Response of piglets to the standardized ileal digestible isoleucine,histidine and leucine supply in cereal–soybean meal-based diets

Improving the amino acid (AA) profile of the diet by using l-Lys, l-Thr, dl-Met, l-Trp and l-Val helps to reduce the dietary CP content, thereby reducing nitrogen excretion while maintaining the performance of pigs. Valine is the fifth limiting AA in cereal–soybean meal-based diets. The extent to which the CP content in the diet can be reduced further without compromising performance depends on the requirement of the next limiting AA. In cereal–soybean meal-based diets, Ile, His and Leu may be the limiting AAs after Val, although information on the requirements for these AAs is scarce. Six experiments were conducted to determine the effect of supplementing a low-CP diet with l-Ile, l-His and l-Leu on the performance of pigs weighing 10 to 20 kg. Experiment 1 was designed to determine the most limiting AA with respect to performance among Ile, His and Leu. A diet 10% deficient in Ile, Leu and His relative to the National Research Council (NRC, 1998) requirement estimates tended to decrease daily feed intake and daily gain by 6% and 8%, respectively. A 10% deficiency in His alone had no effect, whereas a 10% deficiency in Ile or Leu slightly reduced daily feed intake and gain. In the remaining experiments, the standardized ileal digestible (SID) Ile : Lys, His : Lys and Leu : Lys requirements were estimated. In Experiments 2, 3, 4, 5 and 6, 14 blocks of six pigs each were assigned to six levels of SID Ile : Lys (40%, 43%, 46%, 49%, 52% and 55%), His : Lys (20%, 24%, 28%, 32%, 36% and 40%), His : Lys (21%, 24%, 27%, 30%, 33% and 36%), Leu : Lys (70%, 78%, 86%, 94%, 102% and 110%) and Leu : Lys (80%, 90%, 100%, 110%, 120% and 130%), respectively. Across experiments, the estimated SID Ile : Lys, His : Lys and Leu : Lys requirements for maximizing daily gain were 49%, 32% and 102%, respectively, using a curvilinear plateau model. When Ile, His and Leu levels were 10% below the requirement estimate, daily gain was reduced by 9%, 3% and 3%, respectively. The results of this study indicate that the Ile requirement estimate is lower than the current NRC requirement estimate, whereas the Leu and His requirements correspond to those proposed by the NRC.     

Determination of standardized ileal crude protein and amino acid digestibilities in protein supplements for piglets

The objective of the study was to determine standardized ileal digestibilities (SID) of crude protein (CP) and amino acids (AA) in six ingredients commonly used in weanling pigs diets. The ingredients consisted of extruded soybeans (SBe), high-protein soybean meal (SBMhp), soy protein concentrate (SPC), hydrolyzed wheat gluten (WGh), conventional fish meal 1 (FM1) and extracted fish meal 2 (FM2e). Each assay feed ingredient was added to a purified cornstarch-based basal diet supplemented with casein and crystalline AA, and SID of CP and AA of assay ingredients were estimated using the difference method. A total of 12 3-week-old barrows were surgically fitted with T-cannulas at the distal ileum. The piglets were allocated to four simultaneous 3 × 3 Latin-square designs with three animals and three periods each, resulting in six observations per assay diet. After 3 to 5 days recovery from surgery, each assay diet was fed at a level of 30 g/kg body weight. Each experimental period consisted of 5 days for adaptation to the assay diets and 2 days for ileal digesta collection. The SID of CP, Lys, Met, Thr and Trp were 73%, 78%, 76%, 66% and 71% in SBe; 80%, 84%, 87%, 75% and 81% in SBMhp; 86%, 89%, 89%, 78% and 83% in SPC; 87%, 60%, 88%, 76% and 79% in WGh; 87%, 92%, 94%, 86% and 86% in FM1; and 79%, 86%, 89%, 80% and 74% in FM2e, respectively. The greatest SID of indispensable AA were observed for FM1 and SPC (SID 85% for most indispensable AA), followed by WGh, FM2e and SBMhp (SID 80% for most indispensable AA) and the smallest SID were obtained for SBe (SID < 80% for most indispensable AA). The SID of CP and indispensable AA in both types of fish meal, SBMhp and WGh were similar to SPC (P = 0.063 to 0.855), except for Arg (P = 0.010) and Lys (P = 0.001) in WGh, and Phe (P = 0.044) and Trp (P = 0.037) in FM2e. The SID of CP and indispensable AA were smaller in SBe compared with SPC (P < 0.001 to P = 0.017), except for Lys (P = 0.136). The SID of CP and indispensable AA were consistently smaller in FM2e compared with FM1 with significant differences for CP (P = 0.035), Phe (P = 0.028) and Trp (P = 0.008). Digestibility values measured in the present study can be used to formulate diets for piglets based on standardized ileal digestible contents of CP and AA.     

Estimation of the leucine and histidine requirements for piglets fed a low-protein diet

Reduction of the CP content in the diets of piglets requires supplementation with crystalline essential amino acids (AA). Data on the leucine (Leu) and histidine (His) requirements of young pigs fed low-CP diets are limited and have primarily been obtained from nonlinear models. However, these models do not consider the possible decline in appetite and growth that can occur when pigs are fed excessive amounts of AA such as Leu. Therefore, two dose-response studies were conducted to estimate the standardised ileal digestible (SID) Leu: lysine (Lys) and His: Lys required to optimise the growth performance of young pigs. In both studies, the average daily gain (ADG), average daily feed intake (ADFI) and gain-to-feed ratio (G: F) were determined during a 6-week period. To ensure that the diets had sub-limiting Lys levels, a preliminary Lys dose-response study was conducted. In the Leu study, 60 35-day-old piglets of both sexes were randomly assigned to one of five treatments and fed a low-CP diet (15%) with SID Leu: Lys levels of 83%, 94%, 104%, 115% or 125%. The His study used 120 31-day-old piglets of both sexes, which were allotted to one of five treatments and fed a low-CP diet (14%) with SID His: Lys levels of 22%, 26%, 30%, 34% or 38%. Linear broken-line, curvilinear-plateau and quadratic-function models were used for estimations of SID Leu: Lys and SID His: Lys. The minimum SID Leu: Lys level needed to maximise ADG, ADFI and G: F was, on average, 101% based on the linear broken-line and curvilinear-plateau models. Using the quadratic-function model, the minimum SID Leu: Lys level needed to maximise ADG, ADFI and G: F was 108%. Data obtained from the quadratic-function analysis further showed that a ±10% deviation from the identified Leu requirement was accompanied by a small decline in the ADG (−3%). The minimum SID His: Lys level needed to maximise ADG, ADFI and G: F was 27% and 28% using the linear broken-line and curvilinear-plateau models, respectively, and 33% using the quadratic-function model. The preferred model to estimate the His requirement was the curvilinear-plateau model. However, a 10% reduction in the SID His: Lys level was associated with an 11% reduction in the ADG. In conclusion, the SID Leu: Lys level needed to maximise growth was 108% when using the quadratic-function model as the best-fitting model. The minimum SID His: Lys level required to optimise growth was 28% when using the curvilinear-plateau model as the best-fitting model.     

Evaluating the standardized ileal digestible lysine requirement of 7- to 15-kg weanling pigs fed corn-soybean meal-based diets

Continued genetic improvement necessitates the verification of nutrient requirements for newly developed pig genotypes. Therefore, the objective of this research was to determine the standardized ileal digestible (SID) lysine (Lys) requirement of 7- to 15-kg weanling pigs (TN70 × TN Tempo; Topigs Norsvin) fed a corn-soybean meal-based diet. A total of 144 piglets with an initial BW of 6.51 ± 0.56 kg (mean ± SD) were assigned to one of six diets using a randomized complete block design based on BW to give eight replicate pens with three pigs per pen. The six diets contained 1.00, 1.16, 1.32, 1.48, 1.64, and 1.80% SID Lys, achieved by adding crystalline l-Lys·HCl at the expense of cornstarch. Other indispensable amino acids were provided to meet the requirements. Piglets had free access to diets and water for 21 days. Individual BW of pigs and feed disappearance were recorded weekly and blood samples were collected on day 1, 14, and 21. Average daily gain (ADG) and average daily feed intake were not affected by dietary SID Lys content during the first 7 days. However, the addition of dietary SID Lys quadratically increased (P < 0.05) gain:feed (G:F) during the first 7 days of the experiment. A quadratic increase (P < 0.05) was found in both ADG and G:F when SID Lys content increased in the diets from day 14 to 21. During the overall experimental period, increasing dietary Lys content quadratically increased (P < 0.05) ADG and G:F, whereas plasma urea nitrogen quadratically decreased (P < 0.05) as SID Lys content increased. The SID Lys requirements were estimated for linear and quadratic broken-line models. In conclusion, the SID Lys requirement for optimal growth performance of 7- to 15-kg weanling pigs fed corn-soybean meal-based diets based on linear and quadratic broken-line models were 1.27% (95% confidence interval (CI): [1.01, 1.53]) and 1.30% (95% CI: [0.94, 1.66]) for ADG and 1.27% (95% CI: [1.14, 1.40]) and 1.43% (95% CI: [1.11, 1.75]) for G:F, respectively, thus giving an overall average value of 1.32%.     

Requirement of standardized ileal digestible valine to lysine ratio for 8- to 14-kg pigs

The objective was to define the Val requirement for weaned piglets in the context of reducing the dietary protein content. A dose–response experiment was conducted to estimate the standardized ileal digestible (SID) Val to Lys ratio required to support the optimum growth of post-weaned piglets. In this study, 96 pigs weighing 8 kg were allotted to one of six dietary treatments (16 pigs for each dietary treatment) and were housed individually. Diets were formulated to provide 0.58, 0.62, 0.66, 0.70, 0.74 and 0.78 SID Val : Lys by adding graded levels of crystallinel-Val to the 0.58 SID Val : Lys diet. Lysine was sub-limiting and supplied 90% of the recommendation (10.95 g SID Lys/kg equal to 11.8 g/kg total Lys). Average daily feed intake (ADFI), average daily gain (ADG) and gain to feed ratio (G : F) were determined during a 14-day period ofad libitum feeding. Blood and urine samples were taken at the end of each week (day 7 and 14 of the experiment) 3 h after feeding the experimental diets. The maximum ADFI and ADG were obtained in pigs fed the 0.78 SID Val : Lys diet; it was not different from the results of pigs fed 0.70 SID Val : Lys diet. The highest G : F was obtained in pigs fed 0.70 SID Val : Lys. The plasma concentration of Val increased linearly (P<0.001) as the dietary SID Val : Lys increased. The increasing dietary Val : Lys also resulted in a linear increase in Cys (P<0.001) and a quadratic increase in Arg (P=0.003), Lys (P=0.05) and Phe (P=0.009). The plasma Gly showed a quadratic decrease (P=0.05) as the dietary Val : Lys increased. Neither plasma nor urinary urea to creatinine ratio was affected by treatment. The minimum SID Val : Lys required to maximize ADFI, ADG and G : F was estimated at 0.67 SID Val : Lys by a broken-line model, and at 0.71 SID Val : Lys by a curvilinear plateau model. The Val deficiency caused a reduction in ADFI, and Val supplementation above the requirement did not impair animal performance. In conclusion, 0.70 SID Val : Lys is suggested as the Val requirement for 8 to 14 kg individually housed pigs.     

Effect of partial dehulling of two- and six-row barley varieties on precaecal digestibility of amino acids in pigs

Five barrows (German Landrace; initial BW 58 kg, final BW 80 kg) fitted with an ileo-rectal anastomosis were used to determine the effect of partial dehulling and addition of barley hulls of two- and six-row barley varieties on the precaecal digestibility (pD) of CP and amino acids. The following diets were provided according to a standardized diet formulation and tested in seven consecutive periods (repeated group-period design): two-row barley (TRB) + casein (C), dehulled TRB + C, TRB + C + 10% hulls, six-row barley (SRB) + C, dehulled SRB + C, SRB + C + 1% hulls, and wheat starch + C. The diets were supplied at daily rates of 79-86 g DMI x kg BW(-0.75) in barley containing diets and at 49 g DMI x kg BW(-0.75) in the casein diet. The digestibility of amino acids in barley varieties was determined by the difference method (casein as basal diet) using quantitative digesta collection. In both varieties of barley the pD of CP and amino acids did not differ. The pD of CP was unchanged in regard to the treatments in both barley varieties. Due to dehulling in TRB the pD was improved significantly for most indispensable amino acids and in SRB for Met and Cys. Addition of 10% hulls to TRB led to equivalent pD of Arg, His, Leu, Tyr, and Trp compared to TRB, but the pD of Lys, Phe, Thr and Val was significantly decreased below the levels of TRB. Addition of even 1% hulls to SRB impaired the pD of Lys below the level in SRB. In conclusion, addition of barley hulls to pig diets impairs amino acids absorption in the small intestine. The pD values, measured under standardized experimental conditions (without a correction using basal endogenous amino acids), are similar to the values of true digestibility published by NRC (1998).     

In vitro prediction of standardised ileal crude protein and amino acid digestibilities in grain legumes for growing pigs

The study was conducted to validate in vitro prediction of standardised ileal digestibilities (SID) of crude protein (CP) and amino acids (AA) in grain legumes for growing pigs using six different cultivars of faba beans (Vicia faba), six different cultivars of field peas (Pisum sativum), and five different cultivars of lupins (Lupinus spp.). The SID for CP and AA were predicted from in vitro analysis by means of a two-step enzymatic method using pepsin and pancreatin incubations. In vitro predicted SID values of CP and AA were generally higher than the corresponding SID values measured in vivo. There were strong linear relationships (r2 = 0.73 for Lys to r2 = 0.91 for Cys and Trp) between in vivo and in vitro predicted SID values in the assay feed ingredients if grain legume species (i.e. faba beans, field peas and lupins) was included as a covariate in multiple linear regression analysis. However, to rapidly and accurately predict SID of CP and AA in individual batches of various feed ingredients, further studies are warranted.     

Digestibility of amino acids in organically cultivated white-flowering faba bean and cake from cold-pressed rapeseed, linseed and hemp seed in growing pigs

The study aimed at determining the ileal apparent (IAD) and standardised ileal (SID) digestibility of crude protein (CP) and amino acids (AA) in organically cultivated white-flowering faba beans (Vicia faba), and cakes from hemp seed (Cannabis sativa), linseed (Linum usitatissimum) and rapeseed (Brassica napus). The experiment was designed as a four period cross-over trial with six castrated male Yorkshire pigs fitted with post valve T-caecum (PVTC) cannulas. The IAD and SID of CP for the feed ingredients ranged from 79.2-85.9% and were affected by dietary treatment, with significantly lower values in rapeseed cake. The IAD and SID of most AA in the feed ingredients were also significantly affected by dietary treatment, but without any consistent trend. However, the overall digestibilities were in general comparable with conventional protein feed ingredients. Thus, these alternative protein feed ingredients have the potential to be used to a greater extent when formulating organic pig diets.     

Evaluation of in situ valine production by Bacillus subtilis in young pigs

Mutants of Bacillus subtilis can be developed to overproduce Val in vitro. It was hypothesized that addition of Bacillus subtilis mutants to pig diets can be a strategy to supply the animal with Val. The objective was to investigate the effect of Bacillus subtilis mutants on growth performance and blood amino acid (AA) concentrations when fed to piglets. Experiment 1 included 18 pigs (15.0±1.1 kg) fed one of three diets containing either 0.63 or 0.69 standardized ileal digestible (SID) Val: Lys, or 0.63 SID Val: Lys supplemented with a Bacillus subtilis mutant (mutant 1). Blood samples were obtained 0.5 h before feeding and at 1, 2, 3, 4, 5 and 6 h after feeding and analyzed for AAs. In Experiment 2, 80 piglets (9.1±1.1 kg) were fed one of four diets containing 0.63 or 0.67 SID Val: Lys, or 0.63 SID Val: Lys supplemented with another Bacillus subtilis mutant (mutant 2) or its parent wild type. Average daily feed intake, daily weight gain and feed conversion ratio were measured on days 7, 14 and 21. On day 17, blood samples were taken and analyzed for AAs. On days 24 to 26, six pigs from each dietary treatment were fitted with a permanent jugular vein catheter, and blood samples were taken for AA analysis 0.5 h before feeding and at 1, 2, 3, 4, 5 and 6 h after feeding. In experiment 1, Bacillus subtilis mutant 1 tended (P<0.10) to increase the plasma levels of Val at 2 and 3 h post-feeding, but this was not confirmed in Experiment 2. In Experiment 2, Bacillus subtilis mutant 2 and the wild type did not result in a growth performance different from the negative and positive controls. In conclusion, results obtained with the mutant strains of Bacillus subtilis were not better than results obtained with the wild-type strain, and for both strains, the results were not different than the negative control.     

Ileal digestibility of amino acids of cassava, sweet potato, cocoyam and erythrina foliages fed to growing pigs

Ileal digestibility in growing pigs fed starch-based diets with inclusion of four tropical leaves in a meal form was studied in a 5 × 5 Latin square design. Five diets were formulated with only casein as protein source in the basal diet (CAS), and casein plus dry cassava (CA) leaves, casein plus dry sweet potato (SP) leaves, casein plus dry cocoyam (CO) leaves and casein plus erythrina (ER) leaves in the other four diets. All diets contained the same amount of CP (14%), either provided by only CAS or a combination of casein and 250 g of leaf meal per kg of diet in the other diets. Leaves were separated manually from stems, and only the leaf part was used. A protein-free diet was fed during a sixth period in order to estimate the endogenous protein losses and calculate the CP- and amino-acid (AA)-standardized ileal digestibility (SID) values. The values for the foliages were calculated according to the difference method, assuming no interaction between the foliage and the casein. The ileal tract apparent digestibility of CP, organic matter and energy was higher in diet CAS than in the other diets (P < 0.05). The SID of CP and AA was close to 0.950 for casein, whereas the SID of AA was markedly lower in the foliages; the SID of indispensable and dispensable AA was highest in CO (0.500 and 0.352) and lowest in ER (0.170 and 0.195); intermediate values were obtained for SPs (0.367 and 0.349) and CA (0.232 and 0.242) leaves. Accordingly, the SID of lysine was highest (0.538) for CO leaves and lowest (0.126) in ER leaves; intermediate values were measured for CA and SP leaves. These low SID values in foliage meals must be related to the high levels of dietary fibre and the presence of secondary metabolites (tannins). These results suggest that it is only possible to replace a fraction of the conventional protein sources such as soyabean meal by tropical foliages in growing pig diets with a preference for CO leaves.     

Dose–response evaluation of the standardized ileal digestible tryptophan : lysine ratio to maximize growth performance of growing-finishing gilts under commercial conditions

Environmental regulations as well as economic incentives have resulted in greater use of synthetic amino acids in swine diets. Tryptophan is typically the second limiting amino acid in corn-soybean meal-based diets. However, using corn-based co-products emphasizes the need to evaluate the pig’s response to increasing Trp concentrations. Therefore, the objective of these studies was to evaluate the dose–response to increasing standardized ileal digestible (SID) Trp : Lys on growth performance of growing-finishing gilts housed under large-scale commercial conditions. Dietary treatments consisted of SID Trp : Lys of 14.5%, 16.5%, 18.0%, 19.5%, 21.0%, 22.5% and 24.5%. The study was conducted in four experiments of 21 days of duration each, and used corn-soybean meal-based diets with 30% distillers dried grains with solubles. A total of 1166, 1099, 1132 and 975 gilts (PIC 337×1050, initially 29.9±2.0 kg, 55.5±4.8 kg, 71.2±3.4 kg and 106.2±3.1 kg BW, mean±SD) were used. Within each experiment, pens of gilts were blocked by BW and assigned to one of the seven dietary treatments and six pens per treatment with 20 to 28 gilts/pen. First, generalized linear mixed models were fit to data from each experiment to characterize performance. Next, data were modeled across experiments and fit competing dose–response linear and non-linear models and estimate SID Trp : Lys break points or maximums for performance. Competing models included broken-line linear (BLL), broken-line quadratic and quadratic polynomial (QP). For average daily gain (ADG), increasing the SID Trp : Lys increased growth rate in a quadratic manner (P<0.02) in all experiments except for Exp 2, for which the increase was linear (P<0.001). Increasing SID Trp : Lys increased (P<0.05) feed efficiency (G : F) quadratically in Exp 1, 3 and 4. For, ADG the QP was the best fitting dose–response model and the estimated maximum mean ADG was obtained at a 23.5% (95% confidence interval (CI): [22.7, 24.3%]) SID Trp : Lys. For maximum G : F, the BLL dose–response models had the best fit and estimated the SID Trp : Lys minimum to maximize G : F at 16.9 (95% CI: [16.0, 17.8%]). Thus, the estimated SID Trp : Lys for 30 to 125 kg gilts ranged from a minimum of 16.9% for maximum G : F to 23.5% for maximum ADG.     

Meta-analysis of the response of growing pigs to the isoleucine concentration in the diet

The efficiency of nitrogen utilization will be highest when the amino acid (AA) supply approaches the requirement of the animal. With the availability of different crystalline AA, it is theoretically possible to formulate low-protein diets for growing pigs in which seven AA are co-limiting for performance. In such a diet, the concentration of Lys, Met, Met + Cys, Thr, Trp and Val and a seventh AA would exactly match the requirement. To determine the extent to which low-protein diets can be used, it is important to have reliable information about the requirements for these AA. Isoleucine is often considered the seventh-limiting AA in diets for growing pigs; however, information about the Ile requirement is limited and sometimes conflicting. The purpose of this study was to carry out a meta-analysis of the available literature information to determine the Ile requirement in growing pigs. A total of 46 Ile dose–response experiments were identified that used at least four concentrations of Ile in the diet. Because of differences in experimental design, both the Ile concentration and the response criteria were standardized. In 13 dose–response experiments, there was no indication of a response to an increasing Ile concentration. For the other 33 experiments, a response to the increasing Ile concentration was observed and the Ile requirement estimates ranged from 53% to 114% of that of the National Research Council (1998). An Ile concentration below the requirement resulted in important reductions in both feed intake and growth. A 10% reduction in the Ile concentration (below the requirement) resulted in a 15% reduction in feed intake and a 21% reduction in daily gain. The use of blood products in the diet was the main factor determining whether a response to the Ile concentration was observed or not. Blood meal and blood cells are protein sources with a very low Ile concentration, but with high or very high concentrations of Leu, Val, Phe and His. Some of these AA compete with Ile for catabolic pathways or transport across the blood–brain barrier, thereby potentially increasing the requirement for Ile. In diets without blood products, the Ile requirement appears to be lower than the currently recommended requirement. On the basis of the outcome of this study, we recommend a Ile : Lys requirement ratio of at least 50% on a standardized ileal digestible basis.     

Estimation of the tryptophan requirement in piglets by meta-analysis

There is no consensus concerning the Trp requirement for piglets expressed relative to Lys on a standardized ileal digestible basis (SID Trp : Lys). A meta-analysis was performed to estimate the SID Trp : Lys ratio that maximizes performance of weaned piglets between 7 and 25 kg of BW. A database comprising 130 experiments on the Trp requirement in piglets was established. The nutritional values of the diets were calculated from the composition of feed ingredients. Among all experiments, 37 experiments were selected to be used in the meta-analysis because they were designed to express the Trp requirement relative to Lys (e.g. Lys was the second-limiting amino acid in the diet) while testing at least three levels of Trp. The linear-plateau (LP), curvilinear-plateau (CLP) and asymptotic (ASY) models were tested to estimate the SID Trp : Lys requirement using average daily gain (ADG), average daily feed intake (ADFI) and gain-to-feed ratio (G : F) as response criteria. A multiplicative trial effect was included in the models on the plateau value, assuming that the experimental conditions affected only this parameter and not the requirement or the shape of the response to Trp. Model choice appeared to have an important impact on the estimated requirement. Using ADG and ADFI as response criteria, the SID Trp : Lys requirement was estimated at 17% with the LP model, at 22% with the CLP model and at 26% with the ASY model. Requirement estimates were slightly lower when G : F was used as response criterion. The Trp requirement was not affected by the composition of the diet (corn v. a mixture of cereals). The CLP model appeared to be the best-adapted model to describe the response curve of a population. This model predicted that increasing the SID Trp : Lys ratio from 17% to 22% resulted in an increase in ADG by 8%.     

Evaluation through literature data on standardized ileal digestibility and basal ileal endogenous loss of amino acids associated with barley in pigs

This meta-analysis aimed to estimate the standardized ileal digestibility (SID) and the basal ileal endogenous amino acid losses (IAA_end) in barley for growing pigs. In total, 38 different barley treatments published in 26 peer-reviewed papers were used for the meta-analysis containing information on dietary composition including amino acid (AA) contents of the assay diets, and (or) barley samples, as well as apparent ileal digestibility (AID) of AA in barley. The SID of AA was determined by either correcting AID of AA for their IAA_end or by regression analysis between the apparent ileal digestible and total dietary AA contents. The SID values obtained by correcting the AID values for their IAA_end amounted to 70%, 77%, 74% and 63% for Lys, Met, Thr and Trp, whereas those based on regression analysis method were 82%, 82%, 69% and 55%, respectively. Estimates of basal ileal endogenous loss of CP in ileal digesta varied considerably and averaged 11.84 g/kg dry matter intake (DMI), whereas IAA_end for indispensable AA ranged from 0.05 g/kg DMI for Trp to 1.90 g/kg DMI for Leu. In most cases, these estimates were considerably higher than previously reported values for IAA_end. The results of the present regression analysis indicate for most AA higher SID values compared with SID of most AA that were obtained by correcting AID values for IAA_end. In view of the observed high variations in IAA_end and the low CP content of the barley samples, estimating SID of AA based on literature data by means of the regression method may improve accuracy of SID coefficients for barley. In contrast, transformation of AID values into their corresponding SID values by using a constant correction factor for IAA_end adds an additional source of error, thereby reducing the precision in estimating SID of AA.     

Standardized ileal digestibility of amino acids in eight genotypes of barley fed to growing pigs

To determine chemical composition, physical characteristics and standardized ileal digestibility (SID) of CP and amino acids (AA) in eight current hulled barley genotypes, an experiment with growing pigs has been conducted. These genotypes included Yool, Campanile, Lomerit, Travira, Anisette, Canberra, Metaxa and Fridericus. Growing barrows with an average initial BW of 30±2 kg were surgically fitted with simple T-cannulas at the distal ileum, and allotted to an 8×9 Youden square design with eight periods of 6 days each and nine pigs. Barley was the sole dietary source of CP and AA. On average, the eight genotypes contained on as-fed basis 10.7% CP, 15.2% total non-starch polysaccharides (NSP), 17.1% NDF and 4.1% β-glucan, and had a mean test weight (TW) of 72.2 kg/hl. The SID of CP in the barley genotypes varied from 69% to 74%, and was greater (P<0.01) for genotypes Travira, Anisette and Metaxa compared to Yool and Campanile. Standardized ileal digestibility of Lys, Met and Trp (P<0.05) but not of Thr differed between genotypes. Moreover, barley genotypes differed in their standardized ileal digestible content (cSID) of CP and AA. Furthermore, SID and cSID of CP and most AA linearly decreased (P<0.05) with increasing NDF and total sugar content. Standardized ileal digestibility of CP and some AA and cSID of CP and most AA decreased linearly with increasing TW (P<0.05). Additionally, SID and cSID of CP and AA of most barley genotypes were lower when compared to tabulated values. In conclusion, a comprehensive database on chemical composition and SID of CP and AA in eight current barley genotypes has been made available. However, as present SID values are lower compared to feed tables, adjustments are required to minimize the risk of overestimating the actual protein value of barley for pigs.     

Amino acid utilization and body composition of growing pigs fed processed soybean meal or rapeseed meal with or without amino acid supplementation

Feed ingredients used in swine diets are often processed to improve nutritional value. However, (over-)processing may result in chemical reactions with amino acids (AAs) that decrease their ileal digestibility. This study aimed to determine effects of (over-)processing of soybean meal (SBM) and rapeseed meal (RSM) on post-absorptive utilization of ileal digestible AAs for retention and on body AA composition of growing pigs. Soybean meal and RSM were processed by secondary toasting in the presence of lignosulfonate to obtain processed soybean meal (pSBM) and processed rapeseed meal (pRSM). Four diets contained SBM, pSBM, RSM or pRSM as sole protein source. Two additional diets contained pSBM or pRSM and were supplemented with crystalline AA to similar standardized ileal digestible (SID) AA level as the SBM or RSM diet. These diets were used to verify that processing affected AA retention by affecting ileal AA digestibility rather than post-absorptive AA utilization. The SID AA levels of the protein sources were determined in a previous study. In total, 59 pigs were used (initial BW of 15.6±0.7 kg) of which five were used to determine initial body composition at the start of the experiment. In total, 54 pigs were fed one of six experimental diets and were slaughtered at a BW of 40 kg. The organ fraction (i.e. empty organs plus blood) and carcass were analyzed separately for N and AA content. Post-absorptive AA utilization was calculated from AA retention and SID AA intake. An interaction between diet type, comprising effects of processing and supplementing crystalline AA, and protein source was observed for CP content in the organ fraction, carcass and empty body and for nutrient retention. Processing reduced CP content and nutrient retention more for SBM than for RSM. Moreover, processing reduced (P<0.001) the lysine content in the organ fraction for both protein sources. Supplementing crystalline AA ameliorated the effect of processing on these variables. Thus, the data indicated that processing affected retention by reducing digestibility. Correcting AA retention for SID AA intake was, therefore, expected to result in similar post-absorptive AA utilization which was observed for the RSM diets. However, post-absorptive AA utilization was lower for the pSBM diet than for the SBM diet which might be related to an imbalanced post-absorptive AA supply. In conclusion, processing negatively affected nutrient retention for both protein sources and post-absorptive utilization of SID AA for retention for SBM. Effects of processing were compensated by supplementing crystalline AA.     

Lysine requirements of finishing boars and gilts: A meta-analysis

The expected increase in boar (pig entire male) production while societal concerns for castration increase requires good estimations of their nutrient requirements. In this work, a meta-analytical approach was used to overcome the inconsistent results between studies that compared lysine requirements of boars and gilts. For this meta-analysis, data from 14 different studies analysing the effect of increasing dietary lysine on growth performance of finishing pigs, 70–100 kg average body weight, were extracted from 11 publications. Those studies represented 128 different treatments (53 for boars and 75 for gilts). Diets were reformulated based on NRC (2012) ingredient values to calculate standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and daily SID Lys intake using average daily feed intake (ADFI). As expected, no evidence for differences in ADFI (P = 0.303) was observed between boars and gilts. However, boars grew faster (P < 0.001) and had higher gain to feed (G:F; P < 0.001). The divergent effect of SID Lys:NE on average daily gain (ADG) and G:F was analysed in a quadratic polynomial model showing different parameters for each sex (P < 0.001). Although performance between sexes was similar at low SID Lys:NE, differences were greater at higher SID Lys:NE. Furthermore, broken-line linear, broken-line quadratic (BLQ) and quadratic polynomial (QP) models were fitted to each sex to determine SID Lys:NE and SID Lys daily intake requirements to maximize ADG and G:F. Overall, QP models showed the best fit, and reported that to reach maximum ADG 0.88 (95% CI:[0.82–0.94]) or 1.01 (95% CI:[0.91–1.11]) g SID Lys/MJ, NE was required for gilts and boars, respectively. However, boar ADG was best fitted by BLQ using SID Lys daily intake as independent variable, with the requirement for maximum ADG at 24.2 (95% CI:[21.3–27.2]) g SID Lys/day. The three models reported wide confidence intervals for the requirements at maximum performance, and consequently those were overlapped when comparing boars and gilts. Maximum boars’ productive performance when dietary lysine was not limiting was 116% of gilts, and at those levels the amount of SID Lys intake required per kg gain was similar between both sexes. Thus, because ADFI and Lys efficiency of gain was similar, the requirement differences were driven by the increased growth rate and gain to feed ratio between boars and gilts. In conclusion, the present study confirmed a greater productive response of boars compared to gilts when increasing dietary lysine.     

Reducing the CP content in broiler feeds: impact on animal performance,meat quality and nitrogen utilization

Reducing the dietary CP content is an efficient way to limit nitrogen excretion in broilers but, as reported in the literature, it often reduces performance, probably because of an inadequate provision in amino acids (AA). The aim of this study was to investigate the effect of decreasing the CP content in the diet on animal performance, meat quality and nitrogen utilization in growing-finishing broilers using an optimized dietary AA profile based on the ideal protein concept. Two experiments (1 and 2) were performed using 1-day-old PM3 Ross male broilers (1520 and 912 for experiments 1 and 2, respectively) using the minimum AA:Lys ratios proposed by Mack et al. with modifications for Thr and Arg. The digestible Thr (dThr): dLys ratio was increased from 63% to 68% and the dArg:dLys ratio was decreased from 112% to 108%. In experiment 1, the reduction of dietary CP from 19% to 15% (five treatments) did not alter feed intake or BW, but the feed conversion ratio was increased for the 16% and 15% CP diets (+2.4% and +3.6%, respectively), while in experiment 2 (three treatments: 19%, 17.5% and 16% CP) there was no effect of dietary CP on performance. In both experiments, dietary CP content did not affect breast meat yield. However, abdominal fat content (expressed as a percentage of BW) was increased by the decrease in CP content (up to +0.5 and +0.2 percentage point, in experiments 1 and 2, respectively). In experiment 2, meat quality traits responded to dietary CP content with a higher ultimate pH and lower lightness and drip loss values for the low CP diets. Nitrogen retention efficiency increased when reducing CP content in both experiments (+3.5 points/CP percentage point). The main consequence of this higher efficiency was a decrease in nitrogen excretion (−2.5 g N/kg BW gain) and volatilization (expressed as a percentage of excretion: −5 points/CP percentage point). In conclusion, this study demonstrates that with an adapted AA profile, it is possible to reduce dietary CP content to at least 17% in growing-finishing male broilers, without altering animal performance and meat quality. Such a feeding strategy could therefore help improving the sustainability of broiler production as it is an efficient way to reduce environmental burden associated with nitrogen excretion.     

Effect of increasing the dietary tryptophan to lysine ratio on plasma levels of tryptophan,kynurenine and urea and on production traits in weaner pigs experimentally infected with an enterotoxigenic strain of Escherichia coli‡

This experiment examined if immune system stimulation of weaner pigs, initiated by inoculation an enterotoxigenic strain of Escherichia coli (ETEC), increased the requirement for dietary tryptophan (Trp), modulated the inflammatory response, altered plasma levels of Trp and its metabolite kynurenine (Kyn) and effected post-weaning diarrhoea. Individually housed pigs (n = 72) weaned at 21 d of age were allocated to one of six treatments (n = 12) according to a two by three factorial arrangement of (1) with or without ETEC infection and (2) three dietary ratios of standardised ileal digestible (SID) Trp to lysine (Lys) (SID Trp:Lys) of 0.16, 0.20 or 0.24, in a completely randomised block design. Pigs had ad libitum access to diets (per kg 14.13 MJ ME, 12.4 g SID Lys, 195 g crude protein) for 3 weeks after weaning. Pigs were infected with ETEC (O149:K98:K88) at 72, 96 and 120 h after weaning and then bled on day 3, 11 and 19. An increased dietary Trp:Lys ratio increased plasma Trp and Kyn (p < 0.001) without effect of infection. On day 3, pigs fed 0.24 SID Trp:Lys had lower levels of plasma urea than at 0.20 Trp:Lys (p = 0.047) and on day 11, plasma urea was lower at 0.20 than at 0.16 SID Trp:Lys (p = 0.007). Infection increased (p = 0.039) the diarrhoea index and deteriorated faecal consistency from day 4–10 (p < 0.05). Treatments did not affect haptoglobin and acid soluble glycoprotein levels or daily gain and feed intake. However, 0.24 SID Trp:Lys improved (p = 0.021) feed efficiency without an effect of infection. In conclusion, in the absence of dietary antibiotic growth promotants, increasing the dietary SID Trp:Lys ratio to 0.24 improved feed conversion ratio after weaning and increased plasma levels of Trp and Kyn regardless of infection with E. coli.     

Effects of dietary crude protein level on odour from pig manure

The objective of this study was to determine the effects of dietary crude protein (CP) level on odour emission, odour intensity, hedonic tone, and ammonia emission from pig manure and on manure composition (pH, total nitrogen, ammonium, volatile fatty acids, indolic, phenolic and sulphur-containing compounds). An experiment was conducted with growing pigs (n = 18) in a randomised complete-block design with three treatments in six blocks. Treatment groups were 12%, 15% and 18% CP diets. Barley was exchanged for soya-bean meal. Crystalline amino acids (AA) were included in the 12% CP diet up to the level of pigs' requirement; the same amount of AA was added to the 15% and 18% CP diets. Pigs with an initial body weight (BW) of 36.5 ± 3.4 kg (mean ± s.d.) were individually penned in partly slatted floor pens and offered a daily feed allowance of 2.8 × maintenance requirement for net energy (NE: 293 kJ/kg BW^0.75). Feed was mixed with water, 1/2.5 (w/w). Faeces and urine of each pig were accumulated together in a separate manure pit under the slatted floor. After an adaptation period of 2 weeks, the manure pits were cleaned and manure was collected. In the 5th week of the collection period, air samples for odour and ammonia analyses, and manure samples were collected directly from each manure pit. Air samples were analysed for odour concentration and for hedonic value and intensity above odour detection threshold. Manure samples were analysed for volatile fatty acids, and indolic, phenolic and sulphurous compounds, ammonium and total nitrogen concentrations. Reducing dietary CP from 18% to 12% lowered odour emission ( P < 0.05) and ammonia emission ( P = 0.01) from pig manure by 80% and 53%, respectively. Reduced dietary CP decreased total nitrogen, methyl sulphide, carbon disulphide, ethanethiol, phenol, 4-ethyl phenol, indole and 3-methyl indole concentrations in the manure ( P < 0.05). Volatile fatty acids and cresols concentrations in the manure of pigs fed different dietary CP levels were similar. A reduction of dietary CP and at the same time providing essential AA is an option to reduce odour emission as well as ammonia emission from pig manure.