The extension and freezing of bovine semen
Staples, Robert Edward
Much variation exists in the methods of handling semen from the time of collection to insemination. This applies particularily to the means of estimating semen quality and to the types and levels of extender components. With the exception of actual use of semen in the field to derive conception rates, quality estimates are confined to laboratory determinations. Because these must be conducted at higher temperatures than are compatible with the retention of maximum sperm-cell livability, laboratory tests must be as simple, rapid and accurate as possible. Viability, as determined by proportions of differentially stained live and dead cells (Mayer et al.. 1951) is fairly accurate as a measure of semen quality and it takes very little time to prepare the slides. In spite of the fairly wide use of this test there is little indication in the literature reviewed that sample size in the counting prcedure has been derived from statistical inference. It was for this reason that the first experiment was designed to establish the sample size and counting procedure to obtain statistically adequate results.Several levels of the widely used extender components, sodium citrate, glycerol and egg-yolk, have been suggested as optimum for sperm survival before and after freezing to -79°C. Because of this wide variance a second experiment was undertaken to determine the optima of these extender components for our conditions. From 1949 to 1953 the freezing of bovine semen was achieved by a rather cumbersome method which entailed the reading of temperatures each minute throughout the freezing process (Polge and Lovelock, 1952). In 1953 a simpler method was suggested which is used commercially today (Polge, 1953). In this study a still simpler methed of freezing is investigated which, if as efficient as the freezing methods mentioned above, would serve as a suitable substitute for them.