ARTIFICIAL-INSEMINATION WITH FROZEN-SEMEN IN EWES AT DIFFERENT TIMES OF THE BREEDING-SEASON

Totally 13575 ewes of two different breeds, Dala and Spel, were inseminated with semen, frozen in straws and thawed at 70-degrees-C for 8 sec. An insemination dose of 0.2 ml containing approx. 150 x 10(6) spermatozoa with at least 45 to 50% progressive motility was inserted 5 to 12 mm into the cervix. The insemination was performed once between 12 and 30 h after the onset of heat. The NR rate of the Dala ewes increased significantly during the season. The NR rate of the ewes inseminated before 15. November was 44.3%, from 15. to 20. November 52.2%, from 20. to 25. November 55.3% and from 25. November and later 61.4%. The corresponding values for the ewes of the Spel breed were 57.3, 58.7, 61.5 and 71.0% respectively, and only the difference between the two last values was statistically significant. The difference between the fertility of the two breeds was significant within each of the periods.