The Rural Voice, 2001-05, Page 54Selecting corn
silage hybrids
for quality
By Joel Bagg,
Forage Specialist,
OMAFRA, Lindsay
Traditionally, corn silage was
thought of as being very consistent in
feed value. But as we learn more
about measuring forage digestible
energy in ruminants, we are finding
out that we need to place much more
emphasis on corn silage quality.
Corn silage digestibility is
affected by many factors other than
the hybrid, such as weather, fertility,
moisture. maturity, and harvest and
storage management.
Both silage yield and digestibility
information is needed when selecting
hybrids. Seed companies have
developed, selected and marketed
silage -only and dual-purpose hybrids.
These include "leafy" and BMR
(brown mid -rib) hybrids. The Ontario
Hybrid Corn Performance Reports do
not include silage data. Comparison
of company hybrids by producers is
difficult because of conflicting
quality measures.
Digestible Energy
Corn silage consists of a mixture
of two very different components -
high moisture grain corn, and
relatively mature, lower quality
stover. Determining the true energy
content of corn silage is difficult.
Different hybrids may partition
energy differently. Digestible energy
of corn silage is the cumulative
impact of a number of traits,
including:
• Amount of grain (starch, sugars,
oil)
• Starch digestibility
• Amount of fibre
• Fibre digestibility
Characteristics of the plant, such
as grain content, soft kernel texture,
and plant stature, may give us some
clues as to the digestibility of corn
silage hybrids, but the ultimate tests
are laboratory analysis and animal
performance.
There are no direct chemical
50 THE RURAL VOICE
Advice
methods to analyze for digestible
energy in forages, but we are
becoming much more sophisticated
in how we estimate it. Total
Digestible Nutrients (TDN) and Net
Energy (NE) have been estimated by
analyzing for Acid Detergent Fibre
(ADF) and Neutral Detergent Fibre
(NDF) and using regression
equations. A lower NDF is important
in high -producing rations because it
indicates increased intake potential.
However, these do not measure fibre
or starch digestibility.
In Vitro & In Situ Digestibility
Whole plant and fibre
digestibilities are now measured by
in vitro and in situ fermentation
analysis. Whole plant digestibility is
the best estimate of the corn silage
energy (grain and stover) content.
NDF digestibility is important
because it has a positive impact on
both dry matter intake and energy.
In vitro digestibility fermentation
analysis uses rumen fluid in a test
tube to measure the amount and rate
of digestion under simulated rumen
conditions. Fine grinding of the in
vitro samples may potentially bias
the hybrid starch and fibre
digestibility differences.
In situ digestibility fermentation
analysis uses a nylon bag in the
rumen of a fistulated cow using
undried, unground, fermented corn
silage samples. It is more accurate,
includes kernel texture (starch
digestibility) differences, and allows
for feed interactions, but is much
more difficult and expensive.
Good direct measures of energy
digestibility, such as in vitro and in
situ digestibilities render the indirect
measures of quality, such as
grain/stover ratios, kernel texture, or
plant stature much less relevant.
Dairy Applications
The University of Wisconsin has
developed Milk Per Acre and Milk
Per Ton calculations using their Milk
2000 program to combine yield,
energy digestibility, crude protein
and intake into a single measure.
These can be used to compare the
economic value of various corn
silage hybrids. Milk per ton measures
quality, while milk per acre combines
yield and quality.
Summary
Give the same priority to corn
silage quality as you do to haylage
quality. This includes proper harvest
and storage management, in addition
to hybrid selection and other
agronomic considerations. Without
sufficient independent data, it is very
difficult to select corn silage hybrids
between companies. More research is
needed in this area. For now, a good
strategy may be to deal with a seed
company you trust, and choose
hybrids from the top of their list for
silage.0
Dealing with
herbicide resistent
weeds
By Hugh Martin, OMAFRA
Have you found a herbicide
resistant weed?
Before declaring it to be resistant
make sure that other explanations for
weed escapes and misses are
investigated. Weeds that emerge after
application with non -residual
herbicides can confuse the diagnosis.
Some species are naturally more
tolerant to some herbicides. Improper
equipment setup, poor spray pattern,
canopy penetration, improper weed
stage or weather issues can all lead to
misses that can be misdiagnosed as
weed resistance.
When you do find resistance, the
immediate answer is to use an
alternative herbicide for which there
is no resistance. This may mean
adding another different herbicide to
the spray tank, making a second pass
with an alternative product, or
switching to a completely different
herbicide program. The main concern
with these responses to controlling a
resistant weed population is that they
may lead to multiple resistance as
happened in Ontario with pigweed
and Manitoba with green foxtail.
Resistance is a consequence of
relying too much on herbicides for
weed control. Changing herbicides
may not be viable in the long term if
there is no change in the way we
manage weeds globally. Resistance
1