Semen analysis of boars under intertropical conditions reveals the relevance of proximal and distal cytoplasm droplets for sperm functional integrity.

This work aimed to establish whether the temperature humidity index (THI) under different intertropical zones affects the retention of cytoplasmic droplets (CDs), sperm function and DNA integrity in boars. With this purpose, two separate studies were devised. In the first one, 49 boars from six farms were collected every 45 days (230 ejaculates). THI were measured daily, and sperm parameters were evaluated. Boars were classified into three groups based on the incidence of ejaculates having more than 25% spermatozoa with CDs: persistent (at least three consecutive ejaculates), moderate (less than three ejaculates) and absent (no ejaculate having ≥25% spermatozoa with CDs). Farms were classified based on THI through cluster analysis into two groups. In the second study, 32 liquid-stored semen samples were classified based on three cluster analysis: low and high incidence of proximal (PCDs), distal (DCDs) CDs and a combination of PCD and DCDs. high THI farms presented significantly (p < .05) higher proportions of boars with moderate and persistent incidence of CD than those with low THI. In study 2, the presence of PCDs was negatively correlated with sperm DNA integrity (r = -0.691; p < .01). However, differences between groups were more apparent when ejaculates were classified based on both PCDs and DCDs than when PCDs or DCDs were considered separately. In conclusion, classification of boars according to the severity and persistence of CDs in boars allows understanding more clearly the dynamics of CD retention and the effects of ambient temperature and relative humidity. Additionally, the joint analysis of both PCDs and DCDs is necessary in routine sperm quality analyses.

Relative content of Niemann-Pick C2 protein (NPC2) in seminal plasma, but not that of spermadhesin AQN-1, is related to boar sperm cryotolerance.

Variation between and within boar ejaculates in terms of their ability to withstand freeze-thawing is a limitation for sperm cryopreservation. Consequently, searching for freezability markers not only in sperm but also in seminal plasma (SP) is imperative. The present study aimed to evaluate the relationship between cholesterol content, relative levels of NPC2 and AQN-1 at two different holding times (0 h: HT0 and 24 h: HT24) at 17 °C, and boar sperm freezability. Forty-five ejaculates were cryopreserved and subsequently classified as of good (GFE) or poor (PFE) freezability according to their post-thaw sperm viability and total motility. Prior to cryopreservation, relative abundances of two SP proteins (NPC2 and AQN-1) and cholesterol content in sperm and SP were determined through immunoblotting and colorimetric methods, respectively. These determinations were made after ejaculation (HT0) and after 24 h of storage at 17 °C (HT24). Two bands for NPC2 protein (16 kDa and 19 kDa) were identified. Relative amounts of the 16 kDa-band were significantly (P < 0.05) higher in poor (PFE) than in good (GFE) freezability ejaculates both at HT0 and HT24, whereas those of the 19 kDa-band were significantly (P < 0.05) higher in PFE than in GFE at HT24 only. In the case of AQN-1, no significant differences between GFE and PFE were observed. In addition, no variations in the cholesterol content of sperm and SP were observed either between HT0 and HT24 or between GFE and PFE. We can conclude that the content of two NPC2 isoforms in SP, but not of that of spermadhesin AQN-1, may be involved in the sperm resilience to withstand freeze-thawing procedures and may predict ejaculate freezability. While a possible mechanism through which NPC2 during HT could affect boar sperm cryotolerance is suggested to be related to its ability to bind the plasma membrane cholesterol, further research is warranted.