Grass maturity effects on cattle fed silage-based diets. 2. Cell wall digestibility,digestion and passage kinetics

Four silages were harvested at approximately 1-week intervals from the same timothy-meadow fescue sward and studied in a 4 × 4 Latin square experiment with four ruminally and duodenally cannulated young cattle. The diets comprised silage and concentrate (7:3 dry matter (DM) basis) and were fed at a rate of 70 g DM kg^−0.75 liveweight in two equal meals per day.Neutral detergent fibre (NDF) digestibility was 0.757, 0.765, 0.692 and 0.686 on diets based on the four silages in order of harvest date. Increasing maturity of grass ensiled showed linear (P_L < 0.001) and cubic (P_C < 0.01) trends. NDF was separated into digestible (DNDF) and indigestible (INDF) fractions, which differed clearly in their rate of passage from the rumen (on average 0.0141 vs. 0.0258 h⁻¹). The rate of digestion (k_d) of DNDF was on average 0.076 h⁻¹ when derived from the rumen evacuations but only 0.036 h⁻¹ when calculated from the disappearance from nylon bags incubated in the rumen. Both methods detected decreased k_d of NDF with increasing maturity of grass ensiled.Rate of passage from the rumen increased with increasing maturity of grass both when determined for NDF with rumen evacuation technique and from the faecal excretion of ytterbium calculated with a two-pool model. Mean retention time (MRT) in the non-escapable pool of particles increased (P_L < 0.01) with increasing grass maturity, the opposite being true for the escapable pool (P_L < 0.05), resulting in no change in the total ruminal MRT. Pool sizes of ruminal DM P_L < 0.01) and NDF (P_L < 0.001) increased with increasing maturity of grass. Ruminal NDF digestibility was calculated by different methods. When digestion kinetic parameters were derived from rumen evacuations and two-pool models used for passage kinetics, estimated digestibilities were very close to the observed ones.     

Whole body and tissue cholesterol turnover in the baboon

Cholesterol turnover was studied in four baboons by injecting [14C]cholesterol 186 days and [3H]cholesterol 4 days before necropsy, and fitting a two- or three-pool model to the resulting specific activity-time data. At necropsy, cholesterol mass and specific activity were determined for the total body (minus the central nervous system) and for many tissues. A pool model permits the estimation, from the plasma specific activity-time curve alone, of total body cholesterol within a limited range, depending upon the extent of side pool synthesis. The principal aim of this study was to estimate the extent of cholesterol synthesis in the side pools of the model, by computing the amount of side pool synthesis needed to equal the measured total body cholesterol. Central pool synthesis varied from 61 to 89% of the total cholesterol production rate. Thus, approximately 25% (11 to 39%) of the production rate arose from peripheral (pool 3 for the three-pool, and pool 2 for the two-pool model) cholesterol synthesis. Moreover, the finding that the measured total body cholesterol fell within the range obtained from the kinetic analysis by using reasonable assumptions (namely, that zero or that half the production rate occurred in the side pools), provides evidence for the physiological validity of the model. A second aim of this study was to explore cholesterol turnover in various tissues. A pool model predicts that rapidly turning over tissues will have higher specific activities at early times and lower specific activities at later times after injection of tracer relative to slowly turning over tissues, except where significant synthesis occurs. Tissues were ranked 1 to 17 for 3H and 17 to 1 for 14C cholesterol specific activity values. Except for the GI tract and testis, the tissues had similar ranks for both 3H and 14C, further validating model predictions. Results in all four baboons were similar. Turnover rates for the different tissues loosely fell into three groups which were turning over at fast, intermediate, and slow rates. Finally, the magnitude of variation of cholesterol specific activity was moderate for several distributed tissues (fat, muscle, arteries, and the alimentary tract), but was small for liver. Cholesterol turnover in serial biopsies of skin, muscle, and fat could, however, be fitted with a single pool to estimate tissue turnover rates.     

A simulation model “CTR Dairy” to predict the supply of nutrients in dairy cows managed under discontinuous feeding patterns

A simulation rumen model has been developed to function under non-steady state conditions in order to allow prediction of nutrient availability in dairy cows managed under discontinuous feeding systems. The model simulates availability of glycogenic, aminogenic and lipogenic nutrients to lactating dairy cows fed discontinuously. The model structure considers input of up to three different feeds fed independently at any time during the day. Feeds are described by their nitrogen (N), carbohydrate and fatty acid fractions. The N containing feed fractions include ruminally undegraded crude protein (CP), ruminally insoluble but potentially degradable CP, ruminally soluble CP and ammonia N. The feed carbohydrate fractions include ruminally undegradable neutral detergent fibre (NDF), ruminally degradable NDF, ruminally insoluble starch, ruminally soluble starch and sugars. The fatty acids in the feeds are divided between long chain fatty acids and volatile fatty acids (VFA). Additionally four pools were defined representing absorption of amino acids, glucose, long chain fatty acids and volatile fatty acids. The rumen microbial population is represented as a single pool. Besides a flexible structure, new features to the extant model include adoption of the concept of chewing efficiency (or chewing effectiveness) during eating, variable fractional ruminal absorption rates of VFA and variable fractional ruminal degradation rates of NDF as a function of rumen liquid pH, as well as a variable rumen volume which directly affects rumen concentrations of metabolites. The model continuously (i.e., by minute) predicts release of soluble components from the feeds in the rumen, concentration and absorption of fermentation end products in the rumen, rumen pools of nutrients and microbial biomass dynamics, as well as passage of microbial biomass and non-fermented nutrients from the rumen, in response to various feeding strategies. Model evaluation covered a wide range of feeding strategies that included pasture and housed feeding systems. Overall, the mean square prediction error (MSPE) as a percentage of the observed mean was relatively low (<10%) with a high amount of the total variation explained by random variation (>65%). Deviation from unity varied between 23% (rumen dry matter content) and 25% (NDF), indicating some consistent over and/or under prediction. A more detailed evaluation was done based on studies available that reported diurnal behaviour of key model outputs such as rumen pools, rumen pH, and rumen VFA. The predictions broadly simulated the observed values quantitatively, relative to general diurnal patterns, and relative to differences between treatments in the predicted diurnal patterns. Results show that the model provides a tool to assess potential outcomes of changing feeding strategies which may be particularly valuable in assessing selection of feeds, amounts and times of the day to offer the feeds. The continuous nature of the simulated output also allows determination of the time(s) of the day that ruminal (and/or post-ruminal) delivery of nutrients may limit ruminal output of nutrients (and/or availability of nutrients) to support milk nutrient synthesis.     

Prüfung von neuen Futterphosphaten auf ihre Phosphor-Verfügbarkeit für Broiler,Schweine und Lämmer

A mathematical model of rumen fermentation processes was validated with 65 sheep experiments and 45 cattle experiments, respectively. Further, it was shown how the modell reacts when the feed composition, the level of feed intake and the feeding frequency was changed. The model predictions were satisfactory for the digestibility of organic matter and neutral detergent fibre (NDF) in rumen, the production of volatile fatty acids and the non‐ammonia‐N (NAN) flow to duodenum. The partition of NAN in microbial and feed N was estimated with lower reliability. The effects of variation of feeding level, feeding frequency and roughage quality (crude protein, lignin) on digestion processes have been simulated correctly. On the other hand, the effects of the proportion of roughage to concentrate have not been reproduced sufficiently with the mechanismes included in the model. To make correct predictions in this area too, it is necessary to integrate the rumen pH and its effects on rumen processes into the model. A mechanistic approach for estimation of the velocity constants for passage of substances out of the rumen would improve the model.     

Isozyme and morphological characteristics of the anaerobic fungus Piromyces mae isolated from the duodenum, rumen and faeces of sheep

Abstract Isolates of anaerobic fungi obtained from the rumen, duodenum and faeces of sheep were identified as Piromyces mae based on their morphological characteristics observed using light microscopy. There was no significant morphological variation among the isolates of P. mae from the rumen, duodenum and faeces. Isozymes of 12 isolates of P. mae (one each from the rumen, duodenum and faeces from 4 different sheep) were analysed by PAGE. A total of 12 isozymes were studied and 5 isozyme loci were successfully typed. They were malic enzyme, malate dehydrogenase, shikimate dehydrogenase, α-esterase and β-esterase. All the isolates of P. mae regardless of whether they were from the rumen, duodenum or faeces or from different animals produced very similar isozyme banding patterns for each of the enzyme systems. The similar isozyme profiles of the isolates indicate that they are of the same species although they exist in different regions of the alimentary tract.     

Separating soil CO2 efflux into C-pool-specific decay rates via inverse analysis of soil incubation data

Soil organic matter (SOM) is heterogeneous in structure and has been considered to consist of various pools with different intrinsic turnover rates. Although those pools have been conceptually expressed in models and analyzed according to soil physical and chemical properties, separation of SOM into component pools is still challenging. In this study, we conducted inverse analyses with data from a long-term (385 days) incubation experiment with two types of soil (from plant interspace and from underneath plants) to deconvolute soil carbon (C) efflux into different source pools. We analyzed the two datasets with one-, two- and three-pool models and used probability density functions as a criterion to judge the best model to fit the datasets. Our results indicated that soil C release trajectories over the 385 days of the incubation study were best modeled with a two-pool C model. For both soil types, released C within the first 10 days of the incubation study originated from the labile pool. Decomposition of C in the recalcitrant pool was modeled to contribute to the total CO₂ efflux by 9–11 % at the beginning of the incubation. At the end of the experiment, 75–85 % of the initial soil organic carbon (SOC) was modeled to be released over the incubation period. Our modeling analysis also indicated that the labile C-pool in the soil underneath plants was larger than that in soil from interspace. This deconvolution analysis was based on information contained in incubation data to separate carbon pools and can facilitate integration of results from incubation experiments into ecosystem models with improved parameterization.     

Validation of the doubly labeled water method in rats during isolation and simulated weightlessness

Total energy expenditure (TEE) of rats during simulated microgravity is unknown. The doubly labeled water method (DLW) reliably measures TEE, but the results depend on the methods of calculation. These methods were validated and appraised by indirect calorimetry in eight rats during isolation (7 days) and simulated microgravity (10 days). There were no effects on CO(2) production in the method used to derive constant flux rates as in the regression models. r(CO(2)) estimates were dependent on the assumed fractionation processes, the derivation of constant flux rate methods, and the selected pool models. Use of respiratory or food quotients did not influence TEE estimations, which were similar during isolation and simulation. During either isolation with growth or simulation with a stabilized mass, the one-pool model of Speakman (Speakman JR. Doubly Labelled Water. Theory and Practice. London: Chapman and Hall, 1997) resulted in the more reliable validation (0.8 +/- 2.2 and 2.2 +/- 3.4% vs. calorimetry, respectively). However, during simulation, agreement was also observed with the single pool model of Lifson (Lifson N, Gordon GB, and McClintock R. J Appl Physiol 7: 704-710, 1955) (-2.5 +/- 2.5%), and two two-pool models [Schoeller (Schoeller DA. J Nutr 118: 1278-1289, 1988) (0.5 +/- 3.1%) and Speakman (Speakman, JR. Doubly Labelled Water. Theory and Practice. London: Chapman and Hall, 1997) (-1.9 +/- 2.7%)]. This latter finding seems linked to the stable body mass and to fractionation consideration close to the single-pool model of Speakman. During isolation or simulated microgravity, the other equations underestimated TEE by 10-20%.     

Measurements of cholesterol turnover, synthesis, and absorption in man, carried out by isotope kinetic and sterol balance methods

We have estimated the daily synthesis of cholesterol in man by measuring the excretion of cholesterol and its conversion products during periods of controlled sterol intake (sterol balance method), using isotopic or chromatographic procedures (or a combination of the two). Estimates of daily synthesis by this method are based on the premise that the subject is in the metabolic steady state; i.e., the synthesis of cholesterol is equal to the balance (or difference) between the intake of cholesterol and the excretion of cholesterol and its products. To test this premise, we carried out sterol balances in 11 patients; simultaneously, after administration of isotopic cholesterol, turnover was calculated according to previously described models (one-pool, two-pool, or isotopic steady state models for the distribution of radioactive cholesterol within various pools of the body). With calculations based on the one-pool model, turnover rates were considerably higher than estimates based on all other models, and reasons are given for considering these to be overestimates. Good agreement was obtained between results calculated from the two-pool model and those based on sterol balance data; neither method is theoretically preferable to the other. However, with the sterol balance method supplemented by isotopic techniques, valid measurements of cholesterol absorption can be obtained; this in turn permits the essential distinction to be made between daily synthesis and daily turnover of cholesterol when the diet contains cholesterol. In addition, the use of chromatographic isolation procedures provides an accurate measurement of the balance of -sitosterol. This in turn permits valid corrections to be made for losses (which may be large) of neutral steroids during intestinal transit; this is a unique advantage of the chromatographic method.     

Determining biological tissue turnover using stable isotopes: the reaction progress variable

The reaction progress variable is applied to stable isotope turnover of biological tissues. This approach has the advantage of readily determining whether more than one isotope turnover pool is present; in addition, the normalization process inherent to the model means that multiple experiments can be considered together although the initial and final isotope compositions are different. Consideration of multiple isotope turnover pools allows calculation of diet histories of animals using a time sequence of isotope measurements along with isotope turnover pools. The delayed release of blood cells from bone marrow during a diet turnover experiment can be quantified using this approach. Turnover pools can also be corrected for increasing mass during an experiment, such as when the animals are actively growing. Previous growth models have been for exponential growth; the approach here can be used for several different growth models. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

Characterization of soluble lignin released from alfalfa by sheep digestion

A faecal soluble lignin fraction (FSL) extracted with 90% dioxane from the faeces of sheep fed on alfalfa hay was characterized by chemical analysis, nitrobenzene oxidation, fourier transform infrared spectroscopy and gel permeation chromatography, and compared with milled wood lignin (MWL) isolated from the alfalfa hay. The amount of FSL in the faeces was low, accounting for only 1% of the lignin present in the alfalfa hay. FSL and MWL consisted mostly of lignin components and contained a small amount of carbohydrate. FSL had a much higher proportion of syringylpropane units than MWL and showed a wide molecular size distribution. The results indicate the selective and limited solubilization of syringyl-rich lignin from alfalfa by sheep digestion.     

Alternative kinetic laws to describe the turnover of the microbial biomass

Many models that describe the turnover of the microbial biomass in soil use either first order kinetics where the rate of turnover is directly proportional to the microbial mass, or a variant of the Michaelis-Menten law that describes enzyme kinetics. To account for the different rates of microbial turnover observed at different times after the addition of substrate, some authors have suggested the existence of more than one pool of biomass. Each pool obeys the same kinetic law but with a different rate. In other experiments a disproportionately large increase in the turnover of native organisms has been observed relative to the amount of fresh substrate added. A change in the kinetic law describing the turnover of organisms can account for these observations and yet retain the simplicity of a single pool of micro-organisms. However where multiple pools of organisms are justified a mixed kinetic law with both first and second order terms may be more appropriate; in other words one pool of micro-organisms but two rate constants. The advantage of retaining a single pool of microbial biomass is that models may more readily be constructed in relation to the routine measurements of total microbial mass.     

Relationships of fibre,lignin, and phenolics to in vitro fibre digestibility in three perennial grasses

Livestock performance can be improved by increasing the digestibility of feeds, one of the key elements of nutritional quality. Digestibility of feeds can be improved by breeding forage crops with modified cell-wall structure, increasing the potential availability of energy from the cell wall to rumen microbes and livestock. The objectives of this research were to identify interrelationships among lignin and phenolic components of the fibre fraction of three perennial grasses and to determine their influence on in vitro fibre digestibility. Differences in etherified and esterified ferulate and esterified p-coumarate among clones of three perennial grasses were generally repeatable across harvests. The concentration of neutral detergent fibre (NDF) and Klason lignin within the NDF fraction were the factors most limiting to 24-h in vitro digestibility, with NDF being the most important. Klason lignin and etherified ferulate were the factors most limiting to 96-h in vitro digestibility for all three species. Due to its positive correlation with NDF, selection for low etherified ferulate should be avoided in smooth bromegrass (Bromus inermis Leyss) and cockfsoot (Dactylis glomerata L.). It should be possible to select and breed for low concentrations of lignin to improve digestibility without decreasing NDF in these two species. However, in reed canarygrass (Phalaris arundinacea L.), both lignin and etherified ferulate were positively correlated with NDF, indicating that selection for increased digestibility should be based directly on some measure of in vitro digestibility to avoid the fitness problems associated with reduced NDF.     

Determination of cholesterol turnover rate by a one-and two-pool kinetic analysis.

The cholesterol turnover rate in rabbits with alimentary cholesterol atherosclerosis and in guinea-pigs with chronic vitamin C deficiency was studied by a one- and two-pool kinetic analysis. The one-pool analysis yielded exaggeraged values for the turnover rate, but the turnover rate differences between the control and experimental groups in the one- and the two-pool analysis were very similar. One-pool analysis can be used in initial studies to obtain preliminary data on the effect of nutritional, pharmacological and other factors on cholesterol turnover rate.     

A comparative study of the apparent total tract digestibility of carbohydrates in Icelandic and Danish warmblood horses fed two different haylages and a concentrate consisting of sugar beet pulp and black oats

Four Icelandic (ICE) and four Danish Warmblood (DW) horses were used in a crossover study with two treatments to investigate the effect of breed and the effect of stage of maturity of haylage on the apparent total tract digestibility (ATTD) of a diet consisting of sugar beet pulp, black oats and haylage early or late cut. Fibre was analysed as crude fibre (CF), acid detergent fibre (ADF), neutral detergent fibre (NDF) and dietary fibre (DF = non-starch polysaccharides (NSP) plus lignin). In haylage all analysed fibre fractions increased with advancing stage of maturity, with the cell wall components cellulose, non-cellulosic residue, xylose and lignin causing this increase. Crude protein (CP) and sugars decreased with advancing stage of maturity. Feeding early cut haylage resulted in a significantly (p < 0.05) higher ATTD of dry matter (DM), organic matter (OM), energy, NDF, total NSP, DF and CP compared to feeding late cut haylage. There was a significantly (p < 0.05) higher ATTD of CF, DF and starch in ICE than in DW. Diet affected several faecal parameters with a significantly (p < 0.05) lower pH in faeces when horses were fed the early cut haylage. Concentrations of total short-chain fatty acids were significantly (p < 0.05) higher in faeces from horses fed early cut haylage, reflecting the higher fermentability (higher ATTD) of this diet. There was no marked effect of breed on faecal parameters. The DF analysis method gave the most appropriate differentiation of the fibre fractions and their digestibility, compared to the traditional CF, ADF and NDF analyses. A major advantage of the DF analysis is the capacity of recovering soluble fibres. The results suggested that ICE had higher ATTD of DF than DW, and this was caused by a tendency for a higher ATTD of cellulose, but further studies are required to verify that in general.     

Effect of harvest time and physical form of alfalfa silage on chewing time and particle size distribution in boli,rumen content and faeces

The study examined the effects of physical form and harvest time of alfalfa silage on eating and ruminating activity and particle size distribution in feed boli, rumen content and faeces in dry cows. The alfalfa crop was harvested at two stages of growth (early: NDF 37%, late: NDF 44% in dry matter (DM)), and from each harvest, a chopped (theoretical cutting length: 19 mm) and an unchopped crop was ensiled in bales. The silages were fed restrictively to four rumen cannulated non-lactating Jersey cows (391 ± 26 kg) in a 4 × 4 Latin square design. The cows were fed restrictively 80% of their ad libitum intake twice daily. Chewing activity was recorded for 96 h continuously. Swallowed boli, rumen content, rumen fluid and faeces samples were collected, washed in nylon bags (0.01 mm pore size) and freeze-dried before dry sieving through 4.750, 2.360, 1.000, 0.500 and 0.212 mm pore sizes into six fractions. The length (PL) and width (PW) of particles within each fraction was measured by the use of image analysis. The eating activity (min/kg dry matter intake (P < 0.01) and min/kg NDF (P < 0.05)) was affected by harvest time. The mean ruminating time (min/kg DM) was affected by harvest time (P < 0.01), physical form (P < 0.05) and NDF intake per kg BW (P < 0.01). The proportion of washed particle DM of total DM in boli, rumen content, rumen fluid and faeces was affected by harvest time (P < 0.01) and highest by feeding late-harvested alfalfa silage. Two peaks on the probability density distribution function (PDF) of PW and PL values of boli, rumen content and faeces were identified. Chopping of the silage decreased the mean PL and PW, the most frequent PL (mode) and 95% percentile PL and PW values in boli. In the rumen content, chopping increased the mean PW (P < 0.05). The dimension sizes of faeces particles were not significantly affected by chopping. The mode PW value was lower in rumen content and faeces than in boli (P < 0.001), and the mode PL value was higher in boli and lower in faeces compared with rumen contents (P < 0.001). In conclusion, the mean total chewing activity per kg NDF decreased due to chopping and early harvest time. The mean PL and PW in boli decreased due to chopping and late harvest. The two peak values on the PDF (PL) and PDF (PW) of boli, rumen content and faeces particles are most likely related to the leaf and the stem residues.     

Multi‐locus sequence types of Campylobacter carried by flies and slugs acquired from local ruminant faeces

Aims: To assess whether flies and slugs acquire strains of Campylobacter jejuni and Campylobacter coli present in local ruminant faeces. Methods and Results: Campylobacter was cultured from flies, slugs and ruminant faeces that were collected from a single farm in Scotland over a 19‐week period. The isolates were typed using multi‐locus sequence typing (MLST) and compared with isolates from cattle and sheep faeces. Campylobacter jejuni and Camp. coli were isolated from 5·8% (n = 155, average of 75 flies per pool) and 13·3% (n = 15, average of 8·5 slugs per pool) of pooled fly and slug samples, respectively. The most common sequence type (ST) in flies was Camp. coli ST‐962 (approx. 40%) regardless of the prevalence in local cattle (2·3%) or sheep (25·0%) faeces. Two positive slug pools generated the same ST that has not been reported elsewhere. Conclusions: Despite their low carriage rate, flies are able to acquire Campylobacter STs that are locally present, although the subset carried may be biased when compared to local source. Slugs were shown to carry a previously unreported Campylobacter ST. Significance and Impact of the Study: This study has demonstrated that flies carry viable Campylobacter and may contribute to the transfer of STs within and between groups of animals on farms. Further, they may therefore present a risk to human health via their contact with ready‐to‐eat foods or surfaces.     

Revaluation of the role of cholesterol in stabilizing rafts implicated in T cell receptor signaling

T lymphocytes contain two kinetic pools of cholesterol extractable with methyl-beta-cyclodextrin (m-beta-CD): a fast pool (31.5%, t1/2=17 s) and a slow pool (68.5%, t1/2=15 min). Purification of detergent-resistant membranes (DRMs) shows that the fast pool corresponds to buoyant cholesterol. Cholesterol extraction of the fast pool (i.e. cholesterol from rafts) still allows the buoyancy of signaling proteins and their phosphorylation under CD3 stimulation. Cholesterol depletion of the slow pool (i.e. cholesterol from membranes other than rafts) is accompanied by the extraction of the whole raft followed by the inhibition of CD3-induced tyrosine-phosphorylations. Cholesterol oxidase (COase) allows a specific oxidation of raft cholesterol into cholestenone. Cholestenone leaves the DRMs and accumulates as Triton X-100-soluble material. Specific cholesterol-rich raft disruption by COase does not inhibit the activation of either Jurkat cells or T CD4+ lymphocytes. Our study challenges the real role of cholesterol-rich rafts in CD3/TCR signaling and suggests that a cholesterol-poor subtype of rafts is involved in signal transmission via the TCR.     

Relationship of high density lipoprotein cholesterol to cholesterol metabolism in the baboon (Papio sp.)

Genetic effects on serum high density lipoprotein (HDL) cholesterol concentration and several parameters of a two-pool model of cholesterol metabolism were investigated in 79 baboons, the progeny of 6 sires. Significant differences (P less than 0.05) were observed among the sire progeny groups for HDL cholesterol (HDL-C), cholesterol production rate, cholesterol mass of pool A, and the rate constants KA and KAB. Rank correlations (rs) revealed that the sire progeny group means for HDL-C are closely correlated with those for the cholesterol mass of pool A (rs = 0.89), KA (rs = -0.78), and KAB (rs = -0.94). These strong correlations suggest that pool A, KA, and KAB are influenced to a large degree by the same genes that regulate HDL-C concentration. The strong inverse relationship (rs = -0.78) between HDL-C and KA suggests that the differences among these sire progeny groups for HDL-C are due chiefly to those metabolic processes which regulate cholesterol excretion from pool A. This conclusion is consistent with reports that HDL-C is a preferred precursor for bile acid synthesis.     

Foraging behavior of bay anchovy larvae, Anchoa mitchilli

We investigated the food digestibility of East Pacific green turtles, Chelonia mydas agassizii, at tropical coral reefs of Gorgona National Park in the Colombian Pacific and calculated the intake passage time (IPT) of 3 different diets. We collected 150 faecal samples from turtles (mean straight carapace length 61.3 ± 4.12 cm and mean mass 32.3 ± 6.67 kg) to determine digesta composition and for measurement of neutral detergent fibre (NDF), acid detergent fibre (ADF), sulphuric acid lignin and protein. The mean (± S.D) IPT to recover at least 73% of external markers (plastic beads) in the faeces was 23.3 ± 6.6 days. The true NDF digestibility and dry matter digestibility were determined for high protein (fish), plant (fresh leaves of Araceae, Moraceae and Bombaceae) and mixed (combination of both high protein and plant) diets. NDF values obtained for digestibility of the protein, plant and mixed diets were 1%, 63% and 49% respectively. There was a large amount of undigested plant material in the faeces, dominated by fruits of red mangrove (Rhizophora mangle). We considered the relationships between the type of food, IPT and apparent digestibility in the context of the nutritional contribution of an omnivorous diet. Our results suggest that for juvenile green sea turtles in the Eastern Pacific combined diets are an opportunistic strategy responding to habitat features and supply to maximise energy acquisition in transitional habitats such as Isla Gorgona.