Developments in quality estimation and cropreservation of bull semen

The paper refers selected trends in quality estimation and cryopreservation of bull semen by literature informations and own experimental results. With regard to an improved fertility prognosis by in vitro investigations in semen the concept of a spermatological reference laboratory for semen quality control and comparable estimation of semen quality indices for breeding bulls is represented. Investigations in quality of normally and highly diluted semen charges after cryopreservation in the egg yolk-free diluters BIOXCELL and AndroMed show that these diluters are interesting alternatives for the usual mediums with egg yolk, when 15 millions sperm cells per insemination portion are used. But they don’t solve the problems in fertilization rate existing for a great percentage of bulls after a reduction of the sperm number per portion below 10 millions. Addition of 8 and 12mmol N-acetyl-L-cysteine to the Triladyl-diluter with egg yolk caused a significant stimulation of sperm motility after thawing. This effect was decreased by using the egg yolk-free diluter BIOXCELL. In a field trial semen charges with BIOXCELL, 15 x106 sperm cells/straw and 8mmol Nacetyl- l-cysteine showed a non-significant increase in non return rate of 1,6% in relation to the antioxidant-free control variant. In cryopreservation of bull semen sperm numbers/straw of < 106 require a dilution rate > 1:35. This can cause a dilution stress for some bulls and can be the reason for a decrease in fertilization rate. About 60% of bulls show depressions in non return rate in this range of sperm number per insemination portion. At the tested minimum of 4 x106 inseminated sperm cells the highest decrease in non return rate was 10% for different bulls.

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