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Protect your investment with semen tank management
1/28/2008
Michael Fisher
Area
Extension Agent (Livestock)
Colorado State University Extension
Golden
Plains Area |
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Many cow-calf operations have adopted artificial insemination (AI)
as a key management tool in their business plan. The use of AI offers several
advantages over natural sire service. It allows the producer a wider selection
of bull power and genetic choices. Also, when using AI, the various genetic
choices can be targeted at specific cows or heifers in an effort to exact the
preferred change. The AI herd may require a few clean up bulls but this is
significantly less than the combination of purchase, nutrition, and health
costs of maintaining a full bull battery to compliment the herd. Additionally,
a semen tank in the corner of the barn office is not likely to knock you into
the dirt; while a pen full of salty bulls may consider this to be great
sport.
Even with all of its advantages, AI can be a significant
investment. Enrollment in a quality AI school can cost a surprising amount.
Especially if you are one of those people that just can't get the job done. (AI
is a lot like one of the arts. Most anyone may be able to learn the rules and
guidelines but not everyone possesses the degree of talent needed to be
successful.) Then you have the cost of the AI breeding equipment, including a
semen tank(s). Plus, there is your investment in straws of semen that you
intend to use in the AI process and the additional cost of the semen's validity
certificate.
These straws can vary significantly in cost depending on
the perceived worth of the bull. You may find an unproven sire for $8 per
straw; while the current "got-to-have-'em" bull may be selling at well over
$100 per straw. In some cases, particularly following the recent death of a
famous bull, you may see straws of semen sell at auction for thousands of
dollars. Some of the long term (6 to 8 months) storage semen tanks that are on
the market today can be rated for holding up to 540 straws. Let's assume that
on an example farm, we paid an average of $35 per semen straw and filled one of
these new tanks. That would be just shy of a $19,000 investment. That is a
dollar value worth protecting.
To protect this investment it is
important to understand the tank that the semen straws are stored in. A lot of
people look at the semen tank and see one tank. In reality, you are looking at
a pair of tanks, one inside of the other. The inner shell is suspended from the
neck of the outer shell and the two tanks are sealed together at the neck. This
creates a vacuum between the two shells; which provides an insulator factor to
the tank. Rough handling, heavy impacts, carrying the tank by the neck, or
swinging the tank can all cause fractures in the seal between the two tanks.
This can release the vacuum and significantly reduce the tanks insulating
ability. When this happens, the tank's liquid nitrogen will evaporate quickly
and the tank will quickly lose its cooling ability, limiting or even
eliminating storage capabilities. An indication that this condition may exist
is the accumulation of frost at the top of your semen tank.
It is very
important to select a good place to locate your tank. It should be in a well
lit place where you will be able to make routine, visual inspections. Yet, the
tank should not be kept in direct sunlight. The sun's power can cause thermal
fluctuations on the tank and lead to failure. Another storage factor is that
the tank needs to be in a dry, well ventilated location. The metal that your
tank is made of can react with moisture and have a corrosive effect on your
tank; leading to a loss of vacuum and a tank failure. Therefore, it is highly
recommended that the semen tank be stored in an elevated location on wood.
Never leave a semen tank sitting on cement.
Semen storage is all about
temperature regulation. Thermal injury is permanent and can happen in a matter
of seconds. When transferring straws to or from a semen tank one needs to be
careful to ensure that it is done quickly and that stored semen remains frozen.
Therefore, it is critical that the semen tank be maintained with the
appropriate amount of liquid nitrogen. Many people assume that the temperature
inside of the tank is a constant but this is not the case. In 1974, Richard
Saacke's research showed the AI industry that there is great temperature
variability within a semen tank. At the liquid nitrogen level the temperature
is about minus 320 degrees F. However, at the tank's opening, the temperature
may be as high as 54 degrees F. So over the course of a few inches, we see
nearly a 375 degree rise in temperature. When the temperature of the stored
sperm rises above minus 112 degrees F, ice crystals in the straw become
unstable and can cause thermal damage to the sperm. In Saacke's research, it
was shown that this critical temperature, in a properly filled semen tank,
occurred at a point near three inches from the top of the tank's neck. However,
as liquid nitrogen evaporates from the tank there is an increased potential for
this critical temperature to be reached lower in the tank. Therefore, it is
important that we always maintain the appropriate level of liquid nitrogen in
our semen tanks.
While the obvious technique for maintaining the liquid
nitrogen level is to monitor the level and refill with liquid nitrogen when
needed; there are a couple of other management items that will help. Make sure
that the lid of your tank is properly sealed and that you do not have it open
for any longer than is absolutely necessary. This will cut down on evaporation
time. Also, when purchasing a semen tank, consider buying a tank with a narrow
neck. The wider necks may make it easier to select straws from the holding
canes; however, it also gives a larger escape hatch for evaporating nitrogen. A
smaller neck will help to restrict some of that escape and also limits the
diameter of the "warm zone" in the neck of the tank.
Another important
tool in tank management is to maintain a semen tank log. Many producers will do
this on a clipboard that hangs on the wall above where they keep their tank.
Others will tie a notebook directly to one of the handles on the tank. The log
should keep a record of several items. First, report the dates when you
visually inspect your tank as well as what you observed. Writing these dates
down should help remind you to routinely check the tank. Secondly, keep a
record of when you have to replace liquid nitrogen in your tank. This will help
to keep you aware of how well your semen tank is maintaining its cooling
capabilities. Finally, keep a running inventory of what semen straws you have
stored in the tank and their location in the tank. This will help you to more
readily locate the desired straw, limiting the time that the lid is open and
the time that various straws are held in the "warm zone" of the tank's neck,
while you are hunting for the "chosen one".
There is one more tank
maintenance recommendation that I would like to make today. Try to match your
stored semen inventory to your needs. In other words, if you plan to AI 35 cows
this year, there is not a lot of need to have 500 straws in the tank that you
are working out of. While the savings of two or three dollars per straw on a
bulk purchase (which you justify with the thought that you can use them over
the next ten years) may seem tantalizing; there are a couple of possibilities
that should be realized first. You need to consider the genetic potential of
the current purchase compared to what might be available a few years down the
road. Will today's bargain buy be the type of sire that you are going to want
at that later point? In example, another way of asking this, if you had bought
a bunch of Simmental semen at a bulk discount 15 years ago and used it in cows
this past year, how many straight black calves do you think you will have hit
the ground this spring? Then there is the other side of having too much
inventory. A Washington State study looked at the evaporation rates of liquid
nitrogen from semen tanks. Their research showed a five percent failure rate. A
tank failure can be a disheartening and expensive loss, even if you bought your
inventory with a discount coupon.
These are just a few basic suggestions
for protecting your semen investment. If you wish to discuss this subject
further, most AI company representatives and many Agriculture Extension Agents
should be able to provide you with information about semen tank management.
Also, Michael Fisher can be reached through the Yuma County Extension office at
970-332-4151 or by e-mail at mj.fisher@colostate.edu.
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Page Created and Maintained by: Perry D. Brewer, Area
Extension Agent (Technology Education/Youth)
1/28/2008 |
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