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 language | English |
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Pages (from-to) | 1797-1808 |
Number of pages | 12 |
Journal | Theriogenology |
Volume | 64 |
Issue number | 8 |
DOIs | |
Publication status | Published - Nov 2005 |
Externally published | Yes |
Keywords
- Blastocyst rate
- Cleavage rate
- Fertility
- Frozen-thawed semen
- IVF
- Ram