This study evaluated the effects of three different thermostable phytase variants, based on the AppA gene from E. coli (AppAT1, AppAT2 and AppAT3) on growth performance, nutrient digestibility and bone mineralisation in broiler chickens at inclusion levels of 250 and 500 FTU/kg. The eight treatment groups included a positive control (PC) which was sufficient in Ca and P, a negative control (NC, the same basal formulation as the PC, but reduced in Ca and P), and NC supplemented with AppAT1 at 250 and 500 FTU/kg (AppAT1-250 and AppAT1-500), AppAT2 at 250 and 500 FTU/kg (AppAT2-250 and AppAT2-500) and with AppAT3 at 250 and 500 FTU/kg (AppAT3-250 and AppAT3-500). Over the entire feeding period, body weight (BW) and average daily gain (ADG) were significantly higher in the PC group, with all phytase supplemented groups being statistically the same, compared to the NC group. Feed conversion (FCR) for the PC-fed birds (1.479) was significantly (P<0.05) better compared to the NC birds (1.582) and those fed the AppAT3-250 diet (1.523). Reduced levels of Ca and P in the NC group led to significantly (P<0.05) lower tibia ash (40.9%) compared to the PC group (47.4%). Birds fed the phytase diets had significantly higher tibia ash compared to the NC birds, with those from the AppAT2-500 and AppAT3-500 groups being statistically the same as the PC group. Diets AppAT1-500, AppAT2-250, AppAT2-500 and AppAT3-500 significantly increased Ca digestibility compared to the NC. Apparent total track digestibility (ATTD) of P was improved for AppAT1-500 and AppAT2-250. The ATTD of Ca and P for all of the phytase supplemented groups reached the same level of the PC and AppAT1-500 group. It was concluded that adding any of the phytases tested, especially when included at 500 FTU/kg to a feed reduced in Ca and P, led to improved performance and bone mineralisation back to the same levels as seen for the Ca and P sufficient diet.

The following review covers current and classical knowledge regarding the positive effects of organic acids on phytase activity and phytate P availability in broiler chickens. Despite the improvements achieved for phytase stability under gastrointestinal conditions, intrinsic characteristics of phytic acid, dietary components and the digestive tract favour phytate formation and, consequently, inhibit the degradation of phytic acid and other inositol phosphates by phytase. Organic acids, more frequently citric acid, have been shown to decrease phytate establishment and enhance phytase activity. When supplemented alone, citric acid increased P retention by 16 to 34% and phytate P retention by 105% in broilers. When combined with phytase, 3.27% better tibia ash has been reported. From the available data, it appears that combined use of phytases and organic acids deserves greater consideration in modern poultry nutrition.

In the past, trace minerals have been inadequately considered by poultry nutritionists, as demonstrated by the scarce availability of literature. The practice of using high safety margins between requirements and dietary concentrations and the relative low cost of these essential minerals are possible reasons for this. Environmental considerations and regulations limiting trace mineral supply and improvements in analytical methods to detect putative contaminants in mineral sources have led to a need to a re-examination of trace mineral requirements. In addition, new knowledge regarding trace mineral roles in bone metabolism, anti-oxidant status, homeostatic regulation, product quality, immunology and the development of novel trace mineral sources have favoured, for the past 15 years, interests in optimising trace mineral nutrition considering other parameters than solely the bird performance. This review analyses the role of essential trace minerals (mainly Zn, Cu, Fe, Mn, I, Se) in broiler and laying hen nutrition. This work aims to highlight the evaluation of trace mineral requirement, the bioavailability of trace mineral sources, especially in regards with phytate antagonism, and the main functions of trace minerals in egg, eggshell and meat quality. The impact of trace minerals on the environment (toxicity to plants and microorganisms) is considered and nutritional means to reduce the risk of environmental contamination will be explored. Finally, the possibilities of poultry product's enrichment in some trace minerals for the benefit of human health will be explored.

The objective was to evaluate the effect of microbial phytase (1250 FTU/kg diet with 88% dry matter (DM)) on apparent total tract digestibility (ATTD) of phosphorus (P) in pigs fed a dry or soaked diet. Twenty-four pigs (65±3 kg) from six litters were used. Pigs were housed in metabolism crates and fed one of four diets for 12 days; 5 days for adaptation and 7 days for total, but separate collection of feces and urine. The basal diet was composed of wheat, barley, maize, soybean meal and no mineral phosphate. Dietary treatments were: basal dry-fed diet (BDD), BDD with microbial phytase (BDD+phy), BDD soaked for 24 h at 20°C before feeding (BDS) and BDS with microbial phytase (BDS+phy). Supplementation of microbial phytase increased ATTD of DM and crude protein (N×6.25) by 2 and 3 percentage units (P<0.0001; P<0.001), respectively. The ATTD of P was affected by the interaction between microbial phytase and soaking (P=0.02). This was due to a greater increase in ATTD of P by soaking of the diet containing solely plant phytase compared with the diet supplemented with microbial phytase: 35%, 65%, 44% and 68% for BDD, BDD+phy, BSD and BSD+phy, respectively. As such, supplementation of microbial phytase increased ATTD of P in the dry-fed diet, but not in the soaked diet. The higher ATTD of P for BDS compared with BDD resulted from the degradation of 54% of the phytate in BDS by wheat and barley phytases during soaking. On the other hand, soaking of BDS+phy did not increase ATTD of P significantly compared with BDD+phy despite that 76% of the phytate in BDS+phy was degraded before feeding. In conclusion, soaking of BDS containing solely plant phytase provided a great potential for increasing ATTD of P. However, this potential was not present when microbial phytase (1250 FTU/kg diet) was supplemented, most likely because soaking of BDS+phy for 24 h at 20°C did not result in a complete degradation of phytate before feeding.

A deterministic, dynamic model was developed, to enable predictions of phosphorus (P) digested, retained and excreted for different pig genotypes and under different dietary conditions. Before confidence can be placed on the predictions of the model, its evaluation was required. A sensitivity analysis of model predictions to ±20% changes in the model parameters was undertaken using a basal UK industry standard diet and a pig genotype characterized by British Society Animal Science as being of ‘intermediate growth’. Model outputs were most sensitive to the values of the efficiency of digestible P utilization for growth and the non-phytate P absorption coefficient from the small intestine into the bloodstream; all other model parameters influenced model outputs by <10%, with the majority of the parameters influencing outputs by <5%. Independent data sets of published experiments were used to evaluate model performance based on graphical comparisons and statistical analysis. The literature studies were selected on the basis of the following criteria: they were within the BW range of 20 to 120 kg, pigs grew in a thermo-neutral environment; and they provided information on P intake, retention and excretion. In general, the model predicted satisfactorily the quantitative pig responses, in terms of P digested, retained and excreted, to variation in dietary inorganic P supply, Ca and phytase supplementation. The model performed well with ‘conventional’, European feed ingredients and poorly with ‘less conventional’ ones, such as dried distillers grains with solubles and canola meal. Explanations for these inconsistencies in the predictions are offered in the paper and they are expected to lead to further model development and improvement. The latter would include the characterization of the origin of phytate in pig diets.

Low phosphorus (P) digestibility combined with intensive pig production can increase P diffuse pollution and environmental load. The aim of this paper was to develop a deterministic, dynamic model able to represent P digestion, retention and ultimately excretion in growing and finishing pigs of different genotypes, offered access to diets of different composition. The model represented the limited ability of pig endogenous phytase activity to dephosphorylate phytate as a linear function of dietary calcium (Ca). Phytate dephosphorylation in the stomach by exogenous microbial phytase enzymes was expressed by a first order kinetics relationship. The absorption of non-phytate P from the lumen of the small intestine into the blood stream was set at 0.8 and the dephosphorylated phytate from the large intestine was assumed to be indigestible. The net efficiency of using digested P was set at 0.94 and assumed to be independent of BW, and constant across genotype and sex. P requirements for both maintenance and growth were made simple functions of body protein mass, and hence functions of animal genotype. Undigested P was assumed to be excreted in the feaces in both soluble and insoluble forms. If digestible P exceeded the requirements for P then the excess digestible P was excreted through the urinary flow; thus the model represented both forms of P excretion (soluble and insoluble) into the environment. Using a UK industry standard diet, model behaviour was investigated for its predictions of P digestibility, retention and excretion under different levels of inclusion of microbial phytase and dietary Ca, and different non-phytate P : phytate ratios in the diet, thus covering a broad space of potential diet compositions. Model predictions were consistent with our understanding of P digestion, metabolism and excretion. Uncertainties associated with the underlying assumptions of the model were identified. Their consequences on model predictions, as well as the model evaluation are assessed in a companion paper.

Zinc (Zn) is essential for swine and poultry and native Zn concentrations in feedstuffs are too low to meet their Zn requirement. Dietary Zn bioavailability is affected by phytate, phytase and Zn supplemented in organic form is considered as more bioavailable than inorganic sources. A meta-analysis using GLM procedures was processed using broiler and piglet databases to investigate, within the physiological response of Zn, (1) the bioavailability of inorganic and organic Zn sources (Analysis I); (2) the bioavailability of native and inorganic Zn dependent from dietary phytates, vegetal and supplemental phytase activity (Analysis II). Analysis I: the bioavailability of organic Zn relative to inorganic Zn sources ranged, depending on the variable, from 85 to 117 never different from 100 (P > 0.05). The coefficients of determination of the regressions were 0.91 in broilers and above 0.89 in piglets. Analysis II: in broilers, bone Zn was explained by supplemental Zn (linear and quadratic, P < 0.001) and by supplemental phytase (linear, P < 0.001). In piglets, the interaction between dietary Zn and phytates/phytases was investigated by means of a new variable combining dietary phytic phosphorus (PP) and phytase activity. This new variable represents the remaining dietary PP after its hydrolysis in the digestive tract, mainly due to phytase and is called non-hydrolyzed phytic phosphorus (PPNH). Bone Zn was increased with native Zn (P < 0.001), but to a lower extent in high PP or low phytase diets (ZNN × PPNH, P < 0.001). In contrast, the increase in bone zinc in response to supplemental Zn (P < 0.001) was not modulated by PPNH (P > 0.05). The coefficients of determination of the regressions were 0.92 in broilers and above 0.92 in piglets. The results from the two meta-analyses suggest that (1) broilers and piglets use supplemented Zn, independent from Zn source; (2) broiler use native Zn and the use is slightly enhanced with supplemental phytase; (3) however, piglets are limited in the use of native Zn because of the antagonism of non-hydrolyzed dietary phytate. This explains the higher efficacy of phytase in improving Zn availability in this specie.

Protein–phytate interactions are fundamental to the detrimental impact of phytate on protein/amino acid availability. The inclusion of exogenous phytase in pig and poultry diets degrades phytate to more innocuous esters and attenuates these negative influences. The objective of the present review is to reappraise the underlying mechanisms of these interactions and reassess their implications in pig and poultry nutrition. Protein digestion appears to be impeded by phytate in the following manner. Binary protein–phytate complexes are formed at pH levels less than the isoelectric point of proteins and complexed proteins are refractory to pepsin digestion. Once the protein isoelectric points are exceeded binary complexes dissociate; however, the isoelectric point of proteins in cereal grains may be sufficiently high to permit these complexes to persist in the small intestine. Ternary protein–phytate complexes are formed at pH levels above the isoelectric point of proteins where a cationic bridge links the protein and phytate moieties. The molecular weights of protein and polypeptides in small-intestinal digesta may be sufficient to allow phytate to bind nutritionally important amounts of protein in ternary complexes. Thus binary and ternary complexes may impede protein digestion and amino acid absorption in the small intestine. Alternatively, phytate may interact with protein indirectly. Myo-inositol hexaphosphate possesses six phosphate anionic moieties (HPO42–) that have strong kosmotropic effects and can stabilise proteins by interacting with the surrounding water medium. Phytate increases mucin secretions into the gut, which increases endogenous amino acid flows as the protein component of mucin remains largely undigested. Phytate promotes the transition of Na+ into the small-intestinal lumen and this suggests that phytate may interfere with glucose and amino acid absorption by compromising Na+-dependent transport systems and the activity of the Na pump (Na+-K+-ATPase). Starch digestion may be depressed by phytate interacting with proteins that are closely associated with starch in the endosperm of cereal grains. While elucidation is required, the impacts of dietary phytate and exogenous phytase on the site, rate and synchrony of glucose and amino acid intestinal uptakes may be of importance to efficient protein deposition. Somewhat paradoxically, the responses to phytase in the majority of amino acid digestibility assays in pigs and poultry are equivocal. A brief consideration of the probable reasons for these inconclusive outcomes is included in this reappraisal.

Calcium is the most prevalent mineral in the body and is important for many physiological processes. However, the amount of calcium in modern diets has both economic and nutritional consequences for producers. Dietary calcium has been shown to reduce the efficacy of both endogenous and exogenous phytases resulting in decreased phytate-phosphorus availability, increased phosphorus excretion as well as facilitating the formation of mineral-phytate complexes. Reducing the concentration of dietary calcium has been reported to improve phytase efficacy and phytate-phosphorus availability, however, this is often at the expense of optimal skeletal integrity. Choice feeding employs the principle that poultry have the ability to select a nutritionally balanced diet from multiple sources and previous studies have shown that poultry have a calcium specific appetite. However, the evaluation of choice feeding systems for broilers has predominantly focussed on the effects of providing separate sources of protein and energy concentrates. Though literature is available for laying hens, scant information is available pertaining to choice feeding of a separate calcium source for broilers. This paper reviews the available information on choice feeding systems in poultry with focus on the application of this in broiler production systems.

Phytases have been used commercially since the early 1990s and have been the focus of considerable and sustained research for many decades. Despite this heroic effort there are still areas of persistent uncertainty such as the obscurity surrounding total compared with digestible calcium, appropriate modification to dietary sodium (and other electrolyte) concentrations, the usefulness of the amino acid and energy digestibility improvements and ultimately the effect of phytase on nutrient requirement. One further area which has attracted some attention recently is the effect of unconventionally high doses of phytase (i.e. >2,500 FTU/kg from Aspergillus niger or Escherichia coli) in an attempt to ostensibly ‘de-phytinise’ the diet. The effects of such ‘super’ doses of phytase can be considerable, and often beyond that which may be reasonably expected based on improvement in P digestibility per se. This review article addresses these effects and suggests mechanisms by which they may be explained.

The aim was to evaluate the effect of heat-treatment, microbial phytase addition and feeding strategy (dry feeding v. fermented liquid feeding) on degradation of phytate (myo-inositol hexakisphosphate, InsP6) and formation and further degradation of lower inositol phosphates (myo-inositol pentakisphosphate–myo-inositol bisphosphate, InsP5–InsP2) at the distal ileum of pigs. Furthermore, the apparent ileal digestibility/degradability (AID) of phosphorus (P), InsP6–P and calcium (Ca) and the apparent total tract digestibility (ATTD) of P and Ca were studied. Pigs were fitted with a T-shaped ileal cannula for total collection of digesta at 2 h intervals during an 8 h sampling period after feeding the morning meal. Each period lasted for 2 weeks: 8 days of adaptation followed by 3 days of total collection of faeces and 3 days of total collection of ileal digesta. The experiment was designed as a 4 × 4 Latin square with four pigs fed four diets. A basal wheat/barley-based diet was fed either as non-heat-treated or heat-treated (steam-pelleted at 90°C). The heat-treatment resulted in an inactivation of plant phytase below detectable level. Diet 1 (non-heat-treated basal diet fed dry); diet 2 (heat-treated basal diet fed dry); diet 3 (as diet 2 but with microbial phytase (750 FTU/kg as fed) fed dry); diet 4 (as diet 3 fed liquid (fermented for 17.5 h nighttime and 6.5 h daytime at 20°C with 50% residue in the tank)). Chromic oxide (Cr2O3) was included as marker and ATTD was determined both by total collection of faeces (ATTDTotal) and Cr2O3 (ATTDCr). InsP6 was completely degraded in diet 4 before feeding resulting in no InsP6–P being present in ileal digesta. InsP6–P concentration in ileal digesta decreased with increasing dietary levels of plant or microbial phytase in pigs fed the dry diets. Consequently, AID and ATTD of P and Ca were greatest for pigs fed diet 4 followed by diets 3, 1 and 2. The ATTD of P depended on the used method as ATTDTotal of P was 72%, 61%, 44% and 34%, whereas ATTDCr of P was 65%, 52%, 38% and 23% for diets 4, 3, 1 and 2, respectively. In all pigs the ileal concentration of InsP5–InsP2–P was extremely small, and thus unimportant for maximisation of ATTD of plant P. In conclusion, fermented liquid feeding with microbial phytase seems to be an efficient approach to improve ATTD of plant P compared with dry feeding. This opens up for further reductions in P excretion.

The objective of the present study was to investigate the effect of dietary phytate and microbial phytase on the lipase activity, lipid metabolism and mRNA expressions of fatty acid synthase (FASN) and leptin in broiler chickens. The study was conducted as a 2 × 3 factorial arrangement of treatments with phytate phosphorus at 0·20 and 0·40 % (added as the sodium phytate) and supplemental microbial phytase at 0, 500, or 1000 phytase units/kg. The results showed that phytase improved (P < 0·05) the growth performance and ileal digestibility of nutrients of broilers, but phytate had no effect (P>0·05) on these parameters, except the decrease (P < 0·01) in the digestibility of Ca. Phytate decreased (P < 0·05) the lipase activity, serum total cholesterol (T-CHO) and hepatic TAG, and elevated (P < 0·01) serum NEFA and HDL cholesterol. Phytase decreased (P < 0·05) serum NEFA, but increased (P < 0·01) serum T-CHO and hepatic TAG. Phytate and phytase also influenced (P < 0·01) the mRNA expressions of leptin in the liver. There were significant (P < 0·05) interactions of phytate and phytase on the concentrations of serum TAG and LDL cholesterol, hepatic NEFA and T-CHO, and the mRNA expressions of FASN. The results suggest that phytate and phytase can affect lipase activity and lipid metabolism of broiler chickens.

As the simultaneous use of carbohydrases and phytases gains momentum it is imperative that formulators understand the magnitude of additivity of effect to allow for appropriate modification to diet nutrient balance. Though carbohydrases and phytases are often thought of as pronutrients with energy, calcium and phosphorus value, within the scientific literature there are dozens of papers on the effect of these enzymes on ileal amino acid digestibility coefficients. The effect of enzymes on ileal amino acid digestibility is instructive as patterns of response allow speculation as to mode of action and likely additivity of admixtures. A review of the scientific literature has revealed that whilst xylanases and phytases may be considered to be broadly additive in effect, on an individual amino acid basis this effect ranges from sub-additive (e.g. threonine) to synergistic (e.g. arginine). Importantly, the mean response to both xylanase and phytase for ileal amino acid digestibility can be predicted (R2=0.65 and 0.56 respectively) by polynomial equations based only on the nutritional value of the control diet. The fact that control diets with an inherently high digestibility respond poorly to enzymes explains why the use of a second enzyme will likely yield a lesser response when used on top of another, since the former has already improved digestibility characteristics. The implications of these responses, as well as suggested mechanisms of action, are discussed within practical diet formulation constraints.

The study was conducted to evaluate the effects of dietary zinc addition (0 or 15 mg/kg of Zn as inorganic or organic zinc) to three maize–soybean meal basal diets varying in their native Zn, phytic P contents and phytase activity (expressed in kg of feed: P− with 25 mg Zn and 1.3 g phytic P, P+ with 38 mg Zn and 2.3 g phytic P or P+/ENZ being P+ including 500 units (FTU) of microbial phytase per kg) in two monogastric species (piglets, broilers). Measured parameters were growth performance, zinc status (plasma, and bone zinc) and soluble zinc in digesta (stomach, gizzard and intestine). The nine experimental diets were fed for 20 days either to weaned piglets (six replicates per treatment) or to 1-day-old broilers (10 replicates per treatment). Animal performance was not affected by dietary treatments (P > 0.05) except that all P− diets improved body weight gain and feed conversion ratio in piglets (P < 0.05). Piglets fed P− diets had a better Zn status than those fed P+ diets (P < 0.05). In both species, Zn status was improved with supplemental Zn (P < 0.05), irrespective of Zn source. Phytase supplementation improved piglet Zn status to a higher extent than adding dietary Zn, whereas in broilers, phytase was less efficient than supplemental Zn. Digestive Zn concentrations reflected the quantity of ingested Zn. Soluble Zn (mg/kg dry matter) and Zn solubility (% of total Zn content) were highest in gizzard contents, which also presented lower pH values than stomach or intestines. The intestinal Zn solubility was higher in piglet fed organic Zn than those fed inorganic Zn (P < 0.01). Phytase increased soluble Zn in piglet stomach (P < 0.001) and intestine (P = 0.1), but not in broiler gizzard and intestinal contents. These results demonstrate (i) that dietary zinc was used more efficiently by broilers than by piglets, most probably due to the lower gizzard pH and its related higher zinc solubility; (ii) that zinc supplementation, irrespective of zinc source, was successful in improving animal’s zinc status; and (iii) suggest that supplemented Zn availability was independent from the diet formulation. Finally, the present data confirm that phytase was efficient in increasing digestive soluble Zn and improving zinc status in piglets. However, the magnitude of these effects was lower in broilers probably due to the naturally higher Zn availability in poultry than in swine.

An investigation was carried out to determine whether there were significant changes in the intake of dietary fibre (NSP) and phytate of adult men and women in the UK from 1982 (aged 36 years) to 1999 (aged 53 years). The 1253 subjects studied were members of the Medical Research Council National Survey of Health and Development; a longitudinal study of a nationally representative cohort of births in 1946. Food intake was recorded in a 5 d diary at age 36 years in 1982, 43 years in 1989 and 53 years in 1999. The food composition database was amended with revised values for phytate. Outcome measures were mean intakes of total NSP and phytate by year, sex and food source. There were significant changes in total NSP and phytate intake over the three time points. Intakes of NSP rose significantly between 1982 and 1999 for men and women but phytate intakes rose significantly only between 1989 and 1999. Cereal foods were the most important source of both NSP and phytate. Between 1989 and 1999 there was a significant increase in the contribution from pasta, rice and other grains. The present study shows that an increase in dietary fibre that is in accordance with dietary guidelines would almost inevitably be accompanied by a rise in phytate. The increased dietary phytate is discussed in relation to its recognised inhibition of mineral absorption and its merits with regard to protection against some cancers and other diseases of an ageing population.

The effect of phytate and phytase on the bioavailability of phosphorus has been appreciated for many years and phytase has been exploited commercially since the late-1990s to considerable global success. Although a number of authors have reported improved digestibility of amino acids, energy and other minerals (most notably calcium) by the addition of phytase to poultry diets, these so-called ‘extra-phosphoric’ effects of phytase are less well understood. Recent work has shed light on the underlying mechanisms by which phytase influences the apparent digestibility of amino acids, energy and minerals and much of the improvements are thought to be related to enhanced absorption of exogenous and re-absorption of endogenous amino acids. The synthesis and loss of endogenous protein is nutritionally expensive for animals and is negatively correlated with metabolisable energy, net energy, and the digestibility of nitrogen and amino acids. It has been estimated that as much as 50% of the total nitrogen present in the small intestine during digestion is of endogenous origin, resulting in negative digestibility coefficients in the proximal small intestine. Clearly the successful resorption of the secreted protein in the small intestine is critical to maintain favourable nitrogen balance and most endogenous proteins will eventually be digested and absorbed. However, a considerable proportion of endogenous secretions leave the terminal ileum and represent a net cost to the animal, the environment, and, importantly, to the poultry producer. Thus, dietary anti-nutrients that induce secretion and/or impair absorption e.g. tannins, trypsin inhibitors, or phytate can have substantial adverse consequences for productivity. The measurement and nutritional significance of endogenous losses in poultry, specifically with regard to the effect of phytate and phytase, are examined in the current review, in an attempt to explain the extra-phosphoric nutrient matrices assigned to commercial phytase products.