L. Gillan

In vitro and in vivo assessment of functional capacity of flow cytometrically sorted ram spermatozoa after freezing and thawing.

The effect of sex sorting and freeze-thawing on the viability and fertility of ram spermatozoa was investigated in the present study. Non-sorted (control) frozen-thawed spermatozoa had a higher motility and forwards progressive motility (FPM) than sorted frozen-thawed spermatozoa (60.9 +/- 2.9% v. 57.0 +/- 3.3% and 4.0 +/- 0.1 v. 3.5 +/- 0.1 FPM, respectively; P < 0.001) after incubation (6 h at 37 degrees C). Sorted and non-sorted (control) frozen-thawed spermatozoa had similar acrosome integrity (73.7 +/- 1.8% v. 75.2 +/- 2.1%, respectively) after thawing and incubation. A greater proportion of sorted spermatozoa displayed chlortetracycline staining patterns that were characteristic of capacitation (22.0 +/- 2.8%; P < 0.05) than non-sorted (control) spermatozoa (15.4 +/- 2.6% B pattern) before freezing. Overall, more sorted frozen-thawed spermatozoa showed patterns characteristic of being acrosome reacted (12.8 +/- 0.7%; P < 0.01) and less were uncapacitated (35.5 +/- 0.6%; P < 0.05) than non-sorted (control) frozen-thawed spermatozoa (7.7 +/- 0.8%; and 38.6 +/- 0.6% for AR and F pattern, respectively). Similar numbers of non-sorted (control) and sorted frozen-thawed spermatozoa migrated through artificial cervical mucus after 1 h (76.4 +/- 11.9 v. 73.9 +/- 11.9 spermatozoa, respectively). The distance travelled by the vanguard spermatozoon was also similar (56.9 +/- 7.8 v. 38.6 +/- 5.8 mm for control and sorted spermatozoa, respectively). Sorted and control frozen-thawed spermatozoa displayed a similar pattern of binding to, and release from, an oviduct epithelial cell monolayer (OECM), but sorted frozen-thawed spermatozoa were released more rapidly (P < 0.05) than non-sorted (control) frozen-thawed spermatozoa. The pregnancy rate was higher for ewes inseminated with 100 x 10(6) (commercial control) frozen-thawed spermatozoa (59%) than for 5, 10, 20 and 40 x 10(6) total sorted frozen-thawed spermatozoa (41% overall; P < 0.001). Insemination of 16 x 10(6) resulted in a higher pregnancy rate (31%) than 10(6) (17%; P < 0.05), but was similar to ewes that received 4 x 10(6) sorted frozen-thawed spermatozoa (24%). Time of insemination (54, 58 and 62 h after sponge removal) had no effect on pregnancy rate. Pregnancy in gonadotrophin-releasing hormone-treated ewes was affected by insemination dose (P < 0.05) but not sperm type (sorted and non-sorted) or ram. Pregnancy was higher after insemination of 40 x 10(6) than 5 or 20 x 10(6) non-sorted (control) or sorted frozen-thawed spermatozoa (70%, 33% and 35%, respectively; P < 0.05). Sorted frozen-thawed spermatozoa may have a shorter viability within the female tract than non-sorted frozen-thawed spermatozoa.

Preservation and evaluation of semen for artificial insemination

Many years of research have been devoted to improving the fertility of preserved semen of small ruminants. There have been few significant advances in preservation in recent times, but considerable knowledge has been gained on the effect of preservation on the structure and function of spermatozoa. It has become evident that preservation greatly affects many sperm attributes, such as motility, respiratory activity, membrane status and DNA quality. Consequently, viability is reduced, transport in the female reproductive tract is inhibited, the timing of fertilisation is altered and embryo development is affected following insemination of preserved, compared to fresh spermatozoa. A greater understanding of their functional condition may lead to the development of methods of preventing these alterations or to improved methods of using the preserved spermatozoa for artificial insemination in their altered state.

The interaction of fresh and frozen-thawed ram spermatozoa with oviducal epithelial cells in vitro.

In order to investigate the interaction of fresh and frozen-thawed spermatozoa with oviduct epithelial cells, spermatozoa were co-incubated with ovine oviduct epithelial cell monolayers (OECM) derived from either complete oviducts, at any stage of the oestrous cycle (Experiments 1 and 2), or from different regions of the oviduct at different stages of the cycle (Experiment 3). Fresh and frozen-thawed spermatozoa displayed different patterns of binding to, and release from, the OECM. Frozen-thawed spermatozoa immediately bound to the complete oviduct OECM and were released after 2 h. A small proportion of fresh spermatozoa bound immediately, increasing to a maximum after 2 h, and were gradually released thereafter. When only the cells that were released from the OECM were observed by chlortetracycline staining in Experiment 2, it was found that the presence of an OECM increased the number of capacitated fresh spermatozoa while decreasing the number of capacitated frozen-thawed spermatozoa. Overall, the OECM advanced the membrane state of both types of spermatozoa from uncapacitated to acrosome-reacted. Fresh and frozen-thawed spermatozoa bound to OECM derived from the cells of the isthmus and the ampulla in similar proportions. However, more spermatozoa were capacitated when incubated with OECM derived from isthmic rather than ampullary cells. Higher proportions of fresh spermatozoa bound to, and were acrosome-reacted following incubation with OECM derived from post- rather than pre-ovulatory tracts. Such differences were not observed for frozen-thawed spermatozoa. The findings reported in this study show that fresh and frozen-thawed spermatozoa behave differently when in contact with oviduct cells in vitro. This may be a consequence of the more advanced membrane state of the frozen spermatozoa upon thawing.