A soy lecithin nanoparticles-based extender effectively cryopreserves Holstein bull sperm.

Plant-based semen extenders, typically derived from soybean lecithin, are easier to modulate more and consistent in their composition than animal-based extenders. As large lecithin particles can, however, reduce effectiveness and solubility in bull semen extenders, sonication was used to create nano-lecithin (NL) particles of soybean lecithin. The objective was to determine the effects of lecithin type and concentration on the quality of frozen-thawed bovine sperm. We hypothesized that reducing the size of lecithin improves its interactions with the sperm and enhances the parameters that favor its motility, viability and fertility. Semen was collected from six mature Holstein bulls and ejaculates meeting minimum standards were pooled. Eight Tris-based extenders that contained 1, 2, 3, or 4 % of either conventional lecithin (L1-L4) or NL (NL1-NL4), plus two control extenders (one animal-based extender containing 20 % egg yolk [EY] and a commercial lecithin-based extender [BioXcell®]) were compared. Among soybean lecithin-based extenders, NL3 had the highest total and progressive sperm motility, and average path, straight-line and curvilinear sperm velocity, and was comparable to EY. Additionally, sperm mitochondrial activity was the highest in NL3, whereas sperm viability was highest in EY, NL3, and L4. Following in vitro fertilization of in vitro-matured bovine oocyes, NL3 had cleavage and hatching rates comparable to BioXcell®, but a lower blastocyst rate than EY. Overall, NL3 performed better than the other extenders for most end points, with efficiency comparable to EY. We, therefore, concluded that reducing lecithin particle size to a nano level improves sperm cryopreservation with optimal performance with 3 % NL.

Melatonin improves post-thaw sperm quality after mild testicular heat stress in rams.

The objective was to determine effects of slow-release melatonin on post-thaw sperm quality in rams exposed to mild testicular heat stress (HS; scrotal neck insulation). Twelve yearling Dorset rams were randomly and equally allocated to receive either 36 mg melatonin in 1 ml corn oil or 1 ml corn oil injected subcutaneously (SQ); 15 day later, all rams had HS for 96 h (start of HS = start of Week 0). Semen was collected before HS and once weekly from Weeks 1 to 7, extended in Steridyl CSS One Step, held at 5°C for ~3 h, loaded into 0.5 ml straws, held 5 cm above liquid nitrogen for 10 min and then plunged. Computer assisted semen analysis (CASA) was conducted on frozen-thawed sperm. There were group and week effects for total and progressive motility (p < .001), plus group and week effects and group*week interactions (p < .001) for post-thaw total abnormalities, acrosome integrity, post-thaw sperm DNA fragmentation index (DFI) and high mitochondrial membrane potential (HMMP). Post-thaw sperm total and progressive motility, acrosome integrity and HMMP were higher (p < .05) in melatonin versus control groups from Weeks 1 to 7, and the melatonin group reached baseline level (pre-heat stress) at Week 7 (75.79 ± 0.96, 65.48 ± 1.51, 75.00 ± 0.89 and 67.00 ± 1.06, respectively; mean ± SEM). Conversely, post-thaw sperm total abnormalities and DFI were lower (p < .05) in melatonin versus control, and both reached baseline at Week 7 in the melatonin group (26.00 ± 0.57 and 5.66 ± 0.17, respectively). Coiled tails, distal midpiece reflexes, distal cytoplasmic droplets, ruffled acrosomes, bowed midpieces, pyriform heads and knobbed acrosomes were the most common abnormalities in both groups, with lower percentages in melatonin-treated rams. Results supported our hypothesis that HS reduces post-thaw sperm quality, and that melatonin lessens those reductions, manifested by significantly better total and progressive motility, acrosome integrity and HMMP, and fewer sperm total abnormalities and DFI.

Melatonin improves testicular hemodynamics and sperm quality in rams subjected to mild testicular heat stress.

Melatonin is a potent free-radical scavenger, with anti-inflammatory, anti-oxidative, and anti-apoptotic effects. The objective was to determine whether melatonin promoted testicular blood flow and protected sperm quality in rams after mild heat stress (HS; scrotal neck insulation). Twelve yearling Dorset rams with good semen quality were housed indoors (∼18-20 °C). Once weekly for 2 wk, Doppler indices (resistive index [RI] and pulsatility index [PI]) were measured in the supratesticular artery and semen collected by electroejaculation. Then, rams were randomly allocated into two equal groups, and given either 36 mg melatonin in 1 ml corn oil SQ under the ear (MEL), or only corn oil (CONT). At 15 d after treatment, all rams were subjected to mild HS for 96 h, with blood flow measurements and semen collection done once weekly for 7 wk. There were group, week and group∗week interaction effects (P < 0.005) for total and progressive sperm motility (CASA); total sperm abnormalities and acrosome integrity had effects of group, week and group∗week interaction effects (P < 0.00); and there were group and week effects for RI and PI (P < 0.005), with no significant differences before treatment. Changes in total and progressive motility and sperm abnormalities were evident at Week 1 post-HS in CONT rams, but MEL mitigated (P ˂ 0.05) these effects from Weeks 2-7. Furthermore, both PI and RI were reduced (P ˂ 0.05; i.e., significant increase in blood flow) in MEL versus CONT rams most weeks after HS. In MEL rams, sperm motility and total abnormalities had recovered at Weeks 5 and 6, respectively, whereas CONT rams had not completely recovered by Week 7. There was no difference (P < 0.05) between MEL and CONT groups in scrotal subcutaneous temperatures in the 4-d intervals before, during and after HS. In conclusion, melatonin significantly improved testicular blood flow and protected sperm motility and morphology in rams exposed to testicular HS. Therefore, melatonin has potential for mitigating effects of testicular HS under field conditions.