Effects of Age and Litter-of-origin on Cryopreserved Spermatozoa in Sumava Rams

This study aimed to evaluate the influence of the internal factors of ram age and litter-of-origin on semen quality during the cryopreservation process in Sumava sheep rams. This breed is included in the protected genetic resources of the Czech Republic. The sires were systematically divided into four groups according to age (under 1.5 years, 1.5 to 2.5 years, 2.5 to 3.5 years, and over 4.5 years) and according to litter frequency (singletons vs twins). Semen was evaluated after equilibration, and after cryopreservation using iSperm (R) mCASA and flow cytometry. During cryopreservation, there was a significant decrease in total sperm motility by 53.5%, progressive motility by 38%, and cells with intact plasma membrane and acrosome by 47%. Frozen-thawed sperm kinematic parameters showed significant age-related variations, with rams aged 4.5 and older displaying notably higher total and progressive motility (16.2% and 6.24%, respectively). Rams born as twins exhibited 3.77% (P < 0.05) higher progressive motility and 5.5% (P < 0.05) higher total motility compared to those born as singles. The sperm of older rams (> 4.5 years) exhibited higher viability (10.1%) and lower damage to the plasma membrane after freeze-thawing (23.6%), (P < 0.05). Twins showed significantly higher sperm viability (4.98%, P < 0.05) than singletons. These rams produce a larger quantity of higher-quality insemination doses after cryopreservation. For Sumava rams, in particular, broadening the sire selection base helps to select suitable rams for breeding. As the sire ages, his genetic value within the production herd may decline with time. This contrasts with genetic resource protection, where the aim is to preserve and store as many high-quality semen samples as possible.