Pregnancy Rates in Mares Inseminated with 0.5 or 1 Million Sperm Using Hysteroscopic or Transrectally Guided Deep-Horn Insemination Techniques

Abstract

Placement of sperm deep in the equine uterine horn allows fewer sperm to be inseminated while maintaining acceptable fertility, and has been promoted for use in circumstances when fertility would be expected to be low if standard insemination were used (e.g. semen from a subfertile stallion, or frozen-thawed semen). Two main deep- horn insemination techniques, transrectally guided (TRG) and hysteroscopic (HYS) insemination, have been developed for this purpose; however, there is some controversy regarding their comparative efficacy. This study was conducted to compare pregnancy rates when mares were inseminated by TRG or HYS, utilizing sperm numbers approaching and under the threshold for maximal fertility, resulting in reduced fertility. Pregnancy rates were not different between HYS and TRG techniques when 1 x 106 or 0.5 x 106 sperm were inseminated. Combined pregnancy rates for the two techniques were also not different. Pregnancy rates using a subthreshold number of sperm were not significantly affected by a deep-horn insemination technique.

Dilution of semen to less than 20 x 106 sperm/mL has been reported to decrease semen quality in multiple species, a phenomenon known as the semen ?dilution effect.? The sperm concentrations utilized in Experiment 1 were 5 and 2.5 x 106/mL (1 and 0.5 x 106 sperm doses, respectively). This experiment was performed to evaluate whether the lower pregnancy rates obtained with 0.5 x 106 sperm was due to lower quality plasma membrane integrity (PMI) and sperm motion characteristics (TMOT, PMOT, VCL, VAP, VSL, STR). Treatments evaluated included 2.5 x 106 sperm/mL with the addition of 0, 7.5, and 25% seminal plasma, 30 x 106 sperm/mL, and 3:1 extender: semen. The 2.5 x 106 sperm/mL treatments have lower initial PMI, TMOT, and PMOT, but they maintain their initial quality following 24 and 48 h of cool-storage. The sperm velocity and straightness parameters suggest that sperm swim faster but have a more circular pattern as seminal plasma increases to 25% at a given concentration. Based on the findings from this experiment, the semen ?dilution effect? may not significantly alter stallion sperm characteristics when a commercially-available semen extender is used for semen dilution.