Relationship between in vitro fertilisation of ewe oocytes and the fertility of ewes following cervical artificial insemination with frozen-thawed ram semen

Theriogenology. 2005 Nov;64(8):1797-808. doi: 10.1016/j.theriogenology.2005.04.009. Epub 2005 Jun 4.

Abstract

No laboratory test exists that can reliably predict differences among rams in field fertility after artificial insemination (AI) with frozen-thawed semen. In vitro fertilisation (IVF) has been proposed as a method of predicting these differences. The objectives of this study were to evaluate whether IVF system could discriminate among rams of different fertility in vivo after AI using frozen-thawed semen. Also, to examine effects of lowering sperm concentration on discrimination power between rams used for IVF. The aim of Experiment 1 was to evaluate the effect of altering the sperm concentration from 2 x 10(6) to 0.03125 x 10(6) spermatozoa/mL on subsequent cleavage rate and blastocyst rate in vitro. In Experiment 2, six rams (three High and three Low in vivo fertility; average pregnancy rates of 37.6% and 21.8%, respectively) were compared for their fertilising ability in IVF. Spermatozoa from each of the six rams were added to ewe oocytes using a concentration of either 2 x 10(6) or 0.0625 x 10(6)/mL. There were six replicates with 25 oocytes per well and two wells per ram per replicate. Cleavage rate was monitored at 48 h post-insemination (p.i.) and blastocyst rate determined on Days 6-8 p.i. In Experiment 1, cleavage rate increased with increasing sperm concentration and blastocyst rate was not affected by sperm concentration on any day. When the six rams were tested using 2 x 10(6) spermatozoa/mL, no significant differences were found between High and Low fertility groups for cleavage rate or blastocyst rate on Days 6, 7, or 8 p.i. (P>0.05). When the experiment was repeated using 0.0625 x 10(6) spermatozoa/mL, no differences were found between High and Low group rams for blastocyst rate on any of Days 6, 7 or 8 p.i. (P>0.05). However, there was a significant difference between High and Low fertility rams for percentage of oocytes cleaved (16.4, S.E. 2.02%; P<0.01) and the correlation between fertility in vivo and cleavage rate in vitro was significant (P=0.013). Replicate of IVF was a source of significant variation for both cleavage rate and blastocyst rate and conditions need to be further controlled. However, we suggest that using a low concentration of spermatozoa (0.0625 x 10(6)/mL) for IVF may be a useful method for predicting field fertility of frozen-thawed ram semen.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cervix Uteri
  • Cryopreservation / veterinary*
  • Female
  • Fertility*
  • Fertilization in Vitro / veterinary*
  • Insemination, Artificial / methods
  • Insemination, Artificial / veterinary*
  • Male
  • Oocytes / physiology*
  • Pregnancy
  • Semen / physiology*
  • Semen Preservation / veterinary
  • Sheep
  • Sperm Count