Liquid nitrogen storage tanks are so good at insulating the materials stored inside that if you put a thermos of steaming hot coffee in your tank, you"d still burn your tongue on a cup poured from that thermos 10 years later.
But while designed to be sturdy and dependable, liquid nitrogen tanks are a little more fragile than they appear. They require regular care and attention to ensure they function properly for many years. Failure to do so can lead to lost inventory, or reduced pregnancy rates because semen quality is compromised.
Use these simple, common sense tips to optimize the use of liquid nitrogen storage tanks on your operation.
The following checklist was developed with the help of Heather Jauquet, animal products marketing specialist for ABS Global; John Theder, supplies manager for Alta Genetics; Joel Delzer, reproductive training manager for Cooperative Resources International; Mel DeJarnette, reproductive specialist for Select Sires, and Paul Lydolph, vice president of global AI products for the MVE division of Chart BioMedical.
1. Choose the proper storage location.
Make sure you put your tank in a well-lit, clean, dry environment with easy access so you can keep an eye on it even when not extracting straws from the tank.
It may be tempting to keep your tank in the parlor or where your bulk tank is housed, but experts warn against using locations in the milking center because of moisture levels and the use of sanitation chemicals.
Place tanks near where they will be used, but won"t impede traffic patterns for you and your employees. An office or storage area that you enter often would be a good choice.
Use a wooden pallet or a couple of short 2-inch by 4-inch boards (about as long as the tank is wide) to raise your tank off the floor since water and chemicals commonly used around dairy facilities can cause corrosion, leading to tank failure.
Also, make sure the area is well ventilated. Good air exchange decreases moisture buildup in the storage area and extends tank effectiveness. Avoid drafty situations, because too much extra air movement around the tank will increase nitrogen consumption and reduce the storage life of semen.
Finally, place the tank in a well-lit area. This will help you identify problems sooner and enable you to read canister and semen straw information quickly.
2. Minimize tank movement.
Avoid moving your tank unless absolutely necessary. Any time you move it you risk damage to key tank components, especially the neck tube.
Always pick up the tank with both hands and set it down carefully and squarely.
Never tip the tank over and tap on its neck to extract straws that may be trapped on the bottom. The neck tube is made of fiberglass and is the only part of the inner tank that comes in contact with the rest of the tank and the outer environment. That makes the neck a little more fragile than the rest of the tank and vulnerable to rough or careless tank handling because those activities stress the neck.
Any stress to the neck may lead to hairline cracks or microscopic pinholes. Extremely rough handling can crack or break the tube. Both of these can cause loss of tank vacuum and insulating capacity, which puts your entire inventory in danger.
However, most of these cracks or pinholes are extremely small and not visible to the naked eye. Your only clue may be frosting on the outside of the tank near the top. These leaks can allow liquid nitrogen to escape in a few hours, or more slowly, but there is no way for you to know which is going to happen. Either way, you need to move your inventory to an undamaged tank as soon as possible if frosting has occurred.
3. Monitor nitrogen levels at least weekly.
Genetics company representatives do a good job of keeping your tanks adequately filled with nitrogen. But they are not usually at your dairy every day or even every week. Between visits you need to conduct your own checks.
Ask your representative for a measuring stick or tape, then use it once a week to monitor the liquid nitrogen level so that it doesn"t get too low.
If your tank"s nitrogen level falls below 5 centimeters (3 inches), refill it and be aware that something could be wrong or that you may need to refill more frequently than your current practice because of repeated use. Keep in mind that failing tanks may last three months, or they may completely expire within a day. That makes monitoring of nitrogen levels all the more important.
If you have any questions about your tank"s viability, invest in a new container to protect your genetic investment.
Of course, how often you open your tank will affect how often you need to fill it. If your tank is used quite frequently, check your tank level more regularly and expect a shorter holding time. Studies show that if 48 canisters are pulled a day from a storage tank versus 18 canisters pulled a day, the increased activity decreases tank holding time by about a month.
4. Watch tank for frost.
Frost is one of the key external warning signs prior to tank failure. A properly functioning tank will not develop frost on the outside.
Frost buildup around the outside top of your tank, particularly around the neck, indicates a vacuum loss — which results in rapid volatilization of the liquid nitrogen. Semen quality can be compromised under these circumstances.
Keep in mind that this frosting usually happens quickly and doesn"t last too long because the liquid nitrogen has escaped. Some situations may last longer than others, but all require vigilance on your part. And, when humidity levels are low, you may not notice any frosting, even though the tank has failed.
Still, be sure to look for this warning signal each week when you"re monitoring the internal nitrogen level since it is one more week to protect your investment. And instruct your employees who inseminate cows to check the tank for frost each time they extract a straw of semen.
Also, keep your tank as dust- and dirt-free as possible, because it will be easier to notice frosting on a clean tank.
5. Replace poor quality corks.
Since your tank"s cork is handled frequently — every time you retrieve semen — it should be inspected monthly to make sure it is doing its job.
A poor quality cork increases the boil-off (liquid nitrogen volitization) rate by 20 percent to 30 percent. That"s because insulation properties decrease for these corks and more heat gets into your tank.
You can tell when your cork has been used too long when it becomes shiny. A shiny cork should be replaced as soon as possible. The next time your genetics company representative visits, ask him for a replacement cork if your cork shows signs of wear.
Also, only remove the cork when removing semen from the tank and immediately replace the cork when you"re done. Exposing an open tank to the environment and wind can multiply the boil-off rate by up to 8 times the normal amount.
6. Protect your investment.
Add a padlock to your tank to deter would-be thieves. It"s not unheard of for producers to lose thousands of dollars worth of semen — usually because it is highly accessible.
Locks will also deter a significant percentage of vandals — operating in the name of animal rights or just out for mean-spirited kicks — who would like nothing better than to leave your tank open and destroy its inventory.
Additionally, locks prevent children from being injured by liquid nitrogen when curiosity causes little fingers to explore restricted areas. Children also have been known to use tanks to hide toys, only to be burned when they try to retrieve the objects.
Tank maintenance doesn"t take a lot of time, but it is a worthwhile investment. Although you"ll want to share these strategies with all employees who inseminate cows, you should make one person responsible for checking the tank each week.
Consider posting a checklist that your employees can sign and date each time they check the tank. That way you know your genetic investment is being monitored and protected.
Retrieval technique matters too
Despite how you manage the tank itself, semen quality can still be compromised if your technique for straw retrieval is flawed.
Therefore, keep these hints in mind:
When pulling canisters for semen retrieval, keep the canister inside the neck tube. Boil-off, or nitrogen volatilization, is doubled when you pull canisters outside of the neck tube.
Use a tweezers or angled forceps to retrieve straws so that you can keep canisters lower inside the neck than you can when using your fingers. This also prevents damage to your skin from the nitrogen"s freezing temperatures. And, it keeps straws frozen longer.
Adequate lighting helps make this process easier, since you can better read bull numbers on cane tops and don"t need to bring them into warmer temperatures until it"s necessary.
Finally, remember to work quickly. If you are unable to retrieve the semen straw you want within 10 seconds, return the canister to the bottom of the tank and allow it to re-cool for 15 to 20 seconds. Failure to do so can negatively impact the entire canister inventory because partial thawing begins to occur, threatening semen quality.