Reciprocal knowledge could be gained through the comparative study of artificial reproduction techniques and infertility treatments in women and mares, according to the authors of a just-published review.
Artificial reproduction techniques are used widely in human medicine to overcome infertility, with about one in seven couples having fertility concerns in the Western world.
Due to ethical concerns, animal models are needed to develop new methods. While laboratory animals have been important in this context, they have a short lifespan and are usually fertile.
In contrast, horses are long-lived domestic animals that, because of their high economic and sentimental value to humans, are often bred until old age, often after a career in equestrian activities, Achraf Benammar and his fellow researchers noted in their paper published in the journal Animals.
There has also been considerable investment in developing state-of-the-art artificial reproduction techniques for mares to overcome infertility and to increase foal production.
In their review, Benammar and his colleagues set out to examine the similarities and differences in the reproductive cycle, artificial reproduction techniques, and fertility concerns in women and mares, and assess the opportunity for using the mare as an appropriate model to assist in humans.
The team, which cited 278 studies in their paper, noted that the reproductive functions of mares become altered after 20 years, in a similar way to humans, although there is no menopause per se in horses.
The review team acknowledged that although there are large differences between horses and humans in terms of reproductive anatomy and physiology, there are important similarities in follicular dynamics, mono-ovulation, and embryo development kinetics until the blastocyst stage (a blastocyst is a tiny hollow ball of cells that develops from a fertilized egg.).
However, in contrast to humans, horses are seasonal animals and do not have a menstrual cycle. Moreover, horse implantation takes place 30 days later than in humans.
In terms of artificial reproduction techniques, oocytes (immature eggs) from mares are generally matured in a laboratory setting because ovarian stimulation remains inefficient. This allows the collection of oocytes without hormonal treatments. In humans, matured oocytes are collected from women after ovarian stimulation.
Subsequently, only intra-cytoplasmic sperm injection (ICSI) is performed in horses to produce embryos, whereas both in vitro fertilization and ICSI are applied in humans.
Embryos are transferred only as blastocysts in horses. In contrast, four cells to blastocyst stage embryos are transferred in humans.
The review team noted that embryo and oocyte cryopreservation has been mastered in humans, but not completely in horses.
Despite the differences, the horse may be an excellent model, they said, offering possibilities not enabled by other models to study artificial reproduction techniques for humans.
“Its large size also enables repeated sampling that is not allowed by smaller models,” they said.
“Alternatively, the human may be also a very valuable source of inspiration for scientists and veterinarians working with horses.”
Both species share infertility concerns arising from ageing and obesity, they noted.
“Some techniques have been mastered in humans but not in horses, such as superovulation, as well as embryo and oocyte cryopreservation, whereas others are more advanced in horses, such as in-vitro oocyte maturation (IVM).”
Thus, reciprocal knowledge could be gained through the comparative study of artificial reproduction techniques and infertility treatments both in women and mares, even though the horse could not be used as a single model for human technologies, they said.
The review team comprised Benammar, Emilie Derisoud, François Vialard, Eric Palmer, Jean Marc Ayoubi, Marine Poulain and Pascale Chavatte-Palmer, variously affiliated with a range of French institutions, including the University of Paris-Saclay; the Alfort National Veterinary School; the Department of Gynaecology and Obstetrics at Foch Hospital; and the French Academy of Agriculture.
Benammar, A.; Derisoud, E.; Vialard, F.; Palmer, E.; Ayoubi, J.M.; Poulain, M.; Chavatte-Palmer, P. The Mare: A Pertinent Model for Human Assisted Reproductive Technologies? Animals 2021, 11, 2304. https://doi.org/10.3390/ani11082304