Abstract
Background:
The application of frozen semen in buck artificial insemination (AI) is widely practiced; however, cryopreservation can compromise sperm quality depending on the extender used.

Aim:
This study aimed to evaluate the effects of different commercial extenders on post-thaw sperm quality and kinematic characteristics in bucks.

Methods:
Semen samples were collected from four bucks (two Etawah Grade and two Anglo-Nubian), and five ejaculates were obtained from each individual. Comprehensive evaluations were conducted using three extenders (AndroMed®, BoviFree®, and Steridyl®), with three straws per extender per ejaculate, totaling 180 straws. Frozen semen quality was evaluated based on sperm motility, kinematics, viability, acrosome integrity, and abnormalities.

Results:
The commercial extender type significantly affected sperm motility and kinematics (p < 0.05). Steridyl® yielded the highest total and progressive motility (60.19 ± 1.31% and 58.11 ± 1.33%, respectively). AndroMed® was associated with the highest sperm kinematic values: curvilinear path (VCL), straight-line path (VSL), velocity average path (VAP), distance curved line (DCL), distance average path (DAP), amplitude of lateral head displacement (ALH), and head activity (HAC). Sperm viability, abnormalities, and acrosome integrity were not significantly different among the extenders (p > 0.05). These results indicate that different commercial extenders may exert specific effects on overall sperm motility versus kinematic variables, explaining the observed differences.

Conclusion:
Commercial extenders exhibited function-specific effects on post-thaw sperm quality, with Steridyl® supporting sperm motility, AndroMed® enhancing sperm kinematics, and BoviFree® showing intermediate performance, indicating that no single commercial extender outperformed others across all functional domains.

Key words: Buck semen; Frozen semen; Commercial extender; CASA.