Modelling the relation between energy intake and protein and lipid deposition in growing pigs

Modeling net energy partition patterns of growing-finishing pigs using nonlinear regression and artificial neural networks

The objectives of this study were to evaluate the net energy (NE) partition patterns of growing-finishing pigs at different growing stages and to develop the corresponding prediction models using nonlinear regression (NLR) and artificial neural networks (ANN). Twenty-four pigs with an initial body weight (BW) of ~30 kg were kept in metabolic cages and fed ad libitum and were moved into six respiration chambers in turns until ~90 kg. The NE partition patterns, i.e., NE for maintenance (NEm), NE retained as protein (NEp), and NE retained as lipid (NEl), were calculated based on indirect calorimetry and nitrogen balance techniques. The energy balance data collected through the animal trial was then randomly split into a training data set containing 75% of the samples and a testing data set containing the remaining 25% of the samples. The NLR models and a series of ANN models were established on the training data set to predict the metabolizable energy intake, NE intake, NEm, NEp, and NEl of pigs. The best-fitted ANN models were selected by 5-fold cross-validation in the training data set. The prediction performance of the best-fitted NLR and ANN models were compared on the testing data set. The results showed that the average NE intakes of pigs were 17.71, 23.25, 24.56, and 28.96 MJ/d in 30 to 45 kg, 45 to 60 kg, 60 to 75 kg, and 75 to 90 kg, respectively. The NEm and NEl (MJ/d) kept increasing as BW increased from 30 kg to 90 kg, while the NEp increased to its maximum value and then kept in a certain range of 4.64 to 4.88 MJ/d. The proportion of NEm for pigs at 30 to 90 kg stayed within the range of 42.0% to 48.6%, while the proportion of NEl kept increasing. For the prediction models built based on the animal trial, ANN models exhibited better performance than NLR models for all the target outputs. In conclusion, NE partition patterns changed in different growth stages of pigs, and ANN models are more flexible and powerful than NLR models in predicting the NE partition patterns of growing-finishing pigs.

UPLC‐MS‐based plasma metabolomics for identifying energy metabolism biomarkers of maintenance in growing pigs

The purpose of this study is to explore the potential plasma metabolism biomarkers reflecting the maintenance status of growing pigs. The repeated measurement design was used in this experiment, and six barrows (28.6 ± 0.5 kg BW) were selected and kept in metabolism crates. The feeding level in growing pigs close to ad libitum was 2400 kJ ME/kg BW^0.6 ·day^-1 during Day 1 to Day 7, while a feeding level of 782 kJ ME/kg BW^0.6 ·day^-1 was provided as energy requirement for maintenance during Day 8 to Day 14. Plasma samples of each pig were collected from the anterior vena cava on the morning of Day 8 and Day 15. The metabolites of plasma were determined by high-resolution mass spectrometry using a metabolomics approach. Results showed that metabolomics analysis between ad libitum-fed state and maintained status revealed differences in 16 compounds. Identified compounds were enriched in metabolic pathways related to linoleic acid metabolism, tryptophan metabolism, and alanine, aspartate and glutamate metabolism. In conclusion, linoleic acid metabolism, tryptophan metabolism, alanine, aspartate and glutamic acid metabolism pathways played a major regulatory role in the maintenance status of growing pigs. The potential metabolism biomarkers of maintenance in growing pigs were linoleic acid, glutamine and tyrosine.

The Feeding Behaviour Habits of Growing-Finishing Pigs and Its Effects on Growth Performance and Carcass Quality: A Review

Based on the available data of feeding behaviour habits (FBHs), this work aimed to discuss which type of pig, according to its FBHs, performs better and is more efficient. As pigs grow, average daily feed intake, meal size, and feeding rate increase, whereas small variations or even decreases in time spent eating and daily feeder visits have been reported. Moreover, the sex, breed, space allowance, feeder design, feed form, diet composition, and environmental conditions modify FBHs. On the other hand, the literature indicates the existence of four types of pigs: pigs that eat their daily feed intake in many short meals (nibblers) or in few large meals (meal eaters) combined with eating fast (faster eaters) or slow (slow eaters). The available scientific literature about ad libitum fed pigs suggests that pigs eating faster with bigger meals eat more, gain more weight, and are fatter than pigs eating less, slower, and with smaller meals. However, the feeding rate and the meal size do not influence feed efficiency. In conclusion, studies comparing growing-finishing pigs with similar feed intake, but different feeding rate and meal size are needed to better understand the influence of FBHs on feed efficiency.

Relationship between energy intake and growth performance and body composition in pigs selected for low backfat thickness

Genetic selection of pigs over recent decades has sought to reduce carcass fat content to meet consumer demands for lean meat in many countries (e.g.: Australia). Due to the impacts of genetic changes, it is unknown whether the carcass fat measures are still responsive to energy intake. Thus, the present experiment aimed to quantify the relationship between tissue composition and dietary energy intake in finisher pigs selected for low carcass backfat. Intact male and female pigs (n=56 for each sex; PrimegroGenetics, Corowa, NSW, Australia) were fed seven different amounts of an amino acid adequate wheat-based diet containing 14.3 MJ digestible energy (DE)/kg to provide the following daily DE intakes- 25.8, 29.0, 32.6, 35.3, 38.5, 41.5 and 44.2 (ad libitum) MJ DE/d for males, and 25.8, 28.9, 32.0, 35.6, 38.3, 40.9 and 44.5 (ad libitum) MJ DE/d for females between 60 kg and 108 kg live weight. Body composition of anaesthetised pigs was measured using the Dual Energy X-ray Absorptiometry (DXA) method when individual pigs reached 108 kg, and protein, fat and ash deposition rates were calculated. Pigs were slaughtered on the 2nd day post-DXA scan for carcass backfat measurement. The results showed that the carcass backfat thickness (standardized at 83.7 kg carcass) increased by 0.125 mm for every MJ increase in daily DE intake in male pigs (P = 0.004; R2 = 0.130), but carcass backfat of female pigs (standardized at 85.1 kg carcass) was not responsive to daily DE intake. Whole-body fat composition and fat deposition rate increased linearly (both P < 0.01) in male pigs but quadratically (both P < 0.01) in female pigs in response to DE intake. Every MJ increase of daily DE intake increased the rate of daily protein deposition by 3.8 g in intact male pigs (P < 0.001; R2 = 0.781) and by 2.5 g in female pigs (P < 0.001; R2 = 0.643). In conclusion, the selection for low backfat thickness over the last two decades has altered the response of fat deposition and backfat thickness to energy intake, particularly in female pigs. Despite this change, the linear relationship between DE intake and protein deposition rate was maintained in these modern genetics.

Integrative Analysis of Energy Partition Patterns and Plasma Metabolomics Profiles of Modern Growing Pigs Raised at Different Ambient Temperatures

Simple Summary

Most of the studies focusing on energy partition patterns of growing pigs and the related mechanisms raised at different ambient temperatures were carried out during the 1970s to the early 2000s. With the rapid developments in pig breeding, research updates on such topics concerning modern growing pigs have been absent in the last decade. Therefore, this study focused on the energy partition patterns of modern growing pigs with different bodyweights at gradient-ambient temperatures and investigated the underlying changes in plasma metabolites under such conditions. Modern growing pigs at heavier bodyweight were more sensitive to high temperatures on energy intake and partition. At high ambient temperatures, most of the identified metabolites altered are associated with decreased fatty acid oxidation, increased lipid formation, and increased protein degradation. The findings of this study will provide possible solutions to precisely formulate diets for modern growing pigs raised at different ambient temperatures, and can help to improve our knowledge on potential mechanisms of thermoregulation in modern pig breeds.

Abstract

This study explores the energy partition patterns of modern growing pigs at 25 kg and 65 kg raised at gradient-ambient temperatures. It also investigates the underlying changes in plasma under such conditions, based on the integrative analysis of indirect calorimetry and non-target metabolomics profiling. Thirty-six barrows with initial BW of 26.4 ± 1.9 kg and 24 barrows with initial BW of 64.2 ± 3.1 kg were successively allotted to six respiration chambers with ambient temperatures set as 18 °C, 21 °C, 23 °C, 27 °C, 30 °C, and 32 °C, and four respiration chambers with ambient temperatures set as 18 °C, 23 °C, 27 °C, and 32 °C, respectively. Each pig was kept in an individual metabolic crate and consumed feed ad libitum, then transferred into the respiration chamber after a 7-day adaptation period for 5-day indirect calorimetry assay and 1-day fasting. As the ambient temperature increased from 18 °C to 32 °C, the voluntary feed intake, metabolizable energy intake, nitrogen intake, and retention, total heat production, and energy retention as a protein of growing pigs at 25 kg and 65 kg all linearly decreased (p < 0.05), with greater coefficients of variation for pigs at 65 kg when temperatures changed from 18 °C to 32 °C. The cortisol and thyroid hormone levels in the plasma of 25 kg pigs linearly decreased as the ambient temperature increased from 18 °C to 32 °C (p < 0.05), and 13 compounds were identified through metabolomics analysis, including up-regulated metabolites involved in fatty acid metabolism, such as adrenic acid and down-regulated metabolites involved in amino acid metabolism, such as spermidine at 32 °C. These results suggested that modern growing pigs at heavier bodyweight were more sensitive to high temperatures on energy intake and partition. Most of the identified metabolites altered at high ambient temperatures are associated with suppressed fatty acid oxidation and elevated lipogenesis and protein degradation.

Strategies to Meet Nutritional Requirements and Reduce Boar Taint in Meat from Entire Male Pigs and Immunocastrates

This paper reviews the current knowledge on the nutritional requirements of entire male and immunocastrated pigs to obtain an efficient growth, low boar taint level, and good carcass and meat quality. We present the reasons for offering entire males ad libitum access to the diets in order to optimize their protein deposition potential. Boar taint is one of the major issues in the production of entire males; therefore, the impact of various skatole- and indole-reducing feed ingredients is discussed regarding their efficiency and the possible mechanism affecting skatole and indole production in the hindgut. Entire males have lean carcasses, so their intramuscular fat content can be lower than that of surgical castrates or females and the adipose tissue can be highly unsaturated. The possible nutritional strategies to counteract these effects are summarized. We conclude that immunocastrates can be fed similarly to entire males until the second vaccination. However, due to the metabolic changes occurring shortly after the second vaccination, the requirements for essential amino acids are markedly lower in immunocastrates than in entire males.

The effect of lactose and a prototype Lactobacillus acidophilus fermentation product on digestibility, nitrogen balance, and intestinal function of weaned pigs

The objective of this study was to determine the effects of lactose (LA) and a prototype Lactobacillus acidophilus fermentation product (FP) on growth performance, diet digestibility, nitrogen (N) balance, and intestinal function of weaned pigs. Twenty-eight newly weaned pigs [approximately 21 d of age; initial body weight (BW) = 5.20 ± 0.15 kg] were housed in metabolism crates and assigned to one of four treatments (n = seven pigs per treatment) corresponding to a 2 × 2 factorial design: with (LA+; 15% inclusion) or without (LA-) LA and with (FP+) or without (FP-) the prototype FP (1 g of FP per kilogram of diet; Diamond V, Cedar Rapids, IA). Feed and water were provided ad libitum. At day 5, pigs were orally given lactulose and mannitol to assess small intestinal permeability. Fecal samples were collected on days 5-9 to determine the apparent total tract digestibility (ATTD) of dry matter (DM), gross energy (GE), and N. Total urine output and fecal samples were collected on days 10-13 to determine N retention. On day 15, all pigs were euthanized to collect intestinal lumen and tissue samples. Data were analyzed for the main effects of LA and FP and their interaction using the MIXED procedure of SAS. Lactose improved average daily feed intake (ADFI; P = 0.017), the ATTD of DM (P = 0.014), the ATTD of GE (P = 0.028), and N retention (P = 0.043) and tended to increase the butyric acid concentration in the colon (P = 0.062). The FP tended to increase the digestibility of N (P = 0.090). Neither LA nor the FP affected intestinal barrier function or inflammation markers. The interaction between LA and FP affected intestinal morphology: in the jejunum, pigs fed LA+FP- had increased villus height compared with those fed LA+FP+ and LA-FP-, whereas LA+FP+ was intermediate (interaction P = 0.034). At the terminal ileum, pigs fed LA-FP+ and LA+FP- had increased villus height and villus: crypt compared with those fed LA-FP-, whereas LA+FP+ was intermediate (interaction P = 0.007 and P = 0.007, respectively). In conclusion, the addition of LA brings important nutritional attributes to nursery diets by improving feed intake, digestibility of DM and GE, and the N retention of weaned pigs; however, the functional capacity of LA to improve markers of intestinal function is limited. On the other hand, the FP showed only a mild increase in the digestibility of N but a limited capacity to improve markers of intestinal function.

Effect of different time intervals after feeding on plasma metabolites in growing pigs: an UPLC-MS-based metabolomics study

A diet consumed by pigs provides the nutrients for the production of a large number of metabolites that, after first-pass metabolism in the liver, circulate systemically where they may exert diverse physiologic influences on pigs. So far, little is known of how feeding elicits changes in metabolic profiles for growing pigs. This study investigated differences in plasma metabolites in growing pigs at several intervals after feeding using the technique of metabolomics. Ten barrows (22.5 ± 0.5 kg BW) were fed a corn-soybean meal basal diet and were kept in metabolism crates for a period of 11 days. An indwelling catheter was inserted into the jugular vein of each pig before the experimental period. Plasmas before and 1, 4, and 8 hr after feeding were collected at day 11 and differential metabolites were determined using a metabolomics approach. Direct comparison at several intervals after feeding revealed differences in 14 compounds. Identified signatures were enriched in metabolic pathways related to linoleic acid metabolism, arginine and proline metabolism, lysine degradation, glycine, serine and threonine metabolism, and lysine biosynthesis. These results suggest that plasma metabolites of growing pigs after feeding were modulated through changes in linoleic acid metabolism and amino acid metabolism.

Modelling the effects of thermal environment and dietary composition on pig performance: model logic and concepts

A deterministic, dynamic pig growth model is described that predicts the effects of genotype and the thermal and nutritional environments on food intake, growth and body composition of growing pigs. From the daily potential for protein gain, as determined by pig genotype and current state, the potential gains of the other chemical components, including ‘desired’ lipid gain, are calculated. Unconstrained voluntary food intake is predicted from the current protein and lipid contents of the pig, and the composition of the food, as that which is needed to permit potential growth to be achieved. The model allows compensatory lipid gain. The composition of the food is described in terms of its digestible energy content (DEC), ideal digestible crude protein content (IDCPC) and bulkiness. Both energy and protein can be limiting resources and the bulk of the food may constrain intake. The animal’s capacity for bulk is a function of its size. The thermal environment is described by the ambient temperature, wind speed, floor type and humidity and sets the maximum (HLmax) and minimum (HLmin) values possible for heat loss. A comparison with heat production (HP) determines whether the environment is hot (HP > HLmax), cold (HP < HLmin) or thermoneutral (HLmin< HP < HLmax). A constraint on intake operates in hot environments, while in cold environments, there is an extra thermal demand. If conditions are thermoneutral no further action is taken. Daily gains of each of the chemical components are calculated by partitioning energy intake between protein and lipid gains according only to the energy to protein ratio of the food. The model builds on the work of others in the literature as it allows predictions on how changes in: (i) the kind of pig; (ii) the animal’s current state, which is particularly relevant in cases of compensatory growth; (iii) the dietary composition, and; (iv) the climatic environment, affect food intake and growth, whilst maintaining simplicity and flexibility.

Effect of high ambient temperature on protein and lipid deposition and energy utilization in growing pigs

The effects of high ambient temperature (T) on protein (PD) and lipid deposition (LD) and energy utilization were studied on 36 Piétrain ✕ (Landrace ✕ Large White) barrows according to a factorial design including two temperatures (23ºC for thermoneutrality and 30ºC for the high temperature) and four feeding levels. One feeding level corresponded to the voluntary food intake (VFI) at each temperature. Expressed as proportion of VFI at 23ºC, the actual feeding levels were 1·00, 0·90, 0·80, 0·70 at 23ºC and 0·80, 0·73, 0·68 and 0·62 at 30ºC. Animals were offered a wheat, maize and soya-bean meal based diet containing 187 g crude protein per kg and 0·95 g ileal standardized digestible lysine per MJ of net energy. Pigs were housed individually and had free access to water. The experiment started at 24 kg live weight and animals were slaughtered at 65 kg live weight and their body composition was measured. Slaughter of nine control pigs at the beginning of the experiment allowed calculation of the composition of gain (nutrients and energy) according to the comparative slaughter technique. Reduction of metabolizable energy (ME) intake resulted in a reduced live-weight gain at each T: the maximum gain was 1052 g/ day in pigs offered food ad libitum at 23ºC and the minimum (760 g/day) at the lowest intake at 30ºC. Visceral organ mass was lower at 30ºC than at 23ºC but was not affected by feeding level within T. Growth responses were described as polynomial or broken-line functions of ME intake (linear-plateau for PD). Both the slope and the plateau were influenced by T. At 30ºC, PDmax (143 g/day) was reached at 22·8 MJ ME per day, while at 23ºC PDmax (165 g/day) was reached at 28·4 MJ ME per day. In both cases, PDmax was reached at 0·88 of VFI at this temperature. Also the marginal response of PD to ME intake before the breakpoint was affected by T (5·9 and 4·5 g PD per MJ ME at 23ºC and 30ºC, respectively). At identical high ME intake (e.g. 0·80 of VFI at 23ºC), PD was greater at 23ºC than at 30ºC. In contrast, severe food restriction reduced PD at thermoneutrality more than an identical food restriction obtained at high ambient T. The results indicate that heat stress has a direct negative effect on PD and affects the partitioning of energy gain between protein and fat deposition.

Technical review of the energy and protein requirements of growing pigs: energy

A review of work reported in the literature was used to present quantitative descriptions of energy dispositioning in the growing pig. These are detailed in the text, which points to preferred values, as well as to anomalies and lacunae. The review was prepared with the objective of allowing from its content the inclusive and quantitative modelling of energy requirement. Requirement is approached as the sum of the component factors; maintenance, protein retention and lipid retention. Conventional expressions of maintenance requirement, as some function of pig mass, were found unconvincing in their variety of expression of coefficients and exponents. The review concluded that maintenance is properly related to protein turn-over, and thereby requires at least to include elements of concomitant protein metabolic activity. It was also judged that maintenance costs might be farm-specific. The energy requirements for activity, gaseous losses and disease were identified as important, but unsatisfactory in their quantification. Exploration of the energy costs of uncomfortable ambient temperatures suggested that whilst the responses of the pig are open to sophisticated and relatively exact calculation, the description of comfort remained inexact. The efficiency of retention of lipid by direct incorporation was high and may comprise a substantial proportion of the dietary lipid supply. There was little evidence of variation in the efficiency of utilization of metabolizable energy from carbohydrate for lipid retention. The linear-plateau paradigm for protein retention was adopted. The efficiency of utilization of energy for protein retention measured by a variety of approaches was found to be highly variable, prone to error and the literature confused. It was concluded that the efficiency of use of metabolizable energy for protein retention would be a function of at least: (a) the absorbed substrate being metabolized for the synthesis of body protein, (b) the rate of total protein tissue turn-over associated with the retention of newly accreted protein and not already accounted in the estimate of maintenance, (c) the mass of protein tissue involved in turn-over, and (d) the degree of maturity attained, and any influence maturity may have upon the rate of turn-over of total body protein. Algorithms for energy requirement are presented based upon protein turn-over and these appear to have some consistency with empirical findings.

Technical review of the energy and protein requirements of growing pigs: protein

A review of work reported in the literature was used to present quantitative descriptions of protein use in the growing pig. These are detailed in the text, which also points to preferred values, and to anomalies and lacunae. The review was prepared with the objective of allowing from its content the inclusive and quantitative modelling of amino acid requirement. Requirement was approached as the sum of the component factors: maintenance and protein retention. Ileal true digestible protein and amino acid requirements are presented in a form consistent with that forwarded for energy. Thus both energy and protein elements can be conceptualized within a single coherent framework. Priority uses for absorbed amino acids were assumed to be (a) to support endogenous protein losses resultant from the passage of food and incomplete re-absorption prior to the terminal ileum, (b) to replace lost hair and skin, and (c) to cover the basic maintenance losses which will occur as a result of minimal protein turn-over even when protein retention is zero. The bulk of the protein requirement was directly linked to the daily rate of protein retention, for which the linear-plateau response was accepted. For determination of the maximum rate of protein retention the Gompertz function was proposed, although the use of a single value throughout the growth period was not dismissed. The balance of amino acids for protein retention is specified as different from that for maintenance. Central to the approach was the proposal that the inefficiency of use of ileal digested ideal protein, even when not supplied in excess, was an expression of protein losses occurring as a result of protein turn-over. The requirement for the satisfaction of the losses from protein turn-over occurring as a consequence of protein retention, and therefore additional to the requirements for maintenance, was identified. Quantification was attempted with sufficient success to warrant its inclusion into requirement estimation. It was concluded that this element addressed previously inadequately explained protein utilization inefficiencies. Algorithms are presented based upon protein turn-over which appear to be consistent with empirical findings.

Characterization of dietary energy in Swine feed and feed ingredients: a review of recent research results

Feed is single most expensive input in commercial pork production representing more than 50% of the total cost of production. The greatest proportion of this cost is associated with the energy component, thus making energy the most important dietary in terms of cost. For efficient pork production, it is imperative that diets are formulated to accurately match dietary energy supply to requirements for maintenance and productive functions. To achieve this goal, it is critical that the energy value of feeds is precisely determined and that the energy system that best meets the energy needs of a pig is used. Therefore, the present review focuses on dietary supply and needs for pigs and the available energy systems for formulating swine diets with particular emphasis on the net energy system. In addition to providing a more accurate estimate of the energy available to the animal in an ingredient and the subsequent diet, diets formulated using the this system are typically lower in crude protein, which leads to additional benefits in terms of reduced nitrogen excretion and consequent environmental pollution. Furthermore, using the net energy system may reduce diet cost as it allows for increased use of feedstuffs containing fibre in place of feedstuffs containing starch. A brief review of the use of distiller dried grains with solubles in swine diets as an energy source is included.

Field experience with surgical castration with anaesthesia, analgesia, immunocastration and production of entire male pigs: performance, carcass traits and boar taint prevalence

Male piglets are castrated to reduce boar taint and also to reduce aggressive and sexual behaviour. However, the procedure as traditionally performed is painful and negatively affects performance. Large-scale results about the consequences of implementing alternatives on farms are lacking. We, therefore, investigated the practical applicability of the following five alternatives that can be implemented in the short term: surgical castration (1) without pain relief (CONT, control group), (2) with analgesia (MET, Metacam, 0.2 ml, 10 to 15 min before castration), (3) with general anaesthesia (CO2, inhalation, 100% CO2, 25 s, 3 l/min), (4) vaccination against boar taint (IM, two injections with Improvac) and (5) production of entire males (EM). The study consisted of the following two trials: (1) an experimental farm trial with 18 animals/treatment and (2) a large field trial on 20 farms with ~120 male pigs/farm per treatment and all treatments performed on each farm. Performance results as well as data on carcass traits, boar taint (hot-iron method) and testes development and weight were collected in both trials. Neither castration nor administration of analgesia or anaesthesia had an effect on daily gain of the piglets in the farrowing crates (P>0.05). Farmer records indicated that mortality in the farrowing crates (1.1%), nursery pens (1.8%) and fattening stable (2.2%) was not influenced by MET or CO2 compared with EM, IM or CONT (P>0.05). No significant differences were found for daily gain (P>0.05) nor slaughter age (P>0.05). Immunocastrates and EM had a better gain-to-feed ratio (P<0.05) compared with the groups of barrows (CONT, MET and CO2). Lean meat percentage was higher for EM compared with the barrows, and intermediate for IM (P<0.05). Carcass yield was lowest for IM (P<0.05). The hot-iron method indicated that boar taint was eliminated in barrows and IM compared with EM (P<0.001). Average prevalence of strong boar taint was 3% for EM, but varied from 0% to 14% between farms. As the effect of treatment on performance as well as the level of boar taint of EM was farm dependent, farmers should be encouraged to pre-test the different alternatives in order to make a well-considered choice for the best practical and profitable alternative for their farm.

Modelling the variation in performance of a population of growing pig as affected by lysine supply and feeding strategy

Considerable progress has been made in the nutritional modelling of growth. Most models typically predict (or analyse) the response of a single animal. However, the response to nutrients of a single, representative animal is likely to be different from the response of the herd. To address the variation in response between animals, a stochastic approach towards nutritional modelling is required. In the present study, an analysis method is presented to describe growth and feed intake curves of individual pigs within a population of 192 pigs. This method was developed to allow end-users of InraPorc (a nutritional model predicting and analysing growth in pigs) to easily characterise their animals based on observed data and then use the model to test different scenarios. First, growth and intake data were curve-fitted to characterise individual pigs in terms of BW (Gompertz function of age) and feed intake (power function of BW) by a set of five parameters, having a biological or technico-economical meaning. This information was then used to create a population of virtual pigs in InraPorc, having the same feed intake and growth characteristics as those observed in the population. After determination of the mean lysine (Lys) requirement curve of the population, simulations were carried out for each virtual pig using different feeding strategies (i.e. 1, 2, 3 or 10 diets) and Lys supply (ranging from 70% to 130% of the mean requirement of the population). Because of the phenotypic variation between pigs and the common feeding strategies that were applied to the population, the Lys requirement of each individual pig was not always met. The percentage of pigs for which the Lys requirement was met increased concomitantly with increasing Lys supply, but decreased with increasing number of diets used. Simulated daily gain increased and feed conversion ratio decreased with increasing Lys supply (P < 0.001) according to a curvilinear-plateau relationship. Simulated performance was close to maximum when the Lys supply was 110% of the mean population requirement and did not depend on the number of diets used. At this level of Lys supply, the coefficient of variation of simulated daily gain was minimal and close to 10%, which appears to be a phenotypic characteristic of this population. At lower Lys supplies, simulated performance decreased and variability of daily gain increased with an increasing number of diets (P < 0.001). Knowledge of nutrient requirements becomes more critical when a greater number of diets are used. This study shows the limitations of using a deterministic model to estimate the nutrient requirements of a population of pigs. A stochastic approach can be used provided that relationships between the most relevant model parameters are known.

The Interaction Between Dietary Valine and Tryptophan Content and Their Effect on the Performance of Piglets

Four experimental diets for newly weaned pigs were formulated: (1) low valine and low tryptophan; (2) low valine and high tryptophan; (3) high valine and low tryptophan and (4) high valine and high tryptophan. Dietary standardized ileal digestible (SID) lysine content was 1.06 g/kg. The SID valine to SID lysine ratio was 0.58 and 0.67 for the low and high valine diets, respectively, and SID tryptophan to SID lysine ratios were 0.19 and 0.22 for the low and high tryptophan diets, respectively. In total, 64 pens of 6 pigs (3 barrows and 3 gilts) were divided over the four experimental treatments. No interaction between dietary supply of valine and tryptophan was observed (P > 0.1 for all parameters). Increasing the dietary valine content increased the daily feed intake, daily gain and gain:feed (P < 0.001 for all three parameters). Increasing the dietary tryptophan content improved gain:feed during the first 2 weeks (P < 0.05) and overall (P < 0.05). Valine supply had a greater effect on performance results than tryptophan supply. It may thus be beneficial to provide a diet with an optimal dietary concentration of valine even if other amino acids are at suboptimal dietary levels.

Protein and energy utilization and the requirements for maintenance in juvenile mulloway (Argyrosomus japonicus)

This study describes the digestible protein (DP) and digestible energy (DE) utilization in juvenile mulloway, and determined the requirements for maintenance. This was achieved by feeding triplicate groups of fish weighing 40 or 129 g held at two temperatures (20 or 26 degrees C), on a commercial diet (21.4 g DP mJ DE(-1)) at four different ration levels ranging from 0.25% of its initial body weight to apparent satiation over 8 weeks. Weight gain and protein and energy retention increased linearly with increasing feed intake. However, energy retention efficiency (ERE) and protein retention efficiency (PRE) responses were curvilinear with optimal values, depending on fish size, approaching or occurring at satiated feeding levels. Maximum predicted PRE was affected by body size, but not temperature; PRE values were 0.50 and 0.50 for small mulloway, and 0.41 and 0.43 for large mulloway, at 20 and 26 degrees C respectively. ERE demonstrated a similar response, with values of 0.42 and 0.43 for small, and 0.32 and 0.34 for large mulloway at 20 and 26 degrees C respectively. Utilization efficiencies for growth based on linear regression for DP (0.58) and DE (0.60) were independent of fish size and temperature. The partial utilization efficiencies of DE for protein (k (p)) and lipid (k (l)) deposition estimated using a factorial multiple regression approach were 0.49 and 0.75 respectively. Maintenance requirements estimated using linear regression were independent of temperature for DP (0.47 g DP kg(-0.7) day(-1)) while maintenance requirements for DE increased with increasing temperature (44.2-49.6 kJ DE kg(-0.8) day(-1)). Relative feed intake was greatest for small mulloway fed to satiation at 26 degrees C and this corresponded to a greater increase in growth. Large mulloway fed to satiation ate significantly more at 26 degrees C, but did not perform better than the corresponding satiated group held at 20 degrees C. Mulloway should be fed to satiation to maximize growth potential if diets contain 21.4 g DP mJ DE(-1).

Estimation of whole body lipid mass in finishing pigs

Most nutritional pig growth models are based on the deposition of whole body protein (P) and lipid (L) mass. Chemical analysis of the whole animal is the best method to determine body composition. However, this method is expensive, time consuming and the carcass is lost. Alternatively, P and L may be estimated using simple indicators that should be precise and easily accessible. Although empty body weight (EBW) is a good indicator for P (through the strong relation between water and P), L is more difficult to estimate. This study was carried out to evaluate the relationship between simple carcass measurements and L. Measurements included backfat thicknessin vivoand at slaughter in the hot and cold carcass and the weight of carcass, organs and primal cuts. To maximize variations in adiposity a total of 30 females and barrows from two genotypes (Piétrain×(Landrace×Large White) and Large White) were slaughtered at body weights typically used in Europe (i.e. 90 to 150 kg) and ground for chemical analysis. Backfat mass (in combination with EBW) was the best indicator for L (L (kg)=0·0590×EBW (kg)+2·99×backfat mass (kg),R2=0·96). Different backfat thickness measurements were highly correlated and appeared reasonable indicators for total backfat mass. Backfat thickness measured in the hot carcass between 3rd and 4th last lumbar vertebra at 8 cm from the mid line was the second best indicator for L (L=(0·0855+0·0073×backfat thickness)×EBW,R2=0·94). On average, 18% of total body lipids were located in the backfat. Although these equations can be used to obtain a reasonable estimate of whole body lipid mass, a significant genotype effect remained. Differences between genotypes in the partitioning of lipids between different tissues suggest that the quantification of an external lipid depot alone is insufficient to precisely estimate whole-body lipid mass across genotypes.

Effects of feed restriction and subsequent refeeding on energy utilization in growing pigs

An experiment was carried out to evaluate the metabolic utilization of energy in crossbred barrows during feed restriction and subsequent refeeding. Ten pigs, initially weighing 52 kg, were used in 5 blocks of 2 littermates each. A 7-d adaptation period (P1) was used in which pigs were offered feed at 2.60 MJ of ME.kg of BW(-0.60).d(-1). This adaptation period was followed by a 7-d period (P2), in which 1 pig of each block continued to receive feed at the same level of feeding, whereas for its littermate a 40% reduction in feed intake was imposed (i.e., 1.55 MJ of ME.kg of BW(-0.60).d(-1)). During the subsequent 7-d period (P3), both pigs were offered feed at 2.60 MJ of ME.kg of BW(-0.60).d(-1). After P3, pigs were fasted for 1 d. Heat production (HP) was measured for all pigs during the last 3 d of P1 and on all days for P2 and P3. Heat production was measured using an open-circuit respiration chamber. Energy and N balances were determined for P1, P2, and P3. The HP was partitioned into HP due to physical activity, the short-term thermic effect of feeding, and resting HP. Feed restriction during P2 decreased (P < 0.01) total HP, resting HP, short-term thermic effect of feeding, and retained energy, whereas HP due to physical activity was not affected by feed restriction (P = 0.50). Likewise, fecal and urinary N loss, protein gain, lipid gain, and ADG were reduced during feed restriction (P < 0.01). There were no differences in components of HP and metabolic utilization of energy between the 2 groups during P1 and P3. Nevertheless, urinary N loss was decreased (P < 0.05) and ADG increased (P < 0.01) during P3 for pigs that were restricted in P2. Compensatory growth after a period of feed restriction does not seem to be related to a change in the metabolic utilization of energy for gain but more likely is due to gain in water and gut contents.

Partitioning of limiting protein and energy in the growing pig: description of the problem, possible rules and their qualitative evaluation

A core part of any animal growth model is how it predicts the partitioning of dietary protein and energy to protein and lipid retention for different genotypes at different degrees of maturity. Rules of partitioning need to be combined with protein and energy systems to make predictions. The animal needs describing in relation to its genotype, live weight and, possibly, body composition. Some existing partitioning rules will apply over rather narrow ranges of food composition, animal and environment. Ideally, a rule would apply over the whole of the possible experimental space (scope). The live weight range over which it will apply should at least extend beyond the 'slaughter weight range', and ideally would include the period from the start of feeding through to maturity. Solutions proposed in the literature to the partitioning problem are described in detail and criticised in relation to their scope, generality and economy of parameters. They all raise the issue, at least implicitly, of the factors that affect the net marginal efficiency of using absorbed dietary protein for protein retention. This is identified as the crucial problem to solve. A problem identified as important is whether the effects of animal and food composition variables are independent of each other or not. Of the rules in the literature, several could be rejected on qualitative grounds. Those rules that survived were taken forward for further critical and quantitative analysis in the companion paper.

Energetic efficiency of starch, protein and lipid utilization in growing pigs

Mathematical models are increasingly used to predict the response of an animal to a changing nutrient supply. The objective of this experiment was to provide data that can be used in model development or evaluation and concerns the energetic efficiency with which nutrients are used for protein and lipid deposition. A basal diet (D1), limiting in lysine supply, was fed at 1.7 MJ metabolizable energy (ME)/(kg BW(0.60) x d1) to growing pigs that weighed approximately 60 kg. Four additional diets were formulated: the basal diet and a dietary supplement that consisted of starch (D2), starch and corn gluten meal (D3), starch and casein (D4) or starch and lipid (D5). The latter four diets were fed at 2.55 MJ ME/(kg BW(0.60) x d1) and ensured the same intake of the basal diet across treatments; the difference was supplied by the supplement. Metabolic utilization of the basal diet and supplements was determined using nitrogen and energy balances (indirect calorimetry). The N retention was similar in pigs fed diets D1, D2, D3 and D5 but considerably higher in those fed D4. A data analysis model was developed to account for differences in ME utilization between nutrients. The ME not deposited as protein entered a common pool of energy, which was used for adenosine triphosphate synthesis or lipid deposition. The energetic efficiencies of ME utilization were 0.842, 0.520 and 0.883 for starch, protein and lipid, respectively. Due to the energy cost of protein deposition (or protein turnover), the energetic efficiencies of depositing dietary protein as protein or lipid were similar.

Modelling heat production and energy balance in group-housed growing pigs exposed to low or high ambient temperatures

The effects of ambient temperature (T; 12-29 degrees C), body weight (BW; 30-90 kg) and metabolisable energy intake (ME) on components of energy balance were studied in seven groups of Piétrain x Large White barrows kept in a respiratory chamber. In Expt 1 (groups 1, 2 and 3), T varied in a cyclic way from 22 degrees C to 12 degrees C and then from 12 degrees C to 22 degrees C with three or four consecutive days at each of 22, 19, 16, 14 and 12 degrees C. Similarly, in Expt 2 (groups 4, 5 and 6), T varied from 19 to 29 degrees C and then from 29 to 19 degrees C with three or four consecutive days at each of 19, 22, 25, 27 and 29 degrees C. In both experiments, pigs were offered feed ad libitum. In Expt 3, pigs (group 7) were exposed to the thermic conditions of Expt 1 but their feed allowance was adjusted on a BW basis to the ad libitum intake recorded at 19 and 22 degrees C in Expt 1. Groups 1, 2, 4, 5 and 7 were used over two successive cycles with initial average BW of 37 kg at cycle 1 (four pigs per group) and 63 kg at cycle 2 (three pigs per group). Groups 3 and 6 were studied at an intermediary stage of growth; their initial BW was 45 kg. The O2 and CO2 concentrations, physical activity and feed intake were continuously and simultaneously measured and used to calculate total heat production (HP; HPtot), HP due to physical activity (HPact), activity-free HP (HP0), and thermic effect of feed. HP was modelled as a non-linear function with T, BW and ME as predictors. Results indicate that all components of HP were proportional to BW(0.60). Physical activity was minimal between 19 and 27 degrees C (8 % ME). The estimated lower critical temperature was 24 degrees C. Between 24 and 12 degrees C, total thermic effect of feed decreased from 31 to 16 % ME, but the short-term thermic effect of feed (5.1 % ME) remained constant. Equations for prediction of HPtot, HPact and HP0 according to BW, T and ME are proposed and evaluated according to literature values; values for the feed cost of thermoregulation in pigs are proposed.