Thawing time and nonreturn rate of bovine semen frozen in fine French straws

Bovine semen packaged in fine French straws was thawed for 8 or 25 s in warm water baths (38 +/- 2 degrees C). During 12 months, 43 inseminators performed alternately 87,486 first inseminations. The nonreturn rate was highly and significantly affected by month of first service, region, inseminator within region, herd with our without contract for progeny testing, parity group and the bull. When the semen was thawed for 25 s, the 75-day nonreturn rate was 0.54% and the 120-day nonreturn rate 0.45% higher than for 8 s. Though these differences were barely significant (P<.08, P<.16, resp.), they confirm nevertheless the observations of other authors. No significant interaction was found between thawing time and inseminator. According to the results of this trial, the semen temperature should be brought to the temperature of the water bath (38 +/- 2 degrees C) when thawed. A thawing time of 25 s is recommended.