Corn is the most commonly used cereal grain in diets for pigs and poultry and it can easily be grown under a wide range of environmental conditions. The continuing innovation in corn genetics has resulted in development of a new cultivar that contains more oil than conventional hybrids of corn. This new genetic line was developed by Byron Seeds, in Rockville, Ind. It is possible that the new high-oil corn has greater concentration of energy than conventional hybrids, but this hypothesis has not been experimentally verified. Therefore, two experiments were conducted to test the hypothesis that values for the standardized ileal digestibility (SID) of amino acids (AA), concentration of metabolizable energy (ME), and the standardized total tract digestibility (STTD) of phosphorous (P) in high-oil corn are greater than the values obtained in conventional corn.
Experimental procedures
In the AA digestibility experiment, diets containing each source of corn were fed to pigs that had a cannula installed in the distal part of the small intestine. Samples were collected from the cannulas after pigs were fed the two diets and were analyzed for AA and digestibility values were calculated.
In the second experiment, four diets that contained each source of corn were formulated for a total of eight diets in the experiment. The four diets with each source of corn contained 0, 500, 1,000, or 2,000 units of phytase per kg. Each diet was fed to eight pigs that were placed in metabolism crates, which allowed for separate collection of urine and feces from the pigs. Samples of the diets and feces were analyzed for energy and phosphorus, and urine samples were also analyzed for energy. The STTD of P and the ME were calculated for each diet.
Results of experiments
The analyzed concentrations of crude protein and fat in high-oil corn were 8.73 and 8.98%, respectively, whereas protein and fat in conventional corn analyzed 7.20, and 4.53%, respectively, which demonstrates that the breeding technology used to produce high-oil corn was effective in increasing the oil and protein concentrations in corn.
The SID of Histidine, Isoleucine, Leucine, Lysine, Phenylalanine, Threonine and Valine was greater (P < 0.05) in high-oil corn than in conventional corn (Figure 1, below). The SID of Arginine and Methionine also tended to be greater (P < 0.10) in high-oil corn than in conventional corn, but the SID of Tryptophan was not different between the two sources of corn. The reason values for SID of most AA in high-oil corn were greater than in conventional corn is likely a result of the increased concentration of fat in high-oil corn, because fat may increase AA digestibility by increasing the retention time of the ingested feed, which provides more time for AA digestion and absorption.
Results of the second experiment indicated that the digestibility of gross energy (GE) was not different between diets containing high-oil corn and diets containing conventional corn (Table 1, below). However, because of the greater GE in high-oil corn diets than in conventional corn, the concentrations of digestible energy (DE) and ME in high-oil corn were greater (P < 0.01) than in conventional corn. The quantity of P excreted in feces was reduced (P < 0.01) if 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 (Table 2, below).
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. The observation that high-oil corn had greater concentrations of DE and ME, as well as STTD of P than conventional corn is likely a result of increased concentrations of GE, protein, fat, and non-phytate bound P in high-oil corn.
Overall conclusions
High-oil corn contains more standardized ileal digestible AA, DE, and ME than conventional corn. The STTD of P in high oil corn, regardless of phytase supplementation, was also greater than in conventional corn. These results indicate that high-oil corn can be used as an alternative for other cereal grains in diets for pigs.
Hans H. Stein is a professor of Animal Science at the University of Illinois. Charmaine Espinosa is a post-doctoral research fellow at the Stein Monogastric Nutrition Laboratory.
