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American Agriculturist - May 2007
Dair y & Livestock
20
How to replace corn grain in ration
Milk it !
Key Points
By Vicky
Carson
■ Rumen chemistry requires balance when
replacing corn.
■ Alternatives are also tied to corn prices,
so push the pencil carefully.
■ Feeding Rumensin can make a difference
to the bottom line.
VERY dairy producer in the
country is painfully aware that
the price of corn has skyrocketed
since last fall. The price increase has
been fueled by an increased demand for
ethanol and by speculation.
It’s likely that high corn prices are
here to stay at least in the short term
as demand for ethanol does not seem to
be curtailing. It’s equally as likely that
planting will increase this spring, and
corn prices could be closer to what we
consider normal by late fall, depending
on growing conditions, harvest and exports of corn grain.
E
Why feed corn grain at all?
Corn grain provides energy and starch.
Starch is the preferred energy source
for rumen microbes, and many research
studies have demonstrated a significant
reduction in microbial growth when
starch was limited in the diet, resulting
in reduced diet digestibility and, ultimately, reduced milk and milk component yields.
In the past, with cheap corn grain
prices, nutritionists typically balanced
diets so that starch content was at the
upper limit of requirements plus a little
extra as an insurance policy. I think that
producers can reduce corn grain in the
diet and still meet microbial needs.
What can a producer do now?
Here are several steps you can take now
to balance rations:
■ Calculate starch content of the
diet and determine if it is between 21%
to 28%. I typically like starch content to
be around 25% of the diet dry matter.
Diets high in corn silage are likely to be
between 22% and 25% without any supplemental corn grain.
■ Feed alternative sources of starch
like barley, hominy, wheat middlings,
depending on their price.
■ Blend 2 parts corn meal to 1 part
barley to balance starch availability in
the rumen.
■ Feed sources of corn that are more
rumen-available, like steam-flaked corn,
fine-ground corn meal, high-moisture
ear corn and processed corn silage.
Increasing rumen digestibility means
that we can reduce the amount of corn
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grain that’s in the diet.
■ Balance diets for physically effective neutral detergent fiber. It forms the
rumen mat layer and mitigates the entry
of smaller concentrate particles into the
liquid phase of the rumen digesta. Diets
with adequate peNDF will have a more
stable fermentation and feed dry matter
will be more efficiently converted to organic matter.
■ Add Rumensin to the diet.
Rumensin reduces the formation of
waste products in the rumen, sparing
energy to be used for other productive
purposes. The addition of Rumensin reduces corn requirements by 1.2 to 1.8
pounds per head per day. Rumensin
also increases feed efficiency and can
improve the bottom line for the farm.
■ Replace some of the energy from
corn grain with rumen inert fat. I prefer
Megalac because it has years of laboratory and on-farm research behind it.
I usually stick to around 1% to 2% of
the diet dry matter as rumen inert fat,
depending on the other ingredients.
If diets are high in unsaturated or free
fatty acids, milk fat may be depressed.
■ Consider planting more acres of
corn this spring. Corn silage is a good
source of fiber and typically contains
25% to 35% starch. Investigate corn
silage hybrids and choose varieties that
are more digestible and have higher
starch content.
It is also worth investigating costs of
kernel processing for corn silage harvest. Processing corn silage can reduce
the need for corn grain by as much as
5 pounds of dry matter by making the
corn silage kernels more digestible.
Consider sugar
Numerous research trials have looked
at the influence of replacing starch with
sugar on rumen microbes, milk yield
and milk component yields. Glucose
and fructose are the two most common
simple sugars found in plants, followed
by sucrose (molasses) and lactose
(whey). During the maturation process,
most plants convert sugar to starch —
the energy storage form.
A typical lactating cow diet contains
less than 4% of the diet dry matter as
sugar, and the sugar content of feeds
varies greatly. Corn silage, corn grain,
barley and oats contain very little sugar.
Grass hay and pasture have greater
concentrations of sugar as do molasses,
bakery waste, citrus pulp and almond
hulls.
Replacing dietary starch with sugar
as a source of energy for rumen microbes improves the energy status of
the cow.
Dietary sugar appears to increase butyric acid in the rumen without effecting
acetic or propionic acids. Butyric acid
is the volatile fatty acid that is responsible for maintaining the health of the
rumen epithelium and growing rumen
papillae.
Papillae are fingerlike projections
along the wall of the rumen that increase the absorptive surface area. By
increasing butyric acid, papillae growth
increases, resulting in increased absorption of volatile fatty acids from the
rumen. Increasing dietary sugar also
appears to reduce ammonia concentration in the rumen, likely as a result of
increased fermentation rate.
Environmentally, a reduction in ruminal ammonia is advantageous, and it
also reduces the amount of energy the
cow must expend dealing with waste
products. Replacing starch with sugar
increases diet dry matter and NDF digestibility, suggesting sugars increase
the extent of ruminal fermentation as
long as ruminally degradable protein is
adequate.
What about byproduct feeds?
The amount of corn grain that can
be replaced by byproduct feeds like
citrus pulp, beet pulp, bakery products, ground cereal, etc., depends on
the total diet. Generally, I like to keep
byproduct feeds to around 2% of the
diet dry matter. When forage is limiting,
this number is likely to be greater and
may be as much as 10% of the diet dry
matter. Recent research claims that distillers grain can make up as much as
20% of the diet dry matter. Personally,
I think 2% to 5% of the lactating cow
diet from high-fat byproduct feeds is
enough, and I am more comfortable at
2%. Feeding distillers grain to growing
animals is certainly a great way to spare
corn grain and corn silage on the farm.
There are several alternatives to
replacing the energy in the diet provided by corn grain, but it takes some
creativity to come up with a source to
replace the starch corn grain provides
in the rumen. Because of this, and the
fact that the other ingredient prices
follow corn prices, corn grain should
not be abandoned completely. With the
advanced diet balancing and evaluating
computer models (CPM and CNCPS),
your nutritionist can mix and match dietary carbohydrates to meet the needs
of the rumen and the needs of the cow
without compromising milk and milk
component yields.
Carson and her husband, Steve,
partner in Harkdale Farms, Newbury, Vt.
She’s also a consulting dairy nutritionist.