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

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°C for 8 sec (T70) and mini straws either at 50°C for 9 sec (S50) or at 35°C for 12 sec (S35).Vaginal insemination with 200 × 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°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).A vaginal deposition of frozen ram semen containing approximately 200 × 106 spermatozoa, filled in mini straws and thawed at 35°C is a simplified technique that under field conditions and used on a do-it-yourself regime gives acceptable lambing rates in Norway.The fertility of Norwegian Crossbred ewes is very high, with natural mating being predominant. Because the average flock size is only approximately 52 adult animals, a cooperative scheme for breeding has been developed. During the mating season rams are moved between farms that belong to the same "ram circle" or breeding group, according to their breeding requirements [1,2].In the 1960s cervical insemination with frozen-thawed ram semen was developed in Norway [3] for routine use in artificial insemination (AI). At that time AI was introduced as a supplement to natural mating and therefore only less than one per cent of the ewes were inseminated artificially over the next three decades. The routine cryopreservation protocol developed during this period included m