Stanimir Dimitrov, Zhelyazko Sabev, Georgi Garbev, Vesna Karapetkovska – Hristova
Title: Seasonal and Age-Related Impacts on Semen Production and Cryopreservation in Bulgarian Black and White Bulls [full pdf]

Abstract: Bulgarian Black and White cattle are a crucial part of Bulgaria’s native cow genetic resources, requiring development and conservation. This study aimed to evaluate semen production and the cryopreservation of spermatozoa in this breed. Four bulls were included in the study, with 226 ejaculates analyzed in total.
Results indicated that ejaculate volume was lowest in December-January and tended to increase in September-November. In contrast, spermatozoa concentration (x10⁹/cm³) in fresh semen was highest in December-January and lowest in September-October. Fresh semen mass motility showed its minimum values during March-May and peaked from October to January. The post-thaw spermatozoa parameters (mass motility and thermal resistance at 39°C) followed similar seasonal trends, with the highest values recorded in autumn-winter and the lowest in other months. Additionally, bull age had a significant influence (p<0.0001) on semen parameters. The fertilizing ability of deep-frozen semen, measured by conception rates, ranged from 49.60% to 56.50% for first insemination and from 69.30% to 86.00% for total conception, varying among the bulls.
In the study, it was concluded that semen production and cryopreservation are significantly influenced by seasonal variations and bull age, with optimal parameters observed in the autumn-winter months.

Keywords: bull, semen, age, season, production, cryopreservation.

doi:10.15547/joiah.2025.01.002