Storage of Dairy Bull Spermatozoa

Abstract

An appreciation of the limitations and possibilities of storing dairy bull semen and retaining its fer t i l i ty is necessary in order to define the practical limits of artificial insemination with shipped or stored semen. While various diluents have been proposed and different storage temperatures have been suggested, there still remain many unexplained factors concerning the successful storage of dairy bull semen. One difficulty in semen storage research has been the lack of an accurate criterion of fert i l i ty. Since the time of survival with vigorous motil i ty of bull spermatozoa stored undi luted at 40 ° F. has been shown to be correlated with the fer t i l i ty of bull semen (14), this p roper ty of the semen may be used in evaluating storage methods more accurately than simple determinat ion of time of survival. Refr igerat ion has been recognized for some time as the most effective method of preserving bull semen (15). Spermatozoa normally live only a short while at body temperature, and room temperature (70 ° F.) has likewise been found too high for successful semen storage (17). The highest tempera ture at which spermatozoa may be stored successfully has been given as 50 ° F. (4), and longer viabili ty was secured with reduction of the storage tempera ture to 35 ° to 40 ° F. (4, 7, 8, 17). I t has been emphasized tha t the change of tempera ture of the semen must be gradual or irreversible immotili ty will result f rom temperature shock (2, 6). Many diluents of various composition have been used with bull semen, but their main use has been in increasing the volume (15, 4). The addition of nu t r ien t substances to these diluents did not increase the survival of spermatozoa in them (1). The buffering action provided by some diluents has increased the motil i ty of spermatozoa (8). A diluent using egg yolk plus a buffer has been reported as causing a marked increase in survival and fert i l i ty of stored bull semen (11). The secretions of the accessory sex glands were shown to be harmful to survival of spermatozoa and were ent irely unsuitable as diluting fluid for bull semen (5, 10, 11). ]¥ i th horse and boar semen the removal of the sperm fluid and concentration of the sperfi~atozoa has resulted in greater survival in storage (16, 9). Exper iments along this line with bull semen were not successful in obtaining greater survival in storage. E a r l y investigators excluded air f rom the semen by a layer of paraffin