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by Gord Leathers
Anyone who keeps cattle knows the bottom line is based on
how efficiently a cow can turn fodder into food whether it's
in the form of meat or milk. One theory holds that mixing a yeast
additive into the feed could increase production but before cattle
farmers spend any money on that they should be asking "where's
the beef?"
"Yeast is one type of additive that has been promoted in
the last ten years or so," according to Karen Beauchemin,
a cattle nutrition specialist with Agriculture and Agrifood Canada
in Lethbridge. "One of the advantages of yeast is that it
helps create a more stable rumen environment and that, in turn,
optimizes the digestion of feed."
There are several companies out there offering a wide range of
yeast based feed additives each promising to do exactly that.
This leads to an equally wide range of options in terms of yeast
products and feed programs. Because the working of a cow's stomach
is a complex business, cattle producers should know that there's
no one-size-fits-all solution to optimizing it's performance.
The entire cattle industry rests on the ability of the cow's
stomach, the four chambered rumen, to take low quality forage
and convert it into high quality protein. The cow simply can't
do this without the help of a complex culture of microbes that
live and work in the warm, dark recesses of the rumen.
"The cow's rumen acts as a large fermentation vat and the
digestion of the feed is actually done by microbes which are
bacteria, protozoa and fungi," Beauchemin said. "Some
of those end products become a source of energy for the animal
itself so those are absorbed and the microbes eventually pass
out of the rumen and become a very large source of protein for
the animal. So the animal doesn't get its protein and energy
directly from feed. It's indirectly obtained through the fermentation
of the feed."
In exchange for their services the cow offers the microbes a
stable environment in which they thrive and breed. They like
the constant warm temperature of the foregut as well as the agreeable
moisture level. They also like the complete lack of light and
oxygen.
"Oxygen is toxic to a lot of the bacteria that are present
inside the rumen because they are obligate anaerobes, which means
they can't survive in the presence of oxygen," states Tim
McAllister, a research scientist also with Agriculture and Agrifood
Canada in Lethbridge.
In the last twenty years we've placed higher demands on cattle
to convert feed more efficiently and produce greater amounts
of protein. This is especially true in the dairy industry where
output per cow has markedly increased over the last two decades.
However, we're still working with the same biological engine
even though we're demanding much more out of it then it was ever
meant to deliver.
"If you go back to the original ruminant in Canada, the
buffalo, basically you have a large animal with a large mobile
fermentation vat and a fairly low level of requirement,"
Beauchemin said. "So the feed is consumed and it stays in
the rumen for a long time and it's thoroughly digested."
Since our demands on the rumen are much higher we have to make
it work faster, better and more efficiently. We also have to
do it in a way that's cost effective. One way we can push the
rumen to be more productive is by increasing the quality and
digestibility of the feed. Consequently cattle are now fed large
amounts of very digestible, very fermentable forages and grains.
But this comes at a price.
"It's just like us eating a very rich meal day after day.
It's hard on your system" Beauchemin said. "So when
animals eat very large quantities of very rapidly fermented types
of feed there's a fluctuation in acid conditions being created
and so you have more undesirable end products like lactic acid
being produced."
The microbes that call the rumen home like stability and can't
thrive in an environment where the acidity is constantly changing.
Fluctuations in the pH bring about fluctuations in the populations
and although they can rebound it still lowers the efficiency
of feed conversion.
"So we create conditions of instability which is undesirable
in terms of fermenting feed and digesting feed, " Beauchemin
said. "The end result is that we have a lack of efficiency
so we have animals excreting in the manure feed that actually
could be digested if it was given the proper chance."
Studies have shown that yeast additives can stabilize the rumen
by using some of the end products of more rapid fermentation,
particularly lactic acid and oxygen. It's still controversial
because of the number of different products on the market and
the number of different conditions under which they're supposed
to work.
"We've done experiments here with some of the materials
and most of the time we haven't had too favourable results in
terms of feed efficiency or animal performance," according
to McAllister. "There's a tremendous amount of data that
shows a variety of responses. If you look at the animal performance
data they're used quite routinely in dairy cattle diets but they're
not used extensively in beef cattle diets."
That's because the hardest working ruminants in the cattle industry
are the dairy cows who are required to produce upwards of 30
to 40 liters of milk per day. In terms of feed conversion this
is very demanding and puts tremendous strain on the entire digestive
system. Although beef animals might benefit from yeast additives
the impact is limited and the need is very small.
"I would only feed it during times of high stress so I would
only include it in the diet when the cattle are first coming
into the feedlot, or those kinds of times during the ration transition
but not continuously," McAllister suggested.
For dairy cattle the effect may be more profound so yeast additives
are cheap insurance according to Beauchemin.
"If you can pay a couple of cents per head per day to have
that added insurance then a lot of producers are doing that,"
she said. "It ensures that digestion in the animal is going
to be as good as it can be and the rumen function is going to
be as good as it can be."
If a cattle farmer chooses to use a yeast additive Beauchamin
suggests there is some homework to be done. Buy only from a company
with a proven reputation and ask to see research data. Additionally,
make sure there's field data as well as lab work. Last of all
make sure the research has been done under conditions as close
to your farm as possible.
"These products can be very diet specific. If the product
has been tested that uses the types of feeds and the types of
diets that you're using then that will give you some confidence
that it is going to be effective in your situation," she
said. "I really urge farmers to follow the directions so
the amount to be fed is very crucial so feeding at half the recommended
level or in excess of the recommended level can actually wipe
out the entire effect or cause negative effects."
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