LAUSR

The present study was aimed to evaluate the effect of over dilution of semen with tris extender on motion and functional attributes of bull sperm post‐thaw. Ejaculates (n = 24; mass motility ≥3+) were collected from bulls (n = 4) using artificial vagina, diluted to 20, 15, 10 and 5 million spermatozoa/0.25 ml, and cryopreserved. The results revealed that total motility (%), progressive motility (%) and rapid motility (%), straight linear velocity (μm/s), straightness (%) reduced significantly (p < 0.05) when semen was diluted to 5 million sperm concentration. Among the various sperm function attributes, proportions of live spermatozoa, acrosome intact spermatozoa, hypo‐osmotic swelling responsive spermatozoa and non‐capacitated spermatozoa reduced (p < 0.05) in 5 million spermatozoa, and the proportions of moribund spermatozoa, dead spermatozoa, live acrosome reacted spermatozoa, dead acrosome intact spermatozoa, capacitated spermatozoa and spermatozoa with lipid peroxidation increased significantly (p < 0.05) when semen was diluted from 20 to 5 million. However, the over‐dilution of semen did not affect slow motility, dead acrosome reacted spermatozoa, sperm protamine deficiency and spermatozoa with lipid peroxidation. In conclusion, the over dilution of semen affected sperm motion and functional attributes of frozen–thawed bull semen.