The effect of different thawing procedures for ram semen frozen in mini tubes 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. Mini tubes 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. 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 °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 x 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.
October 16, 2007
Original web page at Acta Veterinaria Scandinavica