Prognostic value of a pre-freeze hypo-osmotic swelling test on the post-thaw quality of dog semen

Throughout cryopreservation, sperm are exposed to major osmotic challenges. Only intact membranes of sperm cells are able to regulate these volumetric changes, which can be determined by the hypo-osmotic swelling test (HOS test). Correlations between the HOS test and conventional semen variables are inconsistent. Therefore, the objectives of this study were (1) to examine relationships between HOS test results and standard semen variables before freezing and after thawing and (2) to evaluate the prognostic value of the HOS assessments on post-thaw quality of dog semen. Semen of 35 dogs was collected and analyzed before freezing and after thawing following a 7-day freeze–thaw interval. Conventional semen variables such as sperm cell motility, membrane integrity morphology were evaluated and the HOS test was conducted with results from this test being recorded. In fresh semen the HOS test was positively correlated with progressive motility of sperm cells: r = 0.52, sperm cell membrane integrity: r = 0.50 and normal sperm cell morphology: r = 0.46 (P < 0.05). In frozen–thawed semen, the data obtained with the HOS test were positively correlated with progressive sperm cell motility: r = 0.67 and membrane integrity: r = 0.86 (P < 0.05). The data obtained with the HOS test in fresh semen were positively correlated with sperm cell membrane integrity: r = 0.50 normal sperm cell morphology: r = 0.55 and data from the HOS test (r = 0.43; P < 0.05) with frozen–thawed semen. For the prediction of individual cryopreservation capacity, results from assessment of the fresh semen variables of good and poor semen quality were statistically compared. Based on these results, it is not possible to predict the quality of frozen–thawed dog semen using the HOS test.