Date Published: September 28, 2007
Publisher: BioMed Central
Author(s): Heiko Paulenz, Tormod Ådnøy, Lennart Söderquist.
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.
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].
No significant effect on fertility, expressed as 25-days non-return- or lambing rate, was seen in the present study for straw type/thawing temperature. A significant influence of farmer, ram, and age of the ewes was seen on the fertility results. Semen filled in mini straws and thawed at 35°C gave numerically the highest lambing rate with 59.2%, while the 25-days NR rate was 62.5%. The overall national fertility results in the same season (2004), only available as 25 days NR rates, were 61.3% (n = 14327) and in accordance with the results obtained in this study [11,17].
The use of 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 DIY basis gives acceptable lambing rates in Norway. Furthermore, freezing of ram semen in mini straws would also result in a more rational semen production and simplified semen handling at the AI centres.
The author(s) declare that they have no competing interests.
HP was main responsible and involved in all parts of the study. LS participated in all parts of the study but not in the statistical analysis. TA participated in the design of the study and performed the statistical analysis. All authors read and approved the final manuscript.