Dietary Protein Digestion Research Articles

An in vitro study of urea and ammonia production and transport by the intestinal tract of fed and fasted rainbow trout: responses to luminal glutamine and ammonia loading

Digestion of dietary protein in teleosts results in high ammonia levels within the intestinal chyme that may reach concentrations that are many-fold greater than blood plasma levels. We used in vitro gut sac preparations of the ammoniotelic rainbow trout (Oncorhynchus mykiss) to investigate the role of the intestine in producing and transporting ammonia and urea, with specific focus on feeding versus fasting, and on responses to loading of the lumen with 2mmol L-1 glutamine or 2mmol L-1 ammonia. Feeding increased not only ammonia production and both mucosal and serosal fluxes, but also increased urea production and serosal fluxes. Elevated urea production was accompanied by an increase in arginase activity but minimal CPS III activity, suggesting that urea may be produced by direct arginolysis. The ammonia production and serosal fluxes increased in fasted preparations with glutamine loading, indicating an ability of the intestinal tissue to deaminate glutamine and perhaps use it as an energy source. However, there was little evidence of urea production or transport resulting from the presence of glutamine. Furthermore, the intestinal tissues did not appear to convert surplus ammonia to urea as a detoxification mechanism, as urea production and serosal flux rates decreased in fed preparations, with minimal changes in fasted preparations. Nevertheless, there was indirect evidence of detoxification by another pathway, as ammonia production rate decreased with ammonia loading in fed preparations. Overall, our study suggests that intestinal tissues of rainbow trout have the ability to produce urea and detoxify ammonia, likely via arginolysis.

Nutrition and Functions of Amino Acids in Aquatic Crustaceans.

Crustaceans (e.g., shrimp and crabs) are a good source of protein-rich foods for human consumption. They are the second largest aquaculture species worldwide. Understanding the digestion of dietary protein, as well as the absorption, metabolism and functions of amino acids (AAs) and small peptidesis essential to produce cost-effective and sustainable aquafeeds. Hepatopancreas (the midgut gland) is the main site for the digestion of dietary protein as well as the absorption of small peptides and AAs into the hemolymph. Besides serving as the building blocks of protein, AAs (particularly aspartate, glutamate, glutamine and alanine) are the primary metabolic fuels for the gut and extra-hepatopancreas tissues (e.g., kidneys and skeletal muscle) of crustaceans. In addition, AAs are precursors for the syntheses of glucose, lipids, H2S, and low-molecular-weight molecules (e.g., nitric oxide, glutathione, polyamines, histamine, and hormones) with enormous biological importance, such as physical barrier, immunological and antioxidant defenses. Therefore, both nutritionally essential and nonessential AAs are needed in diets to improve the growth, development, molt rate, survival, and reproduction of crustaceans. There are technical difficulties and challenges in the use of crystalline AAs for research and practical production due to the loss of free AAs during feed processing, the leaching of in-feed free AAs to the surrounding water environment, and asynchronous absorption with peptide-bounded AAs. At present, much knowledge about AA metabolism and functions in crustaceans is based on studies of mammals and fish species. Basic research in this area is necessary to lay a solid foundation for improving the balances and bioavailability of AAs in the diets for optimum growth, health and wellbeing of crustaceans, while preventing and treating their metabolic diseases. This review highlights recent advances in AA nutrition and metabolism in aquatic crustacean species at their different life stages. The new knowledge is expected to guide the development of the next generation of their improved diets.

Nutrition and Functions of Amino Acids in Fish.

Aquaculture is increasingly important for providing humans with high-quality animal protein to improve growth, development and health. Farm-raised fish and shellfish now exceed captured fisheries for foods. More than 70% of the production cost is dependent on the supply of compound feeds. A public debate or concern over aquaculture is its environmental sustainability as many fish species have high requirements for dietary protein and fishmeal. Protein or amino acids (AAs), which are the major component of tissue growth, are generally the most expensive nutrients in animal production and, therefore, are crucial for aquatic feed development. There is compelling evidence that an adequate supply of both traditionally classified nutritionally essential amino acids (EAAs) and non-essential amino acids (NEAAs) in diets improve thegrowth, development and production performance of aquatic animals (e.g., larval metamorphosis). The processes for the utilization of dietary AAs or protein utilization by animals include digestion, absorption and metabolism. The digestibility and bioavailability of AAs should be carefully evaluated because feed production processes and AA degradation in the gut affect the amounts of dietary AAs that enter the blood circulation. Absorbed AAs are utilized for the syntheses of protein, peptides, AAs, and other metabolites (including nucleotides); biological oxidation and ATP production; gluconeogenesis and lipogenesis; and the regulation of acid-base balance, anti-oxidative reactions, and immune responses. Fish producers usually focus on the content or digestibility of dietary crude protein without considering the supply of AAs in the diet. In experiments involving dietary supplementation with AAs, inappropriate AAs (e.g., glycine and glutamate) are often used as the isonitrogenous control. At present, limited knowledge is available about either the cell- and tissue-specific metabolism of AAs or the effects of feed processing methods on the digestion and utilization of AAs in different fish species. These issues should be addressed to develop environment-friendly aquafeeds and reduce feed costs to sustain the global aquaculture.

Statement on invitro protein digestibility tests in allergenicity and protein safety assessment of genetically modified plants.

This statement supplements and updates the GMO Panel guidance document on allergenicity of genetically modified (GM) plants published in 2017. In that guidance document, the GMO Panel considered that additional investigations on in vitro protein digestibility were needed before providing any additional recommendations in the form of guidance to applicants. Thus, an interim phase was proposed to assess the utility of an enhanced in vitro digestion test, as compared to the classical pepsin resistance test. Historically, resistance to degradation by pepsin using the classical pepsin resistance test has been considered as additional information, in a weight‐of‐evidence approach, for the assessment of allergenicity and toxicity of newly expressed proteins in GM plants. However, more recent evidence does not support this test as a good predictor of allergenic potential for hazard. Furthermore, there is a need for more reliable systems to predict the fate of the proteins in the gastrointestinal tract and how they interact with the relevant human cells. Nevertheless, the classical pepsin resistance test can still provide some information on the physicochemical properties of novel proteins relating to their stability under acidic conditions. But other methods can be used to obtain data on protein's structural and/or functional integrity. It is acknowledged that the classical pepsin resistance test is embedded into international guidelines, e.g. Codex Alimentarius and Regulation (EU) No 503/2013. For future development, a deeper understanding of protein digestion in the gastrointestinal tract could enable the framing of more robust strategies for the safety assessment of proteins. Given the high complexity of the digestion and absorption process of dietary proteins, it is needed to clarify and identify the aspects that could be relevant to assess potential risks of allergenicity and toxicity of proteins. To this end, a series of research questions to be addressed are also formulated in this statement.

Effect of wheat flour substitution and popped amaranth flour content on the rheological, physicochemical and textural properties of hot-press wheat-oat-quinoa-amaranth composite flour tortillas

ABSTRACT The aim of this research was to evaluate the effect of the popped amaranth flour on the rheology, chemical composition, protein digestibility and physical properties of hot-press tortillas elaborated with a wheat, oat and quinoa flour, compared with refined wheat flour. Mixolab C1 (dough stability) increased 33% with amaranth addition. Results showed that tortillas containing 5:5:20 oat:quinoa:amaranth increased 31.4% and 27.1% soluble dietary fiber and protein than control, respectively. Protein “in vitro” digestibility increased 1.02% and crude fat reduced 35.6%. Tortilla treatment 5:5:20 required same force to deform and to rupture at day 6, and showed a lower L* (16.1%) and higher a*(27.4) and b* (23.1%) than control. Texture acceptance was the same, and odor acceptance was lower for tortilla treatment 5:5:20, compared to control. The partial replacement of wheat flour with amaranth:quinoa:oat flour positively influences the protein content, total dietary fiber content and protein digestibility of tortillas.

Important determinants to take into account to optimize protein nutrition in the elderly: solutions to a complex equation.

During ageing, skeletal muscle develops anabolic resistance towards the stimulation of protein synthesis induced by dietary amino acids. The stimulation of muscle protein synthesis after food intake remains insufficient, even with a protein intake recommended for healthy adults. This alteration is one of the mechanisms known to be responsible for the decrease of muscle mass and function during ageing, namely sarcopenia. Increasing dietary protein intake above the current RDA(0⋅83 g/kg/d) has been strongly suggested to overcome the anabolic resistance observed. It is also specified that the dietary protein ingested should be of good quality. A protein of good quality is a protein whose amino acid (AA) composition covers the requirement of each AA when ingested at the RDA. However, the biological value of proteins may vary among dietary sources in which AA composition could be unbalanced. In the present review, we suggest that the quality of a dietary protein is also related to several other determinants. These determinants include the speed of digestion of dietary proteins, the presence of specific AA, the food matrix in which the dietary proteins are included, the processes involved in the production of food products (milk gelation and cooking temperature), the energy supply and its nature, and the interaction between nutrients before ingestion. Particular attention is given to plant proteins for nutrition of the elderly. Finally, the timing of protein intake and its association with the desynchronized intake of energetic nutrients are discussed.

Effect of Escherichia Coli Infection on Metabolism of Dietary Protein in Intestine.

Dietary proteins are linked to the pathogenic Escherichia coli (E. coli) through the intestinal tract, which is the site where both dietary proteins are metabolized and pathogenic E. coli strains play a pathogenic role. Dietary proteins are degraded by enzymes in the intestine lumen and their metabolites are transferred into enterocytes to be further metabolized. Seven diarrheagenic E. coli pathotypes have been identified, and they damage the intestinal epithelium through physical injury and effector proteins, which lead to inhibit the digestibility and absorption of dietary proteins in the intestine tract. But the increased tryptophan (Trp) content in the feed, low-protein diet or milk fractions supplementation is effective in preventing and controlling infections by pathogenic E. coli in the intestine.

Animal fat and vitamin E in rabbit diets: Total tract apparent digestibility, growth performance, carcass and meat quality traits

The present study tested the effect of a dietary inclusion with vitamin E and pork lard on the apparent digestibility of the nutrients, the growth performance, the carcass traits, the physical meat quality, and the α-tocopherol content. A total of 60 hybrid rabbits were reared in individual cages from weaning (35 days of age) until slaughter (78 days of age). A control diet with no supplements, one diet supplemented with 2% pork lard, and two diets that used the aforementioned diets supplemented with an additional 200 mg/kg α-tocopheryl acetate were designed. The diets were isoprotein and isoenergy. The fat inclusion increased the crude protein (P < 0.05) and ether extract (P < 0.001) total tract apparent digestibility, and the same was observed for the vitamin E inclusion (P < 0.001 for both variables). This improved the dietary digestible protein content (P < 0.05), which increased the digestible protein to digestible energy ratio (P < 0.001). The fat × vitamin E interaction was observed for the total tract apparent digestibility of the ether extract (P < 0.001), the neutral detergent fibre (P < 0.05) and the acid detergent fibre (P < 0.01). The growth traits were unaffected, with the exception of the feed conversion ratio that improved with the vitamin E addition (P < 0.05). Similarly, the carcass traits remained unaffected, with the exception of the perirenal and total fat incidence that increased with the fat supplement (P < 0.05), and the scapular fat that was reduced with the vitamin E inclusion (P < 0.05). The meat L* (lightness), a* (redness), b* (yellowness) colour values and ultimate pH were unaffected by the experimental treatments, even though a fat × vitamin E interaction was observed for the a* and chroma values of the Longissimus thoracis et lumborum muscle (P < 0.05). Both the fat (P < 0.05) and vitamin E (P < 0.001) dietary inclusion increased the meat α-tocopherol content. Based on the results, it was concluded that the 2% dietary inclusion of animal fat did not provide more benefits for the considered parameters than the sole α-tocopheryl acetate incorporation, but contributed to the increase in the vitamin E content in the meats.

The impact of Hayward green kiwifruit on dietary protein digestion and protein metabolism

PurposeThe purpose of the study was to determine if an actinidin protease aids gastric digestion and the protein anabolic response to dietary protein.MethodsHayward green kiwifruit (containing an actinidin protease) and Hort 16A gold kiwifruit (devoid of actinidin protease) were given in conjunction with a beef meal to healthy older subjects. Twelve healthy older males (N = 6) and females (N = 6) were studied with a randomized, double-blinded, crossover design to assess muscle and whole-body protein metabolism before and after ingestion of kiwifruit and 100 g of ground beef. Subjects consumed 2 of each variety of kiwifruit daily for 14 d prior to each metabolic study, and again during each study with beef intake.ResultsHayward green kiwifruit consumption with beef resulted in a more rapid increase in peripheral plasma essential amino acid concentrations. There were significant time by kiwifruit intake interactions for plasma concentrations of EAAs, branched chain amino acids (BCAAs), and leucine (P < 0.01). However, there was no difference in the total amount of EAAs absorbed. As a result, there were no differences between kiwifruit in any of the measured parameters of protein kinetics.ConclusionConsumption of Hayward green kiwifruit, with a beef meal facilitates protein digestion and absorption of the constituent amino acids as compared to Hort 16A gold kiwifruit.Clinical trialNCT04356573, April 21, 2020 “retrospectively registered”.

Blood 15N:13C Enrichment Ratios Are Proportional to the Ingested Quantity of Protein with the Dual-Tracer Approach for Determining Amino Acid Bioavailability in Humans

ABSTRACTBackgroundAssessment of amino acid bioavailability is of key importance for the evaluation of protein quality; however, measuring ileal digestibility of dietary proteins in humans is challenging. Therefore, a less-invasive dual stable isotope tracer approach was developed.ObjectiveWe aimed to test the assumption that the 15N:13C enrichment ratio in the blood increases proportionally to the quantity ingested by applying different quantities of 15N test protein.MethodsIn a crossover design, 10 healthy adults were given a semi-liquid mixed meal containing 25 g (low protein) or 50 g (high protein) of 15N-labeled milk protein concentrate simultaneous with 0.4 g of highly 13C–enriched spirulina. The meal was distributed over multiple small portions, frequently provided every 20 min during a period of 160 min. For several amino acids, the blood 15N- related to 13C-isotopic enrichment ratio was determined at t = 0, 30, 60, 90, 120, 180, 240, 300, and 360 min and differences between the 2 meals were compared using paired analyses.ResultsNo differences in 13C AUC for each of the measured amino acids in serum was observed when ingesting a low- or high-protein meal, whereas 15N AUC of amino acids was ∼2 times larger on the high-protein meal (P < 0.001). Doubling the intake of 15N-labeled amino acids increased the 15N:13C ratio by a factor of 2.04 ± 0.445 for lysine and a factor between 1.8 and 2.2 for other analyzed amino acids, with only phenylalanine (2.26), methionine (2.48), and tryptophan (3.02) outside this range.ConclusionsThe amino acid 15N:13C enrichment ratio in the peripheral circulation increased proportionally to the quantity of 15N-labeled milk protein ingested, especially for lysine, in healthy adults. However, when using 15N-labeled protein, correction for, e.g., α-carbon 15N atom transamination is advised for determination of bioavailability of individual amino acids. This trial was registered at www.clinicaltrials.gov as NCT02966704.

Digestion-related proteins in the tobacco hornworm, Manduca sexta

Food digestion is vital for the survival and prosperity of insects. Research on insect digestive enzymes yields knowledge of their structure and function, and potential targets of antifeedants to control agricultural pests. While such enzymes from pest species are more relevant for inhibitor screening, a systematic analysis of their counterparts in a model insect has broader impacts. In this context, we identified a set of 122 digestive enzyme genes from the genome of Manduca sexta, a lepidopteran model related to some major agricultural pests. These genes encode hydrolases of proteins (85), lipids (20), carbohydrates (16), and nucleic acids (1). Gut serine proteases (62) and their noncatalytic homologs (11) in the S1A subfamily are encoded by abundant transcripts whose levels correlate well with larval feeding stages. Aminopeptidases (10), carboxypeptidases (10), and other proteases (3) also participate in dietary protein digestion. A large group of 11 lipases as well as 9 esterases are probably responsible for digesting lipids in diets. The repertoire of carbohydrate hydrolases (16) is relatively small, including two amylases, three maltases, two sucrases, two α-glucosidases, and others. Lysozymes, peptidoglycan amidases, and β-1,3-glucanase may hydrolyze peptidoglycans and glucans to harvest energy and defend the host from microbes on plant leaves. One alkaline nuclease is associated with larval feeding, which is likely responsible for hydrolyzing denatured DNA and RNA undergoing autolysis at a high pH of midgut. Proteomic analysis of the ectoperitrophic fluid from feeding larvae validated at least 131 or 89% of the digestive enzymes and their homologs. In summary, this study provides for the first time a holistic view of the digestion-related proteins in a lepidopteran model insect and clues for comparative research in lepidopteran pests and beyond.

Protein Type, Protein Dose, and Age Modulate Dietary Protein Digestion and Phenylalanine Absorption Kinetics and Plasma Phenylalanine Availability in Humans

ABSTRACTBackgroundDietary protein ingestion stimulates muscle protein synthesis by providing amino acids to the muscle. The magnitude and duration of the postprandial increase in muscle protein synthesis rates are largely determined by dietary protein digestion and amino acid absorption kinetics.ObjectiveWe assessed the impact of protein type, protein dose, and age on dietary protein digestion and amino acid absorption kinetics in vivo in humans.MethodsWe included data from 18 randomized controlled trials with a total of 602 participants [age: 53 ± 23 y; BMI (kg/m2): 24.8 ± 3.3] who consumed various quantities of intrinsically l-[1-13C]-phenylalanine–labeled whey (n = 137), casein (n = 393), or milk (n = 72) protein and received intravenous infusions of l-[ring-2H5]-phenylalanine, which allowed us to assess protein digestion and phenylalanine absorption kinetics and the postprandial release of dietary protein–derived phenylalanine into the circulation. The effect of aging on these processes was assessed in a subset of 82 young (aged 22 ± 3 y) and 83 older (aged 71 ± 5 y) individuals.ResultsA total of 50% ± 14% of dietary protein–derived phenylalanine appeared in the circulation over a 5-h postprandial period. Casein ingestion resulted in a smaller (45% ± 11%), whey protein ingestion in an intermediate (57% ± 10%), and milk protein ingestion in a greater (65% ± 13%) fraction of dietary protein–derived phenylalanine appearing in the circulation (P < 0.001). The postprandial availability of dietary protein–derived phenylalanine in the circulation increased with the ingestion of greater protein doses (P < 0.05). Protein digestion and phenylalanine absorption kinetics were attenuated in older when compared with young individuals, with 45% ± 10% vs. 51% ± 14% of dietary protein–derived phenylalanine appearing in the circulation, respectively (P = 0.001).ConclusionsProtein type, protein dose, and age modulate dietary protein digestion and amino acid absorption kinetics and subsequent postprandial plasma amino acid availability in vivo in humans. These trials were registered at clinicaltrials.gov as NCT00557388, NCT00936039, NCT00991523, NCT01317511, NCT01473576, NCT01576848, NCT01578590, NCT01615276, NCT01680146, NCT01820975, NCT01986842, and NCT02596542, and at http://www.trialregister.nl as NTR3638, NTR3885, NTR4060, NTR4429, and NTR4492.

Polymannuronic acid prevents dopaminergic neuronal loss via brain-gut-microbiota axis in Parkinson's disease model

The study aims to investigate the potentially neuroprotective effects and underlying mechanisms for brown seaweed polysaccharide of polymannuronic acid (PM) against Parkinson's disease (PD) pathogenesis. PD model mice were pretreated with PM via oral gavage once per day for 4 weeks and the preventative effects of PM against neuronal loss together with its modulation on brain-gut-microbiota axis were systematically explored. The results showed PM administration improved motor functions by preventing dopaminergic neuronal loss in the substantia nigra pars compacta (SNpc) and enhanced contents of striatal homovanillic acid (HVA), serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA) and γ-aminobutyric acid (GABA) in PD mice. PM significantly alleviated inflammation in gut, brain and systemic circulation as shown by reduced levels or expressions of pro-inflammatory cytokines concurrently and inhibited mitogen-activated protein kinases (MAPK) signaling pathway in mice colon. Meanwhile, PM greatly improved integrity of intestinal barrier and blood brain barrier (BBB) as indicated by increased expressions of tight junction associated proteins in both mice colon and SNpc. Further studies indicated PM treatment resulted in changes of gut microbial compositions, together with great alterations of digestion and metabolism of dietary proteins and fats, which led to surge increase of fecal short chain fatty acids (SCFAs) in the colon of PD mice. In conclusion, pre-administration of PM could provide neuroprotective effects against PD pathogenesis by suppressing inflammation in gut, brain and systemic circulation, and by improving integrity of intestinal barrier and BBB. PM might modulate brain-gut-microbiota axis, at least in part, via gut microbiota derived SCFAs as mediators.

Silvicultural herbicides and forest succession influence understory vegetation and nutritional ecology of black-tailed deer in managed forests

The increasing intensity of forestry practices, especially using herbicides to promote early survival and growth of planted conifers, has the potential to influence the abundance of nutritious, shade-intolerant forbs and shrubs on which black-tailed deer (Odocoileus hemionus columbianus) and other forest ungulates depend. Therefore, we compared summer forage resources and nutrition of female black-tailed deer in stands that received herbicide treatments paired with stands that did not in Douglas-fir/western hemlock forests of western Washington. We investigated how these responses changed as forests aged from early seral to canopy closure (2–20 years post-harvest) in both treatments, and also in unmanaged mid-seral stands (30–90 years old). We measured the biomass and nutritional quality of understory vegetation and the diet composition, diet quality and nutrient intake of tractable black-tailed deer within each paired stand. We found that herbicides did not affect the rate of closure of the overstory canopy, but influenced plant species composition of the understory vegetation and reduced total and non-conifer understory biomass, primarily in the first 9 years before canopy closure. Herbicides also reduced the biomass of two of the six plant functional groups, evergreen shrubs and deciduous shrubs and trees, but did not reduce forb, graminoid, or fern biomass. Herbicides reduced bite size, harvest rate, daily dry matter intake and daily digestible energy (DE) intake of deer, but increased dietary digestible protein (DP) content, and these effects occurred primarily in the first 3 years post-treatment. Biomass of plants suitable for black-tailed deer, and the deers’ bite rate, daily feeding time, dietary DE, and daily digestible DP intake did not respond to herbicides. Our yearling and sub-adult, non-lactating deer met requirements for yearling growth and adult maintenance for dietary DE in 78%, and DE intake in 27% of plots, but only met the higher requirements for lactating females in 5% of plots. All plots where daily DE requirements of lactation or growth were met were <10 years old. Deer were equally likely to obtain diets that satisfied requirements in treated and untreated plots, indicating that although herbicide application reduced understory biomass and DE intake, it did not explain whether deer were able to meet requirements. We also found that the biomass of deciduous shrubs and trees, forbs, and suitable forage was ~25 times greater in 4–9 year old stands than closed canopy stands (14–90 years old), indicating the importance of maintaining early seral habitat for sustaining populations of black-tailed deer.

Reply to "Limitations of the Digestible Indispensable Amino Acid Score (DIAAS) and Choice of Statistical Reporting. Comment on "A Comparison of Dietary Protein Digestibility, Based on DIAAS Scoring, in Vegetarian and Non-Vegetarian Athletes." Nutrients 2019, 11, 3106".

We appreciate the critique of our paper (Ciuris et al [...].

Evaluation of Antarctic krill ( Euphausia superba ) meal supplementation in diets for olive flounder ( Paralichthys olivaceus )

The supplemental effect of Antarctic krill meal (KM) into a low fish meal (FM) diet was evaluated for olive flounder (Paralichthys olivaceus). A 56% FM-based diet was regarded as a high FM inclusion diet (HFM), and a low-FM diet (LFM) was prepared by replacing 50% FM from the HFM. Four other diets were prepared by supplementing 3%, 6%, 9% and 12% KM into the LFM diet gradually replacing soy protein concentrate and tankage meal (designated as KM3, KM6, KM9 and KM12 respectively). Quadruplicate groups of fish were fed one of the diets for 12 weeks. The growth performance and feed utilization efficiency were improved by the dietary KM supplementation. Digestibility of dietary protein and dry matter was increased by the KM3-9 diets. Haematocrit and haemoglobin were increased by KM supplementation. The innate immunity and antioxidant capacity assessed by Ig, antiprotease, lysozyme, GPx and SOD and the condition factor of fish were significantly increased by KM3-9 diets. Moreover, goblet cell counts, villi length and fillet yield of fish were significantly improved by all the KM-containing diets (KM3-12). A 25-day-long challenge test with the Edwardsiella tarda pathogen showed that the cumulative mortality was higher in fish fed the LFM diet than in fish fed the HFM or KM-supplemented diets. The results indicate that dietary KM supplementation in a LFM diet can increase growth performance and feed utilization efficiency, diet digestibility, intestinal development and functions, innate immunity and disease resistance of olive flounder. The recommended level of KM inclusion in a LFM diet seems to be 6.6% according to quadratic regression analysis.

Nutrition of Genetically Improved Farmed Tilapia (GIFT) in biofloc technology system: Optimization of digestible protein and digestible energy levels during nursery phase

The objective of the present work was to investigate different dietary digestible protein (22%, 26% and 30% of DP) and digestible energy (3000, 3150 and 3300 kcal DE kg−1) levels on growth performance and hematological parameters of Genetically Improved Farmed Tilapia (GIFT) fingerlings (0.99 ± 0.1 g of mean initial weight) over 42 days. In addition, proximate analysis of carcass and biofloc biomass, as well as planktonic community characterization were performed. A factorial design (digestible protein and digestible energy as factors) was applied totaling nine treatments with four replicates each. The FCR (~1.17) and survival (>98%) were similar between all treatments (P > .05). When assessing the final weight of the fish, in terms of weight gain and specific growth rate, the 22% and 26% DP treatments were not affected by the energy level (P > .05); however, the 30% DP level were affected by energy levels (P < .05) with best results using 3150 kcal DE kg−1. In regard to somatic parameters, carcass yield and condition factor of the fish were similar between all treatments (P > .05). Standard length presented an interaction effect (P < .05); while total length and the hepatosomatic index were affected by protein levels. Hematological parameters showed variability according to different dietary protein levels while carcass proximate composition was affected by both protein and energy levels (P < .05). The monitoring of planktonic communitities indicated some variation over the duration of the experiment, specifically on the number of dinoflagellates, rotifers and protozoa groups. These results suggest that the optimal digestible protein and digestible energy levels for tilapia fingerlings raised in freshwater biofloc systems are 26% DP and 3000 kcal DE kg−1.

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.

Amino Acids in Intestinal Physiology and Health.

Dietary protein digestion is an efficient process resulting in the absorption of amino acids by epithelial cells, mainly in the jejunum. Some amino acids are extensively metabolized in enterocytes supporting their high energy demand and/or production of bioactive metabolites such as glutathione or nitric oxide. In contrast, other amino acids are mainly used as building blocks for the intense protein synthesis associated with the rapid epithelium renewal and mucin production. Several amino acids have been shown to support the intestinal barrier function and the intestinal endocrine function. In addition, amino acids are metabolized by the gut microbiota that use them for their own protein synthesis and in catabolic pathways releasing in the intestinal lumen numerous metabolites such as ammonia, hydrogen sulfide, branched-chain amino acids, polyamines, phenolic and indolic compounds. Some of them (e.g. hydrogen sulfide) disrupts epithelial energy metabolism and may participate in mucosal inflammation when present in excess, while others (e.g. indole derivatives) prevent gut barrier dysfunction or regulate enteroendocrine functions. Lastly, some recent data suggest that dietary amino acids might regulate the composition of the gut microbiota, but the relevance for the intestinal health remains to be determined. In summary, amino acid utilization by epithelial cells or by intestinal bacteria appears to play a pivotal regulator role for intestinal homeostasis. Thus, adequate dietary supply of amino acids represents a key determinant of gut health and functions.

Effects of glucocorticoids on the gene expression of nutrient transporters in different rabbit intestinal segments

Glucocorticoids (GCs) are counterregulatory hormones with broad effects on the digestion and absorption of dietary carbohydrates, lipids and proteins, but the underlying molecular mechanisms of these effects remain unclear. The present experiment was conducted to investigate the main expression sites of nutrient transporters and the effects of GCs on the gene expression of these transporters in the rabbit small intestine. The results showed that peptide transporter 1 (PepT1), facultative amino acid transporter (rBAT), neutral amino acid transporter (B0AT), excitatory amino acid transporter 3 (EAAT3), sodium-glucose transporter 1 (SGLT1) and glucose transporter 5 (GLUT5) were mainly expressed in the distal segment, glucose transporter 2 (GLUT2) and fatty-acid-binding protein 4 (FATP4) were mainly expressed in the proximal segment and cationic amino acid transporter 1 (CAT1) was mainly expressed in the middle segment of the rabbit small intestine. In addition, we analysed the effects of 3 h (short-term) or 7 days (long-term) dexamethasone (DEX) treatment on the gene expression of most nutrient transporters. The results showed that short-term DEX treatment significantly decreased PepT1, B0AT, EAAT3, rBAT and SGLT1 expressions in all small intestinal segments, while it significantly decreased GLUT2 in the duodenum and FATP4 in the duodenum and ileum (P < 0.05). Long-term DEX treatment also significantly decreased PepT1, CAT1, B0AT, EAAT3, rBAT and SGLT1 in all small intestinal segments and significantly decreased GLUT2 in the jejunum and FATP4 in the ileum (P < 0.05). In conclusion, DEX could decrease the gene expression of most nutrient transporters (except GLUT5) and affect the transport of intestinal amino acids, monosaccharides and fatty acids.