low-P Diet Research Articles

Hydrolysis of phytate and formation of inositol phosphate isomers without or with supplemented phytases in different segments of the digestive tract of broilers.

The objective was to characterise degradation of myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6) and formation of inositol phosphate (InsP) isomers in different segments of the broiler digestive tract. Influence of an Aspergillus niger (PhyA) and two Escherichia coli-derived (PhyE1 and PhyE2) phytases was also investigated. A total of 600 16-d-old broilers were allocated to forty floor pens (ten pens per treatment). Low-P (5·2g/kg DM) maize-soyabean meal-based diets were fed without (basal diet; BD) or with a phytase added. On day 25, digesta from different digestive tract segments were pooled per segment on a pen-basis, freeze-dried and analysed for P, InsP isomers and the marker TiO2. InsP6 degradation until the lower ileum (74 %) in BD-fed birds showed a high potential of broilers and their gut microbiota to hydrolyse InsP6 in low-P diets. Different InsP patterns in different gut segments suggested the involvement of phosphatases of different origin. Supplemented phytases increased InsP6 hydrolysis in the crop (P<0·01) but not in the lower ileum. Measurements in the crop and proventriculus/gizzard confirmed published in vitro degradation pathways of 3- and 6-phytases for the first time. In the intestinal segments, specifically formed InsP4-5 isomers of supplemented phytases were still present, indicating further activity of these enzymes. Myo-inositol tetrakisphosphate (InsP4) accumulation differed between PhyE1 and PhyE2 compared with PhyA in the anterior segments of the gut (P<0·01). Thus, the hydrolytic cleavage of the first phosphate group is not the only limiting step in phytate degradation in broilers.

Reducing geosmin off-flavor compounds and waste outputs through dietary phosphorus management in rainbow trout aquaculture

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 6:105-117 (2014) - DOI: https://doi.org/10.3354/aei00119 Reducing geosmin off-flavor compounds and waste outputs through dietary phosphorus management in rainbow trout aquaculture Pallab Sarker1,3,*, Alexandre Pilote1, Marc Auffret2, Émilie Proulx1, Richard Villemur2, Marie-Hélène Deschamps1, Grant Vandenberg1 1Département des sciences animales, Université Laval, Québec City, Québec G1V 0A6, Canada 2INRS-Institut Armand-Frappier, 531 Boulevard des Prairies, Laval, Québec H7V 1B7, Canada 3Present address: Environmental Studies Program, Dartmouth College, Hanover, New Hampshire 03755, USA *Corresponding author: pallab.k.sarker@dartmouth.edu ABSTRACT: The aquaculture industry has long recognized the need to reduce phosphorus (P) waste outputs associated with environmental impact, and reduce off-flavor producing compounds, which can impact the quality of the fish product. This study was undertaken to investigate the effects of dietary high P (HP) and low P (LP) on growth, nutrient digestibility, P retention, and P loading as well as their correlation to the synthesis of geosmin-associated off-flavor in a recirculating aquaculture system of rainbow trout Oncorhynchus mykiss. The above diets were fed to quadruplicate tanks of rainbow trout (average mass ± SD: 127.4 ± 3.1 g) for 84 d. Results showed that the effects of the HP and LP diets on growth and P retention were not significantly different. While the apparent digestibility of P and other nutrients were higher in fish fed the LP diet, P waste outputs and geosmin levels in the fillets of fish were higher in fish fed the HP diet. Magnesium (Mg2+), potassium (K+) and zinc (Zn2+) concentrations in tank water were significantly lower in fish fed the HP diet than the LP diet in most of the sampling events. Furthermore, the tank water geosmin concentration was not strongly proportionally correlated with tank water-soluble P concentration for both the LP and HP diets. There was a strong proportional linear relationship between the geosmin concentration in tank water and in trout fillet for both the LP and HP diets. Results suggest that off-flavor contents in fish fillets and water were related to the dietary P level and metabolic P waste outputs into the system, findings that have implications for the formulation of sustainable diets for rainbow trout. KEY WORDS: Recirculating aquaculture system · Metabolic phosphorus waste · Off‑flavor · Geosmin · Oncorhynchus mykiss · Growth · Nutrient digestibility · Nutrient retention Full text in pdf format PreviousCite this article as: Sarker P, Pilote A, Auffret M, Proulx É, Villemur R, Deschamps MH, Vandenberg G (2014) Reducing geosmin off-flavor compounds and waste outputs through dietary phosphorus management in rainbow trout aquaculture. Aquacult Environ Interact 6:105-117. https://doi.org/10.3354/aei00119 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 6, No. 1. Online publication date: December 17, 2014 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2014 Inter-Research.

Preliminary study for description of bone tissue responsiveness to prolonged dietary phosphorus deficiency in rainbow trout,Oncorhynchus mykiss(Walbaum)

Prolonged dietary phosphorus (P) deficiency induces a generalized demineralization of bone tissues; however, the differential responsiveness of the diverse tissues to P deficiency remains unknown. Triploid all-female juvenile rainbow trout (initial mass ~60 g) were fed two practical diets (0.26% and 0.52% digestible P for P-deficient and P-sufficient diets) until P-sufficient fish reached 850 g (241 days; 12°C; 18:6 D:L). Early P-deficient fish were fed from day 0 the low P-diet, while late P-deficient only started feeding at day 134. Growth performance was assessed monthly and carcass samplings were performed at day 0, 134 and 241 to assess mineralization characteristics of different tissues. Ash and content of phosphorus, calcium and magnesium of scales, operculae, ribs and vertebrae as well as the occurrence of abnormalities in ribs and vertebrae were assessed. The tissues most affected by P deficiency were: vertebrae > scales > opercula > ribs. P deficiency affects bone tissues differentially based on the physiological and biomechanical roles of the tissues. As scales were found to be a better indicator to predict abnormalities, understanding of scale metabolism could facilitate P status estimation in fish.

Responses of different body compartments to acute dietary phosphorus deficiency in juvenile triploid rainbow trout (Oncorhynchus mykiss , Walbaum)

Rainbow trout (Oncorhynchus mykiss) is an important production species as well as one of the most studied fish models, particularly regarding nutritional physiology. Due to negative environmental impacts linked with rainbow trout farm effluents, significant restrictions have been established in numerous regions to reduce dietary phosphorus (P) outputs. However, questions have arisen regarding the link between abnormal skeletal development and mineralization and insufficient dietary P availability during rapid fish growth (juvenile fish). Despite significant work to understand the dynamics of P-deficiency and the resulting impact on tissue mineralization, the extent of the early responses in rainbow trout fed low-P diets is not well described. The aim of this study was to explore the early-responses of scales, vertebrae and carcass P and ash in rainbow trout fed low-P vs sufficient-P controls. Two practical diets (sufficient: 0.45% available P and deficient: 0.29% available P) were fed over a 5-week period to triploid rainbow trout (initial mass 60.8 ± 1.6 g). Ash and P contents were used to assess mineral status of the different tissues. The relative loss of mineral and coefficient of variation were also calculated to compare the relative response and the inter-individual variability. After 4 weeks of P deprivation, no detectable effects were observed on growth performance, mortality or feed intake. However, as early as the second week onward, ash and P levels in scales and carcasses were significantly lower (p < 0.05) in fish fed a P-deficient diet compared to those fed a P-sufficient diet. At week 4, the reduction in mineralization reached 19.3 and 18.4% for P and ash contents in scales, respectively. By the same week, P and ash contents in carcasses reached 15.1 and 12.8%, respectively. Interestingly, the absence of significant mineral loss in vertebrae did not prevent the emergence of a high incidence of vertebral deformities in P-deficient fish (45.6 ± 11.0%) when compared to P-sufficient fish (1.5 ± 2.1%). The main vertebral deformities observed in P-deficient trout were specific to impede bone matrix mineralization such as pronounced biconcave (35.5%) and undersized and widely spaced vertebral bodies (9.3%). For the scales compartment (ash and P status) and mineral parameter, the coefficients of variation showed a higher inter-individual variability in P-deficient vs P-sufficient fish, while no such effect was observed in carcass or vertebrae compartment. This study provides a useful comparison of various commonly-used indicators of bone mineral status as well as an approach to assess variability of fish response under low-dietary P level.

Improvements in growth performance, bone mineral status and nutrient digestibility in pigs following the dietary inclusion of phytase are accompanied by modifications in intestinal nutrient transporter gene expression.

Phytase (PHY) improves growth performance, nutrient digestibility and bone structure in pigs; however, little is known about its effects on intestinal nutrient transporter gene expression. In the present study, a 44 d experiment was carried out using forty-eight pigs (11·76 (sem 0·75) kg) assigned to one of three dietary treatment groups to measure growth performance, coefficient of apparent ileal digestibility (CAID), coefficient of apparent total tract nutrient digestibility (CATTD) and intestinal nutrient transporter gene expression. Dietary treatments during the experimental period were as follows: (1) a high-P (HP) diet containing 3·4 g/kg available P and 7·0 g/kg Ca; (2) a low-P (LP) diet containing 1·9 g/kg available P and 5·9 g/kg Ca; (3) a PHY diet containing LP diet ingredients+1000 phytase units (FTU)/kg of PHY. The PHY diet increased the average daily gain (P< 0·05) and final body weight (P< 0·01) and decreased the feed conversion ratio (P< 0·05) compared with the LP diet. Pigs fed the PHY diet had a higher CAID of gross energy compared with those fed the HP and LP diets (P< 0·001). Pigs fed the PHY diet had increased CAID of P (P< 0·01) and CATTD of Ca and P (P< 0·001) compared with those fed the LP diet. The PHY diet increased the gene expression of the peptide transporter 1 (PEPT1/SLC15A1) (P< 0·05) in the ileum compared with the LP diet. The LP diet decreased the gene expression of the sodium-glucose-linked transporter 1 (SGLT1/SLC5A1) and GLUT2/SLC2A2 (P< 0·05) and increased the expression of membrane Ca channel (TRPV6) and calbindin compared with the HP diet (P< 0·001). In conclusion, feeding a diet supplemented with PHY improves growth performance and nutrient digestibility as well as increases the gene expression of the peptide transporter PEPT1.

Effect of microbial phytase on phytate P degradation and apparent digestibility of total P and Ca throughout the gastrointestinal tract of the growing pig1

The effect of a dietary microbial phytase on mineral digestibility throughout the gastrointestinal tract (GIT) of the growing pig was studied. Thirty-two entire male pigs (~22 kg BW) were allocated equally to 4 corn-soybean meal diets. One diet was adequate in total P and Ca, the second diet was deficient in total P and Ca (low-P diet), and the third and fourth diets were the low-P diet with microbial phytase added at 1,107 U/kg or 2,215 U/kg, respectively. Titanium dioxide (3 g/kg) was included in the diets as an indigestible marker. The pigs were fed their respective diets for 42 d. Fecal samples were collected from d 38 to 41 and stomach chyme, terminal jejunal, and terminal ileal digesta samples were collected after euthanasia on d 42. Phytate P degradability and apparent total P and Ca digestibility were determined at the gastric, jejunal, ileal, and total tract levels. Phytate P degradation and apparent total P and Ca digestibility were not significantly different between the 2 microbial phytase inclusion levels. Across both microbial phytase-low-P diets, phytase supplementation increased (P < 0.05) phytate P degradability at the jejunal, ileal, and total tract levels by 101%, 77%, and 10%, respectively, but not at the gastric level. Total tract phytate P degradation was greater (P < 0.05) than ileal phytate P degradation for both the unsupplemented (52% units greater) and phytase-supplemented, low-P (26% units greater) diets. The latter result was not reflected by the apparent total P digestibility estimate, which was not significantly different between the ileal and total tract levels for both the unsupplemented and phytase-supplemented, low-P diets. Consequently, there appeared to be considerable phytate degradation in the hindgut, presumably due to the action of hindgut microbes, but the phytate P released in the hindgut did not appear to be absorbed. Apparent Ca digestibility was not significantly different among jejunal, ileal, and total tract levels for any of the dietary treatments, but apparent Ca digestibility was greater (P < 0.05) for the phytase-supplemented diets compared with the unsupplemented diets. Overall, dietary microbial phytase supplementation led to greater phytate degradation to the end of the jejunum. Because the phytate P released in the hindgut was not absorbed, ileal estimates, rather than total tract estimates, of phytate degradation appear to more accurately reflect P availability.

Assessment of a bacterial 6-phytase in the diets of broiler chickens

Two 21-d broiler experiments were conducted to assess the efficacy of a bacterial 6-phytase expressed in Aspergillus oryzae on growth performance, nutrient utilization, and intestinal molecular markers. Two hundred forty birds in 5 treatments (experiment 1) or 256 birds in 4 treatments (experiment 2) were used. The treatments included a negative control diet that was marginally deficient in P (NC) or NC plus tricalcium phosphate, 500, 1,000, or 2,000 phytase units/kg (experiment 1), and NC or NC plus monocalcium phosphate, 500 or 1,000 phytase units/kg (experiment 2). In both experiments, excreta were collected on d 19 to 21, whereas birds and feed were weighed and ileal digesta collected on d 21. For experiment 1, mucosa scraping was collected from the duodenum, jejunum, and ileum from all birds for quantification of expression level of gut level inflammatory cytokines, Toll-like receptors, and phosphate transporter (NaPi-IIb). In both experiments, tricalcium phosphate, monocalcium phosphate, and phytase supplementation improved (P < 0.05) weight gain and percentage tibia ash. Phosphorus and Ca retention and phytic acid disappearance improved (P < 0.05) with phytase supplementation (experiment 1) and there was an increase (P < 0.01) in Ca and P retention in response to phytase supplementation (experiment 2). Diets did not affect the expression of gut level cytokines, Toll-like receptors, or the mucin gene. Phytase supplementation tended to decrease (P < 0.10) the expression of NaPi-IIb. It was concluded from these studies that the bacterial 6-phytase was effective in enhancing growth of broilers receiving low-P diets as well as in increasing efficiency of P utilization and phytic acid degradation.

Effect of two microbial phytases on mineral availability and retention and bone mineral density in low-phosphorus diets for broilers

1. The efficacy of supplementation of a low-phosphorus (low-P) maize–soyabean meal diet for broiler chickens with two different microbial (fungal and bacterial) phytases was examined. 2. Broiler chickens received a low-P maize–soyabean meal diet containing either no phytase or one of the two phytases included at one and two times the manufacturer's recommended inclusion level for 21 d. 3. Titanium dioxide was included in the diets as an indigestible marker. Excreta were collected quantitatively from d 18 to 21, and at the end of the study the birds were killed and ileal digesta and leg bone samples collected. 4. No differences were observed for body weight gain and feed intake or apparent metabolisable energy (AME) among all dietary treatment groups. 5. Dietary phytase supplementation improved the apparent retention of Ca, Na and Cu and ileal phytate P absorption from 32% to 44% across inclusion levels. 6. Bone mineral density (BMD) was improved for both phytases across inclusion levels by, on average, 9% for the tibia and 13% for the femur. 7. Dietary phytase supplementation of the low-P diet improved apparent ileal digestibility of serine, glycine, valine, isoleucine, tyrosine, histidine, lysine and arginine. 8. When the results from the present study were combined with the results from other similar published studies and analysed statistically, factors such as dietary P and Ca concentration, as well as bird breed and age, rather than the type or activity of microbial phytase, had the greatest impact on the extent to which dietary supplementation improved P and Ca retention. 9. More work is required to explain the interrelationships between the multiple factors influencing the efficacy of phytase on the availability of dietary minerals.

Phosphorus balance and fecal losses in growing Standardbred horses in training fed forage-only diets1

This study examined the P balance and fecal P losses in growing Standardbred horses in training fed a forage-only diet with or without P supplementation and assessed the magnitude and proportion of the soluble, inorganic P (Pi) fraction in feces. Fourteen Standardbred horses (aged 20.0 ± 0.3 mo) adapted to ad libitum intake of grass forage containing 0.25% P were used in a crossover experiment investigating 2 dietary treatments with (high-P) and without (low-P) mineral supplementation for 6 d. Daily feed intake and refusals were weighed. Spot samples of feces were collected twice daily on d 4 to 6 and analyzed for total P and Pi. Acid-insoluble ash was used as a marker for total fecal output. Spot samples of urine were collected once on d 4 to 6 and analyzed for P and creatinine. Daily P intake was greater (P < 0.001) for the high-P diet (32.0 ± 0.6 g) than the low-P diet (17.5 ± 0.6 g), and the individual intake ranged from 13.3 to 38.4 g/d. Total fecal excretion of P was also greater (P < 0.001) for the high-P diet (30.3 ± 0.8 g/d) than the low-P diet (17.0 ± 0.8 g/d) whereas excretion in urine was less than 0.2 g/d on both diets. Using simple regression analysis, fecal endogenous P losses were estimated to be less than 10 mg/kg BW. Phosphorus retention was 1.6 ± 0.6 and 0.3 ± 0.6 g/d on the high- and low-P diets, respectively, but only that for the high-P diet was greater (P < 0.05) than 0 g/d. The proportion of Pi of total fecal P excretion was 100 ± 3% for the high-P diet and 87 ± 3% for the low-P diet (P = 0.005) and Pi increased linearly with P intake (y = 1.10x - 4.44; r(2) = 0.91; CV = 9.9%; P < 0.001). In conclusion, on this forage-only diet significant retention of P occurred at a daily P intake of 7.1 g/100 kg BW. Phosphorus was mainly excreted in feces and both total fecal P and Pi excretion had a strong relationship to P intake. More than 80% of total P appeared to be soluble. Fecal endogenous P losses were similar to those described previously in growing horses.

The supplementation of low-P diets with microbial 6-phytase expressed in Aspergillus oryzae improves P digestibility in sows

Two trials were conducted to evaluate a novel microbial 6-phytase expressed in Aspergillus oryzae (Ronozyme HiPhos; DSM Nutritional Products, Basel, Switzerland) in gestating and lactating sows. In the first trial, 24 sows (Duroc × Landrace; 223 kg BW) were offered, at 16 d of gestation, a low-P control diet (formulated to provide 4.0 g total P/kg; 1.5 g digestible P/kg) supplemented with 0, 500, or 1000 phytase activity (FYT)/kg of phytase. Two weeks later, fresh feces were sampled from all sows and the apparent total tract digestibility of P was measured using TiO(2) as indigestible marker. Phytase supplementation did not (P > 0.10) affect the total tract digestibility of P but reduced (P < 0.05) P concentration in feces (from 14.5 to 12.0 and 12.0 g/kg DM). In the second trial, 32 lactating sows (Duroc × Landrace; 282 kg BW) were used. They were offered, at 7 d of lactation, a low-P control diet (formulated to provide 6.1 g total P/kg; 3 g digestible P/kg) or the same diet supplemented with 500 FYT/kg of phytase. After 2 wk, fresh feces were sampled from all sows and the apparent total tract digestibility of P was measured using TiO(2) as indigestible marker. Phytase supplementation improved (P < 0.001) the apparent total tract digestibility of P from 27.5 to 38.7% and reduced (P < 0.001) P concentration in feces (from 27.5 to 21.4 g/kg DM). In conclusion, the microbial 6-phytase tested increased the apparent total tract digestibility of P in sows and reduced P excretion in feces.

The supplementation of low-P diets with microbial 6-phytase expressed in Aspergillus oryzae increases P and Ca digestibility in growing pigs

A trial was conducted to evaluate the dose response of a novel microbial 6-phytase expressed in Aspergillus oryzae (Ronozyme HiPhos; DSM Nutritional Products, Basel, Switzerland) in pigs. Forty-eight individually housed pigs (Landrace × Pietrain; 52 kg BW; 24 males and 24 females) were distributed among 6 experimental treatments consisting of a low-P diet (3.5 g P/kg; 1.1 g digestible P/kg), which was supplemented with 500, 1000, 2000, or 4000 units of phytase activity/kg, and a standard-P diet (4.5 g P/kg; 1.8 g digestible P/kg) that was supplemented with CaHPO(4). After 17 d, fresh feces were sampled from all pigs and the apparent total tract digestibility of DM, OM, ash, P, and Ca was measured using TiO(2) as indigestible marker. Blood samples were also obtained from each pig and serum was analyzed for P and Ca concentrations. The nonsupplemented low-P diet increased Ca and reduced P blood serum concentrations (P < 0.05) relative to the standard-P diet (10.8 vs. 10.2 and 6.7 vs. 7.7 mg/dL, respectively). Phytase supplementation of the low-P diet reduced Ca (from 10.8 to 9.9 mg/dL; linear, P < 0.001) and increased P concentrations (from 6.7 to 8.0 mg/dL; linear and quadratic, P < 0.001) in serum and reduced P concentration in feces (from 13.7 to 7.6 g/kg DM; linear and quadratic, P < 0.001). Phytase improved the total tract digestibility of P (from 29.0 to 62.3%; linear and quadratic, P < 0.001 and P < 0.05), Ca (from 54.0 to 75.7%; quadratic, P < 0.01), and ash (from 46.2 to 57.7%; quadratic, P < 0.01). In conclusion, the microbial 6-phytase tested improves the apparent total tract digestibility of P in growing pigs and reduces P excretion in feces in a dose-dependent manner.

The Influence of Dietary Calcium and Phosphorus Imbalance on Intestinal NaPi-IIb and Calbindin mRNA Expression and Tibia Parameters of Broilers.

A 2×2 factorial experiment was conducted to study the effect of dietary calcium and non-phytate phosphorus (nPP) imbalance on calbindin and NaPi-IIb mRNA levels in the small intestine and tibia parameters of broiler chicks. One hundred and forty four 1-d-old Arbor Acres male broiler chicks were divided into four treatments consisted of six replicates with six chicks each. The two dietary calcium levels were 1.10% and 0.60%, and two dietary nPP levels were 0.50% and 0.27%. Results showed that a high Ca/nPP ratio diet (4.07:1) significantly depressed feed intake and weight gain of broilers (p<0.05), but a lower Ca:nPP ratio (1.2:1) had no influence (p>0.05). Low-Ca with low-P diet resulted in low tibia minerals and tibia breaking strength of broilers, and all the tibia parameters were further decreased when the dietary ratio of Ca to P was relative higher. Low dietary Ca or P up-regulated the calbindin and NaPi-IIb mRNA expression levels. Low Ca with normal P diet up-regulated duodenal calbindin mRNA expression level to the greatest extent. Low P with a normal Ca diet significantly enhanced NaPi-IIb mRNA expression level to the highest extent. These results suggest that the calbindin and NaPi-IIb mRNA expression were enhanced by the imbalance between dietary Ca and nPP, and their expression were not only influenced by Ca or nPP level, but also the ratio of Ca:nPP.

Productive performance and histological features of intestinal mucosa of broiler chickens fed different dietary protein levels

To evaluate the effect of decreasing dietary protein on growth performance, carcass traits, and intestinal mucosal morphometry, 180 female Hubbard strain broiler chickens were divided into 3 groups and fed 3 isoenergetic diets ad libitum from 14 d of age until slaughter age (49 d). The treatments varied according to 3 protein levels: high-protein diet (HiP, 22.5% CP, DM basis), medium-protein diet (MedP, 20.5% CP), and low-protein diet (LowP, 18.5%). Diets were obtained by replacing wheat middlings with soybean meal and were formulated to meet or exceed broiler amino acid requirements of the NRC. Morphometric indices of duodenum, jejunum, and ileum were measured at the end of the feeding period and included villus height, crypt depth, villus-to-crypt ratio, and apparent villus surface area. The dietary protein level had a significant effect on final BW of birds, whereas ADG, ADFI, and feed efficiency remained unaffected by dietary treatment. The muscle (breast and drumstick) yields were significantly higher in birds fed the HiP diet compared with those of the MedP and LowP diets. Meat quality traits were not affected by the protein level. The villus surface area of all intestinal segments did not change among groups. Instead, reducing the dietary protein level to 20.5% resulted in a higher villus height and villus height to crypt depth ratio in the duodenum and ileum. On the basis of our findings, even if the high-protein diet promoted meat yield, a medium-protein diet could positively support broiler growth performance, as confirmed by favorable morphometric features of the intestine.

The Effect of Dietary Supplementation with Phytase Transgenic Corn on Growth Performance, Phosphorus Utilization and Excretion in Growing Pigs ( Sus scrofa)

Two experiments were conducted to investigate the effect of dietary supplementation with phytase transgenic corn (PTC) on growth performance, phosphorus (P) utilization and excretion in growing pigs. In Exp. 1, 180 pigs (Large White ×Landrace, BW=37.7 kg) were randomly allotted to 4 treatments with 5 replicates of 9 pigs each in order to evaluate the effect of PTC supplementation in low-P diets on growth performance. Four corn soybean meal-based diets consisted of a positive control (PC) diet, a diet containing 500 units (U) of exogenous phytase kg −1 (EP) on the basis of low-P (inorganic P reduced by 0.05% from PC diet) and the low-P+500 (PTC1) or 750 (PTC2) phytase U of PTC kg −1. In Exp. 2, 20 barrows (Large White×Landrace, BW=31 kg, 4 treatments with 5 replicates of 1 pig each) were randomly selected to evaluate the effect of PTC in low-P diets on serum parameters and nutrient utilization. Diets in Exp. 2 were similar to those in Exp. 1 except that the EP group was replaced by a low-P diet without exogenous phytase supplementation as a negative control (NC) group. The results from Exp. 1 showed that the average daily gain (ADG) in the PTC2 group was significantly higher ( P<0.05) than that in the EP group over all periods. On the other hand, the feed:gain (F:G) ratio of the EP group was significantly higher ( P<0.05) than that of the PTC2 group during 1–21 and 1–42 d, respectively. There were no differences in average daily feed intake (ADFI) among all treatments ( P>0.05). The results from Exp. 2 showed that the concentration of serum Ca in the NC group was the highest ( P<0.05), while the concentration of serum P in the PTC2 group was the highest ( P<0.05) among all treatments. There was a significant decrease ( P<0.05) in the P apparent digestibility of the NC group compared with the other groups, and that of PTC2 group was the best. Furthermore, fecal P excretion was reduced ( P<0.05) from 1.80 g d −1 in the PC group to 1.28 g d −1 in the PTC2 group. In conclusion, dietary supplementation with PTC could reduce the application of inorganic P, decrease fecal P excretion, and improve the growth performance of growing pigs.

Effect of phytase level in a low phosphorus diet on performance and bone development in weaner pigs and the subsequent effect on finisher pig bone development

Two experiments (Exp. 1 and Exp. 2) were conducted to investigate the effects of phytase inclusion levels in a low-P weaner pig (from 7.8 to 33 kg) diet and weaner pig nutrition on the finisher pig offered an adequate P diet from 33 to 100 kg. In Exp. 1, which was designed to examine growth performance and bone mineral status, 96 pigs [initial body weight (BW), 7.8 kg; 2 pigs/pen] were allocated to one of four dietary treatments: (T1) basal diet [2.2 g available P (aP)/kg]; (T2) basal diet and 500 phytase units (FTU)/kg; (T3) basal diet and 1000 FTU/kg; and (T4) basal diet and 1500 FTU/kg with 12 pens per treatment. Bones were collected from 12 randomly selected pigs per treatment (one pig/pen) at the end of the study (33 kg BW). The remaining 48 pigs were then offered a diet containing adequate Ca and P until slaughter (100 kg BW). There was a linear improvement in weaner pig feed conversion ratio (FCR; P < 0.01) as the level of phytase inclusion increased. There were linear increases in bone ash ( P < 0.01), bone Ca ( P < 0.01) and bone P ( P < 0.05) concentrations at 33 kg BW as the level of phytase inclusion increased. Offering weaner pig diets with increasing levels of phytase resulted in the finished pig (100 kg BW) showing quadratic ( P < 0.001) responses in bone ash, bone Ca and bone P concentrations with a maximum response obtained at 1000 FTU/kg. In Exp. 2, 16 entire male pigs (18.9 kg BW) were offered identical diets to those offered to the weaner pigs in Exp. 1 (n = 4) to determine coefficients of total tract apparent digestibility and P, Ca and N utilization. There was a linear increase in P ( P < 0.01) and Ca digestibility ( P < 0.05) as the level of phytase inclusion increased. Overall, increasing phytase supplementation in a low-P diet (2.2 g aP/kg) improved FCR and bone mineralization at the weaner stage (33 kg). In addition, phytase supplementation with 1000 FTU/kg in a weaner diet yielded maximum response in bone mineralization at 100 kg BW despite the fact that pigs were offered an adequate Ca and P diet from 33 to 100 kg BW.

The effect of phosphorus restriction during the weaner-grower phase on compensatory growth, serum osteocalcin and bone mineralization in gilts

Ninety-six female pigs with an initial body weight (BW) of 10.0 ± 1.6 kg were assigned to 4 dietary treatments to determine the effects of restricting dietary phosphorus (P) level during the weaner-grower [approximately 10 to 50 kg BW; day (d) 0 to 59] and finisher (approximately 50 to 100 kg BW; d 59 to 131) period on growth performance, serum osteocalcin concentration, bone development and calculated P utilization. The dietary treatments were: (1) 4.0 g total P (tP)/kg from d 0 to 131 (LL); (2) 4.0 g tP/kg from d 0 to d 59 and 6.0 g tP/kg from d 59 to 131 (LH); (3) 6.0 g tP/kg from d 0 to 131 (HH) and (4) 6.0 g tP/kg from d 0 to 59 and 4.0 g tP/kg from d 59 to 131 (HL). During the weaner-grower period (d 0 to 59), pigs offered high P diets had higher daily gain ( P < 0.001), feed intake ( P < 0.05), P intake ( P < 0.001), bone ash ( P < 0.05) and serum osteocalcin concentration ( P < 0.05) compared to pigs offered low-P diets. Pigs offered LH, HH and HL diets had higher average daily gain compared to pigs offered LL diet from d 59 to 131 ( P < 0.01). Pigs offered LL diet had a lower carcass weight compared to pigs offered LH, HH and HL diets on d 131 ( P < 0.05). Pigs offered LL diet had a lower bone ash ( P < 0.05), bone P ( P < 0.01) and bone calcium ( P < 0.05) concentration than pigs offered LH, HL and HH diets on d 131. Pigs offered LH diet had higher concentration of osteocalcin compared to pigs offered LL ( P < 0.01), HH ( P < 0.05) and HL ( P < 0.05) diets on d 88 and 108. In conclusion, compensatory effect occurred in growth performance and bone mineral concentration at the termination of the finisher stage when high P was introduced at the initiation of the finisher stage, following consumption of a low-P diet during the weaner-grower stage. However, pigs offered LH diet did not surpass the level of growth performance or bone mineralization achieved by pigs offered HH diet.

Influence of benzoic acid and phytase in low-phosphorus diets on bone characteristics in growing-finishing pigs1

In 2 simultaneous experiments (Exp. 1 and Exp. 2), the effects of benzoic acid (BA) and phytase (Phy) in low-P diets on bone metabolism, bone composition, and bone stability in growing and growing-finishing pigs were examined. Experiment 1 was conducted with 16 crossbred gilts in the BW range of 25 to 66 kg of BW, whereas in Exp. 2, 32 crossbred gilts (25 to 108 kg of BW) were used. All pigs were individually housed in pens and restrictively fed 1 of 4 diets throughout the experiment. Total P content of the wheat-soybean diets was 4 g/kg (all values on an as-fed basis). The experimental diets were 1) unsupplemented control diet; 2) control diet with 0.5% BA; 3) Phy diet with 750 Phy units (FTU) of Phy/kg and no BA; and 4) PhyBA, control diet with 750 FTU of Phy/kg and 0.5% BA. Blood samples were taken at the beginning of the experiment, wk 3 (only for pigs in Exp. 1), wk 6, and before slaughter to determine P and Ca in serum and concentrations of total alkaline phosphatase, serum crosslaps (marker for bone resorption), and osteocalcin (marker for bone formation). Ash, P, and Ca contents of bones and bone stability were examined using the left metatarsal bones and tibia of the pigs after slaughter. Benzoic acid did not influence any of the blood variables (P > 0.09). The addition of Phy increased (P < or =0.03) P concentration in serum from 2.71 +/- 0.08 to 3.03 +/- 0.07 mmol/L at wk 3 and content of serum crosslaps from 0.39 +/- 0.02 to 0.45 +/- 0.02 ng/mL at wk 6 and decreased (P < 0.05) osteocalcin at wk 6 by 160 ng/mL. No long-term effect of diets on serum mineral concentrations, alkaline phosphatase, and bone markers in serum could be detected. Benzoic acid negatively affected (P < or = 0.03) Ca content in bones and distal bone mineral density, especially in the younger pigs. In the control diet with 0.5% BA and the control diet with 750 FTU of Phy/kg and 0.5% BA, the CA content in bones and distal bone mineral density were reduced by 6 and 11%, respectively. Throughout the whole growing and finishing period, Phy increased (P < or =0.02) ash, P, and Ca contents in bones by 29.4, 4.8, and 11.6 g/kg of DM, respectively. Bone mineral density and bone mineral content were greater in diets with Phy (P < or = 0.03), as well as breaking strength of tibia (+22%) and metatarsal bones (+27%; P < 0.01). The results of this study indicate that for a healthy skeleton, BA should not be used in low-P diets without the addition of Phy.

Sodium-Dependent Phosphate Uptake in the Jejunum Is Post-Transcriptionally Regulated in Pigs Fed a Low-Phosphorus Diet and Is Independent of Dietary Calcium Concentration

In rodents, severe dietary P restriction increases active phosphate absorption by the intestine. However, it remains unknown if moderate dietary P restriction has a similar effect. Weanling pigs (n = 32; body weight 7.4 ± 0.55 kg) were used in a 2 × 2 factorial design and fed dietary available P (aP) concentrations of 0.23 or 0.40% and Ca concentrations of 0.58 or 1.00% for 14 d. Diets were formulated on an aP basis instead of a total P basis, because pigs are unable to absorb phytate-P present in corn and soybean meal. Jejunal segments were mounted in modified Ussing chambers for determination of Na+-dependent nutrient transport. Intestinal mucosal scrapings were taken for RNA isolation and brush border membrane (BBM) vesicle isolation. Na+-dependent phosphate uptake and gene expression of Na-phosphate cotransporter IIb (NaPi-IIb), SGLT-1 (sodium/glucose cotransporter-1), and calbindin D(9k) and protein expression of NaPi-IIb were evaluated. Na+-dependent phosphate transport increased (P < 0.05) 46% as dietary aP concentration was decreased. However, increased Na+-dependent phosphate uptake was not accompanied by increased NaPi-IIb mRNA expression. Expression of NaPi-IIb protein in the BBM increased (P < 0.01) 84% in pigs fed low-P diets compared with pigs fed adequate-P diets. No dietary Ca effects or aP × Ca interactions were detected for Na-dependent P uptake, mRNA or protein expression of NaPi-IIb, or mRNA expression of calbindin D(9k). These data suggest that restricting dietary aP concentration by only 43% stimulates Na+-dependent phosphate uptake and expression of the NaPi-IIb protein in the BBM of the small intestine and through a post-transcriptional mechanism.

Combining suppressive subtractive hybridization and cDNA microarrays to identify dietary phosphorus-responsive genes of the rainbow trout ( Oncorhynchus mykiss) kidney

Phosphorus (P)-responsive genes and how they regulate renal adaptation to phosphorous-deficient diets in animals, including fish, are not well understood. RNA abundance profiling using cDNA microarrays is an efficient approach to study nutrient–gene interactions and identify these dietary P-responsive genes. To test the hypothesis that dietary P-responsive genes are differentially expressed in fish fed varying P levels, rainbow trout were fed a practical high-P diet (R20: 0.96% P) or a low-P diet (R0: 0.38% P) for 7 weeks. The differentially-expressed genes between dietary groups were identified and compared from the kidney by combining suppressive subtractive hybridization (SSH) with cDNA microarray analysis. A number of genes were confirmed by real-time PCR, and correlated with plasma and bone P concentrations. Approximately 54 genes were identified as potential dietary P-responsive after 7 weeks on a diet deficient in P according to cDNA microarray analysis. Of 18 selected genes, 13 genes were confirmed to be P-responsive at 7 weeks by real-time PCR analysis, including: iNOS, cytochrome b, cytochrome c oxidase subunit II , α-globin I, β-globin, ATP synthase, hyperosmotic protein 21, COL1A3, Nkef, NDPK, glucose phosphate isomerase 1, Na+/H+ exchange protein and GDP dissociation inhibitor 2. Many of these dietary P-responsive genes responded in a moderate way (R0/R20 ratio: < 2–3 or > 0.5) and in a transient manner to dietary P limitation. In summary, renal adaptation to dietary P deficiency in trout involves changes in the expression of several genes, suggesting a profile of metabolic stress, since many of these differentially-expressed candidates are associated with the cellular adaptative responses.

Beneficial effects of xylanase and/or phytase inclusions on ileal amino acid digestibility, energy utilisation, mineral retention and growth performance in wheat-based broiler diets

The effects of individual and combined inclusions of xylanase and phytase in broiler diets based on a characterised wheat were evaluated. The positive control diet was formulated to be adequate for phosphorus (P) with 3.8 g kg −1 nonphytate P and the low-P, negative control diet contained 2.6 g kg −1 nonphytate P. The negative control diet was supplemented with xylanase (2000 XU kg −1), or phytase (500 FTU kg −1), or xylanase plus phytase (2000 XU kg −1 and 500 FTU kg −1). Treatment effects on ileal digestibility of amino acids, energy and nitrogen utilisation, ileal digestibility and total tract retention of minerals, toe ash content and the growth performance were determined. In combination, xylanase plus phytase increased mean apparent ileal digestibility (AID) coefficients of 17 amino acids by 8.6%, which exceeded the increases of 4.8% and 5.5% generated by xylanase and phytase, respectively. Increases in AID were significant ( P<0.05) for the majority of amino acids in response to enzyme inclusions with indications of synergistic responses for five amino acids. Xylanase plus phytase increased ( P<0.05) nitrogen-corrected AME by 0.63 MJ kg −1, ileal energy digestibility by 0.89 MJ kg −1 and energy AID coefficient by 6.7% relative to the negative control diet. The enzyme combination increased ( P<0.05) coefficients of ileal nitrogen digestibility by 9.1% and 8.0% relative to positive and negative control diets, respectively. Phytase increased ( P<0.05) ileal calcium digestibility by 32.2% and ileal P digestibility by 28.0% relative to the negative control. Also, phytase increased ( P<0.05) the AID coefficient of sodium to −0.038 from −0.516 in the negative control diet and the combination increased the same coefficient to 0.043. P reduction in the control diet lowered ( P<0.05) bone mineralisation, but toe ash contents were restored by phytase and xylanase plus phytase. P status of the control diets had no effect ( P>0.05) on the efficiency of feed conversion, but xylanase (6.2%), phytase (2.5%) and xylanase plus phytase (3.9%) enhanced ( P<0.05) feed efficiency relative to the negative control. The low-P diet depressed ( P<0.05) weight gain and feed intake but phytase and xylanase plus phytase restored both weight gain and feed intake. Overall, the present data indicate that the simultaneous inclusion of xylanase plus phytase in wheat-based broiler diets was beneficial in terms of nutrient utilisation and growth performance.