Peter H. Selle
University of Sydney
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Nutrition Research Reviews | 2000
Peter H. Selle; Ravindran; Caldwell A; W. L. Bryden
The excretion of large amounts of P in effluent from intensive pig and poultry units is indicative of the poor availability of phytate-bound P in plant-derived feed ingredients. This environmental problem prompted the development and acceptance of microbial phytase feed enzymes for single-stomached animals. Their introduction led to an increasing recognition that phytate may have adverse effects on protein utilisation in addition to P. Consequently, the nutritional relevance of protein-phytate interactions for pigs and poultry is considered in the present review. Since the current understanding of the effects of protein-phytate interactions comes mainly from responses obtained to added phytase, literature on the influence of microbial phytases on amino acid digestibility and utilisation is summarised, followed by a discussion of possible mechanisms contributing to the negative effects of phytate. However, the rationale for the protein responses to added phytase remains largely speculative, and several modes of action are probably involved. It may be that the release of protein from protein-phytate complexes occurring naturally in feed ingredients, the prevention of formation of binary and ternary protein-phytate complexes within the gut, the alleviation of the negative impact of phytate on digestive enzymes and the reduction in endogenous amino acid losses are all contributing factors. A better understanding of the mechanisms of protein-phytate interactions and the modes of action of exogenous phytase enzymes is clearly desirable. Studies are also needed to identify and quantify the factors that contribute to the variable amino acid responses to added phytase. It appears that the relative solubilities of phytate salts and proteins from different feed ingredients and their effects on the extent of protein-phytate complex formation, coupled with variations in the effectiveness of phytase in different dietary contexts, may be the major factors responsible.
British Poultry Science | 2000
V. Ravindran; S. Cabahug; G. Ravindran; Peter H. Selle; W. L. Bryden
1. Male broilers (n =900) were fed on wheat-sorghum-soyabean meal based diets containing 3 concentrations of phytic acid (10.4, 13.2 and 15.7 g/kg; equivalent to 2.9, 3.7 and 4.4 g/kg phytate P), 2 concentrations of non-phytate (or available) phosphorus (2.3 and 4.5 g/kg) and 3 concentrations of microbial phytase (0, 400 and 800 FTU/kg) from day 7 to 25 post-hatch. The dietary concentrations of phytic acid were manipulated by the inclusion of rice pollards. All diets contained celite (20 g/kg) as a source of acidinsoluble ash. 2. The apparent metabolisable energy (AME) concentrations of the diets were determined using a classical total collection procedure during the 3rd week of the trial. On d 25, digesta from the terminal ileum were collected and analysed for phosphorus, nitrogen and amino acids. Nutrient digestibilities were calculated using acid-insoluble ash as the indigestible marker. 2. Ileal digestibilities of nitrogen and essential amino acids were negatively influenced by increasing dietary levels of phytic acid but these negative effects were overcome by the addition of phytase. 3. Supplemental phytase increased AME, ileal digestibilities of phosphorus, nitrogen and amino acids and the retention of dry matter, phosphorus and nitrogen in broilers. There were no differences in the phytase responses between additions of 400 and 800 FTU/kg. 4. The responses in all variables, except AME, were greater in low non-phytate phosphorus diets. 5. In the case of AME, the response to added phytase was greater in adequate non-phytate phosphorus diets. Supplemental phytase increased AME values from 13.36 to 13.54 MJ/kg dry matter in low non-phytate phosphorus diets and from 12.66 to 13.38 MJ/kg dry matter in adequate non-phytate phosphorus diets.
Nutrition Research Reviews | 2012
Peter H. Selle; A. J. Cowieson; Nathan Cowieson; V. Ravindran
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 (HPO(4)(2-)) 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.
Poultry Science | 2008
V. Ravindran; A. J. Cowieson; Peter H. Selle
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 AME(n) 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 AME(n) and ileal N digestibility. The improvements in AME(n) 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.
British Poultry Science | 1999
S. Cabahug; V. Ravindran; Peter H. Selle; W. L. Bryden
1. Seven-day old male broilers (n=900) were fed on wheat-sorghum-soyabean meal-based diets containing 3 concentrations of phytic acid (10.4, 13.2 and 15.7 g/kg; equivalent to 2.9, 3.7 and 4.4 g/kg phytate phosphorus), 2 of non-phytate phosphorus (2.3 and 4.5 g/kg) and 3 of microbial phytase (Natuphos 5000 L; 0, 400 and 800 FTU/kg) in a 19-d trial. The dietary phytic acid contents were manipulated by the inclusion of rice pollard. 2. Each dietary treatment was fed to 5 pens (10 birds/pen) from 7 to 25 d of age. Records of body weight, food intake and mortality were maintained. On d 25, all surviving birds were killed and toe samples were obtained for toe ash measurements. 3. Increasing dietary phytic acid negatively influenced body weight gain, food intake and food/gain. These adverse effects were partially overcome by the addition of microbial phytase. 4. Supplemental phytase caused improvements in weight gain and food efficiency of broilers but the magnitude of the responses was greater in low non-phytate phosphorus diets, resulting in significant non-phytate phosphorus x phytase interactions. 5. Toe ash contents were improved by phytase addition but the response was greater at the highest concentration of phytic acid, resulting in a significant phytic acid x phytase interaction. Responses were also greater in low non-phytate phosphorus diets as indicated by significant non-phytate phosphorus x phytase interaction. 6. In general, there was very little difference in the responses to phytase additions at 400 and 800 FTU/kg. 7. The performance responses to added phytase in birds receiving adequate non-phytate phosphorus diets provide evidence for the influence of the enzyme on animal performance independent of its effect on phosphorus availability.
Worlds Poultry Science Journal | 2009
A. J. Cowieson; M. R. Bedford; Peter H. Selle; V. Ravindran
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.
Poultry Science | 2008
A. J. Cowieson; V. Ravindran; Peter H. Selle
The effects of phytic acid and 2 sources of exogenous phytase (bacterial vs. fungal) on the flow of endogenous amino acids at the terminal ileum of broilers were assessed using the enzyme-hydrolyzed casein method. Phytic acid (as the sodium salt) was included in a purified diet at 8.5 and 14.5 g/kg, and each diet was fed without or with a fungal (Aspergillus niger-derived) or a bacterial (Escherichia coli-derived) microbial phytase at 500 phytase units/kg of diet. Increasing the concentration of phytic acid in the diet from 8.5 to 14.5 g/kg increased (P < 0.001) the flow of all measured amino acids by an average of 68%, with a range from 17% for proline to 145% for phenylalanine. The flow of endogenous aspartic acid, serine, glutamic acid, glycine, leucine, tyrosine, phenylalanine, and histidine were increased by more than the mean, indicating changes in the composition of endogenous protein in response to the presence of higher concentrations of phytic acid. Supplementation of both phytases reduced (P < 0.001) the flow of endogenous amino acids, but the reduction (P = 0.06) was greater for the bacterial phytase compared with the fungal phytase. These data suggest that a substantial part of the amino acid and energy responses observed following phytase supplementation in broiler chickens stems from reduced endogenous amino acid flows and that the capacity of different phytases to counteract the antinutritive properties of phytic acid vary.
British Poultry Science | 2009
L. L. Mikkelsen; J.K. Vidanarachchi; C.G. Olnood; Y. M. Bao; Peter H. Selle; M. Choct
1. The effect of potassium diformate (KDF) on mortality, growth performance, microbial populations, pH and short chain fatty acid concentrations in the intestinal tract of broiler chickens challenged with necrotic enteritis was investigated. 2. An experiment with 1050 Cobb male broiler chickens was conducted from 1 to 35 d of age. There were 7 treatment groups: (1) unchallenged negative control, (2) unchallenged KDF (4·50 g/kg feed), (3) challenged negative control, (4) challenged positive control (100 ppm monensin and 45 ppm Zn-bacitracin), and (5) to (7) challenged KDF (inclusion rate 2·25, 4·50 and 6·75 g/kg feed, respectively). 3. The necrotic enteritis challenge caused significant growth depression except in the challenged positive control group. Inclusion of KDF in feed had no significant effect on weight gain or feed conversion ratio, neither under challenged nor unchallenged conditions. Necrotic-enteritis-related mortalities were reduced in response to the positive control feed and KDF at 2·25 and 4·50 g/kg rates, but with no effect at the 6·75 g/kg rate. 4. There was no effect of KDF on Clostridium perfringens numbers in jejunum during the necrotic enteritis challenge (d 15). Post challenge (d 35), 4·5 g/kg KDF reduced the number of C. perfringens and Enterobacteria in jejunum compared with the negative control group. 5. Intestinal pH was not affected by adding KDF to the feed. The challenge reduced jejunum pH compared with the unchallenged treatment groups and challenged positive control group. 6. Chickens fed the KDF diets had detectable concentrations of formic acid in the jejunum. There was a tendency towards higher concentrations of acetic acid and lactic acid in the small intestine of unchallenged birds, whereas challenged birds had higher concentrations of butyric acid in the caeca. 7. It is concluded that KDF holds promise as an agent to control necrotic enteritis in broiler chickens and it may be possible to enhance the efficacy of KDF by manipulating dietary properties that may influence the dissociation kinetics of KDF in the gut.
Animal Production Science | 2013
Peter H. Selle; Sonia Yun Liu; J. Cai; A. J. Cowieson
A red sorghum was mediumly ground (3.2 mm) and incorporated into broiler diets that were steam-pelleted at conditioning temperatures of 65, 80 and 95°C and offered to male Ross 308 chicks from 7 to 28 days post hatch. This diet was also fed as unprocessed mash, reground mash following steam-pelleting at 95°C and diets steam-pelleted at 80°C were fed without and with exogenous protease. A nutritionally equivalent diet based on a mediumly ground white sorghum steam-pelleted at 95°C completed the seven dietary treatments each of which were offered to seven replicates of six birds per cage. The effects of treatment on growth performance, relative gizzard weights, nutrient utilisation [apparent metabolisable energy (AME), nitrogen (N) retention, and N-corrected AME] and apparent digestibility coefficients of starch and N in four segments of the small intestine (proximal and distal jejunum, proximal and distal ileum) were determined. Elevating conditioning temperatures at which the red sorghum-based diets were steam-pelleted reduced their protein solubilities and linearly reduced concentrations of free sulfydryl groups (P 0.50). Increasing conditioning temperatures influenced N digestibility coefficients in the distal jejunum (P < 0.01) and distal ileum (P < 0.05) in a quadratic manner. N coefficients varied from 0.565 to 0.538 and 0.638 in the distal jejunum with increasing conditioning temperatures; however, starch digestibility coefficients were not significantly influenced by conditioning temperatures. Birds offered the white sorghum-based pelleted diet conditioned at 95°C significantly outperformed (P < 0.05) their red sorghum counterparts in terms of weight gain, feed per gain, AME, N retention, starch and N digestibility coefficients in the distal ileum. The differences in starch digestibility between the two sorghum varieties along the small intestine were pronounced and the possible contributing factors are considered. Diets fed as intact pellets generated greater feed intakes and weight gains than the average of the two mash diets. In red sorghum-based diets, distal ileal starch digestibility coefficients of intact pellets were inferior to the unprocessed and reground mash. However, the distal ileal N digestibility coefficient of the unprocessed mash diet was 3.5% higher than the reground mash diet and 8.3% higher than the intact pelleted diet. The inclusion of a Bacillus lichenformis-derived protease in red sorghum-based steam-pelleted at 80°C significantly (P < 0.05) increased N digestibility coefficients in the distal jejunum, proximal ileum and distal ileum. Also, this protease significantly increased starch digestibility coefficients in the distal jejunum and proximal ileum. The implications of these findings in respect of feeding broiler chickens sorghum-based diets are discussed.
Animal Production Science | 2012
Peter H. Selle; Sonia Yun Liu; J. Cai; A. J. Cowieson
Sorghum grains with red, white and yellow seed colours were coarsely ground and incorporated into nutritionally equivalent diets that were offered to broiler chicks in three feed forms. The diets were fed as mash or steam-pelleted at a conditioning temperature of 90°C and fed as intact pellets or ground back into mash as reground pellets. The effects of a 3 × 3 factorial array of dietary treatments offered to male chicks from 6 to 27 days post-hatch on growth performance, nutrient utilisation and apparent digestibility coefficients of starch and nitrogen (N) at the proximal jejunum, proximal ileum and distal ileum were determined. Feed form had a greater impact on the parameters assessed than did sorghum seed colour, but several interactions between these main effects were observed. Steam-pelleting diets reduced protein solubility and this was correlated with increased concentrations of disulfide bonds and decreased concentrations of free sulphydryl groups. Steam-pelleting diets significantly depressed N retention in broiler chicks and this reduction was appropriately correlated with concentrations of disulfide bonds and free sulphydryl groups and dietary protein solubility. While N retention was depressed, in a curious outcome, steam-pelleting diets did not compromise N digestibility along the small intestine. Steam-pelleting diets significantly increased starch digestibility coefficients in the proximal jejunum, with differing responses among the sorghums, but not in the two ileal levels. Phytate concentrations in the three sorghums were negatively correlated with N digestibility coefficients at the proximal jejunum and proximal ileum. The implications of the present feeding study in relation to the performance of broiler chickens offered steam-pelleted, sorghum-based diets are discussed.