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

C. M. O'Meara, J. P. Hanrahan, A. Donovan, S. Fair, D. Rizos, M. Wade, M. P. Boland, A. C.O. Evans, P. Lonergan

Research output: Contribution to journalArticlepeer-review

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 × 10 6 to 0.03125 × 106 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 × 106 or 0.0625 × 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 × 106 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 × 106 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 × 106/mL) for IVF may be a useful method for predicting field fertility of frozen-thawed ram semen.

Original languageEnglish
Pages (from-to)1797-1808
Number of pages12
JournalTheriogenology
Volume64
Issue number8
DOIs
Publication statusPublished - Nov 2005
Externally publishedYes

Keywords

  • Blastocyst rate
  • Cleavage rate
  • Fertility
  • Frozen-thawed semen
  • IVF
  • Ram

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