Explore the vast range of titles available.

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.

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.

This 21-d experiment was conducted to determine if the response of chicks to a cocktail of xylanase, amylase, and protease (XAP) or Escherichia coli-derived phytase individually or in combination when fed a nutritionally marginal corn-soybean meal diet is age-dependent. Six hundred 1-d-old chicks were allocated to 5 dietary treatments in a randomized complete block design. The treatments were as follows: 1) positive control with supplemental inorganic P; 2) negative control (NC) marginal in P and ME; 3) NC plus XAP to provide (per kg of diet) 650, 1,650, and 4,000 U of xylanase, amylase, and protease, respectively; 4) NC plus phytase added to provide 1,000 phytase units/kg; and 5) NC plus a combination of XAP and phytase. Low ME and P in the NC diet depressed weight gain and gain:feed (P < 0.001). A cocktail of XAP alone did not improve performance, but phytase supplementation improved (P < 0.001) weight gain. The enzymes were additive in their effects on growth performance. The enzymes had no effect on ileal digestible energy. Ileal N digestibility was higher (P < 0.05) in diet with XAP or phytase individually compared with NC. Both phytase and XAP individually and in combination improved (P < 0.01) ileal P digestibility compared with NC. Total tract nutrient retention and ME increased (P < 0.01) as the birds grew older. There were age x diet interactions (P < 0.001) on total tract retention of P and Ca; improvement in P retention due to phytase use decreased by 50% as the chicks matured. The current study shows that a combination of XAP and phytase improved performance, but the enhancement in performance appears to be mainly from phytase. Both XAP and phytase were effective in improving P digestibility and retention of chicks receiving nutritionally marginal corn-soybean meal. The data also shows that the chicks benefited more from the enzyme addition at a younger age and that the contribution of the enzymes to nutrient retention decreased with age in chickens.

The possible interaction between dietary electrolyte balance (DEB = Na + K - Cl, mEq/kg of diet) and microbial phytase on the performance and nutrient utilization of broiler starters and litter quality was examined in this study. A 4 x 2 factorial arrangement of treatments was used with 4 levels of DEB (150, 225, 300, and 375 mEq/kg of diet) and 2 levels of phytase (0 and 500 phytase units/kg of diet). Experimental diets were based on corn, soybean meal, and canola meal and were formulated to contain a nonphytate P level of 3 g/kg. The DEB levels were altered by the use of sodium bicarbonate and ammonium chloride. Each diet was offered to 6 replicates of 8 birds each from d 1 to 21. Increasing the DEB values from 150 to 300 mEq/kg had no effect (P > 0.05) on the weight gains and feed per gain, but the gains were lowered (P < 0.05) and the feed per gain was increased (P < 0.05) at 375 mEq/kg. Feed intake was unaffected (P > 0.05) by DEB levels. Supplemental phytase improved (P < 0.05) the weight gains and feed intake at all DEB levels. Feed per gain was lowered (P < 0.05) by phytase addition, but a tendency for a DEB x phytate interaction (P = 0.06) was also observed, indicating that the responses to phytase may be affected by DEB level. The responses in feed per gain were greater at the lowest DEB level, and phytase addition had no effect on feed per gain at the highest DEB level. Dietary electrolyte balance levels had no effect on the AMEn and ileal N digestibility to 300 mEq/kg, but lowered (P < 0.05) both criteria at 375 mEq/kg. Phytase addition improved (P < 0.05) the AMEn and ileal N digestibility. The improvements in AMEn with 500 U/kg of phytase addition in 150, 225, and 275 mEq/kg DEB were 53, 60, and 38 kcal/kg of DM, respectively. The main effect of DEB was significant (P < 0.05) only for the ileal availability of Na and Cl, whereas added phytase influenced (P < 0.05) the ileal availability of Ca, P, Na, K, and Cl. The effects of DEB were significant (P < 0.05) for apparent ileal digestibility of all amino acids, except Ala (P = 0.09), Arg, Met, and cystine. In general, the digestibilities of amino acids were unaffected when the DEB level was increased from 150 to 225 mEq/kg of diet, but decreased at the 300 and 375 mEq/kg levels. Phytase addition improved (P < 0.06 to 0.05) ileal digestibility of all amino acids, except Met and Tyr. Increasing DEB had adverse effects on excreta scores and DM content. Phytase addition, however, had no effect on excreta quality. The overall results of the present study suggest that variability in phytase responses in nutrient utilization may be explained, in part, by differences in dietary electrolyte levels.

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.

The interaction between calcium (Ca) and non-phytate phosphorus (nPP) in broiler nutrition and skeletal health is highly complex with many factors influencing their digestion, absorption and utilisation. The use of an investigative model such as the geometric framework allows a graphical approach to explore these complex interactions. A total of 600 Ross 308-day-old male broiler chicks were allocated to one of 15 dietary treatments with five replicates and eight birds per replicate. Dietary treatments were formulated to one of three total densities of total Ca+nPP; high (15 g/kg), medium (13.5 g/kg) and low (12 g/kg) and at each density there were five different ratios of Ca : nPP (4, 2.75, 2.1, 1.5 and 1.14 : 1). Weekly performance data was collected and at the end of the experiment birds were individually weighed and the right leg removed for tibia ash analysis. Skeletal health was assessed using the latency to lie (LTL) at day 27. At low Ca and high nPP as well as high Ca and low nPP diets, birds had reduced feed intake, BW gain, poorer feed efficiency and lower tibia ash, resulting in a significant interaction between dietary Ca and nPP (P<0.05). LTL times were negatively influenced by diets having either a broad ratio (high Ca, low nPP) or too narrow a ratio (low Ca, high nPP) indicating that shorter LTL times may be influenced by the ratio of Ca : nPP rather than absolute concentrations of either mineral. The calculated intake arrays show that broilers more closely regulate Ca intake than nPP intake. Broilers are willing to over consume nPP to defend a Ca intake target more so than they are willing to over consume Ca to defend an nPP target. Overall dietary nPP was more influential on performance metrics, however, from the data it may appear that birds prioritise Ca intake over nPP and broadly ate to meet this requirement. As broilers are more willing to eat to a Ca intake target rather than an nPP intake target, this emphasises the importance of formulating diets to a accurately balanced density of Ca : nPP considering the biological importance of both minerals.

To investigate the additive effects of xylanase, amylase, protease, and phytase in the diets of broiler chickens, a study was conducted using 1,152 growing broiler chicks (8 treatments with 12 replicate pens of 12 chicks). The birds were fed a corn/soybean-based negative control (NC) diet that was formulated to be nutritionally marginal in terms of metabolizable energy, Ca, and P. A nutritionally adequate positive control (PC) diet was fed for comparison. The NC diet was supplemented with phytase; a cocktail of xylanase, amylase, and protease (XAP); or a combination of phytase and XAP at 100 or 200 mg of each enzyme/kg (200 mg of XAP/kg provided a guaranteed minimum of 300 U of xylanase, 400 U of amylase, and 4,000 U of protease/kg; 200 mg of phytase/kg provided a guaranteed minimum of 1,000 U of phytase/kg). Growth performance, ileal digestible energy (IDE), and the digestibility coefficients of N, Ca, P, and DM were calculated. Individually and in combination, both phytase and XAP improved (P < 0.05) gain-to-feed ratio compared with the NC diet, particularly at the highest inclusion concentration. Body weight gain followed a similar trend, showing an improvement of approximately 6 to 7% with either enzyme individually and a 14% improvement with a combination of phytase and XAP. The effect of enzymes on IDE and nutrient digestibility coefficients was not as marked, but a 165-kcal/kg reduction in IDE was noted between the NC and PC diets, and a combination of phytase and XAP improved IDE by >100 kcal/kg. It can be concluded that the use of phytase and XAP individually in a corn/soybean meal-based diet is effective in improving nutrient digestibility and performance of broilers fed nutritionally marginal diets. Furthermore, there may be an additive effect of phytase and XAP on broiler performance, giving a cost-effective nutritional strategy for the profitable production of poultry products.

A total of 600 Ross 308-day-old male broiler chicks were used in a 28 day digestibility study to investigate the interaction between dietary calcium (Ca) and non-phytate phosphorus (nPP) on the digestibility of minerals and amino acids. Diets were formulated to be nutritionally adequate except for Ca and nPP. Fifteen mash diets based on corn and soya bean meal with varying concentrations of Ca (6.4 to 12.0 g/kg) and nPP (2.4 to 7.0 g/kg) were used. Diets were clustered around total densities of Ca and nPP of 12, 13.5 or 15.0 (g/kg) and within each density, a range of five Ca : nPP ratios (1.14 : 1, 1.5 : 1, 2.0 : 1, 2.75 : 1 and 4.0 : 1) were fed. Birds had free access to feed and water throughout the study. At day 28, birds were euthanised for the determination of apparent ileal mineral and amino acid digestibility. Data were modelled in R version 2.15 using a linear mixed-effects model and interrogation of the data was performed by fitting a low order polynomial function. At high Ca concentrations, increasing nPP led to an increase in the apparent digestibility of minerals. Apparent ileal digestibility of phosphorus (P) was enhanced with increasing dietary nPP up to 5.5 g/kg beyond which no improvements were found. Maximal Ca digestibility was found in diets with >8.0 g/kg Ca with concomitant low concentrations of nPP. Diets with a broader Ca : nPP ratio improved the digestibility of Ca but were deleterious to the digestibility of P. In this study, apparent digestibility of amino acids was broadly unaffected by dietary Ca and nPP concentrations. However, interactions between Ca and nPP were observed for the digestibility of glutamine, tyrosine and methionine (all P<0.001). Nitrogen digestibility showed discrete optima around 10.0 and 5.0 g/kg nPP and Na digestibility was maximised around 8 to 9.0 g/kg Ca and 4.5 to 5.4 g/kg nPP. These data show that the ratio of Ca : nPP is more influential to mineral digestibility than the absolute dietary concentration of each macro mineral.

The effects of phytic acid and microbial phytase on the flow and composition of endogenous protein at the terminal ileum of broiler chickens were investigated using the peptide alimentation method. Phytic acid (fed as the sodium salt) was included in a synthetic diet at 8·5, 11·5 and 14·5 g/kg (or 2·4, 3·2 and 4·0 g/kg phytate-phosphorus) and each diet was fed without or with an Escherichia coli-derived microbial phytase at 500 phytase units/kg diet. A control containing no phytate was fed as a comparison to estimate basal endogenous flows. Ingestion of phytic acid increased (P < 0·05) the flow of endogenous amino acids and N by an average of 47 % at the lowest phytic acid concentration and 87 % at the highest. The addition of microbial phytase reduced (P < 0·05) the inimical effects of phytic acid on endogenous amino acid flow at all dietary phytic acid levels. The composition of endogenous protein was also influenced (P < 0·10–0·001) by increasing phytic acid concentrations and phytase addition. The effects of phytic acid and phytase on endogenous flow and composition of endogenous protein, however, varied depending on the amino acid. It is concluded that the effects of phytase on amino acid digestibility may be mediated, in part, through a route of reduced endogenous loss.

The effect of the ingestion of myo-inositol hexaphosphate (IP6) and phytase (EC 3.1.3.26) on the digestibility of casein was investigated using growing broiler chickens. A total of 64 female Ross broilers were used in a precision feeding study. One group of 8 birds was fed a solution of glucose to estimate endogenous losses. Seven groups, each of 8 birds, were fed either casein, casein + 1,000 units of phytase activity (FTU), casein + 2,000 FTU, casein + 0.5 g of IP6, casein + 0.5 g of IP6 + 1,000 FTU, casein + 1 g of IP6, or casein + 1 g of IP6 + 1,000 FTU. The excretion of DM, amino acids, nitrogen, minerals, and phytate-phosphorus was determined over a 48-h period and nutrient digestibility coefficients were calculated. Casein was found to be highly digestible, with true coefficients of DM, N, and amino acid digestibility of between 0.85 and 1.0. However, the ingestion of IP6 reduced (P < 0.05) the digestibility coefficients of amino acids, N, and DM of casein compared with birds fed casein alone. Supplementation of the mixture of casein and IP6 with phytase improved (P < 0.05) the digestibility coefficients of amino acids compared with birds fed on casein and IP6 with no supplemental phytase. The excretion of endogenous minerals was increased (P < 0.05) by the ingestion of IP6 and reduced (P < 0.05) by the supplementation of IP6 with phytase. In the absence of exogenous phytase, the recovery of phytate-P in excreta was approximately 80%. However, the recovery of phytate-P was significantly reduced by the addition of exogenous phytase to the IP6/casein mixture. It can be concluded that the ingestion of IP6 reduces the digestibility coefficients of amino acids and the metabolizability of nitrogen of casein. This is likely to be mediated partially through increased endogenous losses. However, the addition of phytase can partially ameliorate the detrimental effects of IP6 on protein utilization.