Effect of a transcervical infusion of seminal plasma prior to insemination on the fertilising competence of low numbers of boar spermatozoa at controlled AI-ovulation intervals

Dilution of boar ejaculates for use in artificial insemination reduces the amounts of seminal plasma components which have important regulative functions in fertilisation. The effects of a transcervical infusion of 50 ml of seminal plasma immediately before insemination on fertilisation rates and accessory sperm counts of day 3–5 embryos were investigated using 0.5 × 109 (Experiment 1, n = 33 gilts), 0.3 × 109 (Experiment 2, n = 20 gilts), or 0.5 × 109 spermatozoa with extended insemination-ovulation intervals to median values of 20 h (Experiment 3, n = 32 gilts). The gilts were inseminated either 24 h after the detection of spontaneous oestrus (Experiments 1 and 2) or 24 h after human chorionic gonadotrophin (hCG) injection following hormonal synchronisation of oestrus (Experiment 3). The time of ovulation was detected by transcutaneous sonography carried out at 8 h intervals. Fertilisation rates were not affected by the infusion of seminal plasma. In Experiment 1, seminal plasma led to a significant shift towards zona classes with higher numbers of accessory spermatozoa compared with the control group. In Experiments 2 and 3, there was no difference in accessory sperm counts between gilts treated with seminal plasma and control gilts. Using 0.3 × 109 spermatozoa (Experiment 2) the percentage of degenerated embryos increased significantly but showed similar numbers of accessory spermatozoa as normal embryos. This indicates that less competent spermatozoa fertilised the oocytes, which showed reduced ability to sustain embryonic development. It is concluded that infusions of seminal plasma are less effective for optimising conditions for fertilisation when conducted prior to insemination (24 h after the detection of oestrus) than at the onset of oestrus, which leads to an advancement of ovulation.