Effects of corn hardness and drying temperature on digestibility of energy and nutrients in diets fed to growing pigs.

Abstract

Two experiments were conducted to test the hypothesis that corn kernel hardness and drying temperature influence the ileal digestibility of starch and amino acids (AA), as well as apparent total tract digestibility (ATTD) of gross energy (GE) and total dietary fiber (TDF) in diets for growing pigs. Two corn varieties with average or hard endosperm were grown and harvested under similar conditions, and after harvest each variety was divided into 2 batches that were dried at 35 oC and 120 oC, respectively. Therefore, four batches of corn were used. In experiment 1, ten pigs (67.00 ± 2.98kg) with a T-cannula installed in the distal ileum were allotted to a replicated 5 × 5 Latin square design with five diets and five periods giving ten replicates per diet. A nitrogen-free diet and four diets containing each source of corn as the only AA source were formulated. Results indicated that neither variety of corn nor drying temperature influenced apparent ileal digestibility of starch in the grain. The standardized ileal digestibility of most AA was less (P < 0.05) in corn dried at 120 oC compared with corn dried at 35 oC resulting in concentrations of most standardized ileal digestible AA being less (P < 0.05) in corn dried at 120 oC than in corn dried at 35 oC. In experiment 2, 40 pigs (20.82 ± 1.74kg) were housed in metabolism crates and allotted to four diets with ten replicate pigs per diet. The four corn-based diets used in experiment 1 were also used in experiment 2. Feces and urine were collected using the marker-to-marker approach with 5-day adaptation and 4-day collection periods. Results indicated that diets containing hard endosperm corn had greater (P < 0.05) ATTD of TDF than diets containing average endosperm corn. The ATTD of GE in hard endosperm corn was also greater (P < 0.05), and concentrations of digestible energy and metabolizable energy in hard endosperm corn were greater (P < 0.01) than in average endosperm corn. Diets containing corn dried at 120 oC had greater (P < 0.05) ATTD of TDF compared with diets containing corn dried at 35 oC; however, drying temperature did not influence the ATTD of GE. In conclusion, endosperm hardness did not influence the digestibility of AA and starch; however, drying corn at 120 oC reduced digestible AA concentrations. Hard endosperm corn had greater ATTD of GE and TDF, but drying temperature did not influence energy digestibility.