Extrusion of cereal grains may be used to improve nutrient digestibility in cereal grains because addition of heat and pressure in combination with addition of moisture during the extrusion may gelatinize the starch, which results in an increase in starch digestibility. It is also possible that AA and energy digestibility are increased by the extrusion, but data to verify this hypothesis have not been published. Therefore, the objective of these experiments was to test the hypothesis that the ileal digestibility of AA and starch and the apparent total tract digestibility (ATTD) of ADF, NDF, and GE as well as the concentrations of DE and ME in corn, wheat, and sorghum are increased by extrusion.

Experimental design

One source of yellow dent corn, one source of wheat, and one source of sorghum were ground and divided into 2 batches. One batch of each grain was used without further processing, whereas the other batches of the 3 grains were extruded. A total of 6 batches of grains were used (Table 1).

Exp. 1. Digestibility of CP, AA, and Starch

Seven diets were formulated. Three diets contained the non-extruded corn, wheat, or sorghum, and 3 additional diets contained the extruded grains. The last diet was an N-free diet that was used to determine the basal endogenous losses of AA from the pigs. Seven ileal cannulated pigs were used and allotted to a 7 × 7 Latin square design with 7 diets and 7 replicate pigs in each period. Therefore, there were 7 replicate pigs per treatment. Pigs were fed their diets in an amount equivalent to 3.4 times the maintenance energy requirement. An AA mixture was provided to all pigs during the initial 5 d of each period, but not during d 6 and 7. The initial 5 days of each period was considered the adaptation period to the diet, but ileal digesta were collected for 8 hours on days 6 and 7. The ileal digesta were analyzed for CP, AA, starch, and chromium to calculated the nutrient digestibility.

Exp. 2. Digestibility of NDF, ADF, and Energy

Six diets were formulated. Three diets contained the non-extruded corn, wheat, or sorghum, and 3 additional diets contained the extruded grain. Forty-eight growing barrows (initial BW = 15.1 ± 3.7 kg) were used. Pigs were fed for 5 days as adaptation period followed by 5 days of total, but separated, urine and fecal collection period. Samples were analyzed for GE, ADF and NDF. Based on the analyzed values, the ATTD of nutrients and the concentrations of DE and ME in each source of grains for extruded or non-extruded were then calculuated. Because all diets contained each source of grains as the sole source of energy, ADF, and NDF, the digestibility values for diets were also considered as values for ingredients

Results

Exp. 1. Digestibility of CP, AA, and Starch

There was no interaction between source of grains and form of ingredients on the AID of starch (Table 2). However, the extruded grains had greater (P < 0.001) AID of starch than non-extruded grains. The AID of CP and AA in wheat and sorghum was not affected by extrusion, but extruded corn had greater AID of CP and all AA except Lys and Pro than non-extruded corn (interaction, P < 0.05).

The SID of CP in corn was increased by extrusion, but SID of CP was not affected in wheat and sorghum (interaction, P < 0.01; Table 3). The SID of all AA was not affected by extrusion in wheat and sorghum, but extruded corn had greater SID of all AA except Lys and Pro compared with non-extruded corn (interaction, P < 0.05). Extrusion in all cereal grains increased (P < 0.05) the values for SID of all AA.

Exp. 2. Digestibility of NDF, ADF, and Energy

The ATTD of GE was increased by extrusion in corn and sorghum-based diets, but not in wheat-based diets (interaction, P < 0.001; Table 4). Values for ATTD of NDF were different among grains and extrusion reduced the ATTD of NDF but there was no interaction between the 2 factors. The ATTD of ADF in diets containing corn or wheat was reduced by extrusion, but the ATTD of ADF in sorghum was not affected by extrusion (interaction, P < 0.001).

Extrusion also increased the DE and ME in all sources of grains compared with non-extruded grains, but the difference was greater if pigs were fed sorghum compared with corn or wheat (interaction, P < 0.001; Table 5). The DE in non-extruded corn was greater (P < 0.05) than in non-extruded sorghum and the DE in extruded corn was greater (P < 0.05) than in extruded wheat. Likewise, the ME in non-extruded corn was greater (P < 0.05) than in non-extruded wheat and sorghum and the ME in extruded corn was greater (P < 0.05) than in extruded wheat.

Key points

• Extrusion of corn, wheat, and sorghum increased the AID of starch compared with the AID of starch in non-extruded grains. Extrusion did not affect AID of CP and AA in wheat and sorghum, but extrusion of corn increased AID of CP and AA. 
• The SID of CP in corn was increased by extrusion, but not in wheat or sorghum. The SID of all AA was increased if the cereal grains were extruded.
• The ATTD of GE was greater in extruded corn and extruded sorghum than in non-extruded corn and sorghum.
• The ATTD of ADF was reduced for extruded corn or wheat.  
• Extrusion increased the DE and ME in corn, wheat, or sorghum.

Table 1. Chemical composition of non-extruded and extruded cereal grains¹

¹All values except DM were adjusted to 88% DM.

Table 2. Apparent ileal digestibility of starch, CP, and AA in non-extruded and extruded cereal grains fed to growing pigs (Exp. 1)

^a-eWithin a row, means without a common superscript differ (P < 0.05).

Table 3. Standardized ileal digestibility of starch, CP, and AA in non-extruded and extruded cereal grains fed to growing pigs (Exp. 1)

^a-cWithin a row, means without a common superscript differ (P < 0.05).

Table 4. Apparent total tract digestibility (ATTD) of nutrients in diets containing non-extruded or extruded cereal grains (Exp. 2)

^a-eWithin a row, means without a common superscript differ (P < 0.05).

Table 5. Concentrations of DE and ME in non-extruded and extruded cereal grains fed to pigs (Exp. 2)

^a-dWithin a row, means without a common superscript differ (P < 0.05).

This report is based on unpublished research by Diego Rodriguez and Hans H. Stein.