61 Swim-up and microfluidic techniques improve the kinetic parameters of selected bovine spermatozoa for in vitro fertilization: Preliminary results

Abstract

For in vitro embryo production, spermatozoa with fertilizing capacity must possess optimal kinetic, morphometric, vitality, and DNA integrity characteristics. The objective of this study was to evaluate the effect of 3 sperm selection methods on sperm quality and in vitro embryonic development in bovine. Frozen commercial semen (0.5 mL/straws) from one bull with known fertility was thawed at 37°C for 20 s and was divided for 3 sperm selection techniques: density gradient, swim-up, and microfluidic sperm sorting. The sperm kinetic parameters (VCL = curvilinear velocity, VSL = straight line velocity, VAP = average path velocity, ALH = lateral displacement of sperm head, BCF = beat frequency cross, STR = path straightness) were assessed using computer-assisted sperm analysis (CASA). Sperm morphometric parameters were evaluated using Diff-Quick staining followed by automated analysis. To assess vitality, the sperm were stained with propidium iodide and acridine orange, then analysed under a fluorescence microscope. In addition, DNA fragmentation was assessed using sperm chromatin dispersion method. Last, the fertilizing capacity of the selected sperm was tested by fertilizing cumulus–oocyte complexes (2 × 10⁶ sperm mL⁻¹) obtained from slaughterhouse ovaries and matured in vitro for 24 h. A standardized in vitro embryo production protocol was used with commercial medium from Vitrogen. The cleavage rate and blastocyst yield were measured on Day 2 and 7, respectively (fertilization = Day 0). The results were calculated with analysis of variance and Tukey’s test (P < 0.05). The values of sperm kinetic parameters obtained with swim-up (VCL 132.5 µm/s; VSL 73.5 µm/s) and microfluidic technique (VCL 129.5 µm/s; VSL 64.4 µm/s) were significantly higher (P < 0.05) than those obtained by density gradient (VCL 98.3 µm/s; VSL 45.01 µm/s). However, the total and progressive motility by density gradient method was slightly higher (89% and 57%) compared with that assessed by swim-up (64% and 43%) or microfluidic technique (74% and 54%) respectively. Microfluidic sorting (11.3%) showed lower (P < 0.05) DNA fragmentation levels compared with density gradient method (16.6%), whereas the swim-up technique (12.5%) was similar between both groups. No significant difference was detected between the 3 groups for sperm morphometric and vitality parameters. Moreover, cleavage rates were similar (P > 0.05) between the 3 sperm selection techniques: density gradient (84.0%), swim-up (75.2%), and microfluidic sorting (67.3%). However, blastocyst yield was significantly higher (P < 0.05) using sperm selected by density gradient (28.1%) and swim-up (21.9%) compared with microfluidic sorting (15.3%). In conclusion, sperm selection using microfluidic and swim-up techniques improved kinetic parameters with lower levels of DNA fragmentation, without affecting sperm morphometry. However, both the density gradient and swim-up techniques are efficient systems for producing in vitro bovine embryo.