Pelleting and extrusion are technologies that have been used in livestock feeding to improve nutrient digestibility and feed conversion. Recent research concluded that reduced performance of pigs fed diets containing high concentrations of fiber was ameliorated if the diets were pelleted. Extrusion is also of benefit in high fiber diets, because it may increase the solubility of dietary fiber. It is possible that the benefits of extrusion and pelleting are greater in high fiber diets than in low fiber diets, but this hypothesis has not been investigated. Therefore, an experiment was conducted to determine effects of extrusion and pelleting on energy and nutrient digestibility in diets containing low, medium, or high concentrations of fiber.

Experimental design

Twenty-four growing barrows were used in the experiment. Diets containing three different levels of fiber were formulated. The low fiber diet was based on corn and soybean meal, the medium-fiber diet was based on corn, soybean meal, and 25% DDGS, and the high-fiber diet was based on corn, soybean meal, 25% DDGS, and 20% soybean hulls. All ingredients were ground to an average particle size of approximately 500 microns and after mixing, each of the three diets were divided into four batches that were either fed in a mash form without further treatment, pelleted, extruded, or extruded and pelleted before feeding. Ileal digesta were collected to determine apparent ileal digestibility (AID) of energy and nutrients. Feces and urine were collected to determine apparent total tract digestibility (ATTD) of energy as well as concentrations of digestible (DE) and metabolizable (ME) energy.

Results

Pelleting increased (P < 0.01) the AID of gross energy, crude protein, and dry matter in low fiber diets, and the AID of starch in medium fiber diets (Table 1). Extrusion increased (P < 0.01) the AID of gross energy, crude protein, and dry matter in all diets, and starch in medium fiber diets. Pelleting of extruded diets did not increase the AID of energy and nutrients compared with extrusion alone.

Pelleting did not increase the mean AID of amino acids compared with meal in the low, medium, or high fiber diets. However, pelleting did increase (P < 0.01) the digestibility of some indispensable amino acids, including lysine, in the low and medium fiber diets.

The mean AID of amino acids was greater (P < 0.01) in extruded diets than in meal or pelleted diets at all levels of dietary fiber. Amino acid digestibility in extruded medium fiber diets was greater (P < 0.01) than in low fiber diets fed in meal or pelleted form, and amino acid digestibility in extruded high fiber diets was equivalent to that of low fiber diets fed in meal form. Pelleting of extruded diets did not improve amino acid digestibility compared with extrusion alone.

Pelleted low and medium fiber diets had greater (P < 0.01) ATTD of gross energy and contained more (P < 0.01) DE and ME than the same diets fed in meal form (Table 2). Extruded diets contained more (P < 0.01) DE and ME on a dry matter basis than meal diets at the high level of fiber. Regardless of fiber level, diets that were both extruded and pelleted always had greater (P < 0.05) ATTD of gross energy and contained more (P < 0.05) DE and ME than diets fed in meal form.

Key points

• Pelleting and extrusion increase the digestibility of energy and amino acids in diets based on corn and soybean meal or corn, soybean meal and DDGS.
• Extrusion also increases the digestibility of energy and amino acids in high fiber diets based on corn, soybean meal, DDGS, and soybean hulls.
• Pelleting and extrusion may reduce the total costs of feed needed to produce a market pig by improving feed conversion and reducing the amount of soybean meal needed in the diets.

Table 1. Apparent ileal digestibility (AID) of gross energy and nutrients in experimental diets with three different levels of fiber and fed in meal, pelleted (Pel), extruded (Ext), or pelleted and extruded (Pel/Ext) form, as-fed basis

^a-hMeans within a row lacking a common superscript letter differ (P < 0.05).

Table 2. Apparent total tract digestibility of gross energy and concentration of digestible and metabolizable energy in experimental diets, as-fed basis

^a-gMeans within a row lacking a common superscript letter differ (P < 0.05).

This report is based on unpublished research by Oscar Rojas and Hans H. Stein.