Grinding cereal grains to improve swine feed efficiency is not a new concept. In fact, the U.S. swine industry has continued to decrease the average particle size of cereal grains to capture feed efficiency improvements, as every 100 microns (µ) decrease in particle size improves feed conversion by 1.0 to 1.2 percent.
Over the past decade, it has become more common for ingredient byproducts to be used in swine diets due to their ability to lower feed cost. These byproducts partially replace corn and soybean meal in diets, and it is not uncommon to find diets with up to 30 to 60 percent of the total diet made of byproducts.
The most common byproduct is dried distillers grains with solubles (DDGS), but, in some regions, wheat middlings and soybean hulls are attractive ingredients for lowering feed cost. All of these ingredients, however, are higher in fiber and lower in energy concentration than corn, thus lowering the dietary energy level. In order to potentially increase their energy value, grinding them to a finer particle size has been theorized as a means to accomplish this. The logic behind this is that if you create more surface area for lower energy ingredients, the more potential for enzyme digestion to occur, which will increase the absorption of nutrients.
Along with byproduct ingredient grinding, published data on potential growth performance changes from feeding a complete diet that is ground finely has been very limited, but recent studies produced interesting results.
Byproduct studies explore the effects of grind size
Kansas State University (KSU) recently conducted a series of studies to help determine the effects of fine grinding byproduct ingredients or whole diets. The main focus was on high byproduct diets with DDGS, wheat middlings and/or soybean hulls fed to both nursery and finishing pigs.
For the purposes of this article, only diets offered in meal (mash) form will be discussed. However, pelleting of diets in most studies was also evaluated and often migrated some of the negative responses seen with fine grinding.
Researchers at KSU conducted four studies on nursery pigs to determine the effects of particle size on animal performance. Here are their findings:
Particle size does not influence caloric efficiency
Experiment 1 used a total of 675 nursery pigs in a 21-day study to evaluate the effects of fine grinding corn (620 vs. 353 µ), DDGS (534 vs. 377 µ) and wheat middlings (701 vs. 357 µ) for nursery pigs. Pigs were either fed a corn-soybean meal diet or diets containing DDGS and wheat middlings. Overall, reducing the particle size of corn did not influence feed efficiency or caloric efficiency, but numerically reduced average daily feed intake (ADFI), which led to a reduction in average daily gain (ADG).
Also, pigs fed the high byproduct diet had reduced ADG, ADFI and final body weight and poorer feed efficiency, but caloric efficiency (defined as the amount of calories needed to produce one unit of gain) was similar to pigs fed the corn-soybean meal diet. Grinding the byproducts reduced ADG, ADFI and final body weight, and did not influence feed efficiency.
Finely ground corn decreases feed intake
Experiment 2 used 687 nursery pigs in a 21-day study to evaluate the effects of fine grinding corn (638 vs. 325 µ) or DDGS (580 vs. 391 µ). Pigs fed fine ground corn had decreased ADG as a result of numerically decreased ADFI. Fine grinding DDGS did not influence growth performance.
Fine grind impacts daily gains, feed intake
Experiment 3 used 996 nursery pigs in a 21-day study to evaluate the effects of corn particle size (737 vs. 324 µ) and complete diet grinding (656 vs. 540 µ). A corn-soybean meal-based diet containing 30 percent DDGS and 10 percent middlings was used. Overall ADG and ADFI decreased when corn was finely ground and fed in meal form.
Also, a numerical decrease in ADFI was found for pigs fed the fine ground complete diet. No difference between fine ground corn and fine ground complete diet were found.
Finely ground soybean hulls produce performance reductions
Experiment 4 used a total of 1,100 nursery pigs in a 42-day growth trial to determine the effects of increasing soybean hulls (10 or 20 percent) and soybean hull particle size (617 vs. 398 µ). Overall, fine grinding soybean hulls reduced ADG and ADFI, which resulted in no change in feed efficiency.
In conclusion, the researchers found in nursery pigs that reducing the particle size of corn, high fiber ingredients, or complete diet when fed in meal form can negatively impact feed intake leading to decreased daily gains. It is believed that fine grinding and providing in a meal diet form adversely affects palatability of the diet.
Results of finishing pig experiments
In contrast to the nursery pigs, the researchers data showed slightly different results that the aforementioned experiments.
Corn particle size improves feed and caloric efficiency
Experiment 1 used a total of 855 finishing pigs in a 111-day trial to determine the effects of corn particle size (650 versus 320 µ) and complete diet grinding. All pigs were fed the same corn-soybean meal-based diet containing 30 percent DDGS and 20 percent wheat middlings. Overall, reducing corn particle size did not affect ADG or ADFI, but improved feed efficiency and caloric efficiency. Also, fine grinding the complete diet reduced performance when fed in meal form.
Ground soybean hulls produce negative effects
Experiment 2 used 1,235 finishing pigs in a 118-day growth trial to determine the effects of 7.5 and 15 percent ground (370 µ) or unground (787 µ) soybean hulls. Overall, feeding diets with the ground soybean hulls resulted in poorer feed efficiency and caloric efficiency compared to diets with unground soybean hulls.
The experiments conducted by KSU researchers showed that fine grinding corn improved feed efficiency and caloric efficiency; however, grinding the complete diet and feeding it in meal form had detrimental effects on all criteria measured. This may be due to reduced palatability of a finely ground diet presented in meal form. With soybean hulls, the ground material worsened feed efficiency compared to the unground ingredient.
To our disappointment, fine grinding DDGS, wheat middlings, and soybean hulls do not provide an additional benefit in nursery or finishing pigs. Additionally, fine grinding the entire complete diet and fed in meal form was generally negative on performance due potentially to reduced palatability. Thus, producers and feed manufactures should forgo fine grinding these ingredients in attempt to improve their caloric value. Finally, fine grinding corn in nursery pigs provided little benefit below 600 µ; however, feed efficiency was improved in finishing pigs.
References available upon request.
Jon De Jong, M.S.; Mike Tokach, PhD; Steve Dritz, DVM, PhD; Bob Goodband, PhD; and Jason Woodworth, PhD, aided in this research and the development of this article. The studies mentioned in this article were funded, wholly or in part, by the National Pork Board.