Effect of Thawing Time in Warm Water on Fertility of Bovine Spermatozoa in Plastic Straws

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Abstract
Thawing times of 12 and 30 s were compared in a fertility experiment involving 21,424 1st service inseminations to 20 Holstein bulls. Milk-diluted semen in 0.3 ml Continental USA straws was thawed in a warm water bath (32-35.degree. C) for 12 or 30 s on alternate days. Based on 66 day nonreturn rates in log-linear models, fertility was significantly higher when semen was thawed for 30 s (72.0%) than for 12 s (70.1%). For 13,543 inseminations by 9 technicians over 10 mo., the improvement with longer thawing was not significantly affected by mo. or season. The difference in nonreturn rate in favor of 30 s over 12 s thawing during summer, fall, winter and spring months averaged 2.0, 1.9, 3.4, and 0.8 percentage units. Raising the seminal temperature in straws above 5.degree. C by thawing in warm water for 30 s during cold weather provided a slight increase in fertility.