DAS 96-20 Evaluating forages and TMRs using the Penn State Particle Size Separator
2
GUIDELINES ON PARTICLE SIZE
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CONTINUED
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It is more critical to chop corn silage so
that a good fermentation can occur yet not
be pulverized. This means that about 40 to
50 percent of the silage material measured is
in both the middle (<0.75 and >0.31 inches)
and bottom (<0.31 inches) pans of the
separator. As corn silage makes up a greater
proportion of the ration, the more that
should be in the middle sieve and less in the
bottom pan.
The newer systems of harvesting corn
silage that includes chopping and rolling in
one process can create a silage with 10
percent or more of the forage material
having long particles without large pieces of
whole cobs or stalks. This forage can still
be excellent quality because adequate
fermentation can occur in the silo due to
packing characteristics.
More conventional choppers that are
operated to create such long particle size in
corn silage would create a forage material
that would be predisposed to mold
formation due to poor silo compaction. The
material usually has large pieces of cob, dry
stalks and leaves that have poor palatability
and may often be refused by high producing
cows.
Haylage
There is a lot of variability with haylage
due to the type and use of machinery, sward
type and density, and most of all, the dry
matter of the crop harvested. Ten to 25
percent of the crop should be in the top sieve
of the particle separator. This means that 10
to 25 percent of the forage particle size is
greater than 0.75 inches. If the distribution
of forage particles is determined, then the
amount of forage particles greater than 1
inch can be approximated.
The type of silo structure may require
altering the particle size distribution
recommended. Forages stored in upright
sealed silos would likely fall at the lower
end of the range (10 to 15 percent). Bunker
silos can have appreciably longer material
ranging from 15 to 25 percent. The middle
pan should contain 30 to 40 percent of the
material and the bottom pan 40 to 50
percent.
TMR
Field investigations conducted at Penn
State have found that there is a high degree
of variability in overall rations. Feeding
management plays an important role in the
particle length needs of the cow. Ideally 10
percent or more of the material should be
greater than 0.75 inches (top sieve). It was
observed that many rations have only 3 to 8
percent of the TMR particles in the top sieve
(> 0.75 inches). This extrapolates to many
rations having less than 1 percent of the
particles as being greater than 1.5 inches.
While this goes against many old thumb
rules, there are many farms feeding these
types of rations with obvious success.
Feeding management, balanced rations,
and attention to total ration NDF and forage
NDF levels are likely a large part of their
success. Some generally preferred
guidelines to follow for TMRs are 6 to 10
percent of the particles in the top sieve, 30
to 50 percent in the middle sieve, and 40 to
60 percent in the bottom pan in rations for
high producing dairy cows.
