DAS 96-20 Evaluating forages and TMRs using the Penn State Particle Size Separator
1
INTRODUCTION
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Having the proper particle size
distribution of forages is an important part
of a total ration formulation program. Until
recently this has been difficult to measure
on farms. Many dairy nutritionists have put
subjective measures on this aspect of the
diet and most have been quite effective in
making ration changes in respect to this
measure.
The new Penn State Forage Particle Size
Separator is currently available to
quantitatively determine the forage particle
size of various components. The concept of
forage particle size analysis and having a
standard method for this is not new. The
American Society of Agricultural Engineers'
standard for particle size analysis and
distribution has been available for many
years. The objective in developing the easy
to handle Penn State separator was to mimic
the cumbersome laboratory method for
measuring forage and total mixed ration
(TMR) particle sizes.
Forage particle size analysis begins with
harvesting forages at the proper stage of
maturity. Chopping the crop at the proper
length allows the forages that can be
combined in a total ration to achieve the
desired ration particle length.
Measuring the particle length of
individual forages is only one part of the
solution. In fact, measuring single forages
for particle size is similar to analyzing that
forage for crude protein. There are
recommended ranges for individual forages,
but the real use of the measurement is in
combining forages to achieve the proper
particle size in the total ration, much like
combining feeds to achieve the proper
protein level in the ration.
The main goal in analyzing the particle
size of the total ration is to measure the
distribution of feed and forage particles that
the cow actually consumes. Examine not
only the particles greater than a particular
size, but also the overall distribution of feed
particles being consumed by the dairy cow.
It is recommended that a TMR be measured
from fresh samples taken from the feed
bunk before the cows eat or sort the feed.
Mixing and distribution equipment can
reduce particle size of feeds and forages and
needs to be accounted for when evaluating
the diet.
GUIDELINES ON PARTICLE SIZE
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Achieving adequate ration particle size
requires using recommended guidelines for
forages and TMRs (Table 1). Particle size
guidelines have been obtained from field
data consisting of a large number of farms
and samples studied over several months.
The results of forage and TMR particle size
distribution can be a tool in formulating
rations, especially for forage neutral
detergent fiber (NDF) intake, total NDF
intake, and forage dry matter intake.
Corn silage
Corn silage can be quite variable and
depends largely on the amount fed in the
diet. If corn silage is the sole forage, then
some longer particle size is suggested. At
least 5 to 10 percent of the particles should
be in the upper sieve of the separator (> 0.75
inches). When corn silage is not the sole
forage, then 2 to 4 percent of the particles in
the top sieve may be adequate.
