Effects of thermotaxis on sperm collected from doberman and American bully breed dogs

Sperm transfer through the reproductive tract is crucial for successful fertilization in most of mammals. After ejaculation, spermatozoa need to go through a complex physiological barrier and environments in the reproductive tract. Also, sperm must respond to many environmental conditions, including temperature. The present study aims to investigate the thermotactic response of sperms collected from American Bully dogs and its impact on motility, viability, membrane integrity, and concentration at different temperatures. Evaluated semen samples, collected from mature dogs incubated at 34°C, 38°C, and 40°C for 60 minutes in a custom-designed thermotaxis model. Some sperm parameters were assessed using computer-assisted sperm analysis (iSperm CASA), Nigrosin-Eosin staining, and the Hypo-Osmotic Swelling Test (HOST). Results showed that sperm motility and concentration were increased at 34°C and 38°C, while exposure to 40°C resulted in a significant decline in motility, progressive motility, and concentration. Slightly higher curvilinear velocity (VCL) and straight-line velocity (VSL) at 38°C suggests optimal motility at this temperature. Membrane integrity (HOST-positive sperm) was significantly compromised at 40°C, with a corresponding decrease in viability, as confirmed by Nigrosin-Eosin staining. Sperm direction towards to different temperature for the sample was also affected, with the highest sperm concentration observed at 34°C, followed by 38°C, and the lowest at 40°C, indicating that higher temperatures (likely due to increased oxidative stress and metabolic exhaustion) are not favourable for canine sperm. As conclusion, the results showed that canine spermatozoa exhibit temperature-dependent survival patterns, with an optimal range between 34°C and 38°C. The thermotaxis for spermatozoa may play a role in natural sperm selection, influencing fertilization efficiency. Future studies should be set up to investigate the molecular mechanisms underlying thermotaxis and its potential use in sperm selection for improved fertility outcomes.