Investigating young children's physical activity through time and place.

BACKGROUND: Previous research indicates the start of primary school (4-5-year-old) as an essential period for the development of children's physical activity (PA) patterns, as from this point, the age-related decline of PA is most often observed. During this period, young children are exposed to a wider variety of environmental- and social contexts and therefore their PA is influenced by more diverse factors. However, in order to understand children's daily PA patterns and identify relevant opportunities for PA promotion, it is important to further unravel in which (social) contexts throughout the day, PA of young children takes place. METHODS: We included a cross-national sample of 21 primary schools from the Startvaardig study. In total, 248 children provided valid accelerometer and global positioning (GPS) data. Geospatial analyses were conducted to quantify PA in (social) environments based on their school and home. Transport-related PA was evaluated using GPS speed-algorithms. PA was analysed at different environments, time-periods and for week- and weekend days separately. RESULTS: Children accumulated an average of 60 min of moderate-to-vigorous PA (MVPA), both during week- and weekend days. Schools contributed to approximately half of daily MVPA during weekdays. During weekends, environments within 100 m from home were important, as well as locations outside the home-school neighbourhood. Pedestrian trips contributed to almost half of the daily MVPA. CONCLUSIONS: We identified several social contexts relevant for children's daily MVPA. Schools have the potential to significantly contribute to young children's PA patterns and are therefore encouraged to systematically evaluate and implement parts of the school-system that stimulate PA and potentially also learning processes. Pedestrian trips also have substantial contribution to daily MVPA of young children, which highlights the importance of daily active transport in school- and parental routines.

The Netherlands Sports Cardiology Map: a step towards sports cardiology network medicine for patient and athlete care.

Sports cardiology is a rapidly evolving subspecialty of cardiology, with a growing demand for expertise. To improve patient care, clinicians, patients, and athletes (recreational to elite) should be able to easily identify specialised care pathways, expertise centres and clinicians with sports cardiology expertise. To this purpose, several international societies and organisations recommend establishing a local and national sports cardiology infrastructure. We therefore aimed to establish The Netherlands Sports Cardiology Map. We conducted a web-based survey, which was published on the Netherlands Society of Cardiology home page (2019-2020) and in which each cardiology department or clinic was asked to provide information on sports cardiology expertise and the current infrastructure. Of the 46 respondent centres, 28 (61%) reported that they had expertise in sports cardiology, of which 22 (79%) had specific expertise in one or more specific types of sports. Integrated multidisciplinary meetings were reported by 43% of the centres (n = 12/28). Only two centres reported ongoing research projects that had been approved by an institutional review board. The Netherlands Sports Cardiology Map is an important step towards improving the existing infrastructure and developing network medicine for sports cardiology.

Return to sports after COVID-19: a position paper from the Dutch Sports Cardiology Section of the Netherlands Society of Cardiology.

The coronavirus disease 2019 (COVID-19) pandemic has led to preventive measures worldwide. With the decline of infection rates, less stringent restrictions for sports and exercise are being implemented. COVID-19 is associated with significant cardiovascular complications; however there are limited data on cardiovascular complications and long-term outcomes in both competitive (elite) athletes and highly active individuals. Based on different categories of disease severity (asymptomatic, regional/systemic symptoms, hospitalisation, myocardial damage, and/or myocarditis), in this point-of-view article we offer the (sports) cardiologist or sports physician in the Netherlands a practical guide to pre-participation screening, and diagnostic and management strategies in all athletes >16 years of age after COVID-19 infection.

Keeping your eye on the target: eye-hand coordination in a repetitive Fitts' task.

In a cyclical Fitts' task, hand movements transition from continuous to discrete movements when the Index of Difficulty (ID) increases. Moreover, at high ID (small target), the eyes saccade to and subsequently fixate the targets at every movement, while at low ID (large target) intermittent monitoring is used. By hypothesis, the (periodic) gaze shifts are abandoned for movement times shorter than about 0.350 s due to systemic constraints (i.e., a refractory period and intrinsic latency). If so, the transition in eye and hand movements is independent. To investigate these issues, the present study examined the effects of changing ID via the targets' width or distance as well as hysteresis in eye-hand coordination. To this aim, 14 participants performed a cyclical Fitts' task while their hand and eye movements were recorded simultaneously. The results show that the transition in eye-hand synchronization (at 2.87 bit; 0.25 s) and in hand dynamics (at 4.85 bit; 0.81 s) neither co-occurred nor correlated. Some small width vs. distance dissociations and hysteresis effects were found, but they disappeared when eye-hand synchronization was viewed as a function of movement time rather than ID. This confirms that a minimal between-saccade time is the limiting factor in eye-hand synchronization. Additionally, the timing between the start of the hand movement and the saccade appeared to be relatively constant (at 0.15 s) and independent of movement time, implying a constant delay that should be implemented in a dynamical model of eye-hand coordination.

Incomplete and incorrect epinephrine auto-injector training to food-allergic patients by pharmacists in the Netherlands.

BACKGROUND: Successful treatment of anaphylaxis in the community relies on early and correct use of epinephrine auto-injectors (EAI). In the Netherlands, pharmacists supply EAIs to patients and have a crucial role in instructing patients in how and when to use EAI. However, there are currently no data in Europe on the quality of such instruction provided by pharmacists. Therefore, the aims of this study were to investigate the knowledge, attitudes, and beliefs regarding food allergy among pharmacists in the Netherlands and to investigate the quality of EAI instructions and demonstrations to patients by pharmacists. METHODS: Pharmacists were asked to complete an online questionnaire. Quality of instructions and demonstration accuracy were assessed in mystery guest visits to randomly selected pharmacies. For the statistical analysis, descriptive methods were used. RESULTS: In total, 25 of 115 questionnaires were completed. Only two (8%) respondents gave correct answers concerning the proper EAI demonstration. Twenty-one (84%) respondents thought that the provision of instructions was the responsibility of pharmacists. In total, ten pharmacies were included in simulated patient visits. Five of them (50%) demonstrated the EAI. None of them demonstrated the EAI use correctly. CONCLUSION: Food-allergic patients at high risk for anaphylaxis who receive their EAI from a community pharmacy are often not instructed on how to use an EAI or receive incorrect instructions. Pharmacists show considerable gaps in knowledge about food allergy and its management. These data suggest that opportunities exist to improve the quality of care provided by pharmacies to high-risk food-allergic patients.

Soluble and pelletable factors in porcine, canine and human notochordal cell-conditioned medium: implications for IVD regeneration.

During intervertebral disc (IVD) maturation, notochordal cells (NCs) are replaced by chondrocyte-like cells (CLCs) in the nucleus pulposus, suggesting that NCs play a role in maintaining tissue health. Affirmatively, NC-conditioned medium (NCCM) exerts regenerative effects on CLC proliferation and extracellular matrix (ECM) production. The aim of this study was to identify NC-secreted substances that stimulate IVD regeneration. By mass spectrometry of porcine, canine and human NCCM, 149, 170 and 217 proteins were identified, respectively, with 66 proteins in common. Mainly ECM-related proteins were identified, but also organelle-derived and membrane-bound vesicle proteins. To determine whether the effect of NCCM was mediated by soluble and/or pelletable factors, porcine and canine NCCM were separated into a soluble (NCCM-S; peptides and proteins) and pelletable (NCCM-P; protein aggregates and extracellular vesicles) fraction by ultracentrifugation, and tested on bovine and canine CLCs in vitro, respectively. In each model, NCCM-S exerted a more pronounced anabolic effect than NCCM-P. However, glycosaminoglycan (GAG) uptake from the medium into the carrier gel prevented more definite conclusions. While the effect of porcine NCCM-P on bovine CLCs was negligible, canine NCCM-P appeared to enhance GAG and collagen type II deposition by canine CLCs. In conclusion, porcine and canine NCCM exerted their anabolic effects mainly through soluble factors, but also the pelletable NCCM factors showed moderate regenerative potential. Although the regenerative potential of NCCM-P should not be overlooked, future studies should focus on unraveling the protein-based regenerative mechanism from NCCM produced from isolated NCs, e.g. by NCCM fractionation and pathway blocking studies.

The effect of a school-centered multicomponent intervention on daily physical activity and sedentary behavior in primary school children: The Active Living study.

The aim of the current study was to examine the effectiveness of a school-centered multicomponent PA intervention, called 'Active Living', on children's daily PA levels. A quasi-experimental design was used including 9 intervention schools and 9 matched control schools located in the Netherlands. The baseline measurement took place between March-June 2013, and follow-up measurements were conducted 12months afterwards. Accelerometer (ActiGraph, GT3X+) data of 520 children aged 8-11years were collected and supplemented with demographics and weather conditions data. Implementation magnitude of the interventions was measured by keeping logbooks on the number of implemented physical environmental interventions (PEIs) and social environmental interventions (SEIs). Multilevel multivariate linear regression analyses were used to study changes in sedentary behavior (SB), light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) between baseline and follow-up. Finally, effect sizes (ESs) were calculated using Cohen's d. No pooled effects on PA and SB were found between children exposed and not exposed to Active Living after 12months. However, children attending Active Living schools that implemented larger numbers of both PEIs and SEIs engaged in 15 more minutes of LPA per weekday at follow-up than children in the control condition (ES=0.41; p<.05). Moreover, children attending these schools spent less time in SB at follow-up (ES=0.33), although this effect was non-significant. No significant effects were found on MVPA. A school-centered multicomponent PA intervention holds the potential to activate children, but a comprehensive set of intervention elements with a sufficient magnitude is necessary to achieve at least moderate effect sizes.

The species-specific regenerative effects of notochordal cell-conditioned medium on chondrocyte-like cells derived from degenerated human intervertebral discs.

During intervertebral disc (IVD) maturation, the main cell type shifts from notochordal cells (NCs) to chondrocyte-like cells (CLCs). NCs secrete factors with regenerative potential, making them an interesting focus for regenerative treatments. During initial development, these strategies preferably employ non-human donors due to easy availability of their NC-rich nucleus pulposus (NP) tissue. To increase the success of translating these strategies for clinical application, this study aimed to delineate whether NC-secreted factors of different species have a regenerative effect on human CLCs. Human, canine and porcine NC-rich NP tissue and NC-conditioned medium (NCCM) were analysed biochemically and histologically. Human CLC micro-aggregates from degenerated IVDs were cultured in human, canine or porcine NCCM. Collagen, glycosaminoglycan (GAG) and DNA content was determined and histology was performed. Canine and porcine NPs were richer in NCs than human NPs. Human NPs contained the highest collagen content, whereas the DNA and GAG content of canine NPs was significantly higher than that of human or porcine NPs. NCCM from all species significantly increased the DNA and GAG content of the human CLC micro-aggregates. Porcine and canine NCCM were significantly more potent than human NCCM in inducing GAG deposition, whereas only human NCCM induced collagen type II production. Secreted factors from human, canine and porcine NC-rich NPs exerted regenerative effects on human CLCs, indicating a cross-species effect. Bioactive compound(s) are present in NCCM of different species that may reverse human IVD degeneration, supporting further research into strategies based on NC-technology employing canine or porcine models for their translation into humans.

Active Living: development and quasi-experimental evaluation of a school-centered physical activity intervention for primary school children.

BACKGROUND: The worldwide increase in the rates of childhood overweight and physical inactivity requires successful prevention and intervention programs for children. The aim of the Active Living project is to increase physical activity and decrease sedentary behavior of Dutch primary school children by developing and implementing tailored, multicomponent interventions at and around schools. METHODS/DESIGN: In this project, school-centered interventions have been developed at 10 schools in the south of the Netherlands, using a combined top-down and bottom-up approach in which a research unit and a practice unit continuously interact. The interventions consist of a combination of physical and social interventions tailored to local needs of intervention schools. The process and short- and long-term effectiveness of the interventions will be evaluated using a quasi-experimental study design in which 10 intervention schools are matched with 10 control schools. Baseline and follow-up measurements (after 12 and 24 months) have been conducted in grades 6 and 7 and included accelerometry, GPS, and questionnaires. Primary outcome of the Active Living study is the change in physical activity levels, i.e. sedentary behavior (SB), light physical activity (LPA), moderate-to-vigorous physical activity (MVPA), and counts-per-minute (CPM). Multilevel regression analyses will be used to assess the effectiveness of isolated and combined physical and social interventions on children's PA levels. DISCUSSION: The current intervention study is unique in its combined approach of physical and social environmental PA interventions both at school(yard)s as well as in the local neighborhood around the schools. The strength of the study lies in the quasi-experimental design including objective measurement techniques, i.e. accelerometry and GPS, combined with more subjective techniques, i.e. questionnaires, implementation logbooks, and neighborhood observations. TRIAL REGISTRATION: Current Controlled Trials ISRCTN25497687 (registration date 21/10/2015), METC 12-4-077, Project number 200130003.

Postoperative 30-day mortality in patients undergoing surgery for colorectal cancer: development of a prognostic model using administrative claims data.

PURPOSE: To develop a prognostic model to predict 30-day mortality following colorectal cancer (CRC) surgery using the Surveillance, Epidemiology, and End Results (SEER)-Medicare-linked data and to assess whether race/ethnicity, neighborhood, and hospital characteristics influence model performance. METHODS: We included patients aged 66 years and older from the linked 2000-2005 SEER-Medicare database. Outcome included 30-day mortality, both in-hospital and following discharge. Potential prognostic factors included tumor, treatment, sociodemographic, hospital, and neighborhood characteristics (census-tract-poverty rate). We performed a multilevel logistic regression analysis to account for nesting of CRC patients within hospitals. Model performance was assessed using the area under the receiver operating characteristic curve (AUC) for discrimination and the Hosmer-Lemeshow goodness-of-fit test for calibration. RESULTS: In a model that included all prognostic factors, important predictors of 30-day mortality included age at diagnosis, cancer stage, and mode of presentation. Race/ethnicity, census-tract-poverty rate, and hospital characteristics were independently associated with 30-day mortality, but they did not influence model performance. Our SEER-Medicare model achieved moderate discrimination (AUC = 0.76), despite suboptimal calibration. CONCLUSIONS: We developed a prognostic model that included tumor, treatment, sociodemographic, hospital, and neighborhood predictors. Race/ethnicity, neighborhood, and hospital characteristics did not improve model performance compared with previously developed models.

Potential application of notochordal cells for intervertebral disc regeneration: an in vitro assessment.

Recent studies suggest that notochordal cells (NCs) might be involved in intervertebral disc homeostasis, a role exploitable to counteract matrix degradation as observed during degeneration. This study aimed to evaluate the potential of NCs to promote matrix production by nucleus pulposus cells (NPCs) and to compare it to the currently proposed addition of bone marrow stromal cells (BMSCs). Using alginate beads, bovine NPCs were exposed for 28 d to porcine NC conditioned medium (NCCM); direct co-culture with porcine NCs or bovine BMSCs; or the combination of BMSCs and NCCM. Effects on cell proliferation, disc matrix production (proteoglycans, collagens) and disc matrix protein expression (aggrecan, collagen 1 and 2, SOX9) were determined and compared to TGFß stimulation. NCCM strongly promoted NPC proliferation (x 2.2) and matrix production (x 3.9) to levels similar to that with TGFß, whereas the direct addition of NCs had no effect. Co-culture of NPCs and BMSCs led to proteoglycan synthesis similar to NPCs alone, which was slightly improved by NCCM (x 1.5). Histological analysis confirmed biochemical data. Gene expression of analysed proteins remained stable for all groups and unaffected by medium conditions. NCs could substantially stimulate NPCs through factors secreted into conditioned medium and in levels similar to the addition of BMSCs. This study showed that molecular agents secreted by NCs constitute a promising alternative to the proposed "standard" injection of BMSCs for disc repair: their effects are similar, do not require the injection of a large number of cells and can be further amplified when the factors are identified.

Effects of processing technologies and pectolytic enzymes on degradability of nonstarch polysaccharides from rapeseed meal in broilers.

Rapeseed meal (RSM) contains a high level of nonstarch polysaccharides (NSP) that are not well degraded in poultry and interfere with digestion of other nutrients as protein, starch, and fat. By altering physicochemical properties of NSP from RSM, processing and enzyme technologies might improve digestive utilization of RSM, enhancing its potential as a source of nutrients in poultry diets. The effects of wet milling and extrusion in combination with pectolytic enzymes on the degradability of RSM in broilers were investigated in a 3 × 2 factorial arrangement. Wet milling and extrusion did not affect total tract apparent digestibility of DM, CP, crude fat, and nonglucose polysaccharides (NGP). Addition of pectolytic enzymes did not affect total tract apparent digestibility of CP and crude fat, but improved degradability of NGP by 9 to 20% units (P < 0.001), independent of prior technological processing of RSM. This coincided with an increased NGP concentration in the ceca (4 to 7 g/g of cobalt, P < 0.001), indicating that more NGP were solubilized such that they could enter the ceca and become available for fermentation. Particle size reduction facilitated solubilization of polysaccharides from RSM, increasing the concentration of NGP found in the ceca (4 g/g of cobalt, P = 0.008). Without help of additional pectolytic enzymes, those solubilized structures could, however, still not be degraded by the cecal microbiota. Feed intake, BW gain, and feed conversion ratio were not affected. No interaction between processing technologies and enzyme addition was found. Apparently, the processing technologies studied were not facilitating accessibility of NSP to pectolytic enzymes added to the feed in vivo.

Separation of digesta fractions complicates estimation of ileal digestibility using marker methods with Cr2O3 and cobalt-ethylenediamine tetraacetic acid in broiler chickens.

Marker methodologies to measure ileal and total tract digestibilities of diets varying in content and degradability of dietary fiber in broiler chickens were evaluated. Chromium sesquioxide (Cr2O3) and cobalt-ethylenediamine tetraacetic acid (Co-EDTA) were used as markers of solid and soluble fractions, respectively, and compared with digestibility values obtained with the total collection method. Groups of broilers (n = 17, 11 broilers/group) were assigned to a low-fiber diet or 1 of 2 high-fiber diets, the latter 2 containing 35% rapeseed meal (RSM). Pectolytic enzymes were added to one RSM diet to improve degradability of the fiber fraction. Excreta were quantitatively collected for 96 h, and contents from ileum and ceca were collected at slaughter at 29, 30, or 31 d of age. Chromium recovery in excreta ranged between 86 and 95%, whereas cobalt recovery was considerably lower (66 to 70%). Chromium:cobalt ratio was higher in ileal digesta than in feed. Hardly any chromium was found in the ceca, indicating that separation of the marker and specific digesta fractions occurs. Estimates of apparent total tract digestibility (ATTD) were lower when calculated using the marker method compared with the total collection method, particularly in high-fiber diets. Using Cr2O3 as a marker, differences were relatively small and effects due to enzyme addition were generally similar. Using Co-EDTA as a marker, ATTD of all components were lower compared with values obtained using the collection method (3 to 45 percentage units, P < 0.001), likely related to the low Co recovery. When estimating apparent ileal digestibility (AID), separation of marker and digesta resulted in unrealistically high estimates for the digestibility of nonglucose polysaccharides (54 to 66%), exceeding ATTD values by 16 to 42 percentage units. Moreover, the effect of pectolytic enzyme addition on the AID of nonglucose polysaccharides was in the opposite direction when compared with total collection. The data illustrate that fractionation of digesta, particularly in high-fiber diets, complicates accurate AID measurements in broilers, regardless of the choice of markers used.

Particle size of insoluble fibres and gelation of soluble fibres influence digesta passage rate throughout the gastrointestinal tract of finishing pigs.

Fibres, as abundant in agricultural by-products, exhibit a large range of physicochemical properties that can influence digestive processes such as digesta mean retention time (MRT), thereby affecting nutrient digestion kinetics. In this study, we investigated the effects of particle size of insoluble fibres, and gelation of soluble fibres on MRT of liquids, fine solids, and fibrous particles in the different segments of the gastrointestinal tract (GIT) of pigs. Twenty-four boars (51.6 ± 4.90 kg) were allocated to four diets; two diets contained 15% wheat straw, either coarsely chopped or finely ground (1-mm screen), two diets contained 27% wheat bran without or with the addition of 10% low-methylated pectin. After 14 days of adaptation to the diet, a total collection of faeces was performed to determine the total tract digestibility of nutrients. Thereafter, pigs were fed diets supplemented with tracers for at least 5 days and dissected following a frequent feeding procedure to approach steady-state passage of digesta. The MRT of liquids (Co-EDTA), fine solids (TiO2), and fibrous particles (Chromium-mordanted fibres) in the different segments of the GIT were quantified. In the stomach, particle size reduction of straw decreased the MRT of fine solids by 02:39 h, and fibrous particles by 07:21 h (P < 0.10). Pectin addition to the wheat bran diet reduced the MRT of fine solids by 03:09 h, and fibrous particles by 07:10 h (P < 0.10), but not of liquids, resulting in less separation between digesta phases in the stomach compared with the bran diet (P < 0.05). In the mid-small intestine (SI), pectin addition reduced the MRT of fibrous particles and the separation between fibrous particles and fine solids. No further effects of particle size reduction of straw nor pectin addition on MRT and digestibility of starch, nitrogen, or fat were observed in the SI. In the large intestine (LI), particle size reduction of straw reduced separation between fibrous particles and fine solids (P < 0.10), while pectin addition had no effects. Total tract, non-starch polysaccharide degradation of straw was poor (∼31%), and unaffected by particle size reduction (P > 0.10). The complete fermentation of pectin did not influence the degradation of wheat bran fibres (∼51%). In conclusion, the effects of particle size of insoluble fibres and gelling properties of soluble fibres on the passage of digesta phases were most pronounced in the stomach, but less prominent in distal segments of the GIT.

Defining the limits of homology modeling in information-driven protein docking.

Information-driven docking is currently one of the most successful approaches to obtain structural models of protein interactions as demonstrated in the latest round of CAPRI. While various experimental and computational techniques can be used to retrieve information about the binding mode, the availability of three-dimensional structures of the interacting partners remains a limiting factor. Fortunately, the wealth of structural information gathered by large-scale initiatives allows for homology-based modeling of a significant fraction of the protein universe. Defining the limits of information-driven docking based on such homology models is therefore highly relevant. Here we show, using previous CAPRI targets, that out of a variety of measures, the global sequence identity between template and target is a simple but reliable predictor of the achievable quality of the docking models. This indicates that a well-defined overall fold is critical for the interaction. Furthermore, the quality of the data at our disposal to characterize the interaction plays a determinant role in the success of the docking. Given reliable interface information we can obtain acceptable predictions even at low global sequence identity. These results, which define the boundaries between trustworthy and unreliable predictions, should guide both experts and nonexperts in defining the limits of what is achievable by docking. This is highly relevant considering that the fraction of the interactome amenable for docking is only bound to grow as the number of experimentally solved structures increases.

Complex interactions of new quantitative trait loci, Sluc1, Sluc2, Sluc3, and Sluc4, that influence the susceptibility to lung cancer in the mouse.

Many complex traits, including susceptibility to lung cancer, are controlled by multiple genes--quantitative trait loci (QTLs). We facilitated the mapping of QTLs by making use of recombinant congenic strains (RCS), a system of mouse inbred strains in which the genetic complexity is reduced, and by applying MQM-mapping (multiple-QTL models or marker-QTL-marker), a multilocus method with an increased power of detecting of individual QTLs and interacting QTLs (epistasis). The mouse strain O20 develops significantly larger N-ethyl-N-nitrosourea induced lung tumours than mice of the RC strain OcB-9 (ref. 5); the latter share approximately 87.5% of their genes with strain O20 and 12.5% with strain B10.O20 (refs 6,7). QTL analysis of 222 (OcB-9 x O20) F2 mice revealed four new loci that influence susceptibility to lung cancer (Sluc genes). They are involved in two significant, partly counteracting interactions which mask their individual main effects: Sluc1 (on chromosome 19) interacts with Sluc2 (chromosome 2), and Sluc3 (chromosome 6) interacts with Sluc4 (chromosome 11). Together with the data of van Wezel et al. in the accompanying report, our results indicate that interactions between tumour susceptibility genes are a common phenomenon which complicates their mapping.

Short communication: Estimation of ileal digestibility in chickens using single- and dual-tracer methods.

Fractionation of digesta, as occurs during gastrointestinal transit in chickens, complicates accurate measurements of ileal digestibility using tracers. Dual-tracer methods using separate tracers for solid and fluid digesta phases may improve the accuracy of digestibility measurements when assumptions of the single tracer method are violated. The aim of the present study was to compare the apparent ileal digestibility (AID) of nutrients calculated with single- and dual-tracer methods in chickens fed diets varying in particle size, anticipating digesta phase separation in the proximal gastrointestinal tract. A total of 112 Dekalb White (BW: 1.53 ± 0.107 kg) and 112 Bovans Black (BW: 1.79 ± 0.127 kg) 29-week-old laying hens were distributed over 32 pens (seven birds/pen). Within breed, pens were randomly assigned to one of two experimental diets (coarse vs fine oat hulls; n = 8 replicate pens per diet/breed combination). Diets were supplemented with TiO2 (3 g/kg) and Co-EDTA (2 g/kg). On days 34, 35, or 36, birds were euthanised and digesta from the ileum was collected for tracer and nutrient analyses. Apparent ileal digestibility was subsequently calculated by single- and dual-tracer methods. Although coarse oat hulls were hypothesised to increase the fractionation of solid and fluid digesta phases, no breed or diet × method interactions were found. Using a single tracer method based on TiO2, AID of nitrogen (N) was overestimated by 3%-units (P < 0.01) compared with the dual-tracer method, whereas AID estimates of DM, starch, fat, and non-starch polysaccharides did not differ (P > 0.09) and precision of all AID estimates was improved. In conclusion, these results show that although from a conceptual perspective, dual-tracer methods are presumed to better account for the variation in flow behaviour of different digesta phases, AID estimates obtained by the commonly used single tracer method using solid-phase tracer TiO2 were more precise and only marginally differed from estimates obtained by a dual-tracer method using distinct tracers for solid (TiO2) and liquid (Co-EDTA) digesta phases. Considering technical and economical constraints, the single tracer method may thus be the method of choice in many situations. Only when digestibility of proteins or amino acids is of specific interest, single tracer methods using a solid-phase tracer may not suffice. Nevertheless, for both single- and dual-tracer methods, tracer selection is critical, and the choice of tracers should depend on the nutrient(s) of interest.

SNAPIG: a model to study nutrient digestion and absorption kinetics in growing pigs based on diet and ingredient properties.

Current feed formulation and evaluation practices rely on static values for the nutritional value of feed ingredients and assume additivity. Hereby, the complex interplay among nutrients in the diet and the highly dynamic digestive processes are ignored. Nutrient digestion kinetics and diet × animal interactions should be acknowledged to improve future predictions of the nutritional value of complex diets. Therefore, an in silico nutrient-based mechanistic digestion model for growing pigs was developed: "SNAPIG" (Simulating Nutrient digestion and Absorption kinetics in PIGs). Aiming to predict the rate and extent of nutrient absorption from diets varying in ingredient composition and physicochemical properties, the model represents digestion kinetics of ingested protein, starch, fat, and non-starch polysaccharides, through passage, hydrolysis, absorption, and endogenous secretions of nutrients along the stomach, proximal small intestine, distal small intestine, and caecum + colon. Input variables are nutrient intake and the physicochemical properties (i.e. solubility, and rate and extent of degradability). Data on the rate and extent of starch and protein hydrolysis of different ingredients per digestive segment were derived from in vitro assays. Passage of digesta from the stomach was modelled as a function of feed intake level, dietary nutrient solubility and diet viscosity. Model evaluation included testing against independent data from in vivo studies on nutrient appearance in (portal) blood of growing pigs. When simulating diets varying in physicochemical properties and nutrient source, SNAPIG can explain variation in glucose absorption kinetics (postprandial time of peak, TOP: 20-100 min observed vs 25-98 min predicted), and predict variation in the extent of ileal protein and fat digestion (root mean square prediction errors (RMSPE) = 12 and 16%, disturbance error = 12 and 86%, and concordance correlation coefficient = 0.34 and 0.27). For amino acid absorption, the observed variation in postprandial TOP (61 ± 11 min) was poorly predicted despite accurate mean predictions (58 ± 34 min). Recalibrating protein digestion and amino acid absorption kinetics require data on net-portal nutrient appearance, combined with observations on digestion kinetics, in pigs fed diets varying in ingredient composition. Currently, SNAPIG can be used to forecast the time and extent of nutrient digestion and absorption when simulating diets varying in ingredient and nutrient composition. It enhances our quantitative understanding of nutrient digestion kinetics and identifies knowledge gaps in this field of research. Already useful as research tool, SNAPIG can be coupled with a postabsorptive metabolism model to predict the effects of dietary and feeding-strategies on the pig's growth response.

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.

A dynamic model to measure retention of solid and liquid digesta fractions in chickens fed diets with differing fibre sources.

Dietary fibres impact multiple digestive processes, and insights into the effects of various types of fibre on digesta retention time are required to optimise current feed formulation systems. Therefore, the objective of this study was to apply a dynamic modelling approach to generate estimates for the retention time of solid and liquid digesta in broilers fed different fibre sources. A maize-wheat-soybean meal control diet was compared against three diets in which wheat was partially substituted with oat hulls, rice husks, or sugar beet pulp (3% w/w). Non-starch polysaccharide (NSP) digestibility was evaluated in broilers between 23 and 25 days of age (n = 60 birds/treatment) using titanium dioxide (TiO2, 0.5 g/kg) as a marker, after feeding the experimental diets for 21 days. Digesta mean retention time (MRT) was measured in another 108 birds at 30 days of age by the administration of an oral pulse dose of chromium sesquioxide (Cr2O3) as solid marker and Cobalt-EDTA as liquid marker, and subsequent measurement of marker recovery in compartments of the digestive tract (n = 2 or 3 replicate birds/time point/treatment). Marker recovery models to estimate fractional passage rates for solid and liquid digesta in crop, gizzard, small intestine, and caeca compartments of the gastrointestinal tract were developed to predict MRT of solid and liquid digesta for each dietary treatment. The models were composed of a series of first-order differential equations, representing the variation of marker concentration in a compartment over time. Estimated MRT of solid and liquid digesta in the gizzard varied from 20 min for oat hulls and 34 min for rice husks diets to 14 min for sugar beet pulp and 12 min for control diets. In the caeca, liquid MRT was decreased compared to the control diet (989 min) for the sugar beet pulp diet (516 min), while it was increased for both the oat hulls and rice husks diets (≈1 500 min). Overall, these estimates are greater than those previously reported, suggesting that liquid digesta retention in the caeca previously has been underestimated. Digestibility of total NSP was increased by dietary fibre inclusion, regardless of the fibre type, although degradation of constituent sugars of NSP varied among diets. In conclusion, the inclusion of fibre sources at a low level (3% w/w) in the diet of broiler modulated retention time mainly in the gizzard and caeca, and increased digestibility of NSP.