Phosphorus bioavailability and digestibility of normal and genetically modified low-phytate corn for pigs.

Abstract

We conducted two studies to determine the bioavailability and apparent digestibility of P in a low-phytate corn hybrid (.28% total P, .10% phytate P) genetically modified to be homozygous for the 1pa1-1 allele and a nearly isogenic corn hybrid (normal) (.25% total P, .20% phytate P). Additionally, we conducted an in vitro assay involving a peptic and pancreatin digestion to estimate P availability. The first study used 50 individually penned pigs (initial body weight 9 kg) and 10 treatments in a randomized complete block design. A cornstarch-soybean meal basal diet (.6% Ca, .2% P) was used. Treatments consisted of the basal diet and the basal diet plus .05, .10, or .15% P from monosodium phosphate (MSP), low-phytate corn, or normal corn. After a 35-d feeding period, pigs were killed to collect the fourth metacarpal for measurements of ash and breaking load. Breaking load was regressed on added P intake, and the bioavailability of P was determined by the slope ratio method. The bioavailabilities of P (relative to MSP) for low-phytate and normal corn were 62 and 9%, respectively. These were similar to the determined in vitro values of 57 and 11% for low-phytate and normal corn, respectively. In the second study, 20 pigs (initial BW 20 kg) were used in a randomized complete block design with a 2 x 2 factorial arrangement of treatments. Two corn lines (low-phytate and normal) and two levels of supplemental P (0 and .2%) from dicalcium phosphate were used. Diets with no added P were formulated to contain .9% lysine, .6% Ca, and .34% P. Apparent nutrient digestibilities were calculated from total collection of urine and feces for 5 d. There were no differences among treatments for energy and nitrogen digestibility. Pigs fed low-phytate corn with no added P had increased digestibility and retention of P and reduced total P excretion (P < .05). We conclude that low-phytate corn contains at least five times as much available P as normal corn. The use oflow-phytate corn greatly reduced the amount of P excreted by the pig and increased the N:P ratio in the manure.

Available phosphorus levels in diets for pigs with high genetic potential for lean meat deposition kept in thermoneutral environment from 15 to 30 kg

“…Bone ash percentage was influenced (P<0.01) by aP levels (Table 2), increasing quadratically up to a maximum response of 0.520% (Figure 6). Similar results were found by O'Quinn et al (1997), Spencer et al (2000) and Hastad et al (2004) with pigs at different stages of production.…”

Available phosphorus for 15- to 30-kg pigs kept in hot environment

“…However, the Linear Response Plateau model provided the best fit to the data, estimating at 0.328% the level of aP from which BA remained on a plateau (Figure 4). This result is consistent with those obtained by O'Quinn et al (1997), Spencer et al (2000) and Hastad et al (2004), who also found increase in the percentage of BA due to the increasing levels of aP in the diets of pigs at different stages of production.…”

Effects of aqueous soaking on the phytate and mineral contents and phytate:mineral ratios of wholegrain normal sorghum and maize and low phytate sorghum

“…The mineral contents of the WS and WM grains (Table 6) were similar to previously reported values for sorghum: P (FAO, 1995;Glew et al, 1997), Fe (FAO, 1995Matuschek ,t al., 2001), Zn (FAO, 1995), Ca (FAO, 1995Kruger et al, 2013) and Mg (FAO, 1995;Glew et al, 1997), and maize: P (FAO, 1992;Spencer et al, 2000), Fe (FAO, 1992;Umeta et al, 2005), Zn (FAO 1992;Beiseigel et al, 2007;Mendoza et al, 1998;), Ca (FAO, 1992Mendoza et al, 2001;) and Mg (FAO, 1992;Mendoza et al, 2001). However, the mineral contents of the RTS and RNTS were higher than the reported ranges for sorghum.…”