Improving the efficiency of insemination with sex-sorted spermatozoa

The sorting of X- and Y-chromosome-bearing spermatozoa by flow cytometry is nowadays one of the most apt assisted-reproduction technologies in livestock production. Potential economic and biological benefits, as well as those related to easier management of herds, have been reported arising out of the application of this technique, especially in cattle. Yet, the sex-sorting procedure induces damage to spermatozoa, affecting their function and fertilizing ability. Different species present varying degrees of susceptibility to damage from the sorting process and each has its own requirements for sex-sorted insemination procedures. Thus, several new protocols and strategies have been designed for the handling of sorted spermatozoa, with the main objective of optimizing their fertilizing ability and the consequent application of flow-cytometric sex-sorting technology. This article reviews current advances in this technology, pointing out the components to be improved before this technology may be widely applied in different domestic species.

Improving the fertilizing ability of sex sorted boar spermatozoa

The sex sorting of spermatozoa by flow cytometry induces damage, since sperm cells are highly diluted, affecting their functionality and fertilizing ability. In this work it was investigated whether the concentration of sex sorted spermatozoa by the sedimentation method, rather than centrifugation, in combination with the presence of the seminal plasma protein PSP-I/PSP-II heterodimer may improve their fertilizing ability. Spermatozoa were sorted by flow cytometry and collected in BTS with 10% of seminal plasma (group C: control) or with 1.5mg/mL of PSP-I/PSP-II heterodimer (group H). Collected spermatozoa from each medium were split into two aliquots. One aliquot of each group was centrifuged (800 x g/5 min) just after sorting and stored 16-18 h at 17 degrees C (groups Cc and Hc) at 6 x 10(6)sperm/mL. The second aliquot was directly stored at 17 degrees C for 16-18 degrees C (group Cs and Hs). After storage the supernatant was discarded and the sedimented pellet adjusted to 6 x 10(6)sperm/mL. Membrane integrity, acrosome status and motility characteristics of spermatozoa from all groups were assessed. Post-weaning pre-ovulatory sows were inseminated by laparoscopy into the oviduct with 0.3 x 10(6) sex sorted spermatozoa to assess their ability to penetrate oocytes in vivo. Putative zygotes were collected 18 h after insemination by washing the oviduct. Penetration and monospermic rates were evaluated. After 16-18 h of storage, centrifuged spermatozoa collected with 10% seminal plasma or 1.5 mg/mL PSP-I/PSP-II heterodimer after sex sorting showed lower (p<0.05) percentages of membrane integrity, motility and fertilization than sedimented spermatozoa. Overall, the presence of 10% seminal plasma or PSP-I/PSP-II heterodimer did not affect the results. However, a positive effect of PSP-I/PSP-II heterodimer (p<0.05) was observed in sedimented spermatozoa. Hence, our results indicate that the sedimentation method in the presence of PSP-I/PSP-II heterodimer improves the in vivo fertilizing ability of sex sorted boar spermatozoa.