In vitro gas and methane production of some common feedstuffs used for dairy rations in Vietnam and Thailand

OBJECTIVE

This study determined fermentation characteristics of commonly used feedstuffs, especially tropical roughages, for dairy cattle in Southeast Asia. This information is considered relevant in the context of the observed low milk fat content and milk production in Southeast Asia countries.

METHODS

A total of 29 feedstuffs commonly used for dairy cattle in Vietnam and Thailand were chemically analysed and subjected to an in vitro gas production (GP) test. For 72 h, GP was continuously recorded with fully automated equipment and methane (CH4) was measured at 0, 3, 6, 9, 12, 24, 30, 36, 48, 60, and 72 h of incubation. A triphasic, nonlinear, regression procedure was applied to analyse GP profiles while a monophasic model was used to obtain kinetics related to CH4 production.

RESULTS

King grass and VA06 showed a high asymptotic GP related to the soluble- and non-soluble fractions (i.e. A1 and A2, respectively) and had the highest acetate to propionate ratio in the incubation fluid. The proportion of CH4 produced (% of GP at 72 h) was found to be not different (p>0.05) between the various grasses. Among the selected preserved roughages (n = 6) and whole crops (n = 4), sorghum was found to produce the greatest amount of gas in combination with a relatively low CH4 production.

CONCLUSION

Grasses belonging to the genus Pennisetum, and whole crop sorghum can be considered as suitable ingredients to formulate dairy rations to enhance milk fat content in Vietnam/Thailand.

Standardisation of the C:N ratio in ileal digesta changes relationships among fermentation end-products during in vitro hindgut fermentation in pigs

Undigested proteins that become available for the microbiota in the hindgut can be used as building blocks for bacterial cells, or can enter various catabolic pathways. Degradation via protein fermentation pathways is least preferred, as several fermentation end-products released can be toxic for the host. Directing microbial protein metabolism towards protein synthesis or degradative pathways that result in less toxic end-products, for example through nutritional interventions, is an interesting strategy for improving health. We studied variation in protein fermentation patterns, resulting from variation in substrate composition. Ileal digesta, obtained from cannulated pigs fed different protein sources, were subjected to fermentation in vitro under different conditions; (1) ileal digesta were fermented as-is, (2) ileal digesta were fermented after standardisation to a constant high C:N ratio, by addition of high fermentable carbohydrates and (3) ileal digesta samples were incubated under limiting N concentrations. Gas production was monitored as an indirect measure of microbial activity, and fermentation end-products at different points in time were analysed by gas chromatography and high resolution mass spectrometry. Using principal component analysis, we identified patterns in protein fermentation end-products and related them to the composition of ileal digesta. Protein-associated fermentation end-product concentrations of e.g. isovaleric-, isobutyric-, phenylacetic acid and p-cresol were negatively affected by the available amount of high fermentable carbohydrates combined with a high C:N ratio. The aforementioned fermentation end-products positively correlated with NH3 concentrations and negatively with short-chain fatty acid (SCFA) concentrations. Standardisation to a constant high C:N ratio changed their relationship; isovaleric-, isobutyric-, phenylacetic acid and p-cresol lost their correlation with NH3 concentrations, became positively correlated with SCFA concentrations, and now showed a positive correlation with available amounts of high fermentable carbohydrates. Our observations demonstrate an important role of the C:N ratio in the relationship between fermentation end-products. At constant C:N, protein fermentation end-products correlate with end-products of carbohydrate fermentation and NH3, often considered as a proxy for protein fermentation, loses its predictive power.

An in vitro model for caecal proteolytic fermentation potential of ingredients in broilers

Fermentation of protein in the caeca of chickens may lead to the production of potentially detrimental metabolites, which can reduce gut health. A poor precaecal digestion is expected to increase protein fermentation (PF), as more proteins are likely to enter the caeca. It is unknown if the undigested protein that enters the caeca differs in fermentability depending on their ingredient source. In order to predict which feed ingredients increase the risk of PF, an in vitro procedure was developed, which simulates the gastric and enteric digestion, subsequent caecal fermentation. After digestion, amino acids and peptides smaller than 3.5 kD in the soluble fraction were removed by means of dialysis. These amino acids and peptides are assumed to be hydrolysed and absorbed in the small intestine of poultry and therefore not used in the fermentation assay. The remaining soluble and fine digesta fractions were inoculated with caecal microbes. In chicken, the soluble and fine fractions enter the caeca, to be fermented, while insoluble and coarse fractions bypass them. The inoculum was made N-free to ensure bacteria would require the N from the digesta fractions for their growth and activity. The gas production (GP) from the inoculum, therefore, reflected the ability of bacteria to use N from substrates and was an indirect measure for PF. The Maximum GP rate of ingredients averaged 21.3 ± 0.9 ml/h (mean ± SEM) and was in some cases more rapid than the positive control (urea, maximum GP rate = 16.5 ml/h). Only small differences in GP kinetics were found between protein ingredients. Branched-chain fatty acids and ammonia concentrations in the fermentation fluid after 24 hours showed no differences between ingredients. Results indicate that solubilised undigested proteins larger than 3.5 kD are rapidly fermented independent of its source when an equal amount of N is present.

Effects of a combination of fibrolytic and amylolytic enzymes on ruminal enzyme activities, bacterial diversity, blood profile and milk production in dairy cows

We hypothesised that adding a combination of fibrolytic and amylolytic enzymes to the diet of early-lactation dairy cows would improve rumen enzyme activity and bacterial diversity, promote energy metabolism, and benefit milk production in cows. Twenty multiparous early-lactation (90 ± 5 d) Holstein cows with similar body conditions were randomly allocated to control (CON, n = 10) and experimental (EXP, n = 10) groups in a completely randomised single-factor design. The CON was fed only a basal total mixed ration diet, and the diet of the EXP was supplemented with a combination of fibrolytic and amylolytic enzymes at 70 g/cow/d (cellulase 3 500 CU/g, xylanase 2 000 XU/g, β-glucanase 17 500 GU/g, and amylase 37 000 AU/g). The experiment lasted 28 days, with 21 days for adaptation and 7 days for sampling. Enzyme addition increased the activity levels of α-amylase and xylanase, and the ammonia-N concentration (P < 0.05) tended to increase the activity of β-glucanase (P = 0.08) in rumen fluid. However, there was no significant difference in the rumen bacterial richness and diversity, phylum (richness > 0.1%) or genus (richness > 1%) composition between the CON and EXP groups (P > 0.05). A tendency of difference was found between CON and EXP (R = 0.22, P = 0.098) in principal component analysis. Ten genera showed different abundances across the CON and EXP groups (linear discriminant analysis effect size, linear discriminant analysis > 2). EXP increased the ratio of albumin to globulin and the concentrations of total cholesterol and low-density lipoprotein cholesterol (P < 0.05) and tended to increase triglycerides (P = 0.09) in blood. Milk yield, 3.5% fat-corrected milk yield and energy-corrected milk yield increased with enzyme supplementation (P < 0.05). The production levels of milk fat and lactose increased, but the percentage of solids, not fat and protein, decreased in EXP (P < 0.05). Although the DM intake was not affected, the feed efficiency tended to increase (P = 0.07) in EXP. In conclusion, dietary supplementation with a mixture of fibrolytic and amylolytic enzymes on multiparous early-lactation dairy cows increased α-amylase and xylanase activity levels in rumen fluid, enhanced milk performance and tended to improve the feed efficiency in cows.

Domesticated equine species and their derived hybrids differ in their fecal microbiota

BACKGROUND

Compared to horses and ponies, donkeys have increased degradation of dietary fiber. The longer total mean retention time of feed in the donkey gut has been proposed to be the basis of this, because of the increased time available for feed to be acted upon by enzymes and the gut microbiota. However, differences in terms of microbial concentrations and/or community composition in the hindgut may also underpin the increased degradation of fiber in donkeys. Therefore, a study was conducted to assess if differences existed between the fecal microbiota of pony, donkey and hybrids derived from them (i.e. pony × donkey) when fed the same forage diet.

RESULTS

Fecal community composition of prokaryotes and anaerobic fungi significantly differed between equine types. The relative abundance of two bacterial genera was significantly higher in donkey compared to both pony and pony x donkey: Lachnoclostridium 10 and 'probable genus 10' from the Lachnospiraceae family. The relative abundance of Piromyces was significantly lower in donkey compared to pony × donkey, with pony not significantly differing from either of the other equine types. In contrast, the uncultivated genus SK3 was only found in donkey (4 of the 8 animals). The number of anaerobic fungal OTUs was also significantly higher in donkey than in the other two equine types, with no significant differences found between pony and pony × donkey. Equine types did not significantly differ with respect to prokaryotic alpha diversity, fecal dry matter content or fecal concentrations of bacteria, archaea and anaerobic fungi.

CONCLUSIONS

Donkey fecal microbiota differed from that of both pony and pony × donkey. These differences related to a higher relative abundance and diversity of taxa with known, or speculated, roles in plant material degradation. These findings are consistent with the previously reported increased fiber degradation in donkeys compared to ponies, and suggest that the hindgut microbiota plays a role. This offers novel opportunities for pony and pony × donkey to extract more energy from dietary fiber via microbial mediated strategies. This could potentially decrease the need for energy dense feeds which are a risk factor for gut-mediated disease.

Multi-kingdom characterization of the core equine fecal microbiota based on multiple equine (sub)species

BACKGROUND

Equine gut microbiology studies to date have primarily focused on horses and ponies, which represent only one of the eight extant equine species. This is despite asses and mules comprising almost half of the world's domesticated equines, and donkeys being superior to horses/ponies in their ability to degrade dietary fiber. Limited attention has also been given to commensal anaerobic fungi and archaea even though anaerobic fungi are potent fiber degrading organisms, the activity of which is enhanced by methanogenic archaea. Therefore, the objective of this study was to broaden the current knowledge of bacterial, anaerobic fungal and archaeal diversity of the equine fecal microbiota to multiple species of equines. Core taxa shared by all the equine fecal samples (n = 70) were determined and an overview given of the microbiota across different equine types (horse, donkey, horse × donkey and zebra).

RESULTS

Equine type was associated with differences in both fecal microbial concentrations and community composition. Donkey was generally most distinct from the other equine types, with horse and zebra not differing. Despite this, a common bacterial core of eight OTUs (out of 2070) and 16 genus level groupings (out of 231) was found in all the fecal samples. This bacterial core represented a much larger proportion of the equine fecal microbiota than previously reported, primarily due to the detection of predominant core taxa belonging to the phyla Kiritimatiellaeota (formerly Verrucomicrobia subdivision 5) and Spirochaetes. The majority of the core bacterial taxa lack cultured representation. Archaea and anaerobic fungi were present in all animals, however, no core taxon was detected for either despite several taxa being prevalent and predominant.

CONCLUSIONS

Whilst differences were observed between equine types, a core fecal microbiota existed across all the equines. This core was composed primarily of a few predominant bacterial taxa, the majority of which are novel and lack cultured representation. The lack of microbial cultures representing the predominant taxa needs to be addressed, as their availability is essential to gain fundamental knowledge of the microbial functions that underpin the equine hindgut ecosystem.

In vitro gas and methane production in rumen fluid from dairy cows fed grass silages differing in plant maturity, compared to in vivo data

The relationship between in vitro rumen CH₄ production of grass silages, using the gas production technique, and in vivo data obtained with the same cows and rations in respiration chambers was investigated. Silages were made from grass harvested in 2013 on May 6th, May 25th, July 1st and July 8th. The grass silages were used to formulate four different rations which were fed to 24 cows in early and late lactation, resulting in a slightly different dry matter intake (DMI; 16.5 kg/day vs. 15.4 kg/day). The experimental rations consisted of 70% grass silage, 10% maize silage, and 20% concentrates on a dry matter basis. Cows were adapted to the rations for 17 days before rumen fluid was collected via oesophageal tubing, and in vitro gas and CH₄ production were analysed. In vitro total gas and CH₄ production of the (ensiled) grass expressed as ml/g OM decreased with advancing maturity of the grass. The in vitro CH₄ production after 48 hr of incubation expressed in ml/g OM did not correlate with the in vivo CH₄ production expressed in g/kg organic matter intake or g/kg DMI (R²  = .00-.18, p ≥ .287). The differences in CH₄ emission per unit of intake observed in vivo were rather small between the different rations, which also contributed to the observed poor relationship. Utilizing stepwise multiple regression improved the correlation only slightly. In vitro gas and CH₄ production varied based on whether donor cows were previously adapted to the respective ration or not, suggesting that careful adaption to the experimental diet should be envisaged in in vitro gas and CH₄ production experiments.

Inclusion of sainfoin (Onobrychis viciifolia) silage in dairy cow rations affects nutrient digestibility, nitrogen utilization, energy balance, and methane emissions

Sainfoin (Onobrychis viciifolia) is a tanniniferous legume forage that has potential nutritional and health benefits preventing bloating, reducing nematode larval establishment, improving N utilization, and reducing greenhouse gas emissions. However, the use of sainfoin as a fodder crop in dairy cow rations in northwestern Europe is still relatively unknown. The objective of this study was to evaluate the effect of sainfoin silage on nutrient digestibility, animal performance, energy and N utilization, and CH4 production. Six rumen-cannulated, lactating dairy cows with a metabolic body weight (BW(0.75)) of 132.5±3.6kg were randomly assigned to either a control (CON) or a sainfoin (SAIN)-based diet over 2 experimental periods of 25 d each in a crossover design. The CON diet was a mixture of grass silage, corn silage, concentrate, and linseed. In the SAIN diet, 50% of grass silage dry matter (DM) of the CON diet was exchanged for sainfoin silage. The cows were adapted to 95% of ad libitum feed intake for a 21-d period before being housed in climate-controlled respiration chambers for 4 d, during which time feed intake, apparent total-tract digestibility, N and energy balance, and CH4 production was determined. Data were analyzed using a mixed model procedure. Total daily DM, organic matter, and neutral detergent fiber intake did not differ between the 2 diets. The apparent digestibility of DM, organic matter, neutral detergent fiber, and acid detergent fiber were, respectively, 5.7, 4.0, 15.7, and 14.8% lower for the SAIN diet. Methane production per kilogram of DM intake was lowest for the SAIN diet, CH4 production as a percentage of gross energy intake tended to be lower, and milk yield was greater for the SAIN diet. Nitrogen intake, N retention, and energy retained in body protein were greater for the SAIN than for the CON diet. Nitrogen retention as a percentage of N intake tended to be greater for the SAIN diet. These results suggest that inclusion of sainfoin silage in dairy cow rations reduces CH4 per kilogram of DM intake and nutrient digestibility. Moreover, sainfoin silage improves milk production and seems to redirect metabolism toward body protein accretion at the expense of body fat.

Prediction and evaluation of enteric methane emissions from lactating dairy cows using different levels of covariate information

The dairy sector contributes to global warming through enteric methane (CH4) emissions. Methane is also a loss of energy to the ruminant. Several studies have developed CH4 prediction models to assess mitigation strategies to reduce emissions. However, the majority of these models have low predictive ability or require numerous inputs that are often not readily available in commercial dairy operations. In this context, the objective of the present paper was to develop CH4 prediction models by using varying levels of information available at the farm level. The seven complexity levels used the following information: (1) dietary nutrient composition, (2) milk yield and composition, (3) Levels 1 and 2, (4) Level 3 plus dry matter intake (DMI), (5) Level 4 plus bodyweight, (6) Level 2 plus DMI, and (7) DMI only. Models were fitted to 489 individual enteric-CH4 measurements from 30 indirect calorimetry studies and evaluated with an independent database comprising 215 treatment means from 62 studies collected from the literature. Within each complexity level, all possible mixed-effect models were fitted and those with the lowest values of Akaike or Bayesian information criteria were selected using lme4 package in R. Models were evaluated using mean square prediction error (MSPE) based statistic, root MSPE (RMSPE) to observation standard deviation ratio, concordance correlation coefficient and Nash–Sutcliffe efficiency methods. All fitted models performed well with an acceptable error estimates (RMSPE as a percentage of observed mean (RMSPE%) = 16–24%), with more than two-thirds of total error originating from random bias. Overall, models with DMI were more accurate (RMSPE% = 16–20%) than those without (RMSPE% = 20–24%). Although the best prediction model (RMSPE% = 16%) was developed using Level 5 information, a model using Level 2 information is recommended for on-farm methane estimates if DMI is not measured. The proposed models offer easy and practical tools to dairy producers for predicting CH4 emissions and evaluating CH4 mitigation strategies.

Adaptation of faecal microbiota in sows after diet changes and consequences for in vitro fermentation capacity

In vitro gas production studies are routinely used to assess the metabolic capacity of intestinal microbiota to ferment dietary fibre sources. The faecal inocula used during the in vitro gas production procedure are most often obtained from animals adapted to a certain diet. The present study was designed to assess whether 19 days of adaptation to a diet are sufficient for faecal inocula of pigs to reach a stable microbial composition and activity as determined by in vitro gas production. Eighteen multiparous sows were allotted to one of two treatments for three weeks: a diet high in fibre (H) or a diet low in fibre (L). After this 3-week period, the H group was transferred to the low fibre diet (HL-treatment) while the L group was transferred to the diet high in fibre (LH-treatment). Faecal samples were collected from each sow at 1, 4, 7, 10, 13, 16 and 19 days after the diet change and prepared as inoculum used for incubation with three contrasting fermentable substrates: oligofructose, soya pectin and cellulose. In addition, inocula were characterised using a phylogenetic microarray targeting the pig gastrointestinal tract microbiota. Time after diet change had an effect (P<0.05) on total gas production for the medium-fast fermentable substrates; soya pectin and oligofructose. For the more slowly fermentable cellulose, all measured fermentation parameters were consistently higher (P<0.05) for animals in the HL-treatment. Diet changes led to significant changes in relative abundance of specific bacteria, especially for members of the Bacteroidetes and Bacilli, which, respectively, increased or decreased for the LH-treatment, while changes were opposite for the HL-treatment. Changing the diet of sows led to changes in fermentation activity of the faecal microbiota and in composition of the microbiota over time. Adaptation of the microbiota as assessed by gas production occurred faster for LH-animals for fast fermentable substrates compared with HL-animals. Overall, adaptation of the large intestinal microbiota of sows as a result of ingestion of low and high fibre diets seems to take longer than 19 days, especially for the ability to ferment slowly fermentable substrates.

Effects of dietary starch content and rate of fermentation on methane production in lactating dairy cows

The objective of this study was to investigate the effects of starch varying in rate of fermentation and level of inclusion in the diet in exchange for fiber on methane (CH4) production of dairy cows. Forty Holstein-Friesian lactating dairy cows of which 16 were rumen cannulated were grouped in 10 blocks of 4 cows each. Cows received diets consisting of 60% grass silage and 40% concentrate (dry matter basis). Cows within block were randomly assigned to 1 of 4 different diets composed of concentrates that varied in rate of starch fermentation [slowly (S) vs. rapidly (R) rumen fermentable; native vs. gelatinized corn grain] and level of starch (low vs. high; 270 vs. 530g/kg of concentrate dry matter). Results of rumen in situ incubations confirmed that the fractional rate of degradation of starch was higher for R than S starch. Effective rumen degradability of organic matter was higher for high than low starch and also higher for R than S starch. Increased level of starch, but not starch fermentability, decreased dry matter intake and daily CH4 production. Milk yield (mean 24.0±1.02kg/d), milk fat content (mean 5.05±0.16%), and milk protein content (mean 3.64±0.05%) did not differ between diets. Methane expressed per kilogram of fat- and protein-corrected milk, per kilogram of dry matter intake, or as a fraction of gross energy intake did not differ between diets. Methane expressed per kilogram of estimated rumen-fermentable organic matter (eRFOM) was higher for S than R starch-based diets (47.4 vs. 42.6g/kg of eRFOM) and for low than high starch-based diets (46.9 vs. 43.1g/kg of eRFOM). Apparent total-tract digestibility of neutral detergent fiber and crude protein were not affected by diets, but starch digestibility was higher for diets based on R starch (97.2%) compared with S starch (95.5%). Both total volatile fatty acid concentration (109.2 vs. 97.5mM) and propionate proportion (16.5 vs. 15.8mol/100mol) were higher for R starch- compared with S starch-based diets but unaffected by the level of starch. Total N excretion in feces plus urine and N retained were unaffected by dietary treatments, and similarly energy intake and output of energy in milk expressed per unit of metabolic body weight were not affected by treatments. In conclusion, an increased rate of starch fermentation and increased level of starch in the diet of dairy cattle reduced CH4 produced per unit of eRFOM but did not affect CH4 production per unit of feed dry matter intake or per unit of milk produced.

Passage kinetics of dry matter and neutral detergent fibre through the gastro-intestinal tract of growing beef heifers fed a high-concentrate diet measured with internal δ13C and external markers

Fractional rumen passage rates (K1) are fundamental in feed evaluation systems for ruminants to predict the extent of nutrient degradation. Data on passage kinetics of growing beef cattle fed high-concentrate diets are scarce and mainly rely on external passage markers which do not provide nutrient-specific K1 estimates. The present study describes the use of carbon stable isotopes (δ13C) as an internal marker to estimate K1 of dry matter (DM) and neutral detergent fibre (NDF) fractions of a compound feed in a high-concentrate diet, and compares them to the external markers ytterbium (Yb)-actetate and chromium mordanted fibre (Cr-NDF). Four rumen-fistulated Holstein heifers received four times per day a basal diet consisting of barley straw and pelleted compound feed offered separately (ratio 10 : 90, DM basis). Compound feed in the basal diet was mainly based on wheat of low natural 13C enrichment (−28.4 δ13C), which was exchanged with a single dose of a maize-based compound feed of higher natural 13C enrichment (−18.9 δ13C). This difference in natural 13C abundance was used to determine K1 values from faecal 13C excretion patterns. At the same time Yb-Acetate and Cr-NDF were introduced into the rumen to determine K1 values from faecal excretions. Faeces were collected over 90 h after pulse dosing. The K1 of δ13C-marked DM (0.062/h) did not differ (P = 0.745) from δ13C-marked NDF (0.060/h). The δ13C-based K1 values also did not differ from Cr-NDF (0.056/h; P = 0.315). These results indicate similar passage behaviour of these fractions in the rumen of beef heifers fed a high-concentrate diet.

Meal pattern analysis for effects of compound feed formulation in mid to late lactating dairy cows fed hay and compound feed both ad libitum

The Kempen System is a dairy feeding system allowing ad libitum access to pelleted compound feed (CF) and hay. This system allows high DM intake (DMI) up to 30 kg DM (80% CF), but small and frequent CF meals are essential to reduce negative ruminal pH fluctuations. Little is known about feed intake patterns of cows on ad libitum and separated access to CF and hay. Meal pattern analysis was performed to evaluate feed intake behaviour of two different isoenergetic and isonitrogenous CF (starch vs fibre), contrasting in neutral detergent fibre, acid detergent fibre and starch content. Twenty primi- and multiparous Holstein-Friesian cows (203 ± 35.4 days in milk) received grass hay ad libitum with one of the two CF also offered ad libitum. Meal criteria, the shortest non-feeding interval between feeding events separating two consecutive meals, were used to cluster feeding events into separate meals. The meal criteria were determined per cow by fitting the log10-transformed feeding intervals to Gaussian–Gaussian probability density functions. The DMI of CF fibre (18.8 ± 0.54 kg) tended to be greater (P = 0.09) than starch (18.1 ± 0.54 kg/day), while that of grass hay (4.8 ± 0.29 kg) was unaffected (P = 0.23). The CF meal size did not differ (P = 0.26) between treatments (starch 2.9 vs fibre 3.0 ± 0.11 kg/meal), but number of meals per day (6.36 ± 0.229, P = 0.87) and meal durations (64 ± 3.5 min, P = 0.87) did not differ between treatments. The differences in CF formulation were insufficient to create detectable differences in feed intake nor intake behaviour patterns.

The production of intrinsically labeled milk and meat protein is feasible and provides functional tools for human nutrition research

Administration of labeled, free amino acids does not allow direct assessment of in vivo dietary protein digestion and absorption kinetics. Consequently, dietary protein sources with labeled amino acids incorporated within their protein matrix are required. The aim of the present study was to produce intrinsically L-[1-(13)C]phenylalanine-labeled milk and meat protein that would permit in vivo assessment of postprandial protein digestion and absorption kinetics in humans. One lactating dairy cow was continuously infused with 420 μmol of L-[1-(13)C]phenylalanine/min for 96 h, with plasma and milk being collected before, during, and after isotope infusion. Twenty-four hours after infusion, the cow was slaughtered to produce intrinsically labeled meat. Levels of L-[1-(13)C]phenylalanine enrichment as high as 40 mole percent excess (MPE) in milk and 1.5 MPE in meat protein were achieved. In a subsequent human proof-of-principle experiment, 2 healthy young males (25±1 yr; 66.2±5.2 kg) each ingested 135 g of L-[1-(13)C]phenylalanine intrinsically labeled minced beef, after which plasma samples were collected at regular time intervals. Plasma L-[1-(13)C]phenylalanine enrichments increased during the first 90 min following beef ingestion, reaching peak plasma enrichment levels of 0.61±0.04 MPE. Whole-body net protein balance, assessed by continuous infusion of L-[ring-(2)H(5)]phenylalanine and L-[ring-(2)H(2)]tyrosine, was higher in the postprandial period compared with basal values (6.4±0.1 vs. -4.5±0.1 μmol/kg per h). In conclusion, the production of intrinsically L-[1-(13)C]phenylalanine-labeled milk and meat protein is feasible and provides functional tools to investigate in vivo protein digestion and absorption kinetics in humans.

Comparative in vitro fermentation activity in the canine distal gastrointestinal tract and fermentation kinetics of fiber sources

The current study aimed to evaluate the variation in fermentation activity along the distal canine gastrointestinal tract (GIT, Exp. 1). It also aimed to assess fermentation kinetics and end product profiles of 16 dietary fibers for dog foods using canine fecal inoculum (Exp. 2). For Exp. 1, digesta were collected from the distal ileum, proximal colon, transverse colon, and rectum of 3 adult dogs. Digesta per part of the GIT were pooled for 3 dogs, diluted (1:25, wt/vol), mixed, and filtered for the preparation of inoculum. A fructan, ground soy hulls, and native potato starch were used as substrates and incubated for cumulative gas production measurement as an indicator of the kinetics of fermentation. In addition, fermentation bottles with similar contents were incubated but were allowed to release their gas throughout incubation. Fermentation fluid was sampled at 4, 8, 12, 24, 48, and 72 h after initiation of incubation, and short-chain fatty acids and ammonia were measured. Results showed comparable maximal fermentation rates for rectal and proximal colonic inocula (P > 0.05). Production of short-chain fatty acids was least for the ileal and greatest for the rectal inoculum (P < 0.05). Therefore, for in vitro studies, fecal microbiota can be used as an inoculum source but may slightly overestimate in vivo fermentation. Experiment 2 evaluated the gas production, fermentation kinetics, and end product profiles at 8 and 72 h of incubation for citrus pectin, 3 fructans, gum arabic, 3 guar gums, pea fiber, peanut hulls, soy fiber, sugar beet fiber, sugar beet pectin, sugar beet pulp, wheat fiber, and wheat middlings. Feces of 4 adult dogs were used as an inoculum source. Similar techniques were used as in Exp. 1 except for the dilution factor used (1:10, wt/vol). Among substrates, large variations in fermentation kinetics and end product profiles were noted. Sugar beet pectin, the fructans, and the gums were rapidly fermentable, indicated by a greater maximal rate of gas production (R(max)) compared with all other substrates (P < 0.05), whereas peanut hulls and wheat fiber were poorly fermentable, indicated by the least amount of gas produced (P < 0.05). Sugar beet fiber, sugar beet pulp, soy fiber, and wheat middlings were moderately fermentable with a low R(max). Citrus pectin and pea fiber showed a similar low R(max), but time at which this occurred was later compared with sugar beet fiber, sugar beet pulp, soy fiber, and wheat middlings (P < 0.05). Results of this study can be used to formulate canine diets that stimulate dietary fiber fermentation along the distal GIT that may optimize GIT health and stimulate the level of satiety in dogs.