(Average of 10 ejaculates)
| Methylene-blue reduction time (minutes) | |||||
| Glycerol only | Glycerol and glucose | Glycerol and arabinose | Glycerol and xylose | Glycerol and rhamnose | |
| Fresh semen | 5.2 | 5.2 | 5.2 | 5.2 | 5.2 |
| After glycerolization | 26.4 | 25.2 | 17.3 | 14.3 | 19.4 |
| After 18 hours equilibration | 7.4 | 6.5 | 6.4 | 5.3 | 6.2 |
| Thawed immediately after freezing | 11.5 | 10.5 | 9.4 | 9.0 | 9.4 |
| Thawed 48 hours after freezing | 14.3 | 10.2 | 11.3 | 10.1 | 9.5 |
[M] Glycerol level in the final frozen mixture was 7 percent. Sugars were added to a level of 1.25 percent.
PRACTICAL FREEZING PROCEDURE
Good results usually can be obtained in freezing bull semen if care is taken in collecting, diluting and processing the semen. Occasionally the semen from certain bulls will not withstand freezing well. The reason for this is not understood at present. However, carefully following the directions and suggestions given below will usually produce satisfactory results with semen samples that are of good quality at the start.
Experience in the field has shown that fertility results with frozen semen are usually slightly lower during the first few months than with liquid semen stored at 5° C. (41° F.). Most units that have worked with frozen semen over a period of a few months are able to improve and do get fertility results as good as, or better than, obtained in their liquid semen program.
Collection of the semen. In order to obtain the best possible semen for freezing, care and cleanliness should be exercised in making the collection. The artificial vagina, and the glassware used should be clean and dry. The underline of the bull should also be clean and dry. The bull should be restrained near the teaser cow for a minute or two prior to collection in order to excite the flow of secretions prior to ejaculation. Allowing the bull to mount the teaser once without serving the artificial vagina is a good practice to use in properly stimulating the bull before collection of the semen.
If the bull has not been used for three or four days, the collection of a second ejaculate for freezing may be advisable. The second ejaculate seems to withstand freezing better than the first in many instances. A clean, dry artificial vagina should be used for each ejaculate collected. Repeated collections in the same artificial vagina may result in contamination of the semen with bacteria, lubricating jelly and minute particles of dirt. The semen sample should be protected from contamination and from sudden temperature drops (cold shock).