Effect of deposition site and sperm number on the fertility of sheep inseminated with liquid semen.

The effect of the deposition site and the numbers of sperm on the fertility of sheep was tested in a field trial in which 1292 Norwegian crossbred ewes aged between six months and five-and-a-half years from 52 farms were inseminated with liquid semen after natural oestrus. Cervical insemination with 150 x 10(6) and 75 x 10(6) spermatozoa resulted in 25-day non-return rates of 63.7 and 56.1 per cent, and vaginal insemination gave non-return rates of 63.3 and 56.6 per cent, respectively. There was no significant difference between the cervical and vaginal inseminations, but the inseminations with 150 x 10(6) spermatozoa gave significantly higher non-return rates (P=0.004). There were significant differences between the non-return rates for different rams (P<0.0001) and farmers (P=0.0002) but the age of the ewe had no significant effect.