Temperature limits for storage of extended boar semen from the perspective of the sperm's energy status

Abstract

The optimum storage temperature for liquid-preserved boar semen has been empirically determined to be between 15 and 20°C. Lower temperatures provide an advantage to inhibit bacterial growth, but are regarded as critical due to the high sensitivity of boar spermatozoa to chilling injury. Higher storage temperatures are supposed to induce energy deficiency due to an insufficient depression of metabolic cell activity. However, experimental evidence for alterations of the sperm's energy status in relation to storage temperature and duration is missing. Therefore, we aimed to revisit the upper and lower storage temperature limits for liquid-preserved boar semen from the perspective of the sperm's energy metabolism. Ejaculates (n = 7 boars) were cooled down in Beltsville Thawing Solution (BTS) to 25, 17, 10, or 5°C and stored for up to 120 h. ATP and adenylate energy charge (EC) levels were assessed at storage temperature (24, 72, and 120 h storage) and after subsequent re-warming (38°C). Sperm quality and energy status remained at a stable level in samples stored at 25 and 17°C. Chilling to and storage at 10 or 5°C in BTS provoked cold shock in a subset of sperm as shown by a loss in viability and motility (P < 0.05), which was accompanied by a significant release of adenine nucleotides into the semen extender. Prolonged storage for 120 h resulted in significantly lower mean ATP concentrations in viable spermatozoa at 5 or 10°C compared to 17°C (P < 0.05). Cluster analysis revealed that the main sperm subpopulation, i.e., sperm with moderate speed and linearity, decreased from 50 to 30% (P < 0.05) in favor of slow-moving spermatozoa (5°C) or spermatozoa with a hyperactivation-like motility pattern (10°C). The results point to a sublethal imbalance in available ATP in a subset of the surviving sperm population, rather than a general decrease in available ATP in all spermatozoa. In conclusion, storing diluted boar semen at a stable temperature between 17 and 25°C is a safe procedure concerning the spermatozoa's energy status. Future concepts for hypothermic boar semen preservation below 17°C require measures which ameliorate the imbalanced energy status in viable spermatozoa.

Post-Thaw Storage Temperature Influenced Boar Sperm Quality and Lifespan through Apoptosis and Lipid Peroxidation

“…Lipid architecture and the fluidity of the sperm plasma membrane can be altered by temperature changes [37,38], resulting in damage to sperm quality and functionality. Therefore, storage temperature at 17-25 • C is recommended for boar semen [39] because sperm quality loss is observed at >20 • C or <15 • C [40]. The results of this study indicate that post-thaw storage at 17 • C leads to better sperm quality than that at 5 • C and 37 • C. Accordingly, lower levels of apoptotic changes in boar sperm were observed at 17 • C in comparison with those at 5 • C and 37 • C, which could explain the results.…”

Arresting calcium-regulated sperm metabolic dynamics enables prolonged fertility in poultry liquid semen storage

“…Previous studies on in vitro semen storage in various species have indicated that sperm mitochondria experience failure under low temperature conditions, leading to reduced sperm fertilizability during storage 22 , 25 , 26 , 49 . Nevertheless, in mechanistic terms, our understanding of how sperm metabolism during cold storage relates to impaired fertility remains limited.…”

“…Sperm mitochondria play a vital role in coordinating ATP production, redox equilibrium, and calcium homeostasis, all of which can contribute to the regulation of sperm fertilization potential. Indicating a cross-genera conserved relevance, events that may be connected to mitochondrial impairments such as increased [Ca 2+ ] i levels, accumulation of reactive oxygen species (ROS), and decrease in mitochondrial membrane potential (ΔΨ M ) have been demonstrated to occur in the early stages of both liquid storage in chicken 20 , 21 and boar 22 , 23 semen. Nevertheless, specific mechanistic associations between increased [Ca 2+ ] i levels and reduced semen quality during storage or impact on mitochondrial function remain unknown.…”

Storage of boar semen at 17°C without conventional antibiotics in an extender containing an organic bactericidal substance

“…Compared to short-term semen extenders, long-term preservation media usually provide higher sperm protection against different stressors like temperature fluctuation (29,30) or long-term exposure of seminal plasma during semen storage (31). Furthermore, they may also protect sperm better from bacterial stress, for example, caused by bacterial secretions (32) or binding to glycoprotein receptors on the sperm surface (33).…”