The effectiveness of an Escherichia coli phytase in improving phosphorus and calcium bioavailabilities in poultry and young pigs.

The effectiveness of an Escherichia coli phytase in comparison with a commercially available Aspergillus phytase in improving the bioavailability of phosphorus in broilers, layers and young pigs was studied in three separate experiments. Three basal diets, marginally deficient in dietary P mainly provided as phytate, were formulated. Both phytases were added to the diets at the rate of 500 U/kg diet. The phytases significantly (P < or = 0.05) improved the availability of phytate P to broilers, layers and young pigs. Aspergillus and E. coli phytases enhanced the pre-caecal digestibility of P by 11 and 29% for broilers and 18 and 25% for layers, respectively. Total tract digestibility of P (P balance) was also enhanced but with smaller magnitude. In pigs, total tract digestibility of P was improved by 33 and 34% by Aspergillus and E. coli phytases, respectively. Under the conditions of this study, it was observed that E. coli consistently, though with small magnitude in layers and pigs, enhanced the availability of phytate P at the same range or slightly better than Aspergillus phytase. It was only in pigs that the availability of Ca was significantly (P < or = 0.05) improved by addition of both phytases. It can be concluded that E. coli phytase is highly effective in improving the bioavailability of phytate P to broilers, layers and young pigs. This seems to be based on the high proteolytic stability of the enzyme in the digestive tract, as shown recently.     

Degradation of phytate in the gut of pigs--pathway of gastro-intestinal inositol phosphate hydrolysis and enzymes involved.

The present study gives an overview on the whole mechanism of phytate degradation in the gut and the enzymes involved. Based on the similarity of the human and pigs gut, the study was carried out in pigs as model for humans. To differentiate between intrinsic feed phytases and endogenous phytases hydrolysing phytate in the gut, two diets, one high (control diet) and the other one very low in intrinsic feed phytases (phytase inactivated diet) were applied. In the chyme of stomach, small intestine and colon inositol phosphate isomers and activities of phytases and alkaline phosphatases were determined. In parallel total tract phytate degradation and apparent phosphorus digestibility were assessed. In the stomach chyme of pigs fed the control diet, comparable high phytase activity and strong phytate degradation were observed. The predominant phytate hydrolysis products were inositol phosphates, typically formed by plant phytases. For the phytase inactivated diet, comparable very low phytase activity and almost no phytate degradation in the stomach were determined. In the small intestine and colon, high activity of alkaline phosphatases and low activity of phytases were observed, irrespective of the diet fed. In the colon, stronger phytate degradation for the phytase inactivated diet than for the control diet was detected. Phytate degradation throughout the whole gut was nearly complete and very similar for both diets while the apparent availability of total phosphorus was significantly higher for the pigs fed the control diet than the phytase inactivated diet. The pathway of inositol phosphate hydrolysis in the gut has been elucidated.     

植酸酶的研究进展

植酸酶是能降解饲料中植酸及其盐的酶。它能提高磷利用率,解除植酸对一些矿物元素如钙、锌、铁、铜等的抗营养效应,不仅对动物具有良好的增重效果,同时可降低动物排泄磷量,有利于环境保护。植酸酶作为饲料添加剂其作用效果受到饲料中钙、磷水平和钙磷比例以及维生素Ｄ含量的影响。植酸酶的运用需要降低饲料中钙、磷水平,维生素Ｄ与植酸酶之间可能存在协同效应。对植酸酶运用的经济分析表明,使用植酸酶能代替饲料中需添加的无机磷。     

Phytate-degrading enzymes in pig nutrition

Phytate, the mixed salt of phytic acid (myo-inositol hexaphosphate), derived from plant-sourced feed ingredients is invariably present in practical diets for pigs. Typically, swine diets contain in the order of 3.0 g kg^− 1 phytate-bound phosphorus (phytate-P) but phytate concentrations are subject to variation. Importantly, phytate-P is only partially utilised by pigs because they do not generate sufficient endogenous phytase activity. Phytate-degrading enzymes, via step-wise dephosphorylation of phytate, have the capacity to liberate phytate-P, thus enhancing P absorption and reducing P excretion, which are both nutritionally and ecologically beneficial consequences. The commercial introduction of microbial phytases in 1991 has greatly magnified the interest in the roles of phytate and phytase in pig nutrition.

The capacity of microbial phytases to enhance growth performance of pigs offered diets with inadequate P levels is well documented. However, in some instances, phytase has been shown to improve performance of pigs offered P adequate diets thus phytase-induced improvements in growth performance should not be attributed entirely to increased P availability. This raises the possibility that phytase is increasing the utilisation of nutrients other than P. These so-called ‘extra-phosphoric’ effects of phytase remain controversial, particularly in relation to protein and amino acid availability. There are conflicting opinions that are reflected in the inconsistent outcomes of studies to determine the effect of phytase on ileal digestibility of amino acids and protein utilisation in pigs. In phytase amino acid digestibility assays, it seems likely the choice of chromic oxide as the dietary marker has contributed to these ambiguous results, which may be further complicated when ileal digesta samples are taken from cannulated pigs fed on a restricted, twice-daily basis. In order to resolve this critical issue, there is an urgent need to assess the impacts of selection of dietary markers, methods of ileal digesta collection and feeding regimen relative on the outcomes of phytase amino acid digestibility assays in pigs.

However, inconsistent results from phytase studies in pigs are not confined to amino acid digestibility assays. Arguably, insufficient attention has been paid to dietary substrate levels in relation to phytase inclusion from both scientific and practical standpoints. Phytate analyses are not straightforward and there is a real need to develop more accurate and rapid methods to facilitate phytate determinations. The properties of phytate vary between (and within) feed ingredients where solubility of phytate may be critical; which, in turn, is a function of gut pH in pigs. Contemporary phytases have the capacity to degrade approximately 50% of dietary phytate at the level of the ileum, which may mean higher inclusion rates are warranted. Consequently, there is scope for the development of more effective ‘second-generation’ phytate-degrading feed enzymes and their possible introduction, coupled with a better scientific understanding of relevant fundamental issues, will ensure that phytate-degrading enzymes will contribute to viable and sustainable pig production to an even greater extent in the future.     

Phytate in pig and poultry nutrition

Phosphorus (P) is primarily stored in the form of phytates in plant seeds, thus being poorly available for monogastric livestock, such as pigs and poultry. As phytate is a polyanionic molecule, it has the capacity to chelate positively charged cations, especially calcium, iron and zinc. Furthermore, it probably compromises the utilization of other dietary nutrients, including protein, starch and lipids. Reduced efficiency of utilization implies both higher levels of supplementation and increased discharge of the undigested nutrients to the environment. The enzyme phytase catalyses the stepwise hydrolysis of phytate. In respect to livestock nutrition, there are four possible sources of this enzyme available for the animals: endogenous mucosal phytase, gut microfloral phytase, plant phytase and exogenous microbial phytase. As the endogenous mucosal phytase in monogastric organisms appears incapable of hydrolysing sufficient amounts of phytate‐bound P, supplementation of exogenous microbial phytase in diets is a common method to increase mineral and nutrient absorption. Plant phytase activity varies greatly among species of plants, resulting in differing gastrointestinal phytate hydrolysis in monogastric animals. Besides the supplementation of microbial phytase, processing techniques are alternative approaches to reduce phytate contents. Thus, techniques such as germination, soaking and fermentation enable activation of naturally occurring plant phytase among others. However, further research is needed to tap the potential of these technologies. The main focus herein is to review the available literature on the role of phytate in pig and poultry nutrition, its degradation throughout the gut and opportunities to enhance the utilization of P as well as other minerals and nutrients which might be complexed by phytates.     

The effect of supplementary bacterial phytase on dietary metabolisable energy, nutrient retention and endogenous losses in precision fed broiler chickens

Thirty-two Ross 308 male broiler chickens were used in a precision feeding assay to investigate the effect of exogenous phytase (EC 3.1.3.26) on dietary apparent metabolisable energy (AME), dry matter digestibility (DMD) coefficient, nitrogen (NR), amino acid and mineral retentions. The excretion of endogenous losses measured as sialic acid (SA) was also determined. Four dietary treatments (control (C), C + 250 FTU (phytase units per kg feed), C + 500 FTU, and C + 2500 FTU) were studied with each treatment replicated eight times in randomised complete block design. Diets were formulated to be nutritionally adequate with the exception of available P content (2.3 g/kg non-phytate P). Over the 48-h collection period, the phytase fed birds retained 29.3 mg more Na and 2.3 mg more Zn (p < 0.05) than the control fed birds, with the relationship between phytase dose and Na and Zn retention being best described by a linear function (p < 0.05 and p < 0.001, for Na and Zn, respectively). Phytase supplementation did not have an effect on dietary AME, DMD and NR. However, increasing the dose of phytase led to a linear increase in dietary amino acid retention (p < 0.05). Dietary phytase decreased total sialic acid excretion in a linear fashion (p < 0.05). It can be concluded that supplementary phytase increases the retention (reduces the excretion) of dietary Zn and Na in broiler chickens. The beneficial effects of the addition of exogenous phytases to poultry diets seems to be mediated through improved dietary nutrients absorption and reduced endogenous losses.     

Phytate and phytase in fish nutrition

Phytate formed during maturation of plant seeds and grains is a common constituent of plant-derived fish feed. Phytate-bound phosphorus (P) is not available to gastric or agastric fish. A major concern about the presence of phytate in the aquafeed is its negative effect on growth performance, nutrient and energy utilization, and mineral uptake. Bound phytate-P, can be effectively converted to available-P by phytase. During the last decade, phytase has been used by aqua feed industries to enhance the growth performance, nutrient utilization and bioavailability of macro and micro minerals in fish and also to reduce the P pollution into the aquatic environment. Phytase activity is highly dependent on the pH of the fish gut. Unlike mammals, fish are either gastric or agastric, and hence, the action of dietary phytase varies from species to species. In comparison to poultry and swine production, the use of phytase in fish feed is still in an unproven stage. This review discusses effects of phytate on fish, dephytinisation processes, phytase and pathway for phytate degradation, phytase production systems, mode of phytase application, bioefficacy of phytase, effects of phytase on growth performance, nutrient utilization and aquatic environment pollution, and optimum dosage of phytase in fish diets.     

Comparative effects of three phytases on phosphorus and calcium digestibility in the growing pig

Phytase addition to swine diets has generally resulted in a marked increase in phosphorus (P) digestibility and in a reduction of faecal excretion of P. The number of phytases present in the market is growing and the origins of the microbial genes are becoming more diversified. The aim of this study was to compare the effects of 3 different phytases on P and calcium (Ca) digestibility in pigs. The control diet was based on soybean meal, maize and barley. The inclusion levels were 250 (Q1) and 500 U/kg (Q2) for an E. coli phytase (Quantum), 500 U/kg (Nat) for A. niger (Natuphos) and 750 U/kg (Ron) for P. lycii (Ronozyme P). All phytases significantly reduced faecal concentration of P. For Q2 this reduction was significantly higher than for Q1. P digestibility was improved by 13.8, 18.6, 18.3 and 17.9 percentage units by Q1, Q2, Nat and Ron respectively. The P equivalencies, considered as supplemental P digested compared to the non-supplemented diet of Q1, Q2, Nat and Ron were 0.492, 0.732, 0.678 and 0.678 g of available P/kg of feed respectively. Ca digestibility was also significantly improved by the phytases. It can be concluded that the 3 phytase preparations improved the digestibility and the apparent absorption of P and Ca in the growing pig fed a diet containing P exclusively from plant origin. The effect of including 500 U/kg of E. coli phytase on P digestibility was similar to those induced by the A. niger and P. lycii phytases at their recommended levels of 500 and 750 U/kg, respectively.     

Evaluation of Phytase Enzyme with Chicks Fed Basal Diets Containing Different Soybean Meal Samples

Soybean meal contains approximately 0.62% total P of which 0.4% can be phytate P, which is considered less biologically available for poultry than other forms of P. Soybean meal is a key ingredient in poultry feeds and information is needed about the range of phytate P and nonphytate P in different soybean meals. The phytate P content of soybeans may vary due to climatic conditions, soil type and soybean variety. Previous research has shown that phytate P can be hydrolyzed in the gastrointestinal tract providing available P by adding a commercial phytase enzyme to poultry feed. The extent of phytate hydrolysis by dietary supplementation of phytase has been shown to vary depending on the type of dietary ingredients such as corn, soybean meal, canola meal, and wheat. Research is needed to determine if different commercially available soybean meals respond in a similar manner to a feed added phytase. Twenty-five soybean meal samples were collected from active soybean crushing plants in the United States and 18 of the samples were selected to evaluate the effect of a microbial phytase on phytate P disappearance using 5-d bioassays. The range of analyzed values in soybean meal samples for total P, phytate P, Ca, protein, and neutral detergent fiber (NDF) were 0.59 to 0.87, 0.32 to 0.42, 0.28 to 0.54, 40.44 to 51.69, and 7.78 to 16.09%, respectively. Bioassay results indicate that body weight, feed consumption, and feed conversion ratio improved significantly (P < 0.05) in some of the groups fed diets with enzyme compared with groups fed the same diet with no added enzyme. The range of total P retention and phytate P disappearance for groups fed diets with no enzyme were 21.35 to 48.41 and 13.64 to 37.13%, respectively. The addition of phytase increased total P retention and phytate P disappearance from 56.81 to 68.62 and 76.18 to 94.08%, respectively. The results indicate no correlation among components (total P, phytate P, Ca, protein, and NDF) of soybean meal samples, percentage of phytate P disappearance, and percentage of total P retention for groups fed diets with and without added phytase.     

In vitro degradation of phytate and lower inositol phosphates in soaked diets and feedstuffs

A series of in vitro experiments simulating liquid feeding were performed to evaluate the effect of microbial phytase addition, heat-treatment and soaking time on degradation of phytate and lower inositol phosphates when soaking compound wheat/soybean meal diets or the single feedstuffs wheat or soybean meal. The effect of phytase addition on phytate degradation was greatest in soybean meal, almost intermediate for wheat/soybean meal diets and not detectable in wheat, which might be due to a better accessibility to phytate in soybean meal compared with wheat. Heat-treatment seemed to enhance the accessibility between phytase and phytate, whereby phytate degradation was stimulated. Additionally, it was shown that wheat phytase is able to stimulate degradation of phytate in soybean meal. Independent of treatment, the amount of IP₅–IP₂ was extremely small in relation to phytate in both wheat and soybean meal, indicating that when one phosphate group is removed from the phytate complex, degradation of IP₅–IP₂ is completed. Consequently, it is anticipated that liquid feeding might result in a higher digestibility of plant P compared with dry feeding of pigs.     

Influence of a novel consensus bacterial 6-phytase variant on mineral digestibility and bone ash in young growing pigs fed diets with different concentrations of phytate-bound phosphorus

A 20-d experiment was conducted to test the hypothesis that phytase increases nutrient digestibility, bone ash, and growth performance of pigs fed diets containing 0.23%, 0.29%, or 0.35% phytate-bound P. Within each level of phytate, five diets were formulated to contain 0, 500, 1,000, 2,000, or 4,000 phytase units (FTU)/kg of a novel phytase (PhyG). Three reference diets were formulated by adding a commercial Buttiauxella phytase (PhyB) at 1,000 FTU/kg to diets containing 0.23%, 0.29%, or 0.35% phytate-bound P. A randomized complete block design with 144 individually housed pigs (12.70 ± 4.01 kg), 18 diets, and 8 replicate pigs per diet was used. Pigs were adapted to diets for 15 d followed by 4 d of fecal collection. Femurs were collected on the last day of the experiment. Results indicated that diets containing 0.35% phytate-bound P had reduced (P < 0.01) digestibility of Ca, P, Mg, and K compared with diets containing less phytate-bound P. Due to increased concentration of total P in diets with high phytate, apparent total tract digestible P and bone ash were increased by PhyG to a greater extent in diets with 0.29% or 0.35% phytate-bound P than in diets with 0.23% phytate-bound P (interaction, P < 0.05). At 1,000 FTU/kg, PhyG increased P digestibility and bone P more (P < 0.05) than PhyB. The PhyG increased (P < 0.01) pig growth performance, and pigs fed diets containing 0.35% or 0.29% phytate-bound P performed better (P < 0.01) than pigs fed the 0.23% phytate-bound P diets. In conclusion, the novel phytase (i.e., PhyG) is effective in increasing bone ash, mineral digestibility, and growth performance of pigs regardless of dietary phytate level.     

High dietary phytase levels maximize phytate-phosphorus utilization but do not affect protein utilization in chicks fed phosphorus- or amino acid-deficient diets

Four trials investigated the effect of high levels of three phytase enzymes on P and protein utilization in chicks. The three phytases were derived from Aspergillus (Fungal Phytase 1), Peniophora (Fungal Phytase 2), and E. coli. Within each assay, 8-d-old male chicks were given ad libitum access to their experimental diet for 10 to 14 d. For Trials 1, 2, and 3, the basal diet was a corn-soybean meal diet deficient in P that was analyzed to contain 23% CP and 0.38% total P (0.10% estimated available P, as-fed basis). Phytase supplementation levels were based on the assessment of phytase premix activity (i.e., P release from Na phytate at pH 5.5 and 37 degrees C). In Trial 1, supplementation of inorganic P from KH2PO4 (0 to 0.20%) resulted in a quadratic (P < 0.05) response in weight gain, gain:feed, and tibia ash concentration but a linear (P < 0.01) increase in tibia ash weight. Tibia ash was higher (P < 0.01) for chicks fed E. coli phytase than for those fed Fungal Phytase 1 at 500, 1,000, and 5,000 phytase units (FTU)/kg, but did not differ between these two phytases at 10,000 FTU/kg. In Trial 2, E. coli phytase supplementation at 1,000 FTU/kg maximized growth and bone responses, whereas addition of either of the two fungal phytases resulted in increasing responses up to 5,000 and 10,000 FTU/kg. Dietary addition of Fungal Phytase 2 resulted in the poorest (P < 0.01) responses among the three phytases. Escherichia coli phytase supplementation at 10,000 FTU/kg in Trial 3 resulted in tibia ash (millligrams) responses that were greater (P < 0.05) than those resulting from either 0.35% inorganic P supplementation or 10,000 FTU/kg of Fungal Phytase 1 or 2. Trial 4 showed that E. coli phytase supplementation at either 500 or 10,000 FTU/ kg did not improve protein efficiency ratio (gain per unit of protein intake) of chicks fed low-protein soybean meal or corn gluten meal diets that were first-limiting in either methionine or lysine, respectively. These results demonstrate that high dietary levels of efficacious phytase enzymes can release most of the P from phytate, but they do not improve protein utilization.     

The effects of phytase and phytic acid on the loss of endogenous amino acids and minerals from broiler chickens

1. The effects of myo-inositol hexaphosphate (IP6) and phytase (EC 3.1.3.26) on the excretion of endogenous compounds were investigated using growing broiler chickens. 2. A total of 32 female Ross broilers were used in a precision feeding assay involving a 2 x 2 factorial arrangement of treatments. The materials administered were glucose, glucose + 1000 units of phytase activity (FTU), glucose + 1 g of IP6 and glucose + 1 g of IP6 + 1000 FTU. Excreta were collected quantitatively over a 48-h period following intubation of the test materials. The excretion of nitrogen, amino acids, minerals, sialic acid and phytate phosphorus was determined. 3. The ingestion of 1 g of IP6 by broilers increased the excretion of endogenous nitrogen, amino acids, iron, sodium, sulphur and sialic acid compared with birds fed on glucose. Supplementation of IP6 with exogenous phytase reduced the excretion of endogenous amino acids, calcium, sodium, phytate phosphorus and sialic acid compared with birds fed IP6. 4. It can be concluded that IP6 increases the excretion of endogenous minerals and amino acids in broiler chickens. Part of the beneficial effects of the addition of exogenous phytases to the diets of poultry appears to be mediated through a reduction in endogenous losses of these nutrients.     

Influence of phytate level on broiler performance and the efficacy of 2 microbial phytases from 0 to 21 days of age

Phytate is an antinutrient in animal feeds, reducing the availability and increasing the excretion of nutrients. Phytases are widely used to mitigate the negative influences of phytate. This trial was designed to compare the efficacy of 2 Escherichia coli-derived phytases on broiler performance and bone ash as influenced by dietary phytate level. A total of 1,024 Arbor Acres male broilers were used with 8 replicate pens of 16 birds/pen. Experimental diets were based on low available phosphorus (avP; 1.8 g/kg) with low (6.40 g/kg) or high (10.65 g/kg) phytate. The low-avP diets were then supplemented with mono-dicalcium phosphate to increase the avP level to 4.5 g/kg, 500 phytase units/kg of phytase A, or 500 phytase units/kg of phytase B to create 8 experimental diets. Feed intake, BW gain, FCR, and livability were influenced by a P source × phytase interaction. Feed intake, BW gain, and livability were reduced and FCR was higher in broilers fed low-avP diets, particularly in the presence of high phytate. Phytase A or phytase B improved feed intake, BW gain, and FCR, particularly in the high-phytate diet. However, broilers fed phytase A ate more and were heavier than broilers fed phytase B. Tibia ash was lowest in broilers fed the low-avP diet and highest in broilers fed the diet supplemented with mono-dicalcium phosphate. Phytase increased tibia ash, and broilers fed phytase A had an increase in tibia ash compared with broilers fed phytase B. In conclusion, high dietary phytate reduced broiler performance. Phytase A and phytase B improved bone ash and growth performance, especially in the high-phytate diets. However, phytase A was more efficacious than phytase B, regardless of the level of phytate.     

Effects of dietary Ca/P ratio, P level and microbial phytase supplementation on nutrient digestibilities in growing pigs: precaecal, post-ileal and total tract disappearances of OM,

Eight female pigs (26–61 kg) provided with a simple T-cannula about 10 cm proximal to the ileo-caecal valve, were used in two experiments to investigate the effects of Ca/P ratio, P level and supplementation with phytase (500 FTU/kg) on precaecal, post-ileal and total tract disappearances of organic matter (OM), phosphorus (P) and calcium (Ca). In experiment 1, two Ca/P ratios and two P levels were tested according to a 2 × 2 factorial arrangement within a Latin square design. In experiment 2, the diets of experiment 1 were supplemented with phytase (500 FTU/kg). There was a substantial absorption of OM, P and Ca in the post-ileal tract for all diets. Precaecal and total tract disappearances of OM were reduced by phytase addition (−4.4 and −0.8%, respectively). Supplementation with phytase resulted in an improvement of total tract and post-ileal P disappearances by 10.3 and 12.1%, respectively, without affecting precaecal P disappearance. Addition of feed phosphate resulted in a higher precaecal disappearance of P (+10.8%), resulting in a higher total tract disappearance of P (+5.9%). Addition of limestone had little effect on disappearances of OM, P and Ca, but reduced activity of supplemental phytase and had a negative influence on growth performance. Precaecal, post-ileal and total tract Ca disappearances were hardly affected by the examined dietary factors. The results might indicate that P from feed phosphate is absorbed primarily prececally and that P from phytate, liberated by microbial phytases, is dominantly absorbed post-illeally.     

In vitro and in vivo characteristics of bacterial phytases and their efficacy in broiler chickens

1. Three bacterial phytases derived from Bacillus, Escherichia coli or Klebsiella were compared with a phytase derived from Aspergillus niger in vitro and in vivo. 2. The in vitro results indicated that Aspergillus, E. coli and Klebsiella phytase displayed their activity optima in an acid pH range while Bacillus phytase did so in neutral pH. 3. The trials also revealed that only Bacillus phytase is more resistant to heat treatments, while E. coli and Klebsiella phytases are more stable against proteolytic inactivation. 4. In vivo phytases derived from Aspergillus, Bacillus, E. coli, Klebsiella or a combination of Bacillus and E. coli improved the utilisation of phosphorus (P balance) significantly to 0.54, 0.54, 0.55, 0.55 or 0.58, respectively, compared to 0.42 in the negative control. 5. The phytases used in this study seemed to be equally effective in improving P utilisation regardless of proposed intestinal site of activity. Combination of phytases acting in the gizzard with phytases acting in the intestine seems to be a promising way to further improving in vivo efficacy of phytases in poultry.     

植酸酶在饲料中的应用

植酸酶是一种畜禽饲料添加剂,能有效地降解植酸盐,将植酸磷(六磷酸肌醇)降解为肌醇和无机磷,解除植酸的抗营养作用。植酸酶应用于饲料中,不仅可以提高植物性饲料中植酸磷的消化率,减少无机磷的添加量和磷排泄污染,还可以改善和提高畜禽对饲料中蛋白质、能量、氨基酸和微量元素的利用率,提高动物的生产性能。     

Enhancement of phosphorus utilization in growing pigs fed phytate-rich diets by using rye bran.

Some cereal by-products, such as bran, exhibit a high phytase activity that may enhance phytate P digestibility. This was studied in growing pigs fed a phytase-rich (1,200 IU/kg) diet containing 20% rye bran. The trial involved 12 animals; six were fed a control diet and six were fed a diet containing rye bran for 2 mo. Both diets contained the same levels of energy, protein, Ca (.7%) and total P (.4%). No inorganic P was added; thus, the dietary P was mainly phytic. Pigs fed the control diet, in contrast to those fed the diet containing rye bran, developed a P deficiency, as indicated by hypophosphatemia, hypophosphaturia, hyperhydroxyprolinuria, hypercalcemia, and hypercalciuria. Phosphorus from the rye bran diet was more completely absorbed (55 vs 36%) and retained (50 vs 36%) than that from the control diet. Calcium absorption was equal for the two diets, but Ca retention was higher in pigs fed rye bran than in controls. Pigs fed the rye bran diet showed greater bone density, ash content, and bending moments than controls. In conclusion, high dietary phytase levels or phytase-rich by-products increased phytate P availability and consequently improved bone scores.     

Modeling the fate of dietary phosphorus in the digestive tract of growing pigs

Environmental effects of excess P from manure and the soaring price of phosphates are major issues in pig production. To optimize P utilization, it is crucial to improve our capacity to predict the amount of P absorbed, while taking into account the main factors of variation. Mathematical modeling can represent the complexity of the processes and interactions in determining the digestive utilization of P in growing pigs. This paper describes and evaluates a model developed to simulate the fate of the dietary forms of P in the digestive tract of growing pigs, with particular emphasis on the effect of dietary Ca and exogenous phytase on P digestive utilization. The model consists of 3 compartments associated with specific anatomical sections: stomach, proximal small intestine, and distal small intestine. The main metabolic processes occurring in these sections are, respectively, P solubilization/insolubilization and phytate P hydrolysis, and P absorption and P insolubilization. Model parameters governing these flows were derived from in vitro and in vivo literature data. The sensitivity analysis revealed that the model was stable within a large range of model parameter values (±1.5 SD). The model was able to predict the efficacy of Aspergillus niger microbial phytase in accordance with literature values, as well as the decreased efficacy of plant phytase compared with microbial phytase. The prediction capabilities of the model were assessed by comparing actual and simulated P and Ca apparent total-tract digestibility (ATTD) based on published pig data not used for model development. Prediction of P digestibility across 66 experiments and 281 observations was adequate [P ATTD observed = 0.24 (SE, 0.943) + 0.98 (SE, 0.0196) × P ATTD predicted; R(2), 0.90; disturbance error (ED), 96.5%], whereas prediction of Ca digestibility across 47 experiments and 193 observations was less accurate (Ca ATTD observed = 11.1 + 0.75 × Ca ATTD predicted; R(2), 0.78; ED, 20.4%). A lack of agreement between experimental and simulated Ca digestibility was found. This model is, therefore, useful in evaluating P digestibility for different feedstuffs and feeding strategies. It can also be used to provide insight for improving dietary P utilization, especially from plant sources, by quantifying the effect of the mean sources of variation affecting P utilization.     

Effects of individual or combined xylanase and phytase supplementation on energy, amino acid, and phosphorus digestibility and growth performance of grower pigs fed wheat-based diets containing wheat millrun

The objective of these studies was to determine if dietary enzymes increase the digestibility of nutrients bound by nonstarch polysaccharides, such as arabinoxylans, or phytate in wheat millrun. Effects of millrun inclusion rates (20 or 40%), xylanase (0 or 4,375 units/kg of feed), and phytase (0 or 500 phytase units/kg of feed) on nutrient digestibility and growth performance were investigated in a 2 x 2 x 2 factorial arrangement with a wheat control diet (0% millrun). Diets were formulated to contain 3.34 Mcal of DE/kg and 3.0 g of true ileal digestible Lys/Mcal of DE and contained 0.4% chromic oxide. Each of 18 cannulated pigs (36.2 +/- 1.9 kg of BW) was fed 3 diets at 3x maintenance in successive 10-d periods for 6 observations per diet. Feces and ileal digesta were collected for 2 d. Ileal energy digestibility was reduced (P < 0.01) linearly by millrun and increased by xylanase (P < 0.01) and phytase (P < 0.05). Total tract energy digestibility was reduced linearly by millrun (P < 0.01) and increased by xylanase (P < 0.01). For 20% millrun, xylanase plus phytase improved DE content from 3.53 to 3.69 Mcal/kg of DM, a similar content to that of the wheat control diet (3.72 Mcal/kg of DM). Millrun linearly reduced (P < 0.01) ileal digestibility of Lys, Thr, Met, Ile, and Val. Xylanase improved (P < 0.05) ileal digestibility of Ile. Phytase improved ileal digestibility of Lys, Thr, Ile, and Val (P < 0.05). Millrun linearly reduced (P < 0.05) total tract P and Ca digestibility and retention. Phytase (P < 0.01) and xylanase (P < 0.05) improved total tract P digestibility, and phytase and xylanase tended to improve (P < 0.10) P retention. Phytase improved Ca digestibility (P < 0.05) and retention (P < 0.01). The 9 diets were also fed for 35 d to 8 individually housed pigs (36.2 +/- 3.4 kg of BW) per diet. Millrun reduced (P < 0.05) ADFI, ADG, and final BW. Xylanase increased (P < 0.05) G:F; phytase reduced (P < 0.05) ADFI; and xylanase tended to reduce (P = 0.07) ADFI. In summary, millrun reduced energy, AA, P, and Ca digestibility and growth performance compared with the wheat control diet. Xylanase and phytase improved energy, AA, and P digestibility, indicating that nonstarch polysaccharides and phytate limit nutrient digestibility in wheat byproducts. The improvement by xylanase of energy digestibility coincided with improved G:F but did not translate into improved ADG.