A comparison of bovine semen frozen in liquid nitrogen vapor and dry ice-alcohol

The world wide consumption of dairy and beef products is increas ing day by day. It is neither possible nor feasible to increase the cattle population to meet the increasing demand, particularly when the human population is growing fast. So the only way left is to improve the overall production level by increasing the production potential and efficiency of individual herds of cattle (29).

Artificial insemination using the semen of high quality proven sires makes possible the maximum genetic progress in improving the level of production of cattle. Even though the advantages of artificial insemination over natural service are many, this is the most important, particularly when the matter is considered with a large population in view.

Although commercial artificial insemination did not start in the United States until 1938, it has made rapid progress and its use is still increasing (56). This necessitates dilution and storing the semen of popular bulls to the maximum possible extent. Preserving semen for long periods would not only benefit existing artificial insemination services, but also will be useful for progeny testing and in making the semen of superior sires available for a longer time.

Attempts to preserve semen by freezing were made at least as early as the work of Spallanzani in 1803 (39). Discovery of use of egg yolk in buffer solution, in 1940 by Phill ips and Lardy (39), was a major improvement in semen processing. The egg yolk contributes a variety of factors to the semen diluents. The major contribution is the protection of spermatozoa from the effects of cold shock (48). This has been shown to be due to the lipid portion, mainly phospholipids, lecithin and cephalin (22).

The rate of cooling during freezing is critical to the survival of bull spermatozoa. This problem can be partially overcome by the use of protective substances in the diluents and by routine use of cooling rates, optimum for spermatozoa survival (48).

With these facts in view, the conventional method of freezing the semen is to cool the semen from 5 to -10 C at a very slow rate never exceeding 2 per minute and at considerably faster rates as the semen reaches lower temperatures.

This is really laborious, time consuming, or with mechanization, expensive to handle large quantities of semen. Currently arguments are fast forthcoming, stating that the rapid freezing of semen from 5 C downwards by directly exposing semen to liquid nitrogen vapor, is not more deleterious than the slow freezing.

With this fact in view, this experiment was designed to compare the effects of liquid nitrogen vapor freezing with dry ice alcohol freezing of bovine semen.