A new study has provided encouraging early data on pregnancy outcomes after the transfer of both fresh and vitrified-warmed equine embryos produced by conventional in vitro fertilisation, or cIVF.
Researchers retrospectively reviewed clinical records from a commercial embryo transfer facility to assess how mares performed after receiving cIVF embryos that were transferred either fresh or after vitrification and warming. Although the dataset was small, the findings suggest that both embryo handling approaches can result in successful early pregnancies under field conditions.
In total, 40 cIVF embryos were transferred to recipient mares, 21 fresh embryos and 19 vitrified-warmed embryos. Pregnancy was assessed six days after transfer, followed by later checks for embryonic heartbeat at day 25 to 30 of gestation.
The pregnancy rates at six days post-transfer were very similar between the two groups. Fresh embryos resulted in a pregnancy rate of 81 percent, while vitrified-warmed embryos achieved 79 percent. Among those pregnancies that were established, embryonic heartbeat was detected in 94 percent of pregnancies from fresh embryos and 100 percent of those from vitrified-warmed embryos.
Only one presumptive early embryonic loss was recorded in the study, and that occurred in the fresh embryo group. Overall, early pregnancy loss was low within this cohort.
Two pregnancies, one from each group, were allowed to continue to term, and both produced clinically normal foals. Notably, the authors report that the foal born from a vitrified-warmed cIVF embryo produced using frozen-thawed semen is, to their knowledge, the first documented full-term foal in the horse from this approach.
Conventional IVF is still an emerging technique in equine reproduction. While intracytoplasmic sperm injection, or ICSI, remains the dominant assisted reproductive technology in horses, cIVF is attracting increasing interest as understanding of equine sperm capacitation improves and laboratory systems develop.
Cryopreservation is also an important part of the picture. Because freezing horse oocytes remains inefficient, embryo vitrification offers a practical option for storing valuable genetics and giving breeders more flexibility around transfer timing. However, until now, there has been limited published information on how well vitrified-warmed cIVF embryos perform after transfer.
The authors are careful to stress that this was a retrospective study with a limited sample size, and the results should be viewed as descriptive rather than proof that fresh and vitrified-warmed embryos perform equally well. Recipient mare management, progesterone support, embryo characteristics and semen-related factors may all have influenced the outcomes.
Even so, the study adds useful clinical data to a developing area of equine reproduction and suggests that vitrified-warmed cIVF embryos may have real practical potential.
The researchers say larger, prospective studies are now needed to better understand pregnancy establishment, embryo viability and longer-term foal outcomes following cIVF embryo transfer
