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 f or 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 i n metabolism pens. Three semipurified diets were created in which corn was the only source of phytate. Diet I contained 72% NC, 0.15% estimated availa ble 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 meas ure 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 D iet 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 rete ntion, 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 greater than or equal to 0.2); ind icating an equal nutritional value for both corn hybrids after adjusting fo r phytate level. The only treatment difference, other than P excretion, bet ween 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 D iet 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 s ystem of the pig, the availability of P for pigs was estimated at 56% for L PC and 11% for NC.