The role of seminal plasma (SP) in the interaction between spermatozoa and the female reproductive tract, particularly the cervix, remains unclear^1,2.  It is not known whether epididymal spermatozoa must be exposed to seminal plasma in order to traverse the complex cervix of the ewe and result in normal fertility.  As such, this study was conducted to determine the effect of seminal plasma on the transport and fertility of epididymal ram spermatozoa in the ewe.
Synchronised merino ewes (n=303) underwent cervical (100x10⁶ motile spermatozoa/ml) or laparoscopic intrauterine (25x10⁶ motile spermatozoa/ml) artificial insemination (AI) 53-55 hours post sponge removal with either ejaculated spermatozoa (Ejac; n=3 merino rams), epididymal spermatozoa (Epi; n=3 merino culled rams) or epididymal spermatozoa exposed to seminal plasma (Epi+SP; 1:1 sperm:SP). Pregnancy was detected via ultrasound 55 days post insemination and results analysed using a binomial logistic regression (Genstat 13th Ed., VSN Intl).
Pregnancy rates in cervically inseminated ewes were positively affected by the presence of SP, as Epi+SP and Ejac spermatozoa had higher fertility compared with Epi spermatozoa (P<0.05; Table 1). Pregnancy rates in laparoscopically inseminated ewes were unaffected by the presence or absence of SP.

Table 1: Pregnancy rate on Day 55 after cervical or laparoscopic insemination of Ejac, Epi or Epi+SP spermatozoa

This is the first study to investigate the ability of epididymal spermatozoa to traverse the cervix. Absence of seminal plasma inhibited the ability of epididymal spermatozoa to traverse the cervix, resulting in a significantly lower pregnancy rate. These results clearly demonstrate the importance of seminal plasma for normal cervical transit of spermatozoa and in vivo fertility in sheep.