Conventional breeding of corn has generated a new variety (i.e., high-oil corn; Byron Seeds LLC, Rockville, IN), which is believed to contain more oil and phosphorus than conventional corn. Because of the increased oil, it is possible that high-oil corn contains more digestible energy (DE) and metabolizable energy (ME) than conventional hybrids, but this hypothesis has not been experimentally verified. Inclusion of microbial phytase in diets for pigs usually improves digestibility of P because phytase hydrolyzes the ester bond that binds P to the phytate molecule in corn. However, there are at this point no data for effects of adding phytase to diets containing high-oil corn and no data to demonstrate the nutritional value of high-oil corn. Therefore, an experiment was conducted to test the hypothesis that the standardized total tract digestibility (STTD) of P, as well as concentrations of DE and ME in high-oil corn are greater than in conventional corn. The second hypothesis was that inclusion of microbial phytase to diets improves the STTD of P in corn sources.

Experimental design

Sixty-four pigs (initial body weight: 18.75 ± 2.17 kg) were allotted to a randomized complete block design with 8 diets and 8 replicate pigs per diet. Two sources of corn (i.e., high-oil corn and conventional corn) were used, and 2 diets based on each source of corn were formulated without adding phytase to the diets. Six additional diets were formulated by adding 500, 1,000, or 2,000 units of microbial phytase to each of the 2 initial diets. Pigs were housed individually in metabolism crates that allow for the total, but separate, collection of urine and fecal samples. Feces and urine were collected with 5-day adaptation and 4-day collection periods. At the conclusion of the experiment, diets, ingredients, fecal samples, and urine samples were analyzed for gross energy (GE), and concentrations of DE and ME in diets and each ingredient were calculated. Diets, ingredients, and fecal samples were also analyzed for P to calculate STTD of P in each diet.

Results

The concentrations of GE, acid-hydrolyzed ether extract, and total P were greater in high-oil corn compared with conventional corn (Table 1). Results indicated that concentrations of DE and ME in diets were not influenced by phytase supplementation (Table 2). The digestibility of GE was not different between diets containing high-oil corn and diets containing conventional corn. However, because of the greater GE in the high-oil corn diets compared with the diets based on conventional corn, the concentrations of DE and ME in high-oil corn were greater (P < 0.01) than in conventional corn.

Inclusion of 500 FTU/kg of phytase in the conventional corn diet reduced the daily P intake of pigs compared with pigs fed the conventional corn diet without phytase; however, pigs fed the high-oil corn diet with 500 FTU/kg of phytase had greater daily P intake than pigs fed diets without phytase (interaction, P < 0.01; Table 3). The quantity of P excreted in feces was reduced (P < 0.01) when phytase was added to the diets, and pigs fed diets based on high-oil corn had less (P < 0.05) excretion of P than pigs fed diets based on conventional corn. As a result, diets containing phytase had greater (P < 0.01) STTD of P than diets without phytase. Absorption of P was also greater (P < 0.01) for pigs fed diets based on high-oil corn than pigs fed diets containing conventional corn, and therefore, the STTD of P was greater (P < 0.01) in high-oil corn than in conventional corn.

Key points

• High-oil corn contains more gross energy, fat, and total P compared with conventional corn.
• Concentrations of DE and ME in high-oil corn were greater compared with conventional corn.
• The energy values in the 2 corn sources were not influenced by phytase, but addition of phytase to diets increased in the STTD of P in high-oil corn and in conventional corn.
• High-oil corn had greater STTD of P than conventional corn.

Table 1. Nutrient composition of high-oil corn and conventional corn, as-fed basis

Table 2. Apparent total tract digestibility (ATTD) of gross energy (GE) and energy concentrations in experimental diets and in 2 sources of corn¹

 ¹Data are least squares means of 7 or 8 observations per treatment.

 ²High oil corn = Byron Seeds, LLC, Rockville, IN; FTU = phytase units.

 ³DE = digestible energy; ME = metabolizable energy.