Effect of seminal plasma vesicular structures in canine frozen-thawed semen

Membrane vesicles (MVs) in the ejaculate have been identified in various species and are considered to affect membrane fluidity due to their characteristic molecular composition. Addition of MV to human frozen semen has been shown to improve post-thaw motility. Similarly, a beneficial effect has been suggested for frozen equine semen. As post-thaw canine semen quality varies widely between dogs, the aim of our study was to test for the effect of addition of canine MV on post-thaw semen quality in dogs. Semen samples from 10 male dogs were purified from MV and prepared for freezing. In experiment 1, three groups were compared: sperm frozen (1) with MV (S1); (2) without MV, but MV added immediately after thawing (S2); and (3) without MV (C). Semen analysis included computer-assisted sperm analysis of motility parameters immediately after thawing (t0), after 10 (t10) and 30 minutes (t30), % living sperm, % membrane intact, % morphologically normal sperm (all t0 and t30). Computer-assisted sperm analysis motility distance and velocity parameters (all P < 0.05) and % living sperm (P < 0.001) were significantly affected by treatment with a temporary increase of distance and velocity parameters at t0 to t10, but a significant decrease of the aforementioned parameters at t30 in samples with MV. In experiment 2, different MV protein concentrations added after thawing were compared: 0.05 mg, 0.1 mg, and 0.2 mg/mL. Computer-assisted sperm motility analysis was performed at t0, t10, and t30. No differences between MV concentrations were identified, only a significant interaction between effect of treatment and time for progressive motility (P < 0.01). Our study identified a short-term beneficial effect of canine MV on post-thaw distance and velocity parameters, whereas at t30 progressive motility, motility parameters and % living sperm were reduced in samples with MV compared to C. The results point to species-specific differences regarding the MV effect on frozen semen and indicate the need for further studies using different semen and MV purification protocols and more frequent analyses. At the moment, addition of MV is not an option to improve post-thaw semen quality in dogs.