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.