Seasonal variation in semen quality of swamp buffalo bulls (Bubalus bubalis) in Thailand.

AIM To test the hypothesis that season affects the semen quality of swamp buffalo (Bubalus bubalis) bulls used for artificial insemination (AI) under tropical conditions in Thailand, as it does in Bos taurus and Bos indicus. METHODS Clinical and andrological examinations, and monitoring of semen production and quality were carried out on five mature, healthy swamp buffalo AI bulls in Thailand from July 2004 to the end of June 2005. Sperm output, motility, morphology and plasma membrane integrity (PMI) were compared between three seasons of the year (rainy, i.e. July-October; winter, i.e. November-February; and summer, i.e. March-June) with distinct ambient temperature and humidity. RESULTS All bulls were diagnosed as clinically healthy and with good libido throughout the study. Ejaculate volume, pH, sperm concentration, total sperm number and initial sperm motility did not differ between seasons, whereas PMI and the relative proportion of morphologically normal spermatozoa were highest in summer and lowest in winter (P<0.05). Buffalo age, week of collection and season influenced sperm morphology (P < 0.05-0.001). Among morphological abnormalities, only proportions of tail defects were affected by season, being highest in the rainy season and lowest in summer (P<0.001). In conclusion, climatic changes did not seem to largely affect semen sperm output or viability. Although the proportions of PMI and tail abnormalities were affected by season, they were always below what is considered unacceptable for AI bull sires. CONCLUSION Seasonal changes did not appear to cause deleterious changes in sperm quality in swamp buffalo AI-sires in tropical Thailand.