Estimate of the variability of the lysine requirement of growing pigs using the indicator amino acid oxidation technique1

Metabolic availability of amino acids in humans

Knowledge of amino acid bioavailability and the effect of combining complementary protein sources are required to determine how to best meet an individual's protein and indispensable amino acid needs. Traditionally, protein quality of foods has been assessed using digestibility data. Digestibility may overestimate bioavailability of some amino acids particularly those more susceptible to heat and processing. The indicator amino acid oxidation (IAAO) method has been validated and applied to determine amino acid bioavailability termed metabolic availability of the first limiting amino acid of a proteinaceous food. The metabolic availability of the limiting amino acid in the test protein is determined as a ratio of the indicator amino acid oxidation response to graded intakes of the test protein compared to the indicator response to a reference protein (crystalline amino acid patterned after egg protein). The IAAO method has also been applied to assess the effect of protein complementation directly in humans on the overall protein quality of the diet. The results demonstrate that protein complementation augments the limiting amino acid supply and increases protein synthesis.

Controlled trial of whole body protein synthesis and plasma amino acid concentrations in yearling horses fed graded amounts of lysine

Lysine has been reported as the first limiting amino acid in typical equine diets. Indicator amino acid oxidation (IAAO) has become the standard method for determining amino acid requirements in other species, but prior to this study, it has not been used to determine equine requirements. The aim of this study was to evaluate whole body protein synthesis and plasma and muscle amino acid concentrations in response to graded levels of lysine intake in yearling horses. Six Thoroughbred colts (358 ± 5 kg) were fed each of six treatment lysine intakes ranging from 76 to 136 mg/kg body weight/day. Blood samples were taken before and 90 min after the morning concentrate meal. Gluteal muscle biopsies were taken ~100 min after the morning concentrate meal. The next day, whole body phenylalanine kinetics were determined using a 2 h primed, constant infusion of [(13)C] sodium bicarbonate followed by a 6 h primed, constant infusion of [1-(13)C] phenylalanine. Plasma lysine concentrations increased linearly (P <0.05) at both the 0 and 90 min time points with increasing lysine intakes. Free muscle asparagine, aspartate, arginine, glutamine, lysine, taurine and tryptophan concentrations responded quadratically to lysine intake (P <0.05). Phenylalanine kinetics did not differ between treatment intakes (P > 0.10). A broken line analysis of lysine intake and phenylalanine oxidation failed to yield a breakpoint from which to determine a lysine requirement. These diets may have been limiting in an amino acid other than lysine, underscoring the lack of data concerning amino acid requirements and bioavailability data in the horse.

Optimal lysine:DE ratio in growing pigs is independent of starch or fat as main energy source at two energy intake levels

In a 2 × 2 factorial arrangement, 28 growing boars (initial BW of 24.7 ± 1.5 kg) were used to examine the effects of energy source (high starch vs. high fat) and DE level (2.2 vs. 2.7 times the DE requirements for maintenance) on Lys requirements. Pigs were allotted to 1 of 4 dietary treatments. A within-animal Lys titration technique was used to assess the responses to changes in Lys to energy ratio. The amount of apparent ileal digestible Lys in the diet decreased stepwise from 1.74 to 0.5 g/MJ DE in 8 equidistant steps of 3 d each. From 48-h urinary nitrogen excretion, the optimal Lys to energy ratio was estimated for each pig using a linear-plateau model. Feces were collected quantitatively over 27 d to determine apparent total tract digestibility (ATTD) of nutrients. The DE to ADG ratio, but not DE intake and ADG, tended ( < 0.1) to be 4% lower in the high-starch group than in the high-fat group. The ATTD of energy and CP tended ( < 0.1) to be lower (0.8% and 0.9% units, respectively) at the high DE level. The ATTD of energy was 2.2% units greater ( < 0.001) for pigs fed the high-starch diet, but the ATTD of CP was not affected by ES. Estimates for the intercept (21.2% to 22.8%), slope (57.4 to 59.6), transition point (0.84 to 0.86 g Lys/MJ DE), and plateau (70.6% to 72.3%) of the linear-plateau Lys titration curves were not affected by the dietary treatments. In conclusion, ES does not affect Lys requirements in growing pigs regardless the level of DE intake.

A Simple Evaluation Method for the Quality of Dietary Protein in Rats Using an Indicator Amino Acid Oxidation Technique

We demonstrated that the indicator amino acid oxidation (IAAO) method could be employed for the evaluation of quality of dietary protein by comparing the protein intakes required to meet metabolic demand in rats fed different proteins. The objective of this study was to validate a simple evaluation method for determining the quality of dietary protein using the IAAO technique. Male Sprague-Dawley rats (5-6 wk old) were fed meals composed of graded protein, using either casein, wheat gluten (WG), soy protein isolate (SPI), or egg white protein (EW), every 3 h from 09:00 to 18:00. Administration of L-[1-(13)C]phenylalanine was performed hourly from 15:00 to 18:00. The (13)CO2 level in breath CO2 was measured at 18:30. The protein intake values required to meet the metabolic demand based on the breath (13)CO2 data for the dietary casein, WG, SPI, and EW intake were 18.0, 22.2, 17.5, and 10.1 g/kg BW/d, respectively. The breath (13)CO2 concentrations corresponding to the protein intake of 7.5 g/kg BW/d for casein, WG, SPI, and EW were 9.8, 10.9, 10.3, and 8.9 (‰)/100 g BW, respectively. A significant correlation was demonstrated between the protein intake required to meet the metabolic demands and the (13)CO2 concentration in the breath for a protein intake of 7.5 g/kg BW/d (r=0.967; p<0.05). These results demonstrated that the protein intake required to meet metabolic demand could be estimated and that the quality of the dietary protein could be evaluated using the (13)CO2 concentration in the breath with a protein intake of 7.5 g/kg BW/d.

The impact of feeding growing-finishing pigs with daily tailored diets using precision feeding techniques on animal performance, nutrient utilization, and body and carcass composition

The impact of moving from conventional to precision feeding systems in growing-finishing pig operations on animal performance, nutrient utilization, and body and carcass composition was studied. Fifteen animals per treatment for a total of 60 pigs of 41.2 (SE = 0.5) kg of BW were used in a performance trial (84 d) with 4 treatments: a 3-phase (3P) feeding program obtained by blending fixed proportions of feeds A (high nutrient density) and B (low nutrient density); a 3-phase commercial (COM) feeding program; and 2 daily-phase feeding programs in which the blended proportions of feeds A and B were adjusted daily to meet the estimated nutritional requirements of the group (multiphase-group feeding, MPG) or of each pig individually (multiphase-individual feeding, MPI). Daily feed intake was recorded each day and pigs were weighed weekly during the trial. Body composition was assessed at the beginning of the trial and every 28 d by dual-energy X-ray densitometry. Nitrogen and phosphorus excretion was estimated as the difference between retention and intake. Organ, carcass, and primal cut measurements were taken after slaughter. The COM feeding program reduced (P < 0.05) ADFI and improved G:F rate in relation to other treatments. The MPG and MPI programs showed values for ADFI, ADG, G:F, final BW, and nitrogen and phosphorus retention that were similar to those obtained for the 3P feeding program. However, compared with the 3P treatment, the MPI feeding program reduced the standardized ileal digestible lysine intake by 27%, the estimated nitrogen excretion by 22%, and the estimated phosphorus excretion by 27% (P < 0.05). Organs, carcass, and primal cut weights did not differ among treatments. Feeding growing-finishing pigs with daily tailored diets using precision feeding techniques is an effective approach to reduce nutrient excretion without compromising pig performance or carcass composition.

A simple amino acid dose-response method to quantify amino acid requirements of individual meal-fed pigs

Two experiments were conducted to develop a simplified dose-response technique to estimate the Lys requirement of individual, meal-fed growing pigs. In Exp. 1, we studied adaptation processes that occur during such a dose-response study in meal-fed pigs, and in Exp. 2, we studied the accuracy of this simplified technique to estimate changes in Lys requirement estimates of pigs following changes in energy intake. In Exp. 1, the effect of the Lys supply strategy on the Lys requirement was assessed in 14 barrows fed an increasing [low to high (LH)] or decreasing [high to low (HL)] total Lys supply, with total Lys levels varying from 0.36 to 1.06 g/MJ DE in 7 equidistant steps of 4 d each. Urinary urea and ammonia excretion and whole body N turnover were measured. In Exp. 2, the accuracy of the dose-response technique to determine a shift in Lys requirement was assessed in 20 barrows fed at either 2.2 [low energy (LE)] or 2.7 [high energy (HE)] times the energy requirements for maintenance, with total Lys supply decreasing from 1.10 to 0.37 g Lys/MJ DE in 9 equidistant steps of 3 d each. In Exp. 1, a lower increment in protein synthesis, breakdown, and whole body N turnover with increasing dietary Lys supply was observed in LH pigs than HL pigs (P < 0.01) and the estimated Lys requirement was 0.06 g/MJ DE greater (P = 0.01) in LH pigs than HL pigs. These results indicated that pigs at a decreasing Lys supply strategy require less time for metabolic adaptation to a change in Lys supply than those at an increasing Lys supply. In Exp. 2, the estimated Lys requirement was 2.6 g/d greater (P < 0.001) in HE pigs than LE pigs. The variation in AA requirement estimates between individual pigs was low (4.9% in LH pigs and 3.0% in HL pigs in Exp. 1 and 8.1% in LE pigs and 6.0% in HE pigs in Exp. 2). The present studies indicated that a dose-response technique with a decreasing Lys supply in time and a step length of 3 d with urinary N excretion as response criteria provides a simple, accurate technique to quantitatively estimate a change in AA requirements of individual meal-fed pigs.

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.

An evaluation of protein intake for metabolic demands and the quality of dietary protein in rats using an indicator amino acid oxidation method

Currently, protein requirements are generally determined based on nitrogen balance studies, but there are a variety of limitations associated with this method. The indicator amino acid oxidation (IAAO) method, with a theoretical base that differs widely from the nitrogen balance method, was developed as an alternative method for humans. The objective of the present study was to evaluate protein intakes for metabolic demands and protein quality, using protein itself, in rats employing the IAAO technique with L-[1-(13)C]phenylalanine. Male Wistar/ST rats (5-6 wk old) received a graded casein (4.3, 8.6, 12.9, 17.2, 21.5, 25.8%), or a wheat gluten (7.2, 10.8, 14.4, 18.0, 21.6, 25.2%) diet, along with L-[1-(13)C]phenylalanine. An isotopic plateau in breath was achieved 210 min after the start of the (13)C ingestion. The protein intakes for metabolic demands were calculated by applying a mixed-effect change-point regression model to breath (13)CO(2) data, which identified a breakpoint at minimal breath (13)CO(2) in response to graded protein intake. The protein intakes for metabolic demands determined by the IAAO method were 13.1 g/kg BW/d for casein and 18.1 g/kg BW/d for wheat gluten, showing a tendency similar to that determined by the nitrogen balance method. These results demonstrated that the IAAO method could be employed to evaluate not only the protein intakes for metabolic demands, but the dietary protein quality in freely living rats, suggesting that this method might be viable in a clinical setting.

Individual response of growing pigs to sulphur amino acid intake

Two N balance experiments were conducted to study the individual response of growing pigs to limiting amino acid (AA) intake. Series of fifteen diets with increasing concentration of sulphur amino acids (SAA, Expt 1) or methionine in the presence of excess cystine (Expt 2) were fed sequentially to nine pigs during a 15-day experimental period. The concentration of the AA under test ranged from 50% to 140% of the requirement while other essential AA were given in a 25% excess relative to the limiting AA. N retention was related to the limiting AA intake using rectilinear and curvilinear models. In Expt 1, the quadratic-plateau model fitted the individual data significantly better (p = 0.01) than the linear-plateau model. No difference was found between the two models in Expt. 2, presumably due to the sparing effect of excess cystine on methionine utilization. Exponential, saturation kinetics or four-parameter logistic models fitted to data for all pigs showed that their goodness of fit was similar to those of quadratic-plateau or linear-plateau models. Significant differences (p < 0.05) were found between individual plateau values for N retention within each experiment while the slopes of the regression lines did not significantly differ either in Expt 1 (p = 0.07) or Expt 2 (p = 0.45). There was a positive correlation between the slope and plateau values of the linear-plateau model in Expt 1 (r = 0.74, p = 0.02) but no significant correlation was found in Expt 2 (r = -0.48, p = 0.13). Marginal efficiencies of SAA and methionine utilization derived from the linear-plateau model were 0.43 and 0.65 respectively. Based on linear-plateau and quadratic-plateau models, daily requirements of SAA and methionine for a 50 kg pig were estimated to be 13.0 and 5.9 g and 14.3 and 6.1 g respectively.

An estimate of the methionine requirement and its variability in growing pigs using the indicator amino acid oxidation technique

Although AA requirements for the mean of a population of growing pigs have been established using traditional methods, there are no estimates of the variability within the population and whether this variation differs among AA. With the increased use of supplemental Lys in pig diets, there will be an increased need to supplement Met, commonly the second or third limiting AA in corn-soybean diets. The indicator AA oxidation method allows repeated measurements in a short period of time so that the AA requirement can be determined for individual pigs at a similar physiological stage. The objective of this study was to determine the mean Met requirement in individual gilts and to estimate the related variability. Six individually housed female pigs (initial BW = 8.8 kg, SD 1.5) each received diets providing 6 levels of dl-Met. The isonitrogenous and isoenergetic diets contained 0.187, 0.250, 0.290, 0.320, 0.350, and 0.377% Met (analyzed, as-fed basis). Cysteine (0.48%) and Lys (1.44%) concentrations were similar for all diets. Pigs were adapted for 6 d to the basal corn-soybean meal diet (0.187% Met), which was offered at 95 g/kg(0.75) of BW to ensure complete consumption of the test diets. During 4-h oxidation studies, 313.4 kBq, (SD 35.6) of L-[1-(14)C]Phe was mixed with each of 8 half-hourly meals, and expired CO(2) was collected. The breakpoint in Phe oxidation, representing the Met requirement, and its variability, was determined using 2-phase linear regression. Phenylalanine oxidation decreased as the Met content increased from 0.187 to 0.29%. Phenylalanine oxidation was not different (P > 0.2) for diets ranging from 0.320 to 0.377% Met. The dietary Met requirement varied from 0.320 to 0.373% for individual pigs. The mean Met requirement for individual pigs was determined to be 0.340% of diet (SD = 0.024%, CV= 7.1%), with 0.340, 0.364, and 0.388% covering the requirement of 50, 66, and 95% of the population, respectively. The present mean population estimate was similar to the recommended dietary Met concentration of 0.325% for pigs of this BW and feed intake. To maximize profitability, Met levels in starter pig diets should be determined, depending on the cost of crystalline Met and the fraction of the population whose requirement is to be met.

Contribution of research with farm animals to protein metabolism concepts: a historical perspective

The roles of proteins, carbohydrates, fats, and micronutrients in animal and human nutrition were broadly described during the late 18th and 19th centuries, and knowledge in protein nutrition evolved from work with all species. Although much of the fundamental and theoretical research in protein metabolism during the 20th century was conducted with laboratory animals, basic protein nutrition research in farm animals complemented those efforts and led to the development and use of new investigative methods (particularly in amino acid nutrition) as well as use of animal models in furthering the understanding of human protein metabolism. All these efforts have led to a contemporary hybrid model of protein nutrition and metabolism applicable to both humans and animal species. Now in the 21st century, farm animals are used in fetal and pediatric nutrition research, and data accruing for excess amino acid feeding in research with farm animals provide direction for assessment of pharmacological effects of amino acids when consumed in excessive quantities. Thus, as nutritional science is moving forward into nutrigenomics, nutriproteomics, and metabolomics, farm animal and human nutrition research interactions will likely continue with genetically modified farm animals produced for agricultural reasons (improved function and product quality) or those produced with human genes introduced to generate even better models of human protein metabolism.