40 L-carnitine protects membrane functionality of boar spermatozoa

Usually, boar semen diluted with long-term storage extender is used for artificial insemination within five days. The longer the storage, the more reactive oxygen and nitrogen species are produced by the sperm. Substances with antioxidant activity, which play an important role in energy synthesis, such as L-carnitine (LC) may be beneficial to sperm viability during semen preservation. The present work aimed to study whether the addition of different concentrations of LC to porcine semen lengthens sperm motility and membrane functionality in addition to decreasing nitrite and hydrogen peroxide concentrations of boar semen cooled and stored at 17°C for eight days. One insemination dose of 10 different boars (n = 10) was stored at 17°C for eight days. On Day 5 (d5) each 10 mL semen sample was distributed in the following treatments: T1) control, semen diluted with long-term storage extender; T2) T1 + 0.5 mM LC; T3) T1 + 1 mM LC; T4) T1 + 5 mM LC; and T5) T1 + 10 mM LC. The LC dosages were selected based on research with equine semen cooling and freezing. On d6 and d8, the sperm kinetics and membrane functionality were evaluated with a computer-assisted sperm analysis (CASA) and a hypoosmotic swelling test. Nitrite and hydrogen peroxide concentrations were measured with spectrophotometry. The statistical analysis was performed with analysis of variance (ANOVA) and the P < 0.05 value was considered statistically significant. The addition of LC did not influence the sperm kinetics (d8 total motility mean value: 42.3%) nor the nitrite concentration (d8 mean value 32.6 μM/μg protein) among the treatments and time (P > 0.05). However, the addition of 10 mM LC to cooled semen decreased the hydrogen peroxide concentration on d8 compared with the control group (52.8 vs 65.8 μM/μg protein). Additionally, on d8, all of the LC treatments showed an increased percentage of sperm with a functional membrane (T2: 35.0%, T3: 40.9%, T4: 37.5%, T5: 38.2%) compared with the control group (30.7%; P < 0.05). In the results, it was shown that the antioxidant activity of 10 mM LC and that all LC concentrations tested were beneficial to protect the functionality of the plasma membrane of boar sperm. In conclusion, 10 mM LC added to cooled boar semen at d5 can be suggested as an alternative to lengthen the sperm lifespan to d8.