An in vitro and in vivo approach to characterize digesta from pigs fed different forms of pea flour.

In vitro models of digestion are useful tools to explore the behavior of dietary fiber sources in gastrointestinal conditions. To evaluate the validity of our digestion model, digesta obtained in vivo and in vitro were characterized and the impact of cell wall integrity on protein bioaccessibility and digestibility evaluated. Six cannulated barrows [Pietrain × (Large White × Landrace)] were included in a 2 × 2 Latin square design where they were fed two diets identical in chemical composition but differing in nutrient bioaccessibility. Pea was given either as flour (R1, most proteins encapsulated by intact cell walls) or reconstituted flour (R2, mixture of proteins and purified, broken cell walls). Digesta were collected at the duodenal and ileal cannulas at regular interval and after slaughtering, following ingestion of either R1 or R2. The two diets were also digested in vitro using a static gastrointestinal model. The original pea ingredients as well as the digesta collected in vivo and in vitro were characterized (i.e., particle size measurement, microscopy observations and gel electrophoresis) and then compared with each other. The degradation of the pea ingredients differed greatly between the two forms of flour, where particles filled with nutrients were recovered at the latest stage of R1 intestinal digestion as observed with the particle size distribution and the microscopy images. These results were consistent with the in vivo and in vitro digestibility analysis that showed lower protein hydrolysis for R1 than that for R2 (about 19% difference in protein digestion regardless of the method). Overall, great similarities were found between the digesta collected in vivo and in vitro, especially regarding the particle size measurements. To summarize, a substantial proportion of the proteins contained in R1 was retained within the pea cells following gastrointestinal digestion. These encapsulated proteins reduced the amount of amino acids and small peptides available for absorption. This mechanism will have consequences on postprandial metabolism of amino acids and bacterial population based on the delivery form of the dietary fiber.

Although dietary fiber plays an essential role in the gastrointestinal health of pigs, it can also compromise the digestion and absorption of nutrients, especially of proteins. New ingredients such as pulses can be both good sources of protein and fiber, with no harmful effect for the animal or the environment, provided they are given in an adequate form (more or less structured). The objective of this work was to investigate how the dietary fibers (intact or broken down, encapsulation mechanism) of a pulse, pea, influenced the digestion of proteins. The approach of this study consisted in combining in vitro and in vivo studies with biochemical and biophysical techniques to determine how dietary fiber affected protein digestibility in pea flour. The results of this study showed good agreement between in vivo and in vitro data. Overall, breaking down of the dietary fibers led to 19% increase in protein digestion. These findings demonstrated that the form of ingestion of dietary fibers is crucial to optimize protein digestion. Moreover, our in vitro model of gastrointestinal digestion was capable of simulating pea degradation in pig during digestion and provide a good estimate of protein hydrolysis.

Apparent jejunal amino acid digestibility, gut morphology, and the expression of intestinal amino acid transporters in pigs fed protein or free amino acids.

Dietary amino acids (AA) supplied as protein or in free form are not only digested and absorbed at different rates but can also induce differences in the intestinal physiology of pigs. We compared the apparent jejunal AA digestibility, intestinal morphology, and gene expression of AA transporters of pigs fed diets providing different forms of AA. Thirty growing pigs (33.7 ± 4.1 kg) were fed one of three experimental diets that provided AA either as protein from feather meal (INT), as free AA and small peptides obtained by extensive acid hydrolysis of feathers (HYD), or as a mix of individual purified AA with the same AA profile as HYD (FAA). Pigs were fed the same quantity of feed, energy, and AA. After 14 d, pigs were slaughtered 3 h after feeding a meal with indigestible markers. Digesta and tissue were collected from different sections of the small intestine. Jejunal digesta was used to measure apparent jejunal digestibility of AA. Samples of the duodenum, jejunum, and ileum were used to measure intestinal morphology and the gene expression of intestinal AA transporters. The measured apparent jejunal digestibility of AA of INT was lower compared to HYD and FAA (P < 0.05). The apparent jejunal digestibility of Cys, Gly, His, Met, and Pro was lower for FAA compared to HYD (P < 0.05). This may be due to the small peptides in HYD, which are absorbed faster than individual AA. The villi area in the ileum of HYD fed pigs was the highest (P < 0.05) among the treatments, which may be associated with the reabsorption of endogenous proteins, which occurs mostly in the ileum. In the duodenum, HYD and FAA had lower expression of PepT1 (P < 0.01) probably due to the rapid transit time of digesta compared to INT fed pigs. Pigs fed HYD expressed more ASCT2 (P = 0.02) and CAT-1 (P = 0.04) in the jejunum compared to the pigs fed the other diets. The expression of these transporters along the intestine depended on the relative abundance of readily absorbable dietary AA. Results showed that dietary AA form can have an influence on the morphology and on the expression of different AA transporters along the different sections of the small intestine.

The amino acids (AA) in the diet of pigs are usually supplied as a mix of proteins and free AA. Proteins need to be digested first before their constituent AA become available to the animal. Free AA, together with small peptides, are readily available without the need for digestion. Moreover, the different forms by which AA are supplied may also have an effect on intestinal physiology. In this experiment, pigs were fed different diets with the same AA profile but were provided either as protein, as free AA and small peptides originating from hydrolyzed protein, or as a mix of individual free AA. Results showed that feeding pigs free AA and/or small peptides resulted in higher apparent jejunal digestibility of AA compared to feeding proteins. Furthermore, the apparent jejunal digestibility of the AA of a hydrolyzed protein was higher than that of free AA. Providing diets with readily absorbable AA resulted in a higher surface area for absorption and an increase in the gene expression of AA transporters as opposed to proteins.

A dynamic mammary gland model describing colostrum immunoglobulin transfer and milk production in lactating sows.

The physiology of the sow mammary gland is qualitatively well described and understood. However, the quantitative effect of various biological mechanisms contributing to the synthesis of colostrum and milk is lacking and more complicated to obtain. The objective of this study was to integrate physiological and empirical knowledge of the production of colostrum and milk in a dynamic model of a single sow mammary gland to understand and quantify parameters controlling mammary gland output. In 1983, Heather Neal and John Thornley published a model of the mammary gland in cattle, which was used as a starting point for the development of this model. The original cattle model was reparameterized, modified, and extended to describe the production of milk by the sow mammary gland during lactation and the prepartum production of colostrum as the combined output of immunoglobulins (Ig) and milk. Initially, the model was reparameterized to simulate milk synthesis potential of a single gland by considering biological characteristics and empirical estimations of sows and piglets. Secondly, the model was modified to simulate more accurately the responses to changes in milk removal rates. This was done by linking the ejectable milk storage capacity to the number of secretory cells rather than being constant throughout lactation. Finally, the model was extended to include the prepartum synthesis of milk and the kinetics of Ig into and out of the mammary gland. A progressive capacity of secretory cells to synthesize milk was used to differentiate the time between the onset of milk synthesis and Ig transfer. Changes in maximum milk removal rate, duration of milk ejection, and nursing interval exerted a great impact on the modeled milk output. Changes by ±60% in one of these parameters were capable of increasing milk output by 28% to 39% during the first 4 wk in lactation compared with the reference parameterization. This suggests that the ability of the piglet to remove milk from the gland exerts a key control on milk synthesis during lactation. Modeling colostrum as the combined output of Ig and milk allowed to represent the rapid decline in Ig concentration observed during the first hours after farrowing. In conclusion, biological and empirical knowledge was integrated into a model of the sow mammary gland and constitutes a simple approach to explore in which conditions and to what extent individual parameters influence Ig kinetics and milk production.

Skeletal muscle proteome of piglets is affected in a muscle-dependent manner by a limiting total sulfur amino acid supply.

PURPOSE: A total sulfur amino acid (TSAA) deficient diet can affect the amino acid composition of skeletal muscles. However, it is unknown how the different muscle proteins are affected by the TSAA deficiency. METHODS: The proteomic profiles of the fast-twitch glycolytic longissimus (LM) and the slow-twitch oxidative rhomboideus (RM) muscles were compared in 42-day-old piglets fed either a 28% deficient (TSAA-) or a sufficient (TSAA+) diet in TSAA for 10 days. Differentially regulated proteins were identified and submitted to Gene Ontology Pathways Analysis to identify biological processes affected by TSAA deficiency. RESULTS: A total of 36 proteins in LM and 24 proteins in RM differed in abundance between the two dietary treatments. In both muscles, an increased oxidative energy metabolism was observed in TSAA- piglets. However, a greater mitochondrial oxidation of pyruvate generated from glycolysis was observed in LM of TSAA- piglets, whereas fatty acid ß-oxidation and glycogen sparing were favored in RM. This suggests a muscle-specific reorientation of energy metabolism in response to a TSAA- deficiency. In both muscles, the protein abundance and enzyme activity of superoxide dismutase were increased in TSAA- piglets. Other enzymes involved in antioxidant defense, heat shock proteins coping with cellular stress, and annexins involved in the regulation of apoptosis were generally found to be more expressed in the LM of TSAA- piglets, with no or minor changes in RM. CONCLUSIONS: Skeletal muscle proteome in young growing piglets was modulated in a muscle-dependent manner by a deficient TSAA supply, with accentuated changes in fast-twitch glycolytic muscle.

Metabolizable energy requirement for maintenance estimated by regression analysis of body weight gain or metabolizable energy intake in growing pigs

Objective: Feed energy required for pigs is first prioritized to meet maintenance costs. Additional energy intake in excess of the energy requirement for maintenance is retained as protein and fat in the body, leading to weight gain. The objective of this study was to estimate the ME requirements for maintenance (MEm) by regressing body weight gain against ME intake (MEI) in growing pigs. Methods: Thirty-six growing pigs (26.3 ± 1.7 kg) were allotted to 1 of 6 treatments with 6 replicates per treatment in a randomized complete block design. Treatments were 6 feeding levels which were calculated as 50, 60, 70, 80, 90 or 100% of the estimated ad libitum MEI (2,400 kJ/kg BW0.60·d). All pigs were individually housed in metabolism crates for 30 d and weighed every 5 d. Moreover, each pig from each treatment was placed in the open-circuit respiration chambers to measure heat production (HP) and energy retained as protein (REp) and fat (REf) every 5 d. Serum biochemical parameters of pigs were analyzed at the end of the experiment. Results: The ADG and HP as well as the REp and REf linearly increased with increasing feed intake (p < 0.010). ß-hydroxybutyrate (BHBA) concentration of serum tended to increase with increasing feed intake (p = 0.080). The regression equations of MEI on ADG were MEI, kJ/kg BW0.60·d = 1.88 × ADG, g/d + 782 (R2=0.86) and MEm was estimated at 782 kJ/kg BW0.60·d. Protein retention of growing pigs would be positive while REf would be negative at this feeding level via regression equations of REp and REf on MEI. Conclusion: The MEm was estimated at 782 kJ/kg BW0.60·d in current experiment. Furthermore, growing pigs will deposit protein and oxidize fat if provided feed at the estimated maintenance level.

Methionine to cystine ratio in the total sulfur amino acid requirements and sulfur amino acid metabolism using labelled amino acid approach for broilers.

BACKGROUND: Assuming that part of Methionine (Met) is converted into Cystine (Cys), but ignoring the rates with which such phenomenon occurs may lead to an excessive supply of Met in poultry diets. Such inconvenient could be easily avoided with the knowledge of the ideal Met:Cys/Total sulfur amino acids (TSAA) ratio and the rates of Met conversion into Cys. RESULTS: Met sources did not affect performance. Met:Cys/TSAA ideal ratio was determined using curvilinear-plateau regression model. Both optimum body weight gain and feed conversion ratio were estimated in 1007 g/day and 1.49, respectively, at 52% Met/TSAA ratio. Feed intake was not affected by Met:Cys/TSAA ratios. In the labelled amino acid assay, the rates with which Met was converted into Cys ranged from 27 to 43% in response to changes in Met:Cys/TSAA ratios, being higher at 56:44. CONCLUSION: Based on performance outcomes, the minimum concentration of Met relative to Cys in diets for broilers from 14 to 28 d of age based on a TSAA basis, is 52% (52:48 Met:Cys/TSAA). The outcomes from labelled amino acid assay indicate that highest the Met supply in diets, the highest is its conversion into Cys.

Integrative analysis of indirect calorimetry and metabolomics profiling reveals alterations in energy metabolism between fed and fasted pigs.

BACKGROUND: Fasting is a simple metabolic strategy that is used to estimate the maintenance energy requirement where the energy supply for basic physiological functions is provided by the mobilization of body reserves. However, the underlying metabolic components of maintenance energy expenditure are not clear. This study investigated the differences in heat production (HP), respiratory quotient (RQ) and plasma metabolites in pigs in the fed and fasted state, using the techniques of indirect calorimetry and metabolomics. METHODS: Nine barrows (45.2 ± 1.7 kg BW) were fed corn-soybean based meal diets and were kept in metabolism crates for a period of 14 d. After 7 d adaptation, pigs were transferred to respiratory chambers to determine HP and RQ based on indirect calorimetry. Pigs were fed the diet at 2,400 kJ ME/(kg BW0.6·d) during d 8 to 12. The last 2 d were divided into 24 h fasting and 48 h fasting treatment, respectively. Plasma samples of each pig were collected from the anterior vena cava during the last 3 d (1 d while pigs were fed and 2 d during which they were fasted). The metabolites of plasma were determined by high-resolution mass spectrometry using a metabolomics approach. RESULTS: Indirect calorimetry analysis revealed that HP and RQ were no significant difference between 24 h fasting and 48 h fasting, which were lower than those of fed state (P <  0.01). The nitrogen concentration of urine tended to decrease with fasting (P = 0.054). Metabolomics analysis between the fed and fasted state revealed differences in 15 compounds, most of which were not significantly different between 24 h fasting and 48 h fasting. Identified compounds were enriched in metabolic pathways related to linoleic acid metabolism, amino acid metabolism, sphingolipid metabolism, and pantothenate and CoA biosynthesis. CONCLUSION: These results suggest that the decreases in HP and RQ of growing pigs under fasting conditions were associated with the alterations of linoleic acid metabolism and amino acid metabolism. The integrative analysis also revealed that growing pigs under a 24-h fasting were more appropriate than a 48-h fasting to investigate the metabolic components of maintenance energy expenditure.

A systemic approach to explore the flexibility of energy stores at the cellular scale: Examples from muscle cells.

Variations in energy storage and expenditure are key elements for animals adaptation to rapidly changing environments. Because of the multiplicity of metabolic pathways, metabolic crossroads and interactions between anabolic and catabolic processes within and between different cells, the flexibility of energy stores in animal cells is difficult to describe by simple verbal, textual or graphic terms. We propose a mathematical model to study the influence of internal and external challenges on the dynamic behavior of energy stores and its consequence on cell energy status. The role of the flexibility of energy stores on the energy equilibrium at the cellular level is illustrated through three case studies: variation in eating frequency (i.e., glucose input), level of physical activity (i.e., ATP requirement), and changes in cell characteristics (i.e., maximum capacity of glycogen storage). Sensitivity analysis has been performed to highlight the most relevant parameters of the model; model simulations have then been performed to illustrate how variation in these key parameters affects cellular energy balance. According to this analysis, glycogen maximum accumulation capacity and homeostatic energy demand are among the most important parameters regulating muscle cell metabolism to ensure its energy equilibrium.

Splanchnic tissues respond differently when piglets are offered a diet 30 % deficient in total sulfur amino acid for 10 days.

PURPOSE: A deficient total sulfur amino acid (TSAA) supply has been reported to differently affect the amino acid composition of tissues, but limited information is available about its effects on the morphology and metabolic properties of splanchnic tissues. METHODS: The amino acid composition, protein metabolism, glutathione concentration of the liver, proximal and distal jejunum, ileum and kidneys, and intestinal architecture were compared in 42-day-old piglets pair-fed either a diet deficient (TSAA-; 28 % deficiency) or sufficient (TSAA+) in TSAA for 10 days. RESULTS: The supply of TSAA had no effect on tissue weights, but influenced the amino acid composition in a tissue-dependent manner. Compared with animals receiving diet TSAA+, the concentrations of Met and Ser were higher in liver protein of TSAA- animals while the Cys concentration in protein was lower in the liver but higher in the distal jejunum. The TSAA supply had no effect on protein synthesis and proteolytic activities of tissues. Villus width and surface, and crypt surface were lower in the proximal jejunum of TSAA- versus TSAA+ pigs. Crypt surface in the ileum of TSAA- pigs was higher. Pigs receiving diet TSAA- had lower GSH and GSSG concentrations in the liver and proximal jejunum, but the GSH/GSSG ratio was decreased only in the liver. CONCLUSIONS: A greater nutritional priority appears to be given to splanchnic tissues so that its growth and protein metabolism can be maintained when the TSAA supply is limiting. The amino acid composition, glutathione status, and intestinal mucosa architecture are affected in a tissue-dependent manner.

Skeletal muscles respond differently when piglets are offered a diet 30% deficient in total sulfur amino acid for 10 days.

PURPOSE: Although amino acids (AA) are required for growth, little is known about the effect of a deficient AA supply on the composition and the contractile and metabolic properties of skeletal muscles. METHODS: Protein metabolism, oxidative catabolism, glutathione system, and fiber-type composition of the longissimus (LM), rhomboideus (RM), and semitendinous (SM) muscles were compared between 42-day-old piglets pair-fed for 10 days either with a diet with a 28% deficient supply of total sulfur AA (TSAA-) or with a diet with a sufficient supply of total sulfur AA (TSAA+). RESULTS: The relative weight, protein mass, and protein synthesis of LM were 10-32% lower in TSAA- pigs compared with TSAA+ pigs, while RM and SM were not affected by the TSAA supply. The TSAA supply affected the AA composition of muscles. Concentrations of Met and branched-chain AA were, respectively, 7 and 3% lower in TSAA- pigs compared with TSAA+ pigs. The His concentration was 30% higher in LM and SM in TSAA- pigs compared with TSAA+ pigs and unaffected in RM. The activity of citrate synthase was 14% higher in all three muscles of TSAA- pigs. In these pigs, the ß-hydroxy-acyl-CoA dehydrogenase activity was 20% higher in RM compared with TSAA+ pigs while that of lactate dehydrogenase was 21% lower in LM. Total and reduced glutathione concentrations were more than 70% greater in RM than in LM or SM, and these concentrations were approximately 10% lower in TSAA- pigs than in TSAA+ pigs. CONCLUSIONS: Results of this study indicate that a TSAA deficiency affects muscle properties in a muscle-dependent manner increasing the oxidative capacity of RM and reducing growth and glycolytic metabolism of LM.

A Methionine Deficient Diet Enhances Adipose Tissue Lipid Metabolism and Alters Anti-Oxidant Pathways in Young Growing Pigs.

Methionine is a rate-limiting amino-acid for protein synthesis but non-proteinogenic roles on lipid metabolism and oxidative stress have been demonstrated. Contrary to rodents where a dietary methionine deficiency led to a lower adiposity, an increased lipid accretion rate has been reported in growing pigs fed a methionine deficient diet. This study aimed to clarify the effects of a dietary methionine deficiency on different aspects of tissue lipid metabolism and anti-oxidant pathways in young pigs. Post-weaned pigs (9.8 kg initial body weight) were restrictively-fed diets providing either an adequate (CTRL) or a deficient methionine supply (MD) during 10 days (n=6 per group). At the end of the feeding trial, pigs fed the MD diet had higher lipid content in subcutaneous adipose tissue. Expression levels of genes involved in glucose uptake, lipogenesis but also lipolysis, and activities of NADPH enzyme suppliers were generally higher in subcutaneous and perirenal adipose tissues of MD pigs, suggesting an increased lipid turnover in those pigs. Activities of the anti-oxidant enzymes superoxide dismutase, catalase and glutathione reductase were increased in adipose tissues and muscle of MD pigs. Expression level and activity of the glutathione peroxidase were also higher in liver of MD pigs, but hepatic contents in the reduced and oxidized forms of glutathione and glutathione reductase activity were lower compared with control pigs. In plasma, superoxide dismutase activity was higher but total anti-oxidant power was lower in MD pigs. These results show that a dietary methionine deficiency resulted in increased levels of lipogenesis and lipolytic indicators in porcine adipose tissues. Decreased glutathione content in the liver and coordinated increase of enzymatic antioxidant activities in adipose tissues altered the cellular redox status of young pigs fed a methionine-deficient diet. These findings illustrate that a rapidly growing animal differently adapts tissue metabolisms when facing an insufficient methionine supply.

Concept and application of ideal protein for pigs.

Knowledge about the amino acid requirements and the response of pigs to the amino acid supply is essential in feed formulation. A deficient AA supply results in a reduction in performance while an oversupply is costly and leads to excessive nitrogen excretion with a potentially negative environmental impact. Amino acid requirements are determined to a large extent by the protein deposition in the body and, for lactating sows, by the protein exported in the milk. The concept of ideal protein was developed more than 50 years ago and refers to a protein with an amino acid profile that exactly meets the animal's requirement so that all amino acids are equally limiting for performance. Because Lys typically is the first-limiting amino acid, the ideal amino acid profile is often expressed relative to Lys. Although the ideal protein profile is often assumed to be constant for a given production stage, (small) changes in the ideal protein profile can occur within a production stage. This can be caused by changes in the relative contribution of the different components of amino acid requirements during the productive life on the animal (e.g. changes in the relative contribution of growth and maintenance). Amino acids requirements can be determined experimentally using dose-response studies. The design of the study, the chosen response criterion, and the statistical model affect the requirement estimate. Although considerable experimental work has been carried out to determine the requirements for Lys, Met, Thr, and Trp in growing pigs (and to a lesser extent in sows), little is known about the requirements for the other essential amino acids. Experimental dose-response studies generally focus on the requirement and less on the overall response (i.e. what are the consequences of an amino acid deficiency?). This latter aspect is, to some extent, accounted for in modelling approaches that quantify the response of the animal to the amino acid supply in a dynamic way. The paper describes the origin of ideal protein and illustrates how fundamental concepts of amino acid nutrition have been integrated in practical modeling approaches for the nutrition of growing pigs and sows.

Using a large-scale knowledge database on reactions and regulations to propose key upstream regulators of various sets of molecules participating in cell metabolism.

BACKGROUND: Most of the existing methods to analyze high-throughput data are based on gene ontology principles, providing information on the main functions and biological processes. However, these methods do not indicate the regulations behind the biological pathways. A critical point in this context is the extraction of information from many possible relationships between the regulated genes, and its combination with biochemical regulations. This study aimed at developing an automatic method to propose a reasonable number of upstream regulatory candidates from lists of various regulated molecules by confronting experimental data with encyclopedic information. RESULTS: A new formalism of regulated reactions combining biochemical transformations and regulatory effects was proposed to unify the different mechanisms contained in knowledge libraries. Based on a related causality graph, an algorithm was developed to propose a reasonable set of upstream regulators from lists of target molecules. Scores were added to candidates according to their ability to explain the greatest number of targets or only few specific ones. By testing 250 lists of target genes as inputs, each with a known solution, the success of the method to provide the expected transcription factor among 50 or 100 proposed regulatory candidates, was evaluated to 62.6% and 72.5% of the situations, respectively. An additional prioritization among candidates might be further realized by adding functional ontology information. The benefit of this strategy was proved by identifying PPAR isotypes and their partners as the upstream regulators of a list of experimentally-identified targets of PPARA, a pivotal transcriptional factor in lipid oxidation. The proposed candidates participated in various biological functions that further enriched the original information. The efficiency of the method in merging reactions and regulations was also illustrated by identifying gene candidates participating in glucose homeostasis from an input list of metabolites involved in cell glycolysis. CONCLUSION: This method proposes a reasonable number of regulatory candidates for lists of input molecules that may include transcripts of genes and metabolites. The proposed upstream regulators are the transcription factors themselves and protein complexes, so that a multi-level description of how cell metabolism is regulated is obtained.

Exploring metabolism flexibility in complex organisms through quantitative study of precursor sets for system outputs.

BACKGROUND: When studying metabolism at the organ level, a major challenge is to understand the matter exchanges between the input and output components of the system. For example, in nutrition, biochemical models have been developed to study the metabolism of the mammary gland in relation to the synthesis of milk components. These models were designed to account for the quantitative constraints observed on inputs and outputs of the system. In these models, a compatible flux distribution is first selected. Alternatively, an infinite family of compatible set of flux rates may have to be studied when the constraints raised by observations are insufficient to identify a single flux distribution. The precursors of output nutrients are traced back with analyses similar to the computation of yield rates. However, the computation of the quantitative contributions of precursors may lack precision, mainly because some precursors are involved in the composition of several nutrients and because some metabolites are cycled in loops. RESULTS: We formally modeled the quantitative allocation of input nutrients among the branches of the metabolic network (AIO). It corresponds to yield information which, if standardized across all the outputs of the system, allows a precise quantitative understanding of their precursors. By solving nonlinear optimization problems, we introduced a method to study the variability of AIO coefficients when parsing the space of flux distributions that are compatible with both model stoichiometry and experimental data. Applied to a model of the metabolism of the mammary gland, our method made it possible to distinguish the effects of different nutritional treatments, although it cannot be proved that the mammary gland optimizes a specific linear combination of flux variables, including those based on energy. Altogether, our study indicated that the mammary gland possesses considerable metabolic flexibility. CONCLUSION: Our method enables to study the variability of a metabolic network with respect to efficiency (i.e. yield rates). It allows a quantitative comparison of the respective contributions of precursors to the production of a set of nutrients by a metabolic network, regardless of the choice of the flux distribution within the different branches of the network.

Partitioning of heat production in growing pigs as a tool to improve the determination of efficiency of energy utilization.

In growing pigs, the feed cost accounts for more than 60% of total production costs. The determination of efficiency of energy utilization through calorimetry measurements is of importance to sustain suitable feeding practice. The objective of this paper is to describe a methodology to correct daily heat production (HP) obtained from measurements in respiration chamber for the difference in energy expenditure related to physical activity between animals. The calculation is based on a preliminary published approach for partitioning HP between HP due to physical activity (AHP), thermic effect of feeding (TEF) and basal metabolic rate (fasting HP; FHP). Measurements with male growing pigs [mean body weight (BW): 115 kg] which were surgically castrated (SC), castrated through immunization against GnRH (IC), or kept as entire male (EM) were used as an example. Animals were fed the same diet ad-libitum and were housed individually in two 12-m(3) open-circuit respiration chambers during 6 days when fed ad-libitum and one supplementary day when fasted. Physical activity was recorded through interruption of an infrared beam to detect standing and lying positions and with force transducers that recorded the mechanical force the animal exerted on the floor of the cage. Corrected AHP (AHPc), TEF (TEFc), and HP (HPc) were calculated to standardize the level of AHP between animals, assuming that the ratio between AHPc and ME intake should be constant. Inefficiency of energy utilization (sum of AHPc and TEFc) was lower than the inefficiency estimated from the slope of the classical relationship between HPc and ME intake but was associated with higher requirements for maintenance. Results indicate that EM pigs had higher FHP but lower TEFc than IC and SC pigs. These results agree with the higher contents in viscera of EM pigs that stimulate their basal metabolic rate and with the reduced utilization of dietary protein to provide energy for maintenance energy requirements and fat deposition (FD).

Maintenance energy requirements of growing pigs and calves are influenced by feeding level.

The conventional regression method for partitioning heat production (HP) in growing animals between HP associated with either maintenance or growth assumes maintenance HP to be independent of feeding level (FL). However, there are indications that this assumption is not correct and an alternative method is proposed in this study from a reanalysis of 3 trials. In trial 1, 73-, 152-, and 237-kg calves received one milk replacer at 77, 84, 92, and 100% of their ad libitum metabolizable energy (ME) intake. In trial 2, 70-kg barrows received one diet at 60, 80, and 100% of their ad libitum ME intake {2600 kJ ME/[kg body weight (BW)(0.60) · d]}. In trial 3, 60-kg barrows received a basal diet [1700 kJ ME/(kg BW(0.60) · d)] or 4 diets consisting of the basal diet plus 850 kJ ME/(kg BW(0.60)·d) of starch alone or starch with corn gluten, casein, or vegetable oil. In the 3 trials (n = 48, 18, and 28, respectively), HP and activity-related HP were measured on individuals pigs and calves in respiration chambers for 6 d (fed state) and fasting HP (FHP; at zero activity) was calculated as the asymptotic value of HP kinetics on d 7 (feed-deprived state). The FHP changed by 0.22 kJ in calves and 0.14 kJ in pigs/kJ ME intake change during the previous days. The efficiency of using ME for maintenance and growth [k(mg); 1- (HP - FHP)/ME] was not affected by FL (calves: 84%, pigs in trial 2: 74%). In trial 3, k(mg) varied between diets in connection with variations in efficiencies between nutrients (from 55% for corn gluten to 85% for lipid). This new method of representing partitioning of ME intake considers FHP as variable with FL, does not require estimates of maintenance ME requirements, includes efficiencies that depend on diet characteristics, and is not biased by metabolic adaptations of the animal to FL.

Oxidation of dietary stearic, oleic, and linoleic acids in growing pigs follows a biphasic pattern.

We used the pig as a model to assess the effects of dietary fat content and composition on nutrient oxidation and energy partitioning in positive energy balance. Pigs weighing 25 kg were assigned to either: 1) a low fat-high starch diet, or 2) a high saturated-fat diet, or 3) a high unsaturated-fat diet. In the high-fat treatments, 20% starch was iso-energetically replaced by 10.8% lard or 10.2% soybean oil, respectively. For 7 d, pigs were fed twice daily at a rate of 1200 kJ digestible energy · kg(-0.75) · d(-1). Oral bolus doses of [U-(13)C] glucose, [U-(13)C] α-linoleate, [U-(13)C] stearate, and [U-(13)C] oleate were administered on d 1, 2, 4, and 6, respectively, and (13)CO(2) production was measured. Protein and fat deposition were measured for 7 d. Fractional oxidation of fatty acids from the low-fat diet was lower than from the high-fat diets. Within diets, the saturated [U-(13)C] stearate was oxidized less than the unsaturated [U-(13)C] oleate and [U-(13)C] linoleate. For the high unsaturated-fat diet, oxidation of [U-(13)C] oleate was higher than that of [U-(13)C] linoleate. In general, recovery of (13)CO(2) from labeled fatty acids rose within 2 h after ingestion but peaked around the next meal. This peak was induced by an increased energy expenditure that was likely related to increased eating activity. In conclusion, oxidation of dietary fatty acids in growing pigs depends on the inclusion level and composition of dietary fat. Moreover, our data suggest that the most recently ingested fatty acids are preferred substrates for oxidation when the direct supply of dietary nutrients has decreased and ATP requirements increase.

Fasting heat production and energy cost of standing activity in veal calves.

Metabolic body size of veal calves is still calculated by using the 0.75 exponent and no data were available to determine energy cost of physical activity during the whole fattening period. Data from two trials focusing on protein and/or energy requirements were used to determine the coefficient of metabolic body size and the energy cost of standing activity in male Prim'Holstein calves. Total heat production was measured by indirect calorimetry in ninety-five calves weighing 60-265 kg and was divided using a modelling approach between components related to the BMR, physical activity and feed intake. The calculation of the energy cost of standing activity was based on quantifying the physical activity by using force sensors on which the metabolism cage was placed and on the interruption of an IR beam allowing the determination of standing or lying position of the calf. The best exponent relating zero activity fasting heat production (FHP 0) to metabolic body size was 0.85, which differed significantly from the traditionally used 0.75. Per additional kJ metabolizable energy (ME) intake, FHP 0 increased by 0.28 kJ; at a conventional daily 650 kJ/kg body weight (BW)0.85 ME intake, daily FHP 0 averaged 310 kJ/kg BW 0.85. Calves stood up sixteen times per day; total duration of standing increased from 5.1 to 6.4 h per day as animals became older. The hourly energy cost of standing activity was proportional to BW 0.65 and was estimated as 12.4 kJ/kg BW 0.65. These estimates allow for a better estimation of the maintenance energy requirements in veal calves.

Deposition of dietary fatty acids, de novo synthesis and anatomical partitioning of fatty acids in finishing pigs.

Predicting aspects of pork quality becomes increasingly important from both a nutritional and technological point of view. The aim of the present study was to provide quantitative information on the relation between nutrient intake and whole-body fatty acid (FA) depositions. This information is essential to develop mechanistic models predicting the FA content of tissues. A serial slaughter study was carried out in which thirty pigs were slaughtered between 90 and 150 kg. The diet included 15 g/kg soyabean oil and contained 44 g/kg fat. Only 0.31 and 0.40 of the digested n-6 and n-3 FA were deposited, respectively. Approximately one-third of the n-3 supply that was deposited resulted from the conversion of 18:3 to other metabolites (i.e. EPA, docosapentaenoic acid and DHA). This proportion was affected by the pig genotype. De novo-synthesised FA represented 0.86 of the total non-essential FA deposition, and its average composition corresponded to 0.017, 0.286, 0.025, 0.217 and 0.454 for 14:0, 16:0, 16:1, 18:0 and 18:1, respectively. Although the average whole-body FA composition was relatively constant during the finishing period, this was not so for the tissues. In the carcass (without backfat), the content of 18:1 increased during the finishing period, whereas that of 16:0 and 18:0 decreased. Backfat captured a proportionally greater fraction of 18:2 than did the carcass of the residual tissues. In contrast, a proportionally greater fraction of the dietary 18:3 supply was deposited in the carcass compared to other tissues.

Previous feeding level influences plateau heat production following a 24 h fast in growing pigs.

Factorial approaches to estimate energy requirements of growing pigs require estimation of maintenance energy requirements. Heat production (HP) during fasting (FHP) may provide an estimate of maintenance energy requirements. Six barrows were used to determine effects of feeding level on components of HP, including extrapolated plateau HP following a 24 h fast (FHPp). Based on a cross-over design, each pig was exposed to three feeding levels (1.55, 2.05 and 2.54 MJ metabolisable energy/kg body weight (BW)(0.60) per d) between 30 and 90 kg BW. Following a 14 d adaptation period, HP was estimated using indirect calorimetry on pigs housed individually. Dynamics of HP were recorded in pigs for 5 d during the fed state and during a subsequent 24 h fast. Metabolisable energy intake was partitioned between thermal effect of feeding (HPf), activity HP (HPa), FHPp and energy retention. Feeding level influenced (P<0.05) total HP during the fed state, HPf and activity-free FHPp (609, 644 and 729 (SE 31) kJ/kg BW(0.60) per d for low, medium and high ME intakes, respectively). The value of FHPp when expressed per kg BW(0.60) did not differ (P=0.34) between the three subsequent experimental periods. Feeding level did not (P=0.75) influence HPa. Regression of total HP during the fed state to zero metabolisable energy intake yielded a value of 489 (SE 69) kJ/kg BW(0.60) per d, which is a lower estimate of maintenance energy requirement than FHPp. Duration of adaptation of pigs to changes in feeding level and calculation methods should be considered when measuring or estimating FHPp, maintenance energy requirements and diet net energy content.