Extrusion results in increased digestibility of energy, which is primarily due to increased gelatinization of starch. Because this process improves flavor of cereal grains, it is known that extrusion improves palatability in pig diets. Particle size reduction in cereal grains results in an improved digestibility of nutrients due to increased surface area of grains, which subsequently increases the interaction with digestive enzymes. However, because grinding changes the textural traits of grains, the palatability of feeds is low and thus feed intake of pigs is often reduced.

The feed preference of pigs may be influenced by the characteristics of feed ingredients included in diets, but it is not known if different particle size of extruded corn affects the feed preference of weanling pigs. Therefore, the objective was to test the null hypothesis that there were no effects of reducing particle size of extruded corn on feed preference by weanling pigs.

Experimental design

One batch of yellow dent corn was procured and extruded and then ground to 3 particle sizes using a hammermill (i.e., 700, 500, and 300 μm).

There were three corn-based diets containing extruded corn ground to 700, 500, or 300 μm. An 8-day feed preference test was conducted with all possible combinations of the three diets. Each pair of diets constituted a treatment group (i.e., 700 vs. 500 μm; 700 vs. 300 μm; 500 vs. 300 μm).

A total of 48 growing pigs (initial weight = 12.1 ± 1.34 kg) were allotted to the three preference test combinations using a randomized complete block design with initial body weight group as the blocking factor, resulting in eight replicate pens per treatment group. Two pigs were housed in each pen. Pigs had ad libitum access to feed and water. For each preference test, each pen contained two feeders with two of the three diets. Feeder positions within each pen were switched daily to minimize positional preference. Feed allotments and feed disappearances were recorded daily. Feed preference (%) was calculated by dividing the amount of feed disappeared for each diet by the total amount of two diets consumed by pigs. Three statistical models for each preference test included particle size of corn as fixed effect and block as random effect.

Results

Results indicated that pigs had greater (P < 0.05) daily feed disappearance and preference for corn with 700 µm on days 1, 4, 5, 7, and 8 when pigs had a choice between 700 µm vs. 500 µm (Table 1). For the other two preference tests, which were 700 µm vs. 300 µm and 500 µm vs. 300 µm, pigs had a greater (P < 0.05) preference for the larger particle size corn (700 and 500 µm, respectively) for days 3 to 8.

In conclusion, it was demonstrated that pigs have a preference for larger particle sizes of extruded corn when given the choice. This may be a result of better texture of feed, a satisfying chewing experience, and the perception of greater bulkiness provided by greater particle sizes. However, further research with longer-term feeding trials is needed because pigs may have already adapted to consuming diets with 700 µm particle size prior to the experiment, which is similar to commercial diets.

Key points

• Pigs have a preference for larger particle sizes of extruded corn when given the choice.

Table 1. Daily feed disappearance and feed preference of weanling pigs (n = 8)