Intestinal excretion of endogenous zinc in Guatemalan school children

The intestine is the major route of excretion of endogenous zinc (Zn) and has a key role in maintaining Zn homeostasis. The principal objective of this paper is to provide an interpretative report of quantities of endogenous fecal Zn (EFZ) excreted by rural Guatemalan school children fed either normal or low phytate maize as their principal food staple. EFZ was measured by a Zn stable isotope technique. EFZ did not differ between control and low phytate maize groups. The overall EFZ (n = 53) was (mean +/- SD) 1.56 +/- 0.69 mg Zn/d or 0.07 +/- 0.03 mg Zn x kg body wt(-1) x d(-1). EFZ was not correlated with the quantity of Zn absorbed. The estimated EFZ at the level of absorption that matched the physiologic requirement (EFZ(PR)) did not differ from the above mean value. The EFZ(PR) of 0.07 +/- 0.03 mg Zn/kg body wt is twice the value currently used in the estimation of Dietary Reference Intakes. Supported by other recent childhood data, these results suggest that the current estimates of EFZ(PR) used in the calculation of Zn requirements for children are misleadingly low.

Comparison of the phosphorus and mineral concentrations in bran and abraded kernel fractions of a normal barley (Hordeum vulgare) cultivar versus four low phytic acid isolines

Phytic acid consists of 65-80% of the total phosphorus (P) in cereal grains. Its salts are concentrated in the germ and aleurone layers, which are typically removed during milling. We hypothesize that concentrations of different types of P and minerals in milled products will be greatly altered in low phytic acid (lpa) barleys. Seeds of cv. Harrington (control) and four lpa isolines-lpa1-1, lpa2-1, lpa3-1, and M955-were abraded by a laboratory method into five surface layer and four remaining kernel fractions. Results show that phytic acid in the four lpa lines ranged from 75% to 5% of the control. The decrease in phytic acid P concentration was matched almost equally by an increase in inorganic P, so that the rest of P (the sum of all P-containing compounds other than phytic acid P and inorganic P) and total P levels remained relatively unchanged among the five genotypes. These trends were also observed for the processed fractions. The major mineral elements in barley seeds were P, K, Mg, S, and Ca, while minor ones were Fe, Zn, Mn, Cu, and Ba. All types of P and other minerals measured were generally concentrated in the outer layers of the grain. Although there were substantial differences in mineral contents of bran fractions among genotypes, the level of phytic acid P had little effect on mineral contents in whole or abraded kernels. One major exception was Fe, which had the highest level in all tissues of M955 genotype. The above findings were all confirmed by analyzing another set of barley samples grown in a different environment. Thus, in general, breeding lpa barleys does not lead to reduced mineral contents in whole grains or elevated mineral levels in milled products.

Effects of low phytate barley (Hordeum vulgare L.) on zinc utilization in young broiler chicks

Two 21-d experiments were conducted to evaluate the effects of low phytate barley (LPB) on Zn utilization by young broiler chicks and to determine the contribution of endogenous phytase, present in LPB. In the first experiment, ninety-six 1-d-old male chicks were assigned to a 2 x 3 factorial arrangement of treatments (4 pens of 4 chicks/treatment). Factors were barley type [wild-type barley (WTB) and LPB mutant M 955] and supplemental Zn (0, 10, or 20 mg of Zn/kg). In the second experiment, two hundred forty 1-d-old straight-run broiler chicks were assigned to a 2 x 2 x 3 factorial arrangement of treatments (4 pens of 5 chicks/treatment). Factors were barley type (WTB and LPB), autoclave treatment [nonautoclaved or autoclaved (121 degrees C, 20 kg/cm(2), 20 min)], and supplemental Zn (0, 10 or 20 mg of Zn/kg). Barley made up 60% of the diets and was the only source of phytate. On average, basal diets contained 26 mg of Zn/kg. Feed intake and body weight gain were greater (P < 0.05) in broilers fed LPB compared with WTB in experiment 2. Zinc concentration in toes and tibias were affected (P < 0.0001) by barley type (LPB > WTB) and supplemented Zn levels (20 > 10 > 0 mg of Zn/kg), and significant barley type x Zn interactions were also observed in both experiments. Substitution of LPB for WTB increased tibia and toe Zn by 46 and 25%, respectively, an increase comparable to that achieved with supplementing the diet with 20 mg of Zn/kg. No effect of autoclaving was observed for any variable in experiment 2. Retention of P and Zn was higher (P < 0.001) in chicks fed LPB compared with WTB in both experiments. Zinc retention was influenced (P < 0.0001) by dietary Zn, and barley type x Zn level interactions (P < 0.05) were observed in both experiments. Chicks fed LPB utilized more dietary Zn and P than those fed WTB, and this improved mineral utilization was not due to endogenous phytase present in barley.

Low-phytate barley cultivars improve the utilization of phosphorus, calcium, nitrogen, energy, and dry matter in diets fed to young swine

A 28-d experiment was conducted using 45 crossbred barrows with an average initial BW of 9.5 kg and age of 35 d to evaluate low-phytate barley (LPB) mutants (M) M422, M635, and M955, which were hulled, near-isogenic progeny of the normal barley (NB) Harrington and had 47, 66, and 80% less phytic acid, respectively, than NB. A hull-less LPB, M422-H, which was not near-isogenic to the other cultivars, was also evaluated. Apparent nutrient balance, bone measurements, and growth performance were the response criteria evaluated. The barrows were fed the diets to appetite in meal form in individual metabolism crates. Barley and soybean meal were the only sources of phytic acid. Dietary protein supplementation and ME/kg were equalized in all diets. The treatments were diets containing NB, M422, M635, or M422-H without or with added inorganic P (iP), or M955 without added iP. Diets with added iP contained 0.30% available P (aP), the same concentration of aP provided by the diet containing M955 without added iP. There were linear increases (P < or = 0.02) in ADG, G:F, metacarpal and radius bone strength, and fat-free dry weight, and in the absorption and retention (g/d and % of intake) of P and Ca with increasing dietary concentration of aP from the near-isogenic cultivars NB, M422, M635, or M955 without added iP. There were linear decreases in the grams (P < or = 0.02) and percentages (P < 0.001) of P and Ca excreted per day with increasing dietary concentration of aP without added iP. There were no responses for N or energy balance. Growth performance and bone response criteria did not differ for barrows fed the diet containing M955 or the near-isogenic diets containing NB, M422, or M635 with added iP. However, barrows fed the diet containing M955 had greater (P < or = 0.02) percentages of P, N, and energy absorption and retention, Ca absorption, and DM digestibility and had less (P < or = 0.02, g/d and %) excretion of P, N, energy, and Ca (g) per day than barrows fed the diets containing the near-isogenic NB or LPB cultivars with added iP. When dietary aP was equalized with iP, the excretion of P in feces plus urine (g/d) was reduced by 20.2, 27.9, and 44.6%, respectively, in barrows fed the diets containing M422 + iP, M635 + iP, or M955 compared with barrows fed the diet containing NB + iP. Energy utilization did not differ for barrows fed the diets containing hulled or hull-less LPB when ME/kg was equalized with lard. In conclusion, the apparent utilization of P and Ca, the bone strength and fat-free dry weight, and growth performance increased with increasing dietary concentration of aP provided by LPB, in association with linear decreases in P and Ca excretion. Barrows fed the diet containing M955 also had greater utilization and less excretion of P, Ca, N, energy, and DM than barrows fed the diets containing the near-isogenic NB or LPB cultivars with added iP to equalize aP at 0.30%.

The effects of phytase supplementation on nutrient digestibility, plasma parameters, performance and carcass traits of pigs fed diets based on low-phytate barley without inorganic phosphorus

A total of 80 crossbred pigs (25.5 ± 2.6 kg) were assigned to one of eight dietary treatments. A positive control, based on Harrington barley, was formulated to meet requirements for total phosphorus. Three experimental diets (low in total phosphorus) were formulated based on either Harrington barley (0.28% phytate phosphorus) or the low phytate genotypes LP422 (0.14% phytate phosphorus) and LP 635 (0.09% phytate phosphorus). The four diets were fed with and without 1000 FTU kg-1 phytase. Calcium and phosphorus digestibility were significantly higher (P < 0.05) as a result of supplementation with phytase. For the barley diets formulated without dicalcium phosphate, calcium digestibility averaged 69.6, 73.3 and 72.2% while phosphorus digestibility averaged 36.5, 50.5 and 57.7% for pigs fed the Harrington, LP 422 and LP 635 diets, respectively. The addition of phytase to the diet consistently reduced the percentage of phosphorus excreted in feces and fecal phosphorus excretion declined as the level of phytate in the barley declined. The addition of phytase tended to improve weight gain (P < 0.10) and significantly improved feed conversion (P < 0.05). For pigs fed the barley diets formulated without dicalcium phosphate, daily gain averaged 0.90, 0.99 and 1.01 kg d-1 while feed conversion averaged 2.70, 2.39 and 2.38 for the Harrington, LP 422 and LP 635 diets, respectively. The overall results of this experiment indicate that the performance of pigs fed diets containing low-phytate barley formulated without a source of inorganic phosphorus is at least equal to that of pigs fed diets containing normal-phytate barley and inorganic phosphorus. In addition, the increased availability of organic phosphorus reduced the amount of phosphorus excreted thus reducing the amount of phosphorus that can potentially pollute the environment. Key words: Low phytate barley, phytase, pigs, performance, digestibility

Zinc absorption in Guatemalan schoolchildren fed normal or low-phytate maize

BACKGROUND

Poor bioavailability of zinc from high-phytate diets is an important contributory factor to zinc deficiency in low-income populations.

OBJECTIVE

The objective of this study was to determine the effect of low-phytate maize consumption on zinc absorption.

DESIGN

The participants were apparently healthy children from the Central Highlands of Guatemala. Sixty children (20 per group) were randomly assigned to be fed only the low-phytate maize or 1 of 2 control maizes, the isohybrid wild-type maize or a local maize, for a 10-wk period. During the final week, the fractional absorption of zinc for all meals was measured during 1 d with the use of zinc stable isotopes and a dual isotope ratio technique based on urine enrichment data.

RESULTS

Mean (+/-SD) phytate intakes for the low-phytate, wild-type, and local maize groups were 1536 +/- 563, 2056 +/- 517, and 2253 +/- 687 mg/d, respectively. Corresponding zinc intakes were 8.6 +/- 2.5, 8.1 +/- 2.0, and 9.7 +/- 2.6 mg/d, and the dietary phytate:zinc molar ratios were 18 +/- 5, 26 +/- 6, and 23 +/- 5. Corresponding fractional absorptions of zinc were 0.32 +/- 0.07, 0.28 +/- 0.07, and 0.29 +/- 0.06. The respective values for total absorbed zinc were 2.72 +/- 0.88, 2.30 +/- 0.96, and 2.78 +/- 1.04 mg/d. No significant differences in either the fractional absorption of zinc or total absorbed zinc were seen between the maize groups.

CONCLUSION

Under the conditions of the present study, zinc absorption was not increased by the long-term use of low-phytate maize in children whose major dietary staple is maize.

The concentrations and distributions of phytic acid phosphorus and other mineral nutrients in wild-type and low phytic acid Js-12-LPA wheat (Triticum aestivum) grain parts

Concentrations of P, phytic acid (myo-inositol hexakisphosphate, IP6), and other mineral storage elements were studied in wild-type and low phytic acid (lpa) genotype Js-12-LPA wheat (Triticum aestivum L.) embryos and rest-of-grain fractions. Environmental scanning electron microscopy images revealed a decreased average size and an increased number of aleurone layer globoids in lpa grains compared with the wild type. Energy-dispersive X-ray analyses of unfixed aleurone layer and scutellum cell cytoplasm revealed mainly C, O, P, K, and Mg in both grain types. The starchy endosperm contained virtually no P, K, or Mg, demonstrating no shift of mineral nutrients to that compartment. Scanning transmission electron microscopy – energy-dispersive X-ray analyses of scutellum and aleurone layer globoids in both genotypes revealed that P, K, and Mg were the main mineral nutrients in globoids with low amounts of Ca, Fe, and Zn. Traces of Mn were only in scutellum globoids. Total P was similar between genotypes for the rest-of-grain fractions, which are 97% of grain mass. The main inositol phosphate was IP6, but a small amount of IP5 was present. Both lpa grain fractions exhibited major reductions in IP6 compared with the wild type and a threefold increase in inorganic P. The concentration of K decreased in both fractions, while Ca increased 25% in the Js-12-LPA rest-of-grain compared with the wild type. The lack of large differences in mineral concentration and distribution between the wild type and Js-12-LPA indicates that there is no direct role of localization of IP6 synthesis in mineral distribution.

Absorption of calcium from tortilla meals prepared from low-phytate maize

BACKGROUND

Calcium fortification of maize has been achieved for millennia in Central America by the process of nixtamalization. Bioavailability of calcium is, however, compromised by phytate, which is present in large quantities in maize kernels and is only modestly reduced by nixtamalization.

OBJECTIVE

The objective was to compare the absorption of calcium from tortilla meals prepared from low-phytate maize with that from meals prepared from maize with typical phytate content.

DESIGN

At 1-mo intervals, 5 healthy adult women were fed 2 test meals of approximately 140 g tortillas in lieu of breakfast. On one occasion, the tortillas were prepared from maize with approximately 60% phytate reduction, and, on the other occasion, they were prepared from the matching isohybrid wild-type maize. Beginning midway through the test meal, (44)Ca (0.3 mg/kg body wt) was administered in water as an extrinsic label; (42)Ca (0.06 mg/kg body wt) was administered intravenously immediately after the test meal. Isotope ratios of (42)Ca to (43)Ca and of (44)Ca to (43)Ca were measured by inductively coupled plasma mass spectrometry in urine collected as an 8-h pool from the period 16-24 h after intravenous tracer administration and prepared by the oxalate precipitation method. Fractional absorption of calcium was determined by using a dual-isotope ratio technique.

RESULTS

Mean fractional absorption of calcium from tortillas prepared from the low-phytate maize (0.50 +/- 0.03) was significantly (P = 0.003) greater than that from tortillas prepared from the control maize (0.35 +/- 0.07).

CONCLUSION

The increase in the quantity of calcium absorbed could be of practical importance for calcium nutriture when the intake of dairy products is limited.

myo-Inositol and sucrose concentrations affect the accumulation of raffinose family oligosaccharides in seeds

Raffinose family oligosaccharides (RFOs) fulfil multiple functions in plants. In seeds, they possibly protect cellular structures during desiccation and constitute carbon reserves for early germination. Their biosynthesis proceeds by the transfer of galactose units from galactinol to sucrose. Galactinol synthase (GolS), which mediates the synthesis of galactinol from myo-inositol and UDP-galactose, has been proposed to be the key enzyme of the pathway. However, no significant relationship was detected between the extractable GolS activity and the amount of RFOs in seeds from seven pea (Pisum sativum L.) genotypes selected for high variation in RFO content. Instead, a highly significant correlation was found between the levels of myo-inositol and RFOs. Moderately strong relationships were also found between sucrose and RFO content as well as between myo-inositol and galactinol. Further evidence for a key role of myo-inositol for the synthesis of galactinol was obtained by feeding exogenous myo-inositol to intact pea seeds and by the analysis of four barley (Hordeum vulgare L.) low phytic acid mutants. In seeds of three of these mutants, the reduced demand for myo-inositol for the synthesis of phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate) was associated with an increased level in myo-inositol. The mutants seeds also contained more galactinol than wild-type seeds. The results suggest that the extent of RFO accumulation is controlled by the levels of the initial substrates, myo-inositol and sucrose, rather than by GolS activity alone.

Zinc absorption from low-phytate hybrids of maize and their wild-type isohybrids

BACKGROUND

Identification of allelic variants in a single gene that determine the phytate content of maize kernels and the subsequent breeding of low-phytate maize have facilitated studies designed to determine quantitatively the effects of maize phytate on the bioavailability of minerals in maize.

OBJECTIVE

The objective was to determine the relation between the fractional absorption of zinc (FAZ) and the phytate content and phytate:zinc molar ratios of maize tortillas prepared from hybrids with different phytate contents.

DESIGN

Six healthy adults were fed, as the only food for 2 d, maize tortillas prepared from 1 of 2 low-phytate mutants: lpa1-1 (lpa1-1-LP) or Nutridense Low Phytate (ND-LP), which have phytate reductions of approximately 60% and approximately 80%, respectively, compared with their respective wild-type isohybrids. Four additional subjects were fed tortillas prepared from the corresponding wild-type isohybrids (lpa1-1-WT and ND-WT) according to the same study design. Meals were extrinsically labeled with zinc stable isotopes, and FAZ was determined with a dual-isotope-tracer ratio technique. Overall FAZ values were examined in relation to dietary phytate and phytate:zinc molar ratios by using a mixed nonlinear regression model.

RESULTS

The mean (+/-SD) FAZ values from tortillas prepared from ND-LP, lpa1-1-LP, lpa1-1-WT, and ND-WT were 0.38 +/- 0.07, 0.28 +/- 0.04, 0.15 +/- 0.07, and 0.13 +/- 0.05, respectively. A negative relation (P < 0.001) was found between FAZ and both dietary phytate and the phytate:zinc molar ratio. The effect of dietary zinc (8-14 mg Zn/d) under these experimental conditions was not significant.

CONCLUSIONS

FAZ from maize tortillas is positively related to the extent of phytate reduction achieved with low-phytate hybrids.

Effect of phytase supplementation on phosphorus digestibility in low-phytate barley fed to finishing pigs

Forty crossbred barrows (Camborough 15 Line female x Canabred sire) weighing an average of 79.6 +/- 8.0 kg were used in a factorial design experiment (5 barleys x 2 enzyme levels) conducted to determine the effects of phytase supplementation on nutrient digestibility in low-phytate barleys fed to finishing pigs. The pigs were assigned to one of 10 dietary treatments comprised of a normal 2-rowed, hulled variety of barley (CDC Fleet, 0.26% phytate) or 2 low-phytate hulled genotypes designated as LP422 (0.14% phytate) and LP635 (0.09% phytate). A normal, hulless barley (CDC Dawn, 0.26% phytate) and a hulless genotype designated as LP422H (0.14% phytate) were also included. All barleys were fed with and without phytase (Natuphos 5000 FTU/kg). The diets fed contained 98% barley, 0.5% vitamin premix, 0.5% trace mineral premix, 0.5% NaCl and 0.5% chromic oxide but no supplemental phosphorus. The marked feed was provided for a 7-day acclimatization period, followed by a 3-day faecal collection. In the absence of phytase, phosphorus digestibility increased substantially (P < 0.05) as the level of phytate in the barley declined. For the hulled varieties, phosphorus digestibility increased from 12.9% for the normal barley (0.26% phytate) to 35.3 and 39.8% for the two low-phytate genotypes (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 9.2% for the normal barley (0.26% phytate) to 34.7% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In contrast, when phytase was added to the diet, there was little difference in phosphorus digestibility between pigs fed normal barley and those fed the low-phytate genotypes (significant barley x enzyme interaction, P = 0.01). For the hulled varieties, phosphorus digestibility was 50.1% for the barley with the normal level of phytate (0.26% phytate) compared with 51.1 and 52.4% for the varieties with 54 and 35% of the normal level of phytate (0.14 and 0.09% phytate respectively). For the hulless varieties, phosphorus digestibility increased from 47.1% for the normal barley (0.26% phytate) to 54.4% for the hulless variety with 54% of the normal level of phytate (0.14% phytate). In conclusion, both supplementation with phytase and selection for low-phytate genotypes of barley were successful in increasing the digestibility of phosphorus for pigs. Unfortunately, the effects did not appear to be additive. Whether or not swine producers will choose low-phytate barley or supplementation with phytase as a means to improve phosphorus utilization, will likely depend on the yield potential of low-phytate barley and the additional costs associated with supplementation with phytase.

Evaluation of low-phytate corn and barley on broiler chick performance

Grains produced by low-phytate barley and corn isolines homozygous for each species' respective low phytic acid 1-1 allele were compared to grain produced by near-isogenic normal or wild-type barley and corn in broiler chick feeds. Cobb x Cobb (384) chicks were used in a 10-d study. A randomized complete block design with a factorial arrangement of 2 x 2 x 3 was used with 4 replicates (8 chicks / replicate) per treatment. Twelve isocaloric and isonitrogenous treatment diets were formulated to contain 2 types of grain (barley and corn), 2 levels of grain (40% and 60%), and 3 sources of available P (wild-type grain, wild-type P-supplemented grain, and low-phytate grain). Growth parameters, bone parameters, total bone mineral, and apparent digestibilities were measured. The mean growth and bone responses were 1) higher for barley diets compared to corn diets, 2) higher for 60% grain inclusion compared to 40%, 3) higher for low-phytate compared to wild-type grains, and 4) not different for low-phytate compared to P-supplemented wild-type grain diets. Chicks fed low-phytate-based diets excreted 33 and 43% less P than chicks fed wild-type and P-supplemented wild-type diets, respectively. Correlations between percentage bone ash, total bone ash, and bone strength indicated a strong relationship and appear to support the use of bone strength analysis as a simpler method than ash content determination as an indication of P status. Feeding low-phytate grains will reduce the need for supplemental P in chick diets.

myo-Inositol-1,2,3,4,5,6-hexakisphosphate

myo-Inositol-1,2,3,4,5,6-hexakisphosphate (Ins P(6)) was first described as an abundant form of phosphorus in plant seeds and other plant tissues and dubbed "phytic acid". Subsequently it was found to be a common constituent in eukaryotic cells, its metabolism a basic component of cellular housekeeping. In addition to phosphate, myo-inositol (Ins) and mineral storage and retrieval in plant organs and tissues, other roles for Ins P(6) include service as a major metabolic pool in Ins phosphate and pyrophosphate pathways involved in signaling and regulation; possibly as an effector or ligand in these processes; as a form of energy currency and in ATP regeneration; in RNA export and DNA repair; and as an anti-oxidant. The relatively recent demonstration that pyrophosphate-containing derivatives of Ins P(6) can function as phosphate donors in the regeneration of ATP is reminiscent of the proposal, made four decades ago in studies of seed development, that Ins P(6) itself may serve in this function. Studies of Ins P(6) in non-plant systems rarely include the consideration that this compound might represent a significant fraction of cellular P; cellular phosphate nutrition has been viewed as either not interesting or of little importance. However, there may be few fundamental differences among diverse eukaryotes in both the metabolic pathways involving Ins P(6) and the spectrum of possible roles for it and its metabolites.

Phosphorus digestibility in low-phytate barley fed to finishing pigs

Twenty-four crossbred barrows (Camborough 15 Line female × Canabred sire) weighing an average of 51.3 ± 5.1 kg were used in a trial conducted during two periods according to a completely randomized block design. The pigs were assigned to one of six dietary treatments comprised of a normal two-rowed, hulled variety of barley (CDC Bold) or three low-phytate genotypes selected to contain approximately 68, 41 or 3% of the normal level of phytate. A normal hulless barley (CDC Dawn) and a hulless genotype selected to contain 54% of the normal phytate content were also included. The diets fed contained 99.5% barley and 0.5% chromic oxide. The marked feed was provided for a 7-d acclimatization period, followed by a 3-d fecal collection. At the conclusion of the first replicate, the pigs were assigned to different treatments and the procedure was repeated resulting in eight observations per treatment. Selection for phytate content had no effects on the apparent fecal digestibility of dry matter, crude protein or gross energy (P > 0.05). The digestibility coefficients for dry matter and energy were significantly higher for the hulless varieties of barley than the hulled genotypes. Phosphorus digestibility increased as the level of phytate in the barley declined. The linear relationship relating phosphorus digestibility (y) to phytate content (x) was: y = 67.7 − 12.54x       (r2= 0.64; P < 0.0001).

Seed phosphorus and inositol phosphate phenotype of barley low phytic acid genotypes

myo-Inositol-1,2,3,4,5,6-hexakisphosphate (Ins P(6) or "phytic acid") typically represents approximately 75% of the total phosphorus and >80% of soluble myo-inositol (Ins) phosphates in seeds. The seed phosphorus and Ins phosphate phenotypes of four non-lethal barley (Hordeum vulgare L.) low phytic acid mutations are described. In seeds homozygous for M 635 and M 955 reductions in Ins P(6), approximately 75 and >90% respectively, are accompanied by reductions in other Ins phosphates and molar-equivalent increases in Pi. This phenotype suggests a block in supply of substrate Ins. In seeds homozygous for barley low phytic acid 1-1 (lpa1-1), a 45% decrease in Ins P(6) is mostly matched by an increase in Pi but also accompanied by small increases in Ins(1,2,3,4,6)P(5). In seeds homozygous for barley lpa2-1, reductions in seed Ins P(6) are accompanied by increases in both Pi and in several Ins phosphates, a phenotype that suggests a lesion in Ins phosphate metabolism, rather than Ins supply. The increased Ins phosphates in barley lpa2-1 seed are: Ins(1,2,3,4,6)P(5); Ins(1,2,4,6)P(4) and/or its enantiomer Ins(2,3,4,6)P(4); Ins(1,2,3,4)P(4) and/or its enantiomer Ins(1,2,3,6)P(4); Ins(1,2,6)P(3) and/or its enantiomer Ins(2,3,4)P(3); Ins(1,5,6)P(3) and/or its enantiomer Ins(3,4,5)P(3) (the methods used here cannot distinguish between enantiomers). This primarily "5-OH" series of Ins phosphates differs from the "1-/3-OH" series observed at elevated levels in seed of the maize lpa2 genotype, but previous chromosomal mapping data indicated that the maize and barley lpa2 loci might be orthologs of a single ancestral gene. Therefore one hypothesis that might explain the differing lpa2 phenotypes is that their common ancestral gene encodes a multi-functional, Ins phosphate kinase with both "1-/-3-" and "5-kinase" activities. A putative pyrophosphate-containing Ins phosphate, possibly an Ins P(7), was also observed in the mature seed of all barley genotypes except lpa2-1. Barley M 955 indicates that at least for this species, the ability to accumulate Ins P(6) can be nearly abolished while retaining at least short-term ( approximately 1.0 years) viability.

Low-phytic acid barley improves calcium and phosphorus utilization and growth performance in growing pigs

Thirty-five crossbred barrows averaging 13.5 kg starting BW were used in a 35-d experiment to compare the availability of P and the nutritional value of two near-isogenic progeny of the barley cultivar 'Harrington'. Low-phytic acid barley (LPB, 0.35% total P, 0.14% phytic acid P) was homozygous for the low-phytic acid 1-1 allele, and the normal barley (NB, 0.35% total P, 0.24% phytic acid P) was homozygous for the normal allele of that gene. Pigs were fed individually twice daily in metabolism pens. Barley was the only source of phytate in semipurified diets, 1 to 3. Diet 1 contained 75% NB, 0.14% estimated available P (aP), and 0.50% Ca. Diet 2 contained 75% LPB, 0.22% aP, and 0.50% Ca. No inorganic P (iP) was added to Diets 1 and 2 in order to measure the animal response to the different concentrations of aP in these cultivars. Diet 3 was NB Diet 1 supplemented with iP to equal the concentration of aP in LPB Diet 2. Practical barley-soybean meal (SBM)-type diets, NB Diet 4 and LPB Diet 5, were formulated to meet all minimum nutrient requirements, and contained 0.30% aP and 0.65% Ca. For the semipurified diets, pigs fed LPB Diet 2 had higher (P < or = 0.05) bone ash weight, bone breaking strength, P absorption and retention, and Ca absorption and retention compared with pigs fed NB Diet 1, with a trend (P = 0.10) for pigs fed LPB Diet 2 to have a higher ADG and gain:feed ratio than pigs fed NB Diet 1. However, pigs fed LPB Diet 2 or NB Diet 3 were not different (P > or = 0.3) in growth performance, fresh bone weight, fat-free dry bone weight, bone ash, bone breaking strength, or N utilization. This indicates that LPB and NB were equal in nutritional value after supplementation of NB with iP to equal the estimated aP in LPB. For the practical barley-SBM diets, there were no differences (P > or = 0.4) between pigs fed NB Diet 4 or LPB Diet 5 for growth performance, fresh bone weight, bone breaking strength, the percentages of P and Ca utilization, or N, DE, and ME utilization. The use of LPB in pig diets reduced P excretion in swine waste by 55% and 16% in our semipurified and practical diets, respectively, compared with NB. Using our in vitro procedure designed to mimic the digestive system of the pig, the availability of P for pigs was estimated at 52% for LPB and 32% for NB.