Freezing of Semen

Freezing of semen is the process of preserving sperm cells at extremely low temperatures (typically –196°C in liquid nitrogen) to maintain their viability and fertility for long-term storage and future use in artificial insemination (AI).

Freezing the Straws in Liquid Nitrogen Vapour (Manual Freezing)

Freezing is carried out in a wide mouthed container (LR 320, LR 250) especially designed for freezing of straws.

The actual freezing is done by holding the equilibrated straws at 4.5 cm form the level of liquids nitrogen thereby exposing to the vapours of liquid nitrogen.

When the temperature of semen reaches –130°C to –150°C they are transferred to goblets and submerged in liquid nitrogen for storage at –196°C.

The main advantage of horizontal freezing is the efficiency and simplicity of the method.

The racks hold the straws at a constant level and the straws are frozen at even rate all along the length of the straw. Ensure that the level of liquids nitrogen is 1-2 mm above the safety freezing net.

After that the vapour temperature is adjusted by wafting and the racks with straws are kept on the freezing net so that the straws are about 4-5 cm form the level of liquid nitrogen.

The recommended temperature for freezing semen is LR 320 unit is:

• Medium straws: -150°C to -160°C for 7 minutes.
• Mini straws: -120°C to -130°C for 9 minutes

These containers are used for freezing as well as storage of semen.

Freezing in Bio Freezer

Where large scale freezing is carried out the freezing is done by using bio freezer. Here the freezing programme is already fed in a computer.

It can be altered whenever required. The bio freezer is connected with liquid nitrogen tank and the chamber temperature is brought to +5°C.

Transfer of freezing rack from cold handling cabinet to freezing unit should be done is the shortest possible time to avoid any increase of semen temperature above +5°C.

To achieve this cold handling cabinet and freezing unit is kept in the same lab.

The freezing racks are placed inside the bio freezer and it is allowed for 5 minutes to get stabilized at +5°C.

Then freezing is started. The entire process will take 9 minutes where the temperature will reach from +5°C to -140°C.