Aging may reveal biological differences between x-and y-bearing sperm

Overall objective of this thesis was to use aging as a way of investigating potential biological differences between X- and Y-bearing sperm. Specific objectives included the following: 1) examine effects of aging sperm 19.5 h postthaw in an incubator at 38.5°C by evaluating embryonic development after fertilization: 2) examine effects of aging sperm within an artificial insemination (Al) straw for 8 and 14 h post-thaw in a water bath at 34.4°C or 23 h post-thaw in a refrigerator at 4°C by evaluating sperm motility and embryonic development after fertilization; 3) investigate effects of aging sperm within an Al straw 14 h post-thaw in a water bath or 23 h in a refrigerator for altering sex ratio of embryos after fertilization; and 4) examine effects of aging sperm within an Al straw 8 and 14 h post-thaw in a water bath for altering sex ratio of embryos after fertilization. Fertilization of oocytes with sperm aged 19.5 h in an incubator reduced proportion of putative zygotes (PZ) cleaved (P<0.05). However, ability of cleaved embryos to develop to 8-16 cell (P>0.1) or blastocyst was not compromised (P>0.1). Aging sperm in an Al straw 14 h post-thaw in a water bath or 23 h post-thaw in a refrigerator reduced proportion of motile sperm (P<0.0001). Moreover, fertilization of oocytes with sperm aged in an Al straw 14 h post-thaw in a water bath reduced proportion of PZ which cleaved (P<0.05); however, ability of cleaved embryos to develop to 8-16 cell (P>0.1) and blastocyst was not compromised (P>0.1). Interestingly, fertilization of oocytes with sperm aged in an Al straw 14 h post-thaw in a water bath altered sex ratio of embryos, resulting in more females (P<0.05). In contrast, fertilization of oocytes with sperm aged in an Al straw 23 h post-thaw in a refrigerator did not alter sex ratio. Surprisingly, fertilization of oocytes with sperm aged in an Al straw only 8 h post-thaw in a water bath did not alter sex ratio of embryos. Blastomere numbers in male and female embryos did not differ (P>0.2). Results suggest the possibility that biological differences may exist between X- and Y-bearing sperm. If results are shown to be repeatable, such differences between X- and Y-bearing sperm may be exploited for the development of alternative methods of sex selection.