeared to consistently occur with alfalfa-based HFFS. It was clear that SCFA production was largely dependent upon HFFS, because cecal inoculum alone yielded little or no detectable SCFA production. For HFFS incubations without cecal inocula, acetate production was highest; propionate and butyrate were similar, and isobutyrate, valerate, and isovalerate production were in trace amounts. Polymerase chain reaction-based denaturing gradient gel electrophoresis results from both trials indicated 69 and 71% similarity for comparison of all feed mixtures in trials 1 and 2, respectively. All alfalfa-based HFFS yielded a higher similarity coefficient in trial 2 than in trial 1 with a band pattern of 90% similarity; diets containing 90% alfalfa + 10% commercial layer ration and 80% alfalfa + 20% commercial layer ration in trial 2 formed a subgroup with a 94% microbial similarity coefficient. These data suggest that high fiber sources may contribute to the fermentation and microbial diversity that occurs in the ceca of laying hens.

Influence of the antibiotic erythromycin on anaerobic treatment of a pharmaceutical wastewater

A laboratory-scale anaerobic sequencing batch reactor was used to treat a model substrate mixture representing pharmaceutical wastewater at an organic loading rate of 2.9 g COD/(L d). After reaching stable operation the reactor was first exposed to low (1 mg/L) and, subsequently, to high (200 mg/L) concentrations of the antibiotic erythromycin. The addition of low levels of erythromycin resulted in a significant but limited reduction of biogas production by 5% and the higher level of erythromycin did not impact biogas production further, suggesting that a substantial fraction of the microbial populations in the ASBR were resistant to the antibiotic. Effluent soluble COD could not be accounted for in measured volatile fatty acids, perhaps suggesting the production of soluble microbial products. In batch tests evaluating the specific methanogenic activity, conversion of the model substrate mixture was only slightly affected by the presence of erythromycin. However, the conversion of butyric acid was inhibited when erythromycin was present. After 47 days of exposure to erythromycin, the conversion of butyric acid was inhibited to a lesser extent, suggesting the development of antibiotic resistance in the biomass. Exposure to antibiotics can affect specific substrate degradation pathways, leading to the accumulation of volatile fatty acids, soluble microbial products, and potentially to overall system instabilities.

A fermentation assay to evaluate the effectiveness of antimicrobial agents on gut microflora

The measurement of gas produced as a fermentation end product in vitro was correlated with absorbance as a measure of bacterial growth and was used as a rapid screening procedure to test the antimicrobial activity of certain essential oil and tannin secondary plant metabolites on gastrointestinal microorganisms from chickens. The assay was optimised using Clostridium perfringens and Lactobacillus fermentum, and tested in antimicrobial assays against C. perfringens; the minimum inhibitory concentration for each essential oil and condensed tannin was determined. The effect of penicillin-G on C. perfringens, in both growth and fermentation assays, was similar, and for all secondary metabolites tested, concentrations that inhibited fermentation were also bacteriocidal. The assay was also used to demonstrate the effect of dietary composition and enzyme supplementation on fermentation of mixed gut microflora in vitro; results are compared with in vivo results for the same dietary treatments. The data demonstrate that the effects of bioactive secondary plant products and feed composition on individual organisms or mixed gut microflora can be tested by analysis of fermentative activity in vitro, and that this provides a rapid assay for testing potential poultry feed additives before in vivo trials.

Effects of nitro compounds and feedstuffs on in vitro methane production in chicken cecal contents and rumen fluid

Short-chain volatile fatty acids (VFA) and methane are the products from a wide variety of microorganisms living in the gastrointestinal tract. The objective of this study was to examine effects of feedstuff and select nitro compounds on VFA and methane production during in vitro incubation of laying hen cecal contents and rumen fluid from cattle and sheep. In the first experiment, one of the three nitro compound was added to incubations containing cecal contents from laying hens supplemented with either alfalfa (AF) or layer feed (LF). Both feed material influenced VFA production and acetic acid was the primary component. Incubations with nitro ethanol and 2-nitropropanol (NP) had significantly (P<0.05) higher propionate concentrations than incubations with added nitroethane (NE). The results further indicated that incubations containing LF produced significantly (P<0.05) more butyrate than incubations with added AF. Addition of NP and LF to incubations of avian cecal flora may promote Gram-positive, saccharolytic, VFA-producing bacteria, especially Clostridium spp. which is the predominant group in ceca. Similar to VFA production, both feed materials fostered methane production in the incubations although methane was lower (P<0.05) in incubations with added nitro compound, particularly NE. In experiments 3-8, NE was examined in incubations of bovine or ovine rumen fluid or cecal contents containing either AF or LF. Unlike cecal contents, LF significantly (P<0.05) supported in vitro methane production in incubations of both rumen fluids. The results show that NE impedes methane production, especially in incubations of chicken cecal contents.

Effects of enzyme supplementation on performance, nutrient digestibility, gastrointestinal morphology, and volatile fatty acid profiles in the hindgut of broilers fed wheat-based diets

A growth trial and a metabolism trial were conducted as 2 experiments to investigate the effects of dietary enzyme supplementation (primarily xylanase and beta-glucanase) on performance, nutrient digestibility, intestinal morphology, digestive organ size, and volatile fatty acid profiles in the hindgut of broiler chickens fed wheat-based diets. The experimental diets in both trials consisted of a wheat-based control diet supplemented with 0, 200, 400, 600, 800, or 1,000 mg/kg enzyme. Diets were given to the birds from d 7 to 42 of age. In the growth trial, enzyme supplementation improved performance of the broilers; daily gain and feed conversion increased linearly (P < 0.01) with increasing levels of enzyme supplementation. Enzyme inclusion decreased the size of the digestive organs and the gastrointestinal tract to some extent. The relative length of each intestinal segment decreased linearly (P < 0.05). The relative weight of the anterior intestine on d 21 and ileum on d 42 also decreased linearly (P < 0.01). On d 21 and 42, there were negative linear (P < 0.05) relationships between increasing enzyme supplementation and the relative weight of the liver and pancreas, respectively. Furthermore, there was a linear (P < 0.01) increase in total volatile fatty acid content in ileum on d 21 and in the cecum on d 21 and 42. During each period of the metabolism trial, apparent crude protein digestibility increased linearly (P < 0.05), whereas no differences were detected (P > 0.05) in AME.

Effects of animal or plant protein diets on cecal fermentation in guinea pigs (Cavia porcellus), rats (Rattus norvegicus) and chicks (Gallus gallus domesticus)

Monogastric herbivores such as the guinea pig depend on energy supply from enteric fermentation as short-chain fatty acids (SCFA) corresponding to 30-40% of their maintenance energy requirements. They evolved specific digestive system to adapt their indigenous microflora to plant polysaccharides fermentation. No information has been available about the adaptability of microbial fermentation in hindgut of the monogastric herbivorous to an animal protein diet. We investigated if the guinea pig can fully retrieve energy of an animal protein diet by hindgut fermentation compared with a plant protein diet. For comparison, we also studied two omnivores. End products of in vitro cecal fermentation (SCFA, ammonia and gases) were measured to judge how well an animal protein diet could be fermented. The animal protein diet resulted in the less intensive fermentation with increased feed intake and volume of cecal contents than the plant protein diet only in guinea pigs. This may be due to a limited capacity of the hindgut microflora to adapt to the substrate rich in animal protein. We also found that chick cecal contents produced methane at higher emission rate than ruminants.