Styrofoam thickness (Fig. 2). This method resulted in good results
for freezing poultry (Woelders et al., unpublished) and turkey [32]
semen.
A similar method, suitable for high-throughput freezing of
larger batches of straws, uses ventilated LN 2 vapor in a large cabinet
at a constant vapor temperature. The cooling rate is determined by
the vapor temperature and the ventilation rate (“windchill factor”).
Several 70-straw or 100-straw racks can be accommodated and
frozen simultaneously with little effort. The CGN animal genetic
resource (AnGR) bank is equipped with several of such custombuilt devices to freeze mammalian and avian semen (Fig. 3). This
freezing method also provides highly repeatable sigmoidal freezing
curves, similar to that obtained with the static vapor method with
the Styrofoam raft method (cf. Fig. 2).
2 Materials
2.1 General
Laboratory Materials
and Equipment
1. Semen collection tubes.
2. Thermostatic cold box (4–6
C).
3. Tubes, tube racks.
4. Open top cooler cabinet or cold room (4–6
C).
5. Semen sperm concentration apparatus/photometer (IMV,
L’Aigle, France, or similar).
6. (Fluorescence) microscope with phase contrast.
7. Dewar.
8. LN 2 .
9. LN 2 storage tank, with canisters, goblets, etc.
Fig. 3 Custom-built ventilated nitrogen vapor freezer, with a constant vapor temperature. These machines are
robust and reproducible and easy to work with, providing very easy access for placing the racks and for
removing the straws. They give reproducible sigmoidal freezing curves (similar to the curves shown in Fig. 2).
The cooling rate depends on the set freezing chamber temperature and the ventilation rate (windchill) in the
freezing chamber
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Henri Woelders