The effect of temperature on semen characteristics of beef bulls in South Africa

Abstract

The aim of the study was to determine the effect of temperature on semen characteristics of beef bulls over a seven-year period. Data analysis was performed using ANOVA GLM Proc for 22 099 fresh semen data records used from eight provinces and nine bull breeds while 3 003 thawed semen data records was used from seven provinces and six bull breeds in South Africa. The semen characteristics analysed included semen volume, percentage live sperm, sperm count, sperm viability, linear movement, non-linear movement, major defects, minor defects, five individual major defects and three individual minor defects. The percentage semen records per province varied from 3.02 % to 31.59 %. Breed had a significant effect on some fresh and frozen-thawed semen characteristics. The Drakensberger bulls had superior (P <0.05) fresh semen characteristics compared to Bos Indicus, Bos taurus and composite breed bulls. Bos Indicus bulls had higher quality semen characteristics than Bos taurus bulls. The composite breed bulls had superior (P <0.05) frozen-thawed semen characteristics. Seasonal differences were observed with the highest (P <0.05) quality semen characteristics from semen produced during spring collected in summer. Temperature had significant effect with lower quality semen above 32 °C. Sperm motility in fresh semen was significantly reduced at temperatures >38 °C compared to temperatures between 32 °C to 37 °C. At temperatures > 38 °C sperm maturation exhibited significantly higher abnormal loose heads. Frozen-thawed semen had increasingly poor sperm count, major defects and minor defects when bulls produced semen while exposed to temperatures > 38 °C. Frozen-thawed semen tended to have lower significant differences between individual major defects but was still in the acceptable range. Temperature is a factor that requires more research, especially in regions with temperatures above 32 °C. Results indicated that a range of factors influence semen characteristics which need to be considered before bulls are included in planned breeding programs to ensure high fertility.