Thawing optimums for bovine spermatozoa processed by three methods and packaged in Continental and French straws

A modified two-dimensional central composite rotatable design was used to study the effect of thaw bath temperature and time on acrosomal integrity in Continental (.3 ml) and French (.5 ml) straws. Ejaculates from 18 bulls were packaged in both containers. Semen from 6 of the 18 bulls was processed by each of three methods: 6 bulls for egg yolk-Tris-glycerol, 6 bulls for egg yolk-citrate-glycerol, and 6 bulls for skim milk-glycerol. Thaw bath temperatures ranged from 18 to 92 degrees C, and thaw times ranged from 4.5 to 50 s. Interaction of thaw bath temperature with thaw time was detected within each processing procedure and package. Maximum cell quality, measured by intact acrosomes after incubation of semen 3 h at 37 degrees C for .3-ml and .5-ml straws, was predicted to be achieved by thaw bath temperatures and times (degrees C/s) as follow: egg yolk-Tris-glycerol 40/32, 49/16; egg yolk-citrate-glycerol 43/30, 37/19; skim milk-glycerol 50/24, 36/24. Thawing procedures to maintain best acrosomal retention, regardless of processing method, were 44 degrees C for 29 s for .3-ml straws and 40 degrees C for 20 s for .5-ml straws.