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

An acute challenge with a deoxynivalenol-contaminated diet has short- and long-term effects on performance and feeding behavior in finishing pigs

Mycotoxins are toxic secondary metabolites produced by various fungi and are known to contaminate animal feed ingredients especially cereals. One of the most common mycotoxins in swine diets is deoxynivalenol (DON) which is known to decrease growth performance. The objective of the present study was to evaluate the effects of single or repeated short-term DON challenges on growth performance, and feeding behavior in finishing pigs. A total of 160 pigs were distributed to four experimental groups in two successive replicates with each pig individually measured for live BW and individually fed using an electronic feeding station. The pigs in control group CC were fed with a standard finisher diet during the whole duration of the experimental period. Groups DC, CD, and DD were given the DON-contaminated diet (3.02 mg DON/kg feed) for 7 d at 113 d, at 134 d, and at 113 and 134 d of age, respectively. The DON-contaminated diet was formulated with a naturally contaminated corn. During challenge periods, ADFI was decreased by 26% to 32% (P < 0.05) and ADG by 40% to 60% (P < 0.05). The drop in ADFI during DON challenges was associated with changes in the feeding behavior: when compared to the nonchallenged pigs, pigs fed with DON-contaminated diet had lower number of meals per day (9.6 versus 8.2 meals per day on average; P < 0.05) and slower feeding rate (42.0 g/min versus 39.9 g/min on average; P < 0.05). For the whole trial period, pigs submitted to the DON challenge at the end of the experiment (i.e., first time for CD group and second time for DD group) had a lower (P < 0.05) ADFI (2.67 and 2.59 kg/d, respectively) when compared to the control CC group of pigs (2.87 kg/d). An intermediate value was reported for the DC groups (2.79 kg/d). All challenged groups, i.e., DC, CD, and DD pigs, had lower (P < 0.05) overall ADG (970, 940, and 900 g/day, respectively) than CC (1,050 g/day) for the whole trial period. Pigs challenged early in the trial, i.e., DC and DD groups, had a higher (P < 0.05) FCR than CC group (3.00 and 3.06 versus 2.80, respectively) while group CD showed intermediate results (2.92). This study demonstrates that the severity of DON toxicity in pig performance can be related to the age of exposure (113 or 134 d) and the number of exposures to the toxin (one or two). Exposure to DON also resulted to long-term effects because challenged pigs showed limited ability to recover after the DON-induced reduction of feed intake.

Life cycle assessment of alternative swine management practices

Life cycle assessment of various alternative management strategies in the swine industry was performed to evaluate their impact on greenhouse gas (GHG) emissions, cumulative energy use, and cumulative water use. The management strategies included the use of immunocastration (IC), production without ractopamine (NoRAC), production without antimicrobials used for either growth promotion (NoAGP) or disease prevention (NoPREV), production of entire males (boars) (EM), and use of gestation pens (PENS). A common baseline scenario representing standard management practices in the swine industry was created against which all alternative management practices were compared pairwise. The study scope was from cradle-to-farm gate with a functional unit of 1 kg live weight at the farm gate. The baseline and each alternative management scenario was simulated in Pig Production Environmental Footprint Calculator (PPEC) model by varying key variables to populate life cycle inventory inputs for SimaPro V7.3 (Pre' Consultant, the Netherlands), a life cycle assessment modeling program. Increase in GHG emissions, energy use, and water use were observed for NoAGP (1.56, 1.75, and 1.03%, respectively), NoPREV (17.32, 18.40, and 15.58%, respectively), and NoRAC (6.52, 4.87, and 7.52%, respectively) scenarios. For EM scenario, GHG emissions and energy use increased by 2.09 and 3.75%, respectively but water use decreased by 2.29%. Lower GHG emissions, energy use, and water use were observed for PENS (0.97, 1.50, and 0.97%, respectively) and IC (2.39, 2.57, and 2.96%, respectively) scenarios. These changes in the impact categories were statistically significant (P < 0.05) for all scenarios except for changes to GHG emissions for EM and changes to water consumption for PENS and NoAGP. However, the uncertainty analysis showed that the tails of distribution for baseline and alternative management scenario pair overlapped. The impact of management practices on sustainability metrics resulted from differences in pig performance parameters, manure production, feed consumption, etc. between various management practices and the baseline scenario. Due to uncertainties in input parameters, the results should be interpreted as general trends which specifically highlight trade-offs that may result from shifts in production practices. The study identified some of the hot spots in pig production and can be useful in determining best management practices to make swine production more environmentally sustainable.

Sensitivity to dietary lysine: energy content in pigs divergently selected for components of efficient lean growth rate

The sensitivity to dietary lysine: energy content of pigs from lines divergently selected over seven generations for components of efficient lean growth rate was quantified by the within-selection line regression of performance test traits on diet class. Large White pigs were performance tested over three 14-day test-periods starting at 30, 50 and 75 kg and offered, to appetite, isoenergetic diets differing in dietary total lysine: energy (0•59, 0•69, 0•81, 0•91, 1•01, 1•12 and 1•23 g/MJ digestible energy (DE)). Within each litter, full-sibs were performance tested on different diets. Pigs were also performance tested on a diet-choice procedure using diets with total lysine: energy of 0•69 and 1•12 g/MJ DE to determine the correlation between performance on phase-feeding and diet-choice.

The study consisted of 578 animals with 459 pigs tested with phase-feeding and 119 tested on diet-choice procedures. The study detected significant selection line and dietary effects on performance test traits, but no significant between-selection line differences in sensitivity to dietary total lysine: energy. When combinations of performance test traits were transformed into predicted lysine and energy utilization traits there were significant selection line effects on predicted nutrient allocation, but not in responses to increasing dietary total lysine: energy. The lack of between-selection line differences in sensitivity to dietary total lysine: energy indicated that the consequences of changing dietary total lysine: energy will be broadly similar across a range of genotypes, as spanned by the selection lines of the study.

Genetic correlations between performance traits of phase-fed and diet-choice pigs suggested that predictions of genetic merit will be similar with animals tested on either procedure between 30 and 75 kg but post 75 kg predicted genetic merit for growth rate and lysine intake should be estimated separately for performance on diet-choice or for performance on a given diet. In contrast, predicted genetic merit for fat deposition with performance testing on diet-choice will be highly correlated with predicted genetic merit with testing on a single diet.

Architecture of a harmonized model of the growing pig for the determination of dietary net energy and protein requirements and of excretions into the environment (IMS Pig)

The model incorporates, amongst its novel components, variable efficiency coefficients in the simulation of the responses of growing pigs to nutrient inputs, and thereby increases the accuracy and efficacy of control of feeding and nitrate excretion. The model determines (rather than is presented with) net energy and required amino acid level and balance. The estimation of protein turn-over as a function of rate of protein retention, protein mass and the maturity of the pig was found to be central to both the energy (ATP) and protein economy. Protein turn-over varied from around 0·14 to 0·08 of the protein mass depending upon the size of the pig. Efficiencies of energy yield from lipid, starch (and sugar), protein and (fibre-derived) volatile fatty acids were calculated to be 0·98, 0·86, 0·56 and 0·58 for ATP production and 0·90, 0·70, 0·50, and 0·44 for lipid retention, respectively. The maximum efficiency of use of ileal digestible amino acids was determined as around 0·85. The energy cost of protein synthesis was equivalent to 4·2 MJ metabolizable energy (ME) per kg, and the efficiency of use of ME for protein retention varied from 0·55 to 0·40 depending on the protein mass of the pig. The components of the model and the biochemical drivers are described in detail, and proof of principle of the main elements is presented. The model is different in its architecture to other published simulation models, and is considered to add to the present knowledge base in this discipline.

Integrating economic parameters into genetic selection for Large White pigs

The objective of the study was to integrate economic parameters into genetic selection for sow productivity, growth performance and carcass characteristics in South African Large White pigs. Simulation models for sow productivity and terminal production systems were performed based on a hypothetical 100-sow herd, to derive economic values for the economically relevant traits. The traits included in the study were number born alive (NBA), 21-day litter size (D21LS), 21-day litter weight (D21LWT), average daily gain (ADG), feed conversion ratio (FCR), age at slaughter (AGES), dressing percentage (DRESS), lean content (LEAN) and backfat thickness (BFAT). Growth of a pig was described by the Gompertz growth function, while feed intake was derived from the nutrient requirements of pigs at the respective ages. Partial budgeting and partial differentiation of the profit function were used to derive economic values, which were defined as the change in profit per unit genetic change in a given trait. The respective economic values (ZAR) were: 61.26, 38.02, 210.15, 33.34, -21.81, -68.18, 5.78, 4.69 and -1.48. These economic values indicated the direction and emphases of selection, and were sensitive to changes in feed prices and marketing prices for carcasses and maiden gilts. Economic values for NBA, D21LS, DRESS and LEAN decreased with increasing feed prices, suggesting a point where genetic improvement would be a loss, if feed prices continued to increase. The economic values for DRESS and LEAN increased as the marketing prices for carcasses increased, while the economic value for BFAT was not sensitive to changes in all prices. Reductions in economic values can be counterbalanced by simultaneous increases in marketing prices of carcasses and maiden gilts. Economic values facilitate genetic improvement by translating it to proportionate profitability. Breeders should, however, continually recalculate economic values to place the most appropriate emphases on the respective traits during genetic selection.

Mathematical modelling of energy expenditure during tissue deposition

Predicting the magnitude and rate of weight gain for a given increase of energy intake requires a model of whole-body energy expenditure that includes the energy cost of tissue deposition. Here, I introduce a mathematical framework for modelling energy expenditure that elucidates conceptual problems with the classical Kielanowski method for estimating the efficiencies of body fat and protein deposition. An alternative approach uses the theoretical biochemical efficiencies for protein and fat synthesis in combination with models of energy expenditure that include body fat and protein turnover costs. I illustrate this alternative approach using a simple mathematical model applied to previously published data from growing rats and human infants and compare the simple model results with the classical Kielanowski model. While both models fit the data reasonably well (R2>0.87 in rats and R2>0.67 in infants), the Kielanowski method resulted in parameter estimates that varied widely across experiments, had poor precision, and occasionally produced efficiency estimates greater than 1. In contrast, the new method provided precise parameter values and revealed consistencies across different experiments. The proposed mathematical framework has implications for interpreting studies of animal nutrition as well as providing a roadmap for future modelling efforts.

Estimating the continuous-time dynamics of energy and fat metabolism in mice

The mouse has become the most popular organism for investigating molecular mechanisms of body weight regulation. But understanding the physiological context by which a molecule exerts its effect on body weight requires knowledge of energy intake, energy expenditure, and fuel selection. Furthermore, measurements of these variables made at an isolated time point cannot explain why body weight has its present value since body weight is determined by the past history of energy and macronutrient imbalance. While food intake and body weight changes can be frequently measured over several weeks (the relevant time scale for mice), correspondingly frequent measurements of energy expenditure and fuel selection are not currently feasible. To address this issue, we developed a mathematical method based on the law of energy conservation that uses the measured time course of body weight and food intake to estimate the underlying continuous-time dynamics of energy output and net fat oxidation. We applied our methodology to male C57BL/6 mice consuming various ad libitum diets during weight gain and loss over several weeks and present the first continuous-time estimates of energy output and net fat oxidation rates underlying the observed body composition changes. We show that transient energy and fat imbalances in the first several days following a diet switch can account for a significant fraction of the total body weight change. We also discovered a time-invariant curve relating body fat and fat-free masses in male C57BL/6 mice, and the shape of this curve determines how diet, fuel selection, and body composition are interrelated.

The unrelenting obesity epidemic has resulted in intensive basic scientific investigation into the molecular mechanisms of body weight regulation—with the mouse being the organism of choice for such studies. We know that any mechanism of body weight regulation must exert its effect by influencing food intake, energy output, fuel selection, or some combination of these factors over extended time scales (∼weeks for mice). While food intake and body weight can be frequently measured in mice, current methods prohibit corresponding measurements of energy output or fuel selection on such long time scales. We address this deficiency by developing a mathematical method that quantitatively relates measurements of food intake, body weight and body fat to calculate the dynamic changes of energy output and net fat oxidation rates during the development of obesity and weight loss in male C57BL/6 mice. The mathematical model is based on the law of energy conservation, makes very few assumptions, and provides the first continuous-time estimates of energy output and fuel selection over periods lasting many weeks. Application of our methodology to various mouse models of obesity will improve our understanding of body weight regulation by placing molecular mechanisms in their whole-body physiological context.

Use of theoretical efficiencies of protein and fat synthesis to calculate energy requirements for growth in pigs

From the observation that fasting heat production includes the cost of body protein resynthesis and the evidence that protein resynthesis is included in the regression estimate of protein retention efficiency it is conjectured that the estimate of maintenance from fasting heat production must be conceptually equal to the regression intercept estimate of maintenance plus the cost of body protein resynthesis. Experimental evidence for comparable situations shows an approximate observational equality in agreement with the conjectured conceptual equality. This approximate equality implies that the theoretical (stiochiometric) efficiency of protein synthesis should be used in conjunction with the estimate of maintenance from fasting heat production for the prediction of growth energy requirements. The approximate maintenance equalities suggest furthermore approximate equality of theoretical fat synthesis efficiency and regression fat retention efficiency. This conjecture is also supported by experimental evidence. Some practical nutrition and pig breeding implications of the foregoing conclusions are indicated.

Influence of energy intake on protein and lipid deposition in Creole and Large White growing pigs in a humid tropical climate

Twenty-four castrated males were used to study the effect of breed (Large Whitev. Creole (LWv. CR)) and feeding level (0·70, 0·80, 0·90, and 1·00 ad libitum) on growth performance and protein deposition (PD) and lipid deposition (LD) between 30 and 60 kg in growing pigs under tropical climatic conditions; the CR pigs are raised in the Caribbean area and can be qualified as fat and slow growing pigs. Daily protein and amino acids supplies were calculated to be non-limiting for protein gain. Total PD and LD were measured according to the comparative slaughter technique. Digestibility coefficients of energy and nutrients were estimated over a 10-day period at 45 kg live weight. Neither the breed nor the feeding level influenced the apparent digestibility coefficients of dietary nutrients; only energy digestibility was increased at reduced feeding levels (P<0·05). Average daily gain increased linearly with the increase of metabolizable energy (ME) intake and the slope of the relationship was lower in CR than in LW pigs (30·4v. 36·6 g per additional MJ ME). The food conversion ratio was not affected by feeding level but it was significantly higher in CR than in LW pigs (2·88v. 2·36 kg /kg;P<0·001). Daily PD increased with ME intake according to a linear relationship in both breeds and the slope was significantly affected by breed (3·1v. 4·2 g/MJ ME in CR and LW pigs, respectively;P<0·001). In contrast, the increase of LD and total energy retained with ME were higher in CR than in LW pigs (8·4v. 6·4 g/MJ and 0·40v. 0·36 MJ/ MJ ME, respectively;P<0·001).

Incorporating turn-over in whole body protein retention ef.ciency in pigs

The magnitude of the discrepancy between conventional regression estimates of protein retention efficiency and theoretical estimates of synthesis efficiency indicates a major contribution ascribable to protein turn-over in the generally accepted estimates. As protein turn-over is known to be influenced by diet, feeding level and degree of maturity, this suggests the development of an estimator of protein efficiency that can be adapted for such differences. Therefore, based on generally accepted formulas for growth description, a method of estimating protein retention efficiency was developed which is flexible enough to accommodate different diets, feeding levels and degrees of maturity. Moreover, a formula was derived to convert one type of estimate to the other by regarding constant efficiency as equivalent to variable efficiency at the mid point of the estimation interval. Increase in scientific depth to this descriptive approach is provided by a theoretical consideration of a possible mechanism of hormonal control of protein synthesis and breakdown, ultimately expressed as proportionalities to powers of whole body protein (P). Molecular considerations on cellular synthesis and breakdown indicate a difference between breakdown and synthesis powers equal to (2/9)Q. The factor (2/9) is indicated by an argument based on insulinlike growth factor derived activator diffusion attributes by nucleus and body tissue geometries, whileQis equal to the proportion of nuclei activated by insulin-like growth factor. This proportion is likely to be a function of the concentration of growth factor in the blood. Hence, a linear relationship between intake and blood insulin-like growth factor concentration suggests thatQcan be represented by a scaled transformation of intake, 0 ≤Q≤ 1, such that a value ofQ= 1 represents ad libitum intake on a suitable diet andQ= 0 intake at the maintenance requirement. The quantification of breakdown and synthesis power differences by (2/9)Qleads to kP= {1 + [1 − (P/α)(2/9)Q]−1/6}−1, for turn-over related protein retention efficiency (kP), with α the limit value of P at maturity, so that 0 ≤ (P/α) ≤ 1. Experimental estimates, derived from direct estimates of whole body protein synthesis and breakdown at predetermined levels of intake, are in excellent agreement with the theoretical (2/9)Qin the power associated with (P/α) in kP. Furthermore, conventional multiple regression retention efficiencies satisfactorily approximate the turn-over related retention efficiency that can be calculated at a given level of intake for the mid point of the interval covered by the regression estimates.

Genetic improvement of lean meat growth and feed efficiency in pigs

Optimising selection procedures for feed efficiency and lean meat growth in pigs is important because feed costs form a high cost component of production. In this paper a number of breeding objectives used in pig industries are reviewed and the concept of the linear-plateau growth model is outlined. This concept allows optimisation of selection for feed intake of the growing pig taking the pigs potential for protein deposition into account. This is a first step towards further collaboration between geneticists and scientists from other disciplines in order to gain a better understanding of physiological consequences of selection. The necessity of recording individual feed intake in group housed pigs has led to the development of electronic feeders. These computerised systems provide additional data including repeated weight and feed intake records as well as feeding pattern traits. How to make best use of this extra information in breeding programmes needs to be explored further. Implications of testing pigs under ad libitum and restricted feeding are outlined and results from selection experiments and commercial group house environments are summarised. The comparison of testing procedures shows that restricted feeding benefits selection for lean meat growth. However, in commercial environments the benefits depend on how well variation in feed intake can be controlled. Testing procedures should be expanded to explain a larger part of variation in daily feed intake, as is currently the case. This unexplained variation may be related to the animal’s activity, social interactions between animals and response to various stressors that occur in commercial group housed environments.