Comparison of fertility results after vaginal insemination using different thawing procedures and packages for frozen ram semen

BACKGROUND The effect of different thawing procedures for ram semen frozen in minitubes and mini straws on the fertility of sheep was tested in a field trial. METHODS Altogether, 719 Norwegian Crossbred ewes, aged between six months and six-and-a-half years from 8 farms, were inseminated vaginally in natural oestrus with frozen-thawed semen. Minitubes were thawed at 70 degrees C for 8 sec (T70) and mini straws either at 50 degrees C for 9 sec (S50) or at 35 degrees C for 12 sec (S35). RESULTS Vaginal insemination with 200 x 106 spermatozoa resulted in 25-days non-return rates of 63.2, 59.6, and 62.5% (overall 61.8%), respectively, and lambing rates of 56.8, 55.0, and 59.2% (overall 57.0%), respectively. No significant effect on fertility (as 25-days non-return- or lambing rate) was seen for straw type/thawing temperature (P = 0.5/0.5), but semen filled in mini straws and thawed at 35 degrees C resulted numerically in the highest lambing rate (59.2%). A significant effect was, however, seen for farmer (P = >0.0001/>0.0001) and ram (P = 0.009/0.002). Moreover, age of the ewes had a significant effect on the NR rate (0.007), but not on lambing rate (P = 0.2). CONCLUSION A vaginal deposition of frozen ram semen containing approximately 200 x 106 spermatozoa, filled in mini straws and thawed at 35 degrees C is a simplified technique that under field conditions and used on a do-it-yourself regime gives acceptable lambing rates in Norway.