The depth of cervical insemination and site of intrauterine insemination and their relationship to the fertility of frozen-thawed ram semen

Abstract

The study describes three experiments. The first experiment, comprising four trials, was conducted to examine the fertility of frozen-thawed ram semen in relation to depth of cervical insemination, the number and time of inseminations and the number of spermatozoa inseminated at the first or second oestrous period after removal of progestagen sponges. There was a significant linear increase in fertility as the depth of insemination increased ( b=6.6–12.2% per cm past the cervical os). The pregnancy rates at Day 35 were not significantly different for 80, 160, 240 or 320× 10 6 frozen-thawed motile spermatozoa (16.4%, 21.4%, 19.9% and 27.7%, respectively) and there was no interaction between depth of insemination and the number of spermatozoa inseminated. There was no benefit in dividing the inseminate and inseminating at both 12 and 24 h after detection of oestrus. The mean pregnancy rates 45 days after insemination at 12 h, 24 h or at both 12 h and 24 h after detection of oestrus were 24.0%, 8.9% and 28.6%, respectively ( P < 0.01). The mean depth of insemination increased with increasing age of ewe (4–7 years old), and was greater at 12 h compared with 24 h after the onset of oestrus, but age of ewe had no effect on pregnancy rate. There was no difference in mean depth of insemination or pregnancy rate at Day 35 between ewes inseminated with a standard 4 mm or 2 mm diameter bent tipped pipette (1.16 ± 0.09 cm vs. 1.41 ± 0.09 cm and 43.8 ± 7.2% vs. 41.3 ± 6.3%, respectively). Similarly, there was no difference in mean depth of insemination or lambing rate between ewes inseminated with a bent tipped or a helicoid tipped pipette (1.04±0.05 cm vs. 1.08±0.05 cm and 33.2±5.9% vs. 36.3±5.6%, respectively). In the second experiment measurements were made of the cervical structure of maiden and adult ewes, and the relationships between the measurements and depth of insemination were determined. All cervical measurements, except number of internal folds, were greater in adult than in maiden ewes and it was possible to penetrate the cervix deeper in adults than in maidens. Depth of insemination was correlated only to the distance from the cervical os to the first ( r=0.35; P < 0.05) and second ( r=0.41; P < 0.01) cervical fold. The third experiment examined the effect of site of intrauterine insemination and number of frozen-thawed spermatozoa on fertilization at a synchronized oestrus. There was a linear increase in fertilization rate of ova as the number of motile spermatozoa inseminated increased (13.9% vs. 38.4% vs. 40.3% vs. 72.8% for 1, 4, 16 and 64 × 10 6), but the percentage of ova fertilized following insemination into the uterine body was not different to that following insemination into the left uterine horn (45.2% and 37.5%). There was no interaction between site of insemination and dose of spermatozoa on fertilization rate. In ewes inseminated into the uterine body there was no difference between the left and right oviduct in the percentage of ova that were fertilized (40.0% vs. 35.0%).