World Grain - August 2021 - 42

FEED QUARTERLY: FEED OPERATIONS
Pelleting's impact on
nutrient digestibility
The process influences many chemical
and physical characteristics of feed
by Chad Paulk and Kara Dunmire
Components of the pelleting process, such as steam conditioning
and feed retention time in the conditioner and die, expose
feed to various degrees of heat, moisture, pressure, and sheer,
which changes its physical and chemical characteristics.
When ingredients that make up a diet formulation are
exposed to the steam conditioning process and extrusion
through the die, the heat and moisture plasticize the soluble
fractions of the diet and increase the agglomeration of dietary
components (Lundblad et al., 2009). Pelleting swine
and poultry diets is commonly used to improve nutrient utilization,
feed efficiency, feed handling characteristics and
bulk density. Most of the improvement in swine or poultry
feed efficiency due to pelleting can be attributed to a decrease
in feed wastage. However, it is often discussed how
much of the pelleting benefit can be attributed to improvements
in nutrient digestibility.
Previous research observed that feeding pelleted diets increased
DM, N, and GE digestibility compared to feeding meal
diets when fed to pigs (Wondra et al., 1995). More recently,
Rojas et al. 2017 observed that pelleting a corn-soybean meal
diet increased the digestibility of DM, N, and GE by 5% to 8%
compared with feeding the same diet in a mash form.
Although these reports demonstrated improvements in digestibility,
there is still discussion about how pelleting affects
different nutritional components and which nutrients are leading
to the benefits in performance. In addition, recent issues
of feed safety and importance of pellet quality have led feed
manufacturers to steam condition diets at higher temperatures
42
to decrease pathogen load and improve pellet quality.
This begs the question: Are there potential negative impacts
on nutrient digestibility when pelleting diets at high temperatures?
Ultimately, the improved performance response to pelleting
is multifactorial. However, this article will focus on the
impacts it has on specific nutrient digestibility.
Starch
Starch is the major energy source in livestock diets, comprising
up to 50% of monogastric diets primarily supplied by
grains. Starch digestion largely is driven by amylase, a glycolytic
enzyme that degrades starch into sugars that are more
readily available for absorption in the small intestine. Pelleting
of corn- and soybean meal-based diets increase starch
availability through a process known as starch gelatinization.
Gelatinization is a four-step process that irreversibly solubilizes
raw starch granules through the addition of heat and
moisture. Different cereal grains have different starch gelatinization
characteristics (Lund 1984) where gelatinization
temperatures of wheat (137°F) and sorghum (163°F) starches
are lower and higher, respectively, than that of corn (153°F).
When exposed to the conditioning process, starch granules
begin to swell and as feed passes through the die the frictional
heat and pressure drives starch gelatinization (Truelock et al.
2020). The pelleting process increases starch gelatinization
from approximately 6% in mash feed to 10% to 11% in pelleted
feed (Lewis et al., 2015).
This demonstrates how the degree of gelatinization is
August 2021 / World Grain / World-Grain.com
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World Grain - August 2021

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