Effect of Semen Extender and Storage Temperature on Motility of Ram Spermatozoa

Abstract

Cryopreservation of ram semen results in low post-thaw survival. Thus, studies were conducted to optimize liquid-storage of chilled semen. In Experiment 1, semen collected from rams (n = 5) was extended using either milk, TRIS (tris[Hydroxymethyl]aminomethane), TEST (N-Tris (hydroxymethyl)-methyl-2-aminoethane sulfonic acid), or CJ-2 (choline-based extender) and stored at either 4℃ and 15℃. All extenders were supplemented with 5% (v/v) egg yolk. In Experiment 2, semen collected from 9 rams was distributed across TRIS or milk extenders supplemented with 5% or 20% (v/v) egg yolk, and 0 or 1% ethylene glycol (EG), during storage for 72 hours at 4℃. The effect of penicillamine, hypotaurine, and epinephrine (PHE) on motility parameters was also evaluated following storage. In Experiment 1, most of the sperm motility parameters were higher after extension, and storage at 4℃ compared with 15℃ (P < 0.05). Ram semen extended using milk or TRIS based extenders and stored at 4℃ maintained similar sperm progressive motility over time, but was higher compared with TEST or CJ-2 extenders (P < 0.05). However, progressive motility of ram sperm declined by 75% when stored at 4℃ for 24 hours, and continued to decline over time. In Experiment 2, milk extender supplemented with 1% EG and 20% egg yolk before storage and addition of PHE after storage had higher sperm motility parameters than other extender and supplement combinations. Further studies are needed to assess in vivo sperm viability and conception rates when using extended, stored semen for artificial insemination of ewes.