The study was conducted with an objective to evaluate the relative efficacy of different concentrations of quail egg yolk (QEY) over chicken egg yolk (CEY) and to investigate the effect of decline in the concentration of quail egg yolk in cryodiluents on the freezability of Nili-Ravi buffalo bull spermatozoa. A total of twenty one semen samples (seven for each bull, two ejaculates at the same day per bull per week) from three experimental buffalo bulls were collected. Every semen sample was divided into five aliquots and diluted with one of the five experimental extenders namely A, B, C, D, and E having tris, fructose, citric acid, glycerol, egg yolk and antibiotics. Extender A was supplemented with 20% CEY which served as control, while extenders B,C,D, and E were supplemented with 5%, 10%, 15%, and 20% QEY respectively. Extended semen samples were allowed to cool at 4ºC for 2 hours and equilibrated for 4 hours at 4ºC. Semen straws were then frozen in biological cell freezer at -140ºC and stored in liquid nitrogen at -196ºC. Semen samples were evaluated for post-thaw quality parameters after freezing and 24 hours storage in liquid nitrogen. Post-extension sperm cells motility and intact DNA percentile showed non-significant differences between extender A (control) and E (20% QEY). However, the post-thaw percentile of motile spermatozoa with intact plasmolemma, functional acrosome, and viable count, was found to be significantly higher (P≤0.05) in extender E when compared to extender A. The same was true for various CASA based evaluation parameters of spermatozoa including progressive sperm cells motility, straight line velocity (VSL), average path velocity (VAP), beat cross frequency (BCF), straightness (STR) and linearity index (LIN). While curvilinear velocity (VCL), and amplitude of lateral head displacement (ALH) of spermatozoa were significantly higher in extender B (5% QEY) as compared to extender A (control) and extender E (20% QEY). Furthermore, it was observed that decline in the concentration of quail egg yolk from 20% to 5% resulted in decreased post-thaw sperm cells motility, viability, plasmolemma integrity, functional acrosome percentage and other CASA based motility characteristic indices. The results of the present study revealed that substitution of 20% CEY with 20% QEY in cryodiluents improves the post-thaw semen quality parameters of Nili-Ravi buffalo bull spermatozoa. 1489516343.php