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* Department of Animal Sciences, University of Illinois-Urbana 61801;
and
United Feeds, Inc., Sheridan, IN 46069; and
and
Department of Animal Science, Cornell University, Ithaca, NY 14853
2 Correspondence:
E-mail:
dhbaker{at}uiuc.edu.
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Key Words: ChicksE. • Phytase • Pigs
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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The appA and appA2 genes originate from E. coli, the latter isolated from an E. coli strain present in pig colon (Rodriguez et al., 1999a). The proteins encoded by appA and appA2 exhibited only 15 and 19% amino acid sequence homology, respectively, with phyA, the gene that encodes Natuphos phytase; they exhibited 95% homology to each other (Rodriguez et al., 1999a,b). The r-appA phytase exhibited a higher resistance to the gastric protease pepsin than r-phyA phytase (Rodriguez et al., 1999a,b). The r-appA2 phytase exhibited a single pH optima range (2.5 to 3.5), which was similar to the single pH optimum of r-appA phytase of 2.5, but different from the two pH optima of 2.5 and 5.5 for Natuphos (Rodriguez et al., 1999a).
The resistance to pepsin and the superior in vitro P release for the E. coli phytases make these enzymes viable options for supplementing monogastric diets. Preliminary in vivo results indicated that r-appA phytase was as efficacious as Natuphos in both chicks and pigs (Leeson et al., 2000; Stahl et al., 2000). The objective of our research was to compare the P-releasing efficacy of r-appA2 phytase (derived from an E. coli strain in pig colon and expressed in yeast) with the commercial phytases Natuphos and Ronozyme in both chicks and pigs fed P-deficient corn-soybean meal diets.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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All phytase enzymes were assayed for phytase activity prior to inclusion in experimental diets as described previously by Han et al. (1999). Duplicate phytase premix samples were diluted in 0.2 M citrate buffer, pH 5.5, dissolved by stirring for 1 h, and filtered to separate the solids from the soluble enzyme. Aliquots (0.5 mL) of samples were incubated in a water bath at 37°C for 5 min, after which 0.5 mL of 10.8 mM sodium phytate (diluted in 0.2 M citrate buffer, pH 5.5) was added and the reaction carried out for 15 min in a water bath at 37°C. The reaction was stopped by adding 1 mL of 15% trichloroacetic acid. Blanks were run by adding the trichloroacetic acid to enzyme samples and incubating in the water bath for 15 min before adding the sodium phytate. Samples were then centrifuged (2,000 x g, 10 min) and 0.2 mL of supernatant was mixed with 2.0 mL of color reagent [a 3:1:1 mixture 1 M sulfuric acid, 2.5% ammonium molybdate (wt/vol), and 10% ascorbic acid(wt/vol)], after which the mixture was incubated at 50°C for 15 min. Free-phosphorus concentration was measured colorimetrically at 820 nm. One phytase unit (FTU) was defined as the amount of enzyme required to release 1 µmol of inorganic phosphorus (iP) per minute from sodium phytate at 37°C.
The same methodology as that described for premix analysis was used to determine phytase activity in some of the final diets used in the chick trials. This was done as a check on the accuracy of premix analysis as well as diet mixing, the two factors that could influence phytase levels in final diets.
General Procedures (Chick Trials)
The University of Illinois Institutional Animal Care and Use Committee approved all housing, handling, and euthanasia procedures. Four chick trials were conducted using New Hampshire x Columbian Plymouth Rock male chicks. Chicks were housed in thermostatically controlled starter batteries with raised wire floors in an environmentally controlled building that provided 24-h light. Both feed and water were provided for ad libitum consumption. During the first 7 d posthatch, 30 to 50% more chicks than that needed for an individual assay were fed a corn-soybean meal diet adequate in all essential nutrients (NRC, 1994). After a period of overnight feed withdrawal, all chicks appearing normal and healthy were weighed, and those chicks within a narrow weight range were selected. The selected chicks were then wing-banded and randomly assigned to pens, which were randomly assigned to dietary treatments. Five replicate pens of four chicks per treatment were allowed to consume their experimental diet from d 8 to d 21 or 22 after hatching.
The basal diet (Table 1
) was a corn-soybean meal diet with no supplemental iP, designed to be deficient in P but superadequate in cholecalciferol (i.e., 25 µg/kg diet). It contained 0.35 to 0.37% total P (depending on the specific trial) and an estimated 0.10% bioavailable P (NRC, 1994). Previous research in our laboratory had demonstrated that chicks fed this basal diet would respond linearly to supplemental iP levels (reagent-grade KH2PO4, 22.76% P) between 0 and 0.15% (Biehl et al., 1995; Biehl and Baker, 1997a). Calcium in the basal diet was set at 0.75%, a level lower than the requirement of 1.00% (NRC, 1994) in an effort to control Ca:P imbalance and thereby allow maximum responses to supplemental iP or phytase. In all cases, experimental diets were first limiting in bioavailable P (Biehl and Baker, 1997a,b).
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Chick Trial 1
The first chick trial was conducted to compare the P-releasing efficacy of Natuphos and ECP. The standard curve was constructed by feeding graded doses of iP from reagent-grade KH2PO4 (Diets 1 to 3), and tibia ash (milligrams) was then regressed on supplemental iP intake. Weight gain and tibia ash responses to 500 FTU/kg of Natuphos (manufacturer’s guarantee 5,000 FTU/g premix, analyzed activity of 5,000 FTU/g premix) and ECP (analyzed activity of 2,290 FTU/g premix) were measured.
Chick Trial 2
Based on the results of Chick Trial 1, this assay was designed to further evaluate the P-releasing efficacy of several phytase products when added to the same corn-soybean meal basal diet (Table 1
) as that used in Chick Trial 1. Natuphos, Ronozyme, and ECP were evaluated. The basal diet was supplemented with 0.05, 0.10, and 0.15% iP to construct the standard curve (Diets 1 to 4). To investigate the unexpectedly low bone ash responses to Natuphos in the first trial, a second batch of Natuphos (manufacturer’s guarantee of 600 FTU/g premix, analyzed activity of 572 FTU/g premix) was procured from a commercial supplier, and 500 FTU/kg diet of Natuphos from Batch 1 was compared to 500 and 1,000 FTU/kg diet of Natuphos from the second batch. Ronozyme (manufacturer’s guarantee of 2,500 FTU/g premix, analyzed activity of 2,875 FTU/g premix) was added to the diet at activity levels of 500 and 1,000 FTU/kg diet. Tibia ash response to ECP at 500 FTU/kg diet was also measured.
Chick Trial 3
This trial used standard-curve methodology to investigate the effect of graded doses of ECP on tibia ash and bioavailable P release in the corn-soybean meal basal diet (Table 1). The standard curve was constructed as in Chick Trial 2, and four levels of ECP (0, 500, 1,000, and 1,500 FTU/kg), along with one level of Natuphos (500 FTU/kg, Batch 2) were compared.
Chick Trial 4
The purpose of this trial was to investigate possible additivity or interactivity between 3-phytases and 6-phytases. A four-point standard curve was constructed as in previous trials (Diets 1 to 4). Natuphos (Batch 2), Ronozyme, and ECP were compared at both 500 and 1,000 FTU/kg. Additivity or interactivity was investigated by combining Natuphos and Ronozyme together at levels of 500 FTU/kg and also by combining Natuphos and ECP together at levels of 500 FTU/kg and comparing the results to each of the phytases fed individually at 1,000 FTU/kg.
General Procedures (Pig Trial)
The University of Illinois Institutional Animal Care and Use Committee approved all housing, handling, and euthanasia procedures. The pig trial was conducted at the United Feeds Burton-Russell Research Farm at Frankfort, IN, using 90 AusGene barrows. The pigs were weaned at approximately 15 d of age and housed in an environmentally controlled nursery with ad libitum access to a corn-soybean meal-whey-plasma starter diet adequate in all essential nutrients (NRC, 1998). At 1 wk postweaning, pigs were moved to the experimental building equipped with individual pens (0.5 m x 0.9 m) and allowed 4 d to acclimate to the facility. Pigs were then deprived of feed for 12 h, weighed, assigned to uniform blocks based on ancestry and body weight, and then allotted randomly to treatment diets from within blocks. Pigs were penned individually and given ad libitum access to the experimental diets for a period of 23 d, during which time pigs and feeders were weighed weekly. Ten pigs received each of nine experimental diets.
The basal diet (Table 1) was formulated to be deficient in P, containing an analyzed level of 0.34% total P. Using average P bioavailability estimates of 25% for soybean meal and 15% for corn (Cromwell, 1992), the basal diet contained an estimated 0.075% available P. The diet was also moderately deficient in Ca (0.60%). With the exceptions of Ca and P, the diet was formulated to be adequate to superadequate in all other nutrients, including cholecalciferol (16.5 µg/kg), for 10- to 20-kg pigs (NRC, 1998).
After the 23-d feeding period, pigs were fasted for 12 h and then weighed for determination of weight gain and gain/feed ratio. The five median weight blocks of pigs were killed via CO2 inhalation, after which the right fibula was removed from each pig for determination of bone ash. Ashing procedures were conducted as described previously for the chick assays.
The pig trial was designed to measure the effects of Natuphos, Ronozyme, and ECP on fibula ash and bioavailable P release in young pigs fed a P-deficient corn-soybean meal diet (Table 1). The basal diet was supplemented with 0.05, 0.10, and 0.15% iP from KH2PO4 to construct the standard curve (Diets 1 to 4). Fibula ash responses to 400 FTU/kg of Natuphos, Ronozyme, and ECP were measured to determine their effect on P release.
Diet Analysis
Crude protein in all basal diets was determined in triplicate (AOAC, 1995), and amino acids were quantified in duplicate by chromatographic analysis (Beckman model 6300, Beckman Instruments, Palo Alto, CA) following 24-h hydrolysis in HCl. Quadruplicate samples of basal diets from each of the five trials were dry ashed as described for the bones and then wet ashed (Wedekind et al., 1991) according to AOAC (1995) procedures.
Briefly, following dry ashing, 1.67 g diet samples were solubilized in 20 mL of 8.1 N HCl, and six drops of 15.8 N HNO3 were then added, after which the solution was brought to the boiling point. After allowing samples to cool, the samples were filtered (Whatman 541 filter paper) into 50 mL volumetric flasks. Deionized H2O was then used to dilute the samples to a final volume of 50 mL. To determine total P, 1 mL of sample was combined with 2 mL of molybdovanadate reagent and 7 mL deionized H2O. After the solutions were allowed to stand for 10 min, they were read at 400 nm against the 30 µg P (from KH2PO4) standard set at zero absorbance. Total P was then calculated from the standard iP curve.
Calcium was determined in the corn and soybean meal used in the various trials, but it was not determined in basal diets. The wet-ashed samples were analyzed for Ca (AOAC, 1995) by atomic absorption spectrophotometry (Model 306, Perkin-Elmer, Norwalk, CT). Based on these analyses, together with the Ca provided in the form of limestone (38% Ca assumed), the average calculated level of Ca was 0.75% in the chick basal diet and 0.60% in the pig basal diet.
Statistical Analysis
For the chick trials, ANOVA was performed on pen means data using the general linear models (GLM) procedure of SAS (SAS Inst. Inc., Cary, NC) appropriate for a completely randomized design. For the pig trial, analysis of variance was performed using the GLM procedure of SAS, appropriate for a randomized complete-block design. Treatment means were compared using nonorthogonal single-df comparisons. Tibia ash (mg) for chicks or fibula ash (mg) for pigs was regressed on supplemental iP intake (g) to construct the standard curves. Using bone ash responses to supplemental phytase, the regression equation was solved for bioavailable P intake (g) and the solution was divided by feed intake and multiplied by 100 to yield bioavailable P release.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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). Supplementation of 500 FTU/kg of ECP resulted in similar weight gain and tibia ash (percentage) compared with the diet supplemented with 0.10% iP (P > 0.05), but 500 FTU/kg of Natuphos resulted in weight gain and bone ash values that were lower (P < 0.01) than those resulting from 500 FTU/kg of ECP. Because of the unexpectedly high bone-ash value (milligrams) for ECP that was, in fact, higher (P < 0.05) than that produced by the highest standard-curve dose of iP, P-release values were not calculated for the phytase treatments in this trial. A spot check of the dietary phytase activity in the complete diets revealed levels of 504 and 485 FTU/kg for Natuphos and ECP-supplemented diets, respectively (Diets 4 and 5).
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). All performance and bone responses did not differ (P > 0.05) between the two batches of Natuphos at 500 FTU/kg. Weight gain and gain/feed were greater for 1,000 FTU/kg (P < 0.01) compared to 500 FTU/kg for both Natuphos and Ronozyme. However, tibia ash and bioavailable P release were not affected by the increased dietary phytase activity of either Natuphos or Ronozyme (P > 0.10). Bioavailable P release was also not different (P > 0.10) for Natuphos and Ronozyme at similar activity levels. Superior (P < 0.01) responses in weight gain, tibia ash and bioavailable P release were observed for the ECP-supplemented diet compared to diets containing either Natuphos or Ronozyme at both 500 and 1,000 FTU/kg activity levels. An additional spot check of the diets in this assay revealed dietary phytase activity levels of 492 FTU/kg for 500 FTU/kg Natuphos (Batch 1, i.e., Diet 5); 937 FTU/kg for 1,000 FTU/kg Natuphos (Batch 2, i.e., Diet 7); and 484 FTU/kg for the 500 FTU/kg ECP (i.e., Diet 10).
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). Addition of graded doses of ECP resulted in quadratic (P < 0.01) increases in both weight gain and tibia ash. Natuphos supplementation at 500 FTU/kg resulted in lower (P < 0.01) weight gain, gain/feed, tibia ash and bioavailable P release than ECP fed at the same 500 FTU/kg dose level.
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), and responses to Natuphos and Ronozyme at either 500 or 1,000 FTU/kg were similar (P > 0.10) in this assay. Also, at either 500 or 1,000 FTU/kg, ECP was superior (P < 0.01) to either Natuphos or Ronozyme, releasing greater than three times more P than either of the two commercial enzymes. When 500 FTU/kg of Natuphos (a 3-phytase) was combined with 500 FTU/kg of either Ronozyme or ECP (6-phytases), efficacy in improving weight gain and bone ash was no better than that occurring when 1,000 FTU/kg of any of the three phytases were fed alone. Thus, no synergism was apparent when 3- and 6-phytases were fed in combination. A check of the phytase activity of a few of the diets in this trial revealed final dietary phytase activities of 498 and 858 FTU/kg for the diets formulated to contain 500 and 1,000 FTU/kg of ECP (Diets 7 and 12), respectively, and 563 FTU/kg for the diet formulated to contain 500 FTU/kg of Natuphos (Diet 5).
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). Supplementation with 400 FTU/kg of Natuphos, Ronozyme, or ECP resulted in similar (P > 0.10) weight gain responses. Fibula ash (milligrams) values were greater (P < 0.05) for ECP than Ronozyme, with an intermediate value for Natuphos. Bioavailable P release followed the same pattern. Variability, as expected, was greater in the pig trial than in the chick trials, and as a result, the numerical advantage of Natuphos over Ronozyme was not statistically significant (P > 0.05), but both of these commercial phytase products were more efficacious (in terms of P release) in pigs than in chicks.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Comparisons of iP releasing efficacy of one phytase enzyme with another is fraught with interpretive problems. The standard assay procedure for measurement of specific activity of phytase premixes involves determination of iP release from sodium phytate at pH 5.5. The pH optima for phytase activity is bimodal for Natuphos (pH 2.5 and 5.5), whereas it occurs at 4.0 to 4.5 for Ronozyme and 2.5 to 3.5 for ECP. Hence, the standard phytase assay system (pH 5.5) is used to establish the quantity of each phytase product that needs to be added to diets to attain equal phytase activity. The real question is where, and at what pH, is iP released in the gut from the phytate complexes present in corn and soybean meal. Another question, however, concerns whether measurement of phytase activity at pH 5.5 may have underestimated the specific activity of ECP and Ronozyme. If so, this would have caused us to add more phytase activity (from these two phytase enzymes) than we intended, i.e., when we were trying to make efficacy comparison at equal dietary phytase activity levels. Rodriguez et al. (1999a) showed that ECP retained about 65% of its original (pH 3.5) activity when assayed at pH 5.5. Assuming this relative activity difference can be applied to gut conditions, one might suggest that instead of adding 500 FTU/kg of ECP, we really added 769 FTU/kg (i.e., based on the premix assay at pH 5.5). Even if this were the case, our chick data in Tables 3 and 5 in which 500 FTU/kg of ECP (pH 5.5 assay) was shown to release over twice as much iP as 1,000 FTU of either Natuphos or Ronozyme suggest that ECP is decidedly superior in iP-releasing efficacy to either of the fungal phytases.
The phytate present in corn and soybean meal is an inositol phosphate complex that contains several different cations bound to it and may also contain bonds to either protein or carbohydrates or both (Erdman, 1979; Cosgrove, 1980; Reddy et al., 1982). Thus, it is very different from the sodium phytate used as a substrate in the phytase specific activity assay. Clearly, all three phytase enzymes evaluated herein were found to be efficacious in releasing iP from corn and soybean meal phytate fed to young chicks and pigs. Indeed, unpublished chick data from our laboratory have shown that Natuphos and ECP are equal in iP-releasing efficacy (both releasing more than 0.20% iP) when phytase is included in the diet at 10,000 FTU/kg. Nonetheless, under the standard phytase activity determinations used herein and in chick diets with no iP supplementation, both Ronozyme and Natuphos at 500 FTU/kg diet released less than 0.05% iP from phytate. Why the relative efficacy advantage of ECP in comparison with Ronozyme and Natuphos under our assay conditions is substantial in chicks but much less in pigs remains vexing.
The differences in biochemical properties between the E. coli phytase and Natuphos may manifest through greater efficacy of P release for the E. coli phytase. The phytase derived from E. coli shows little similarity to Natuphos (19% homology, Rodriguez et al., 1999a, b). Natuphos exhibited bimodal pH optima of 2.5 and 5.5, compared to a single pH optimum of 2.5 to 3.5 for ECP, respectively (Rodriguez et al., 1999a). In addition, ECP released more P from soybean meal in vitro than Natuphos (Rodriguez et al., 1999a). Natuphos was found to be less resistant to the gastric enzyme pepsin but more resistant to the pancreatic enzyme trypsin compared to an E. coli-derived phytase (Rodriguez et al., 1999b).
Yi and Kornegay (1996) found that in young (17 kg) pigs the main site of phytase activity was in the stomach, exhibiting a pH of approximately 3.7. At this pH, E. coli-derived phytases had higher activity levels than Natuphos (Rodriguez et al., 1999a) and would presumably retain more activity due to their higher resistance to the gastric enzyme pepsin compared to Natuphos (Rodriguez et al., 1999b). In light of these findings, one might expect that the efficacy of ECP for releasing P in monogastrics would be greater than that of Natuphos. Our data confirmed this expectation. However, earlier research involving comparisons of Natuphos with an E. coli derived r-appA phytase found only similar responses in tibia ash in young chicks (Leeson et al., 2000) and plasma iP in young pigs (Stahl et al., 2000). The discrepancy may be due to the fact that Leeson et al. (2000) used an r-appA phytase expressed in E. coli, whereas our E. coli-derived phytase was expressed in Pichia pastoris yeast. Also, Stahl et al. (2000) did not examine bone criteria, which are more sensitive and reliable indicators of P bioavailability than either weight gain or blood parameters.
Phosphorus-release values in chicks for both Natuphos and Ronozyme were unexpectedly low in these trials. In our assays, supplementation of either enzyme up to 1,000 FTU/kg failed to release greater than 0.067% P (1,000 FTU/kg Natuphos in Chick Trial 4). Other research has shown lower-than-expected P-release values in young chicks. Angel et al. (2001a) reported that tibia ash responses to supplementation of 200 and 500 FTU/kg phytase to a P-deficient diet corresponded to P-release values of only 0.014 and 0.048%, respectively. Simons et al. (1990) reported improvements in apparent digestibility of P when phytase was supplemented to a P-deficient diet, and these improvements corresponded to approximate P-release values of only 0.044 and 0.057% for diets containing 500 and 1,000 FTU/kg phytase and only 0.038 and 0.046% for diets containing 375 and 750 FTU/kg phytase, respectively. Earlier work by Nelson et al. (1971) indicated 0.09% P release from a diet containing 950 FTU/kg of phytase, and Biehl et al. (1995) reported that 1,200 FTU/kg of phytase (Natuphos) released 0.116% P.
The efficacy of the commercial phytases to release P was higher in the pig than in the chick, in contrast to the similar P-release values across species for ECP. Natuphos released 0.081% P at 400 FTU/kg in the young pig, compared to an average of 0.033% P from 500 FTU/kg of Natuphos in the chick trials. Simons et al. (1990) reported positive responses of grower pigs to 1,000 FTU/kg of Natuphos in apparent digestible P that correlated to P-release values of approximately 0.086%, compared with the 0.057% P released from 1,000 FTU/kg of Natuphos in chicks. Kemme et al. (1997) reported that 500 FTU/kg of Natuphos in diets for nursery and growing-finishing pigs resulted in the release of 0.066 and 0.083% P, respectively. Similar to pigs, P-release values in turkey poults have been numerically higher than those in chicks; inclusion of 600 FTU/kg Natuphos in diets of turkey poults resulted in the release of 0.090% P (Angel et al., 2001b). The reason for the differences in P release in chicks compared to pigs and poults is not known but may be related to differences in digestive conditions among the species.
This is not the first time we and others have encountered species differences in phytate-P utilization. The chicken vs pig comparison as shown herein for utilization of fungal phytases is particularly intriguing. Chickens have more endogenous gut phytase than pigs (Yi and Kornegay, 1996; Biehl and Baker, 1997b), which probably explains why P bioavailability in corn is at least twice as high in chickens (Douglas et al., 2000; Li et al., 2000) as in pigs (Cromwell, 1992; Spencer et al., 2000a,b). Moreover, previous work in our laboratory showed that chickens and pigs fed supplemental 1
-hydroxycholecalciferol (Biehl et al., 1995; Biehl and Baker, 1996) and citric acid (Boling et al., 2000a,b; Boling-Frankenbach, 2001) responded strikingly different in terms of P release from phytate-P. Thus, chick bone ash responses to either 1-hydroxycholecalciferol or citrate are marked, whereas pig bone ash responses are small to citrate and nonexistent to 1-hydroxycholecalciferol. This together with the species differences shown herein for P release caused by Natuphos and Ronozyme (but not ECP) suggest that either the structural differences or the differences in proteolytic enzyme susceptibility between ECP and the fungal phytases may somehow affect chicks differently than pigs. Clearly, the anatomy and physiology of the gut, as well as the rate of passage, is very different in the chicken and pig. This along with the species difference in gut endogenous phytase activity may explain why phytase products with different structural and kinetic characteristics exhibit different P-releasing efficacy in chickens vs pigs.
To calculate P-release values in these trials, bone ash responses to phytase supplementation of P-deficient diets were compared to those from iP-supplemented diets. Dietary available P was set low enough that iP-supplementation up to 0.15% would result in marked linear responses in bone ash. Previous research in both chicks (Chung and Baker, 1990; Biehl et al., 1995; Biehl and Baker, 1997a) and pigs (Biehl and Baker, 1996) had shown large bone ash responses to iP supplementation of these diets. Recent chick data in our laboratory (Augspurger et al., 2002) have suggested that P release due to Natuphos is similar at several deficient levels of available P tested (0.10, 0.20, and 0.30% available P). That information, combined with recent findings that the requirement for available P in young chicks is not greater than 0.35% (Boling-Frankenbach et al., 2001; Augspurger et al., 2002), a value lower than the 0.45% recommendation of NRC (1994), support the use of our diet containing an estimated 0.10% available P for chick assays designed to estimate P release from phytase products.
We based our P-release values in these assays exclusively on bone ash. Although both weight gain and bone ash responded linearly (P < 0.01) to iP supplementation, regression fits for bone ash in chicks (r2 = 0.95 to 0.97) were better than those for weight gain (r2 = 0.84 to 0.91, data not reported). The difference in r2 values was more dramatic in the pig, with regression fits of bone ash being 0.87 and regression fits of weight gain being only 0.55 (data not reported).
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Implications |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Footnotes |
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Received for publication May 20, 2002. Accepted for publication September 26, 2002.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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-hydroxycholecalciferol and microbial phytase for young pigs fed phosphorus- or amino acid-deficient corn-soybean meal diets. J. Anim. Sci.74:2960–2966.[Abstract]
-hydroxycholecalciferol does not increase the specific activity of intestinal phytase but does improve phosphorus utilization in both cecectomized and sham-operated chicks fed cholecalciferol-adequate diets. J. Nutr.127:2054–2059.-hydroxylated cholecalciferol compounds act additively with microbial phytase to improve phosphorus, zinc and manganese utilization in chicks fed soy-based diets. J. Nutr.125:2407–2416.
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T. L. Veum, D. W. Bollinger, C. E. Buff, and M. R. Bedford A genetically engineered Escherichia coli phytase improves nutrient utilization, growth performance, and bone strength of young swine fed diets deficient in available phosphorus J Anim Sci, May 1, 2006; 84(5): 1147 - 1158. [Abstract] [Full Text] [PDF]
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J. A. Jendza, R. N. Dilger, S. A. Adedokun, J. S. Sands, and O. Adeola Escherichia coli phytase improves growth performance of starter, grower, and finisher pigs fed phosphorus-deficient diets J Anim Sci, August 1, 2005; 83(8): 1882 - 1889. [Abstract] [Full Text] [PDF]
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T. W. Kim and X. G. Lei An improved method for a rapid determination of phytase activity in animal feed J Anim Sci, May 1, 2005; 83(5): 1062 - 1067. [Abstract] [Full Text] [PDF]
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O. Adeola, J. S. Sands, P. H. Simmins, and H. Schulze The efficacy of an Escherichia coli-derived phytase preparation J Anim Sci, September 1, 2004; 82(9): 2657 - 2666. [Abstract] [Full Text] [PDF]
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C. H. Stahl, K. R. Roneker, W. G. Pond, and X. G. Lei Effects of combining three fungal phytases with a bacterial phytase on plasma phosphorus status of weanling pigs fed a corn-soy diet J Anim Sci, June 1, 2004; 82(6): 1725 - 1731. [Abstract] [Full Text] [PDF]
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N. R. Augspurger, J. D. Spencer, D. M. Webel, and D. H. Baker Pharmacological zinc levels reduce the phosphorus-releasing efficacy of phytase in young pigs and chickens J Anim Sci, June 1, 2004; 82(6): 1732 - 1739. [Abstract] [Full Text] [PDF]
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N. R. Augspurger and D. H. Baker High dietary phytase levels maximize phytate-phosphorus utilization but do not affect protein utilization in chicks fed phosphorus- or amino acid-deficient diets J Anim Sci, April 1, 2004; 82(4): 1100 - 1107. [Abstract] [Full Text] [PDF]
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J. M. Gentile, K. R. Roneker, S. E. Crowe, W. G. Pond, and X. G. Lei Effectiveness of an experimental consensus phytase in improving dietary phytate-phosphorus utilization by weanling pigs J Anim Sci, November 1, 2003; 81(11): 2751 - 2757. [Abstract] [Full Text] [PDF]
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