====================================================================== Methylene-blue reduction time (minutes) ------------------------------------------------ Glycerol Glycerol Glycerol Glycerol Glycerol only and and and and glucose arabinose xylose 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 deg. C. (41 deg. 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.