Effects of strain and embryo transfer model (embryos from one versus two donor does/recipient) on results of cryopreservation in rabbit.

Differential effects of 2 transfer models for normal thawed embryos of 1 donor doe were studied on the offspring rate and their embryo survival at birth from 3 selected rabbit strains (SY and SB: synthetic strains, NZ: New Zealand White). Morulae were obtained 64-66 h post-coitum from 93 adult does treated with 25 IU of hCG (SY:36, NZ:27, SB:30). Morphologically normal morulae were frozen in the presence of 1.5M DMSO and stored in liquid nitrogen. Normal thawed embryos were transferred into the oviducts of synchronized recipient does of the same strain 48 h after being injected with 25 IU of hCG (SY:28, NZ:21, SB:24). Each recipient received embryos from 1 (single transfer) or 2 different donor does (double transfer). Significant differences were observed in the post-thawing percentage of normal embryos between strains (SY:95 +/- 1% and SB:85 +/- 3%, P < 0.05; NZ: ,91 +/- 2%). After transfer, no significant differences were observed in pregnancy rate and offspring rate between the transfer models, whereas significant differences were only found in survival rate when all transfers were analyzed (double: 24 +/- 4% vs single: 14 +/- 3%, P < 0.05). An effect of strain was detected in the pregnancy rate (NZ: 33% vs SB: 71%, P < 0.05; SY: 61%) and in the survival rate per donor doe on pregnant recipient doe (SY: 42 +/- 5 vs SB: 19 +/- 5, P < 0.05; NZ: 34 +/- 7%). These results suggest a differential embryo sensitivity with respect to their genetic origin in both the freezing-thawing and transfer procedures.