Abstract
Growing importance of upcycling agricultural by-products, food waste, and food processing by-products through livestock production strongly increased the variation in the nutritional quality ...of feed ingredients. Traditionally, feed ingredients are evaluated based on their measured extent of digestion. Awareness increases that in addition to the extent, the kinetics of digestion affects the metabolic fate of nutrients after absorption. Together with a growing body of evidence of complex interactions occurring within the lumen of the digestive tract, this urges the need of developing new approaches for feed evaluation. In a recently developed approach, we propose combining in vitro and in silico methods for feed ingredient evaluation. First steps in the development of such a systems were made by (1) evaluating in vitro the digestion potential of feed ingredients, regarding this as true ingredient properties and (2) predicting in silico the digestive processes like digesta transit, nutrient hydrolysis and absorption using dynamic, mechanistic modeling. This approach allows to evaluate to what extent the digestion potential of each ingredient is exploited in the digestive tract. Future efforts should focus on modeling digesta physicochemical properties and transit, applying in vitro digestion kinetic data of feed ingredients in mechanistic models, and generating reliable in vivo data on nutrient absorption kinetics across feed ingredients. The dynamic modeling approach is illustrated by a description of a modeling exercise that can be used for teaching purposes in digestive physiology or animal nutrition courses. A complete set of equations is provided as an on-line supplement, and can be built in modeling software that is freely available. Alternatively, the model can be constructed using any modeling software that enables the use of numerical integration methods.
For design of healthy and sustainable diets and food systems, it is important to consider not only the quantity but also the quality of nutrients. This is particularly important for proteins, given ...the large variability in amino acid composition and digestibility between dietary proteins. This article reviews measurements and metrics in relation to protein quality, but also their application. Protein quality methods based on concentrations and digestibility of individual amino acids are preferred, because they do not only allow ranking of proteins, but also assessment of complementarity of protein sources, although this should be considered only at a meal level and not a diet level. Measurements based on ileal digestibility are preferred over those on faecal digestibility to overcome the risk of overestimation of protein quality. Integration of protein quality on a dietary level should also be done based on measurements on an individual amino acid basis. Effects of processing, which is applied to all foods, should be considered as it can also affect protein quality through effects on digestibility and amino acid modification. Overall, protein quality data are crucial for integration into healthy and sustainable diets, but care is needed in data selection, interpretation and integration.
Abstract
There is increasing importance of upcycling of low-opportunity-cost feed, food waste, and food processing byproducts into animal products, strongly increasing the variation in the ...nutritional quality of feed ingredients. Traditionally, feed ingredients are evaluated based on their measured extent of digestion. Increasing awareness that not only the total yield of nutrients, but also their absorption kinetics, affect their metabolic fate after absorption, and a growing body of evidence of complex interactions taking place inside the gastro-intestinal tract urges development of new approaches. In a recently developed approach (Schop, 2020), we propose a combination of in vitro methodology and dynamic modelling of the digestion process as an alternative to conventional feed ingredient evaluation, and made the first steps in the development of such a system. The digestion potential, evaluated in vitro, is considered as the true property of feed ingredients. Then, prediction of digesta transit, nutrient hydrolysis and absorption, following the intake of a complete feed, determines the extent to which the digestion potential of each ingredient is exploited. The dynamic, mechanistic model developed by Schop for growing pigs comprises 48 state variables representing dietary nutrients, hydrolysis products, endogenous components, and microbial biomass. Driving variables are ingested nutrients from feed ingredients, characterized in vitro (solubility, undegradable fraction, maximum rate of digestion). Passage of digesta is modelled as a function of nutrient solubility, diet viscosity and feed intake. The extent of protein digestion and extent and rate of starch digestion, but not absorption of amino acids, were adequately predicted by the model. Future efforts should focus on modelling digesta properties and transit, translation of in vitro digestion kinetic data and generating reliable in vivo data on nutrient absorption kinetics across feed ingredients. Schop, T.A. 2020 Modelling digestion kinetics in pigs. Predicting nutrient absorption based on diet and ingredient properties. PhD thesis, Wageningen University, Wageningen, NL.
There is increasing importance of upcycling of lowopportunity-cost feed, food waste, and food processing byproducts into animal products, strongly increasing the variation in the nutritional quality ...of feed ingredients. Traditionally, feed ingredients are evaluated based on their measured extent of digestion. Increasing awareness that not only the total yield of nutrients, but also their absorption kinetics, affect their metabolic fate after absorption, and a growing body of evidence of complex interactions taking place inside the gastrointestinal tract urges development of new approaches. In a recently developed approach (Schop, 2020), we propose a combination of in vitro methodology and dynamic modelling of the digestion process as an alternative to conventional feed ingredient evaluation, and made the first steps in the development of such a system. The digestion potential, evaluated in vitro, is considered as the true property of feed ingredients. Then, prediction of digesta transit, nutrient hydrolysis and absorption, following the intake of a complete feed, determines the extent to which the digestion potential of each ingredient is exploited. The dynamic, mechanistic model developed by Schop for growing pigs comprises 48 state variables representing dietary nutrients, hydrolysis products, endogenous components, and microbial biomass. Driving variables are ingested nutrients from feed ingredients, characterized in vitro (solubility, undegradable fraction, maximum rate of digestion). Passage of digesta is modelled as a function of nutrient solubility, diet viscosity and feed intake. The extent of protein digestion and extent and rate of starch digestion, but not absorption of amino acids, were adequately predicted by the model. Future efforts should focus on modelling digesta properties and transit, translation of in vitro digestion kinetic data and generating reliable in vivo data on nutrient absorption kinetics across feed ingredients. Schop, T.A. 2020 Modelling digestion kinetics in pigs. Predicting nutrient absorption based on diet and ingredient properties. PhD thesis, Wageningen University, Wageningen, NL.
Feeding food losses and food waste (FLW) to livestock can reduce the environmental impact of livestock production, but practical implications for feed quality and feed production systems are ...currently unclear. The aim of this paper is to address the potential implications for pigs and poultry feeding systems when FLW would (fully or partly) replace conventional ingredients of animal feed within the European Union. FLW streams, such as (prohibited) animal-based foods or household waste, constitute a substantial and valuable part of available FLW. Feeding FLW, however, also includes challenges regarding the (anti-) nutritional value, physical and sensory characteristics, and contamination risks of animal feed. Mixing various FLW streams can be a solution for the large variability in nutritional value and physical characteristics, but more knowledge is needed about the various properties of FLW streams, best handling and processing methods, validated analysis techniques and inclusion levels in animal feeds. We discuss the scale and location of processing FLW, as well as the required infrastructure for dealing with supply and demand. Different approaches may be taken to increase the use of FLW into livestock diets and transition into a sustainable and circular food system. How this could be best implemented will likely be a trade-off between costs and benefits. It should be discussed both among direct users and within the wider society which costs and risks are acceptable.
•Food losses and waste (FLW) potentially can replace conventional feed ingredients•FLW properties, inclusion levels and feed formulation affect feed quality•This also depends on supply, handling and processing of FLW and demand for feed.•Infrastructure, cooperation, scale and location of processing FLW might need change•It should be decided upon by society which risks that generate costs are acceptable
Due to an increasing world population and wealth per capita, the competition for resources for food, feed, and fuel production increases. In pig production, one of the strategies to cope with this ...competition is to increase production efficiency, i.e. ↓ resources (input)/↑ products (output). In pig production, production efficiency is effectuated by formulating diets that meet the pigs’ nutrient requirement for maintenance and production (i.e. growth, reproduction). The amount of nutrients available to the pig, depends on the nutrient content of the diet and on the ability of pigs to digest and absorb these nutrients from their gastrointestinal tract. The availability, but also the utilization of absorbed nutrients for metabolic processes (e.g. heat production, protein and fat synthesis), depends on the kinetics of nutrient digestion after ingestion of feed. Digestion is the aggregated process of passage, hydrolysis, and absorption of nutrients and endogenous secretions by organs and tissues involved. These processes determine at what rate and to what extent (i.e. kinetics) nutrients are digested and absorbed. Current feed evaluation systems, used to formulate pig diets, do not take into account the kinetics of nutrient digestion. To gain insight into the impact of nutrient digestion kinetics on absorption of nutrients in pigs we developed a computer model (‘SNAPIG’).To parameterise the model, we studied the kinetics of digesta passage in the stomach and small intestine of growing pigs (Chapter 2 and 3). Special focus was on the passage of solids and liquids, and the quantitative impact of diet viscosity (Chapter 2), and nutrient solubility in the diet (further mentioned as diet solubility) and feed intake level (Chapter 3). Two studies were performed in male growing pigs (30-35 kg initial body weight). The pigs were individually housed and assigned to different dietary treatments. Diets contained two indigestibility markers, one insoluble (TiO2) and one soluble (Cr-EDTA) marker, to quantify the passage of digesta solids and liquids. After a 17-day adaptation period, including a period of feeding to steady-state of digesta passage, the pigs were euthanised for total digesta collection. Digesta was collected from the stomach, small intestine (proximal and distal half), caecum, and colon (proximal and distal half). Digesta was analysed to assess the mean retention time (MRT) of solids and liquids, and the digestibility of starch and protein in the stomach and small intestinal segments, and the apparent viscosity (i.e. measure of resistance to flow) and water-binding capacity of digesta in all segments.Results presented in Chapter 2 relate to the study investigating the relation between diet viscosity, induced by oat β-glucans, and the passage and physicochemical properties of digesta. We hypothesized that feeding diets with incremental levels of dietary viscosity would increase digesta viscosity in the stomach and potentially in the small intestine. This increase in digesta viscosity was expected to slow down the passage of digesta in these segments. To this end, twenty pigs were individually assigned to one of five diets with increasing dietary concentrations of oatβ-glucans (BG; from 0% to 10 %), in exchange for maize starch. Results showed that the MRT of liquids, but not of solids, in the stomach increased (from 39 to 99 min) when pigs were fed diets with increasing viscosity. The separation of solids and liquids in stomach digesta was hereby reduced. Concomitantly, the dry matter concentration of digesta in the stomach decreased, as well as, the apparent viscosity of digesta. In contrast to our hypothesis, the results indicate that increasing diet viscosity does not necessarily increases digesta viscosity, and that digesta viscosity is a consequence of, rather than a determinant for, digesta passage in the stomach. Diet viscosity did not influence physicochemical properties of digesta in the proximal small intestine, which might related to low dry matter concentrations for digesta in this segment. The WBC of digesta in the distal small intestine and colon increased when dietary BG level increased, as did apparent digesta viscosity in the proximal colon. This likely reflects the increase in concentration of BG in digesta when moving through the gastrointestinal tract.In Chapter 3, the relationship between diet solubility and feed intake level was studied. It is known that the passage of solids and liquids through the stomach differs and that digesta passage kinetics can be affected by feedback mechanisms based on nutrient sensing in the gastrointestinal tract. As solubility of nutrients in the diet affects the nutrient load of the solid and liquid digesta fractions, we were interested in the effect of diet solubility on digesta passage kinetics in pigs. Forty pigs were individually assigned to one of four dietary treatments consisting of three levels of diet solubility (8, 19 and 31% of soluble protein and sucrose in the diet) and two levels of feed intake (low: 1.9 × maintenance requirement for energy; high: 2.8 × maintenance requirement for energy). Overall, solids were retained 2 h longer in the stomach than liquids. In the stomach, when diet solubility increased from 8 to 19%, the MRT of solids and liquids numerically increased, but it decreased significantly when diet solubility increased from 19 to 31%. Hence, a non-linear relationship was observed between diet solubility and the kinetics of digesta passage in the stomach. No effect of diet solubility was observed in the small intestine. Considering the effects of feed intake level, the MRT of solids and liquids in the stomach increased, depending on solubility of the nutrients provided to increase the level of feed intake. When provided as insoluble nutrients, the MRT of solids and liquids increased by about 45 min, whereas no effect was observed when the level of feed intake increased by soluble nutrients. In contrast, in the small intestine, independent of diet solubility, increasing feed intake level caused the MRT of solids to decrease by 24 min. For MRT over the stomach and small intestine combined, no effects of diet solubility and feed intake were observed. These results show that diet solubility affects digesta passage kinetics in the stomach. Feed intake affects both digesta passage kinetics in the stomach and small intestine, although for the prior it depended on nutrient solubility.In order to provide input variables for the model presented in Chapter 5, we aimed to quantify the kinetics of protein hydrolysis of feed ingredients using an in vitro assay described in Chapter 4. The in vitro assay was used to simulate stomach and small intestinal enzymatic hydrolysis of protein of nineteen feed ingredients (barley, fishmeal, extracted linseed, maize, maize gluten meal, maize DDGS, oats, peas, potato protein, full-fat rapeseed, rapeseed meal, rye, soy hulls, soybean meal, sunflower meal, wheat, wheat middlings, whey powder, and whey protein isolate). Protein hydrolysis kinetics in the stomach was based on determination of the soluble protein fraction, whereas for the small intestine it was based on the appearance of low-molecular weight (MW) peptides and amino acids (<500 Da). The maximum degradable protein fraction (%) was quantified as total protein (%) minus the undegradable protein fraction in the residue (%) after 6 h of incubation. In the stomach phase, ingredients varied in the fraction (%) of protein that was instantly soluble, i.e. 8% in potato protein and 100% in whey powder and whey protein isolate, and they varied in the fractional solubilisation rate, i.e. 0.031/h in fish meal and 0.43/h in wheat. The maximum degradable protein fraction, determined at the end of the stomach + small intestine incubation, (%) ranged from 55% in soy hulls to 100% in whey powder and whey protein isolate. Part of this fraction was instantly present as low MW peptides at onset of the small intestinal simulation, i.e. 8% in oats and 96% in extracted linseed. At the end of this incubation, the low MW peptide fraction of the degradable protein fraction varied from 60% in soybean meal to >100% in extracted linseed. Data from this study were used as model input variables for the kinetics of protein hydrolysis of diets varying in feed ingredient composition (Chapter 5).Chapter 5 contains the description and evaluation of SNAPIG, an in silico dynamic mechanistic digestion model. The aim of the model was to predict the absorption of nutrients by simulating nutrient digestion kinetics in pigs fed diets varying in feed ingredients and physicochemical properties. Data from own in vivo (Chapter 2 and 3) and in vitro (Chapter 4) studies, and from literature were used to parameterise the model. The model simulates the kinetics of digesta passage in the gastrointestinal tract, including effects of diet viscosity, diet solubility, and feed intake level on digesta passage of solids and liquids in the stomach; the kinetics of nutrient hydrolysis, varying among nutrients and feed ingredients; the kinetics of endogenous secretions, as affected by feed intake level and flow of organic matter through the gastrointestinal tract; and the kinetics of nutrient absorption. In this way the absorption of nutrients after a meal was simulated. The model is driven by the intake of nutrients originating from different feed ingredients. The model is able to predict variation in the absorption kinetics of glucose and amino acids when simulating the digestive process in pigs fed diets varying in feed ingredients and physicochemical properties. Sensitivity analysis of the model indicated that glucose absorptionkinetics is mainly affected by starch hydrolysis kinetics and by the kinetics of passage of solids in the stomach. Amino acid absorption kinetics is mostly affected by passage of solids in the stomach and by protein hydrolysis kinetics in the small intestine. Apparent protein and fat
The passage rate of solids and liquids through the gastrointestinal tract differs. Increased dietary nutrient solubility causes nutrients to shift from the solid to the liquid digesta fraction and ...potentially affect digesta passage kinetics. We quantified: (1) the effect of three levels of dietary nutrient solubility (8, 19 and 31 % of soluble protein and sucrose in the diet) at high feed intake level (S) and (2) the effect of low v. high feed intake level (F), on digesta passage kinetics in forty male growing pigs. The mean retention time (MRT) of solids and liquids in the stomach and small intestine was assessed using TiO2 and Cr-EDTA, respectively. In addition, physicochemical properties of digesta were evaluated. Overall, solids were retained longer than liquids in the stomach (2·0 h, P<0·0001) and stomach+small intestine (1·6 h, P<0·001). When S increased, MRT in stomach decreased by 1·3 h for solids (P=0·01) and 0·7 h for liquids (P=0·002) but only at the highest level of S. When F increased using low-soluble nutrients, MRT in stomach increased by 0·8 h for solids (P=0·041) and 0·7 h for liquids (P=0·0001). Dietary treatments did not affect water-binding capacity and viscosity of digesta. In the stomach of growing pigs, dietary nutrient solubility affects digesta MRT in a non-linear manner, while feed intake level increases digesta MRT depending on dietary nutrient solubility. Results can be used to improve predictions on the kinetics of nutrient passage and thereby of nutrient digestion and absorption in the gastrointestinal tract.
Applying specific circularity interventions to the food system may have environmental benefits. Using an iterative linear food system optimisation model (FOODSOM), we assess how changes in human ...diets, imports and exports, and the utilisation of waste streams impact land use and greenhouse gas emissions (GHG). After including these circularity principles, land use and GHG emissions were on average 40% and 68% lower than in the current food system, primarily driven by a reduction in production volumes and a shift towards feeding the domestic population. Shifting from the current diet to a circular diet decreased land use with 43% and GHG emissions with 52%. Allowing up to half of each nutrient in the human diet to be imported, while balancing imports with equal exports in terms of nitrogen, phosphorus and potassium, also decreased land use (up to 34%) and GHG emissions (up to 26%) compared to no imported food. Our findings show that circularity interventions should not be implemented mutually exclusively; by combining a circular diet with imported food and fully utilising waste streams, the lowest land use and GHG emissions can be realised.
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