Seminal plasma is the semen components that maintain sperm metabolism, pH and osmolality. Fibronectin (FN1) and glutathione peroxidase (GPX5) are the seminal plasma proteins that play an important role on the boar sperm functions. The purpose of the present study was to determine the differences in GPX5 and FN1 contents in the boar semen having good, moderate, and poor freezability. A total of 38 ejaculates from 25 boars with proven fertility were included in the experiment. All the ejaculates included in the study had >70% subjective motility, >75% normal morphology, >75% sperm viability, and volume >100 mL per ejaculate. The semen was collected through semen collection bag with filter and split into 2 portions. The first portion was prepared for the evaluation of seminal plasma proteins (i.e. GPX5 and FN1) and the second portion was cryopreserved and evaluated for post-thaw semen qualities. The seminal plasma samples were collected in cryotube and plug into liquid nitrogen. The samples was stored at –80°C before protein extraction. After thawing, the ejaculates were classified into 3 groups according to their post-thawed sperm motility: poor (14.6 ± 3.9%), modersate (28.5 ± 4.1%), and good (64.0 ± 8.7%) freezability. The amounts of GPX5 and FN1 proteins were evaluated through Western blot analysis. The normalized quantity of proteins was compared among groups by one-way ANOVA. The normalized level of FN1 in seminal plasma was higher in good- than in poor-freezability groups (8.0 ± 0.8% v. 5.7 ± 0.7%, respectively; P < 0.05), but did not differ significantly compared with that of the moderate-freezability group (7.5 ± 0.8%; P > 0.05). The levels of GPX5 in good-, moderate-, and poor-freezability groups were 14.7 ± 3.0%, 16.8 ± 3.2%, and 10.9 ± 3.0%, respectively (P > 0.05). The level of FN1 in seminal plasma was significantly correlated with the post-thaw sperm progressive motility (r = 0.38, P = 0.01), total motility (r = 0.37, P = 0.02), and the proportion of bent tail sperm (r = –0.33, P = 0.04). The level of GPX5 was not correlated with any of the post-thaw sperm qualities (P > 0.05). However, the levels of GPX5 was positively correlated with FN1 (r = 0.40, P = 0.01, n = 38). It can be concluded that FN1 in seminal plasma can be used as a marker of sperm freezability in boar.

The production of reactive oxygen species (ROS) during cryopreservation process impairs the sperm characteristics and fertilizing ability. However, melatonin, an antioxidant, could protect spermatozoa against this cell damage during cryopreservation. Therefore, we attempted to evaluate whether the melatonin supplementing in the semen extender could improve the sperm quality of swamp buffalo during cryopreservation. The semen collected from six swamp buffalo bulls were diluted with tris‐citrate egg yolk extender supplementing with 0, 0.1, 0.5, 1.0, 2.0 and 3.0 mM of melatonin. The parameters of sperm viability and motility were evaluated using computer‐assisted semen analyser (CASA) after cryopreservation on days 1, 7, 15 and 30. The group supplemented with 1.0 mM melatonin exhibited the higher viability after cryopreservation on days 1, 7, 15 and 30 with 58.346 ± 2.1a, 57.586 ± 2.0a, 55.082 ± 1.8a and 55.714 ± 1.8a, respectively, and showed the best results of motility parameters. However, higher concentration of melatonin at 3.0 mM impaired all the parameters. In conclusion, the addition of melatonin at 1 mM to semen extender could exert the best protection against sperm damage in swamp buffalo bull during cryopreservation.

Coomassie blue staining has been reported as an effective and inexpensive method for evaluating the acrosome integrity of spermatozoa, though to date its use to evaluate cryopreserved boar sperm has not been reported. Moreover, there is no information concerning the agreement between Coomassie blue staining and fluorescein isothiocyanate conjugated peanut agglutinin and ethidium homodimer (FITC-PNA/EthD-1) methods for assessing sperm acrosome integrity for any species. The current study was performed to determine the efficacy and agreement between Coomassie blue and FITC-PNA/EthD-1 staining methods for evaluating the acrosome integrity of frozen-thawed boar sperm. A total of 25 semen samples were cryopreserved using lactose-egg yolk-based extender and loaded into 0.5 PVC-French straws. Sperm motility and motion characteristics were determined using a computer-assisted sperm analysis system. Sperm viability and plasma membrane integrity were evaluated using the SYBR-14/EthD-1 and hypo-osmotic swelling test, respectively. Acrosome integrity of frozen-thawed boar sperm was evaluated using both FITC-PNA/EthD-1 and Coomassie blue staining to assess the association between sperm acrosome integrity and agreement between these two methods. The average percent acrosome integrity of frozen-thawed boar sperm as determined by FITC-PNA/ EthD-1 and Coomassie blue staining was 48.8 ± 12.6% and 52.6 ± 13.6%, respectively (P&gt;0.05). Interestingly, Coomassie blue staining found a correlation between sperm viability and acrosome integrity (r=0.609, P=0.002), while FITC-PNA/EthD-1 staining did not (P&gt;0.05). However, the acrosome integrity of frozen-thawed boar sperm evaluated by FITC-PNA/ EthD-1 and Coomassie blue staining was significantly correlated (r=0.448, P=0.025, n=25). The Bland-Altman plot determined that this agreement was acceptable. In conclusion, the acrosome integrity of the frozen-thawed boar sperm assessed via Coomassie blue staining was significantly correlated with that obtained via the FITC-PNA/EthD-1 staining method, and the two methods showed good agreement. Moreover, the significant association between the acrosome integrity of frozen-thawed boar sperm determined by Coomassie blue staining with other sperm quality parameters indicates that this is an effective method for assessing the acrosome integrity of frozen-thawed sperm in pigs.

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