‘Milestone’ in equine breeding techniques as US lab records a world first

The first successful use of frozen sperm to create IVF equine embryos has been recorded in the US, in a “milestone” for breeding.

Researchers at the UC Davis School of Veterinary Medicine in California carried out the study and hope the findings will be useful for clinical applications, as well as opportunities to study fertilisation and embryo development.

They used defrosted sperm to fertilise oocytes (eggs) and create embryos, before analysing stages of embryo development, which they compared to those achieved with ICSI (intracytoplasmic sperm injection – injecting a single sperm into an equine oocyte).

IVF has historically had little success in horses. There have been recent advances, but only using high-quality fresh sperm, which limits its use.

Sperm from five different stallions was used on 109 oocytes, and scientists compared the early stages of development at several different points.

The researchers found a “similar success rate” between IVF and ICSI, using thawed sperm, with IVF embryos showing faster progression to the blastocyst stage – an early embryonic structure, which is a rapidly dividing ball of cells.

“Our team is excited to advance IVP [in vitro production] of equine embryos to overcome historical challenges,” said equine reproductive specialist and study co-author Dr Pouya Dini.

“The ability to use frozen-thawed sperm for IVF would be a valuable addition to current equine-assisted reproductive technologies and would benefit both stallion and mare owners.

“This collaborative effort is the first step in evaluating the expansion of future equine IVF applications in the clinic.”

This is still early days and the authors stressed that more research is needed.

“Caution is warranted in the interpretation of these findings, as no data on pregnancy establishment, early pregnancy loss or foaling rates is available for IVF-produced embryos in this study,” states the study, published in the January 2025 edition of scientific journal Theriogenology.

“Additionally, long-term studies on the effects of the fertilisation technique on the offspring are lacking. Nevertheless, these results mark a promising start in this novel approach.”

It concluded: “Further studies are required to assess the pregnancy potential of these embryos before IVF can be fully established as a commercial tool.

“Nonetheless, IVF in horses is a promising technique that offers valuable opportunities to study fertilisation in an in-vitro setting.”

Tullis Matson, of Stallion AI Services, told H&H this is a “huge breakthrough”.

“There is still work to be done on how viable it would be to transfer these early embryos to a mare,” he said, echoing points raised by the researchers.

Mr Matson also considered other ways in which the technique would compare to ICSI. He noted that specialised labs are required for ICSI, which makes it a costly option. Both techniques require egg removal from mares.

He also said that ICSI can lend itself to stallions with lower sperm counts or poorer quality sperm, as well as situations where semen supplies are limited – such as semen stored from stallions who are now deceased. This is because only one sperm cell is required to be injected into the egg with ICSI, whereas IVF involves combining an egg and multiple sperm in a petri dish.

“It is definitely a milestone, it’s just a question of how easy it is for this knowledge to be transferred into the industry,” he said.

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