Drying temperatures and corn varieties that inherently differ in kernel hardness, virtuousness, and protein solubility index may influence nutrient digestibility in corn. However, information about interactive effects of corn source (i.e., endosperm hardness) and drying method on nutrient digestibility is limited. Therefore, an experiment was conducted to test the hypothesis that the ileal digestibility of starch, crude protein (CP), and amino acids (AA) is influenced by corn source and drying temperature.

Experimental design

Two corn sources (i.e., soft or hard endosperm) were procured. Each source of corn was divided into two batches. One batch was dried at 35 ^oC, whereas the other batch was dried at 120 ^oC. Therefore, four different sources of corn were used (Table 1). Five diets were prepared. Four diets contained each source of corn as the only source of CP and AA. The last diet was a nitrogen-free diet that was used to determine the endogenous loss of AA from the pigs. Each experimental period lasted 7 d. The initial 5 d of each period was considered an adaptation period. Ileal digesta were collected on d 6 and 7 for 9 h using standard procedures. Diets and ileal digesta samples were analyzed for AA and Cr to calculate the apparent ileal digestibility (AID) of CP and AA in corn sources. The AID values were then corrected using the basal endogenous losses of CP and AA to calculate the standardized ileal digestibility (SID) values.

Results

Neither source nor drying temperature influenced the AID of starch in corn (Table 2). No interaction between corn source and drying temperature was observed for SID of CP and AA. No differences were observed between corn sources for SID of CP and AA with the exception that the SID of Leu tended (P < 0.10) to be greater in hard endosperm corn than in soft endosperm corn. The SID of CP, Arg, His, Lys, Met, Thr, Ala, Asp, Cys, Glu, Ser, and Tyr was less (P < 0.05) in corn dried at 120 ^oC compared with corn dried at 35 ^oC. The SID of Ile, Trp, and Val also tended to be less (P < 0.10) in corn dried at 120 ^oC than in corn dried at 35 ^oC. As a result, Concentrations of standardized ileal digestible CP and most AA were less (P < 0.05) in corn dried at 120 ^oC compared with corn dried at 35 ^oC.

Key points

• Neither source nor drying temperature influenced the AID of starch in corn.
• Endosperm hardness did not influence AID of DM or SID of CP and AA (except Leu) in corn.
• The SID values for CP and most AA in corn dried at 120 ^oC were less than in corn dried at 35 ^oC.
• Due to reduced digestibility of AA, corn dried at 120 ^oC had reduced concentrations of most standardized ileal digestible AA than corn dried at 35 ^oC.

Table 1. Starch, crude protein and amino acid composition of four sources of corn, as-fed basis

Table 2. Apparent ileal digestibility (AID) of starch and standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in four sources of corn^1,2,3

¹Data are least squares means of 20 observations per treatment.

²Values for SID were calculated by correcting the values for AID for basal ileal endogenous losses. Basal ileal endogenous losses were determined (g/kg of DMI) as CP, 23.71; Arg, 0.82; His, 0.30; Ile, 0.56; Leu, 0.81; Lys, 1.17; Met, 0.16; Phe, 0.50; Thr, 0.85; Trp, 0.14; Val, 0.68; Ala, 1.13; Asp, 1.32; Cys, 0.30; Glu, 1.69; Gly, 2.76; Ser, 0.80; and Tyr, 0.44.

³Corn source × drying temperature effects were not significant; therefore, only main effects are indicated.