Low-phytic acid corn improves nutrient utilization for growing pigs.

Thirty-five crossbred barrows averaging 14.5 kg initial BW were used in a 5-wk experiment to compare the P availability and nutritional value of a low-phytate hybrid corn (LPC, 0.26% total P, 0.08% phytic acid P) homozygous for the lpa 1-1 allele with a nearly isogenic normal hybrid corn (NC, 0.25% total P, 0.20% phytic acid P). The pigs were fed individually twice daily in metabolism pens. Three semipurified diets were created in which corn was the only source of phytate. Diet 1 contained 72% NC, 0.15% estimated available P (aP) and 0.55% Ca. Diet 2 contained 72% LPC, 0.24% aP, and 0.55% Ca. The only differences between Diets 1 and 2 were the source of corn and the levels of aP. No inorganic P (iP) was added to these diets in order to measure the animal response to the different levels of aP in the corn hybrids. Diet 3 was NC Diet 1 supplemented with iP to equal the level of aP in LPC Diet 2. Diets 4 and 5 were practical corn-soybean meal diets formulated with each corn to meet all minimum nutrient requirements and contained 0.30% aP and 0.65% Ca. For the semipurified diets, pigs fed LPC Diet 2 had higher (P < 0.01) growth performance, bone breaking strength, P absorption and retention, Ca absorption and retention, and N retention than pigs fed NC Diet 1. However, when the NC diet was supplemented with iP to equal the aP in the LPC diet, most criteria were similar (P > or = 0.2), indicating an equal nutritional value for both corn hybrids after adjusting for phytate level. The only treatment difference, other than P excretion, between the practical corn diets supplemented with soybean meal was a higher (P < 0.05) bone breaking strength for pigs fed LPC Diet 5 compared with NC Diet 4. The use of LPC in pig diets reduced P excretion in swine waste by 50 and 18.4% in the semipurified and practical diets, respectively, compared with NC. Using our in vitro procedure designed to simulate the digestive system of the pig, the availability of P for pigs was estimated at 56% for LPC and 11% for NC.

Effects of low phytic acid corn on phosphorus utilization, performance, and bone mineralization in broiler chicks.

In vivo and in vitro experiments were conducted to determine whether P in a low-phytate corn (LPC) containing the lpa 1-1 allele is more available than P in a near-isogenic wild-type corn hybrid (NC). The LPC was analyzed to contain 0.18% nonphytate P and 0.26% total P (TP), whereas NC contained 0.05% nonphytate P and 0.25% TP. For these studies, nonphytate P was considered to be available P (AP). In the in vivo study, 150 1-d-old male chicks were randomly assigned to five treatments (six pens of five chicks each) for 21 d. The dietary treatments included: A) a diet containing 60% NC, 0.2% AP, and 0.8% Ca; B) a diet containing 60% LPC, 0.28% AP, and 0.8% Ca; C) an NC diet similar to Diet A, but with KH2PO4 added to increase the AP to 0.28% to match the AP in Diet B; D) an LPC diet containing 0.45% AP and 1% Ca; and E) an NC diet supplemented with KH2PO4 to provide 0.45% AP and 1% Ca. Diets A, B, and C were semipurified diets, with corn being the sole source of phytate. The only differences between Diets A and B were the source of corn and the amount of AP present in the diets. The levels of AP in these diets were deficient in order to measure the animal response to the different levels of AP. Diets D and E were typical corn-soybean meal diets, and were formulated to contain an optimal level of AP. Performance and bone ash were similar (P > 0.05) in chicks fed Diets B and C and in chicks fed Diets D and E. Chicks fed LPC diets (B and D) retained more P (P < 0.05) than chicks fed NC diets (C and E). Chicks fed Diet B had significantly higher (P < 0.05) Ca retention compared with chicks fed Diet A. An in vitro digestion procedure that simulated the physiological conditions of the gastrointestinal tract of broilers was used to determine P release from LPC and NC. Results showed that 65% (1,420 mg/kg) of the TP in LPC was released, compared with 23% (543 mg/kg) from NC. Results of these experiments indicate that the P in LPC is more available than the P in NC, and reducing the phytate content did not compromise the nutritional value of LPC. The increased P retention in chicks fed LPC suggests that substituting LPC for NC leads to a reduction in manure P. Also, the in vitro procedure accurately predicted differences in in vivo P availability between the two corns.

Origin and seed phenotype of maize low phytic acid 1-1 and low phytic acid 2-1.

Phytic acid (myo-inositol-1, 2, 3, 4, 5, 6-hexakisphosphate or Ins P(6)) typically represents approximately 75% to 80% of maize (Zea mays) seed total P. Here we describe the origin, inheritance, and seed phenotype of two non-lethal maize low phytic acid mutants, lpa1-1 and lpa2-1. The loci map to two sites on chromosome 1S. Seed phytic acid P is reduced in these mutants by 50% to 66% but seed total P is unaltered. The decrease in phytic acid P in mature lpa1-1 seeds is accompanied by a corresponding increase in inorganic phosphate (P(i)). In mature lpa2-1 seed it is accompanied by increases in P(i) and at least three other myo-inositol (Ins) phosphates (and/or their respective enantiomers): D-Ins(1,2,4,5,6) P(5); D-Ins (1,4,5,6) P(4); and D-Ins(1,2,6) P(3). In both cases the sum of seed P(i) and Ins phosphates (including phytic acid) is constant and similar to that observed in normal seeds. In both mutants P chemistry appears to be perturbed throughout seed development. Homozygosity for either mutant results in a seed dry weight loss, ranging from 4% to 23%. These results indicate that phytic acid metabolism during seed development is not solely responsible for P homeostasis and indicate that the phytic acid concentration typical of a normal maize seed is not essential to seed function.