Abstract
Simple SummaryArtificial reproduction techniques (ART) are used widely in human medicine to overcome infertility, with about one in seven couples being concerned in the Western world. Due to ethical concerns, animal models are needed to develop new methodologies. Although laboratory animals are seminal in this context, they have a short lifespan and are usually fertile. Horses are long-lived domestic animals that are bred until old age, often after they have had a career being used for equestrian activities. Their reproductive functions become altered after 20 years, in a similar way to humans, although there is no menopause per se in horses. There is also a concern for rising overweight and obesity concerns in these species. In addition, embryo transfer and ART are developed to overcome infertility, as for humans. This review details similarities and differences in the reproductive cycle, ART, and fertility concerns in women and mares and discusses the opportunity of using the horse as an appropriate model for ART in humans.Although there are large differences between horses and humans for reproductive anatomy, follicular dynamics, mono-ovulation, and embryo development kinetics until the blastocyst stage are similar. In contrast to humans, however, 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 (ART), oocytes are generally matured in vitro in horses because ovarian stimulation remains inefficient. This allows the collection of oocytes without hormonal treatments. In humans, in vivo matured oocytes are collected 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. Embryo and oocyte cryopreservation has been mastered in humans, but not completely in horses. Finally, both species share infertility concerns due to ageing and obesity. Thus, reciprocal knowledge could be gained through the comparative study of ART and infertility treatments both in woman and mare, even though the horse could not be used as a single model for human ART.
Highlights
Animal breeding has been performed by humans since prehistoric times
The aim of this review is to evaluate the horse as a model to study human reproduction and to improve artificial reproduction techniques (ART) considering that (1) selection is not based on reproduction capacity [3,11], (2) infertility seems to impact a large number of stallions and elderly
The expression of 48 genes was analyzed in cumulus–oocyte complexes according to maternal age and showed an age-related differential expression associated with lower quality and reduced developmental competency in oocytes from old mares [204]
Summary
Animal breeding has been performed by humans since prehistoric times. Selective breeding really started in the early 18th century in the UK with Sir Robert Bakewell, who developed objective selection through accurate recording of animal performance and progeny testing [1]. In most selection processes, aged and infertile animals are not considered With these selection objectives, in cattle, assisted reproductive technologies (ART) are used commonly to produce embryos, with an increasing number of embryos produced in vitro each year worldwide (>106 in 2019) whereas the number of in vivo derived embryos declines steadily (around 4 × 105 in 2019) [2], with younger animals, even prepubertal, being used to speed up genetic progress in combination with genomic selection. Many male horses are gelded at an early age (often 2 years) for management, so that only highly valued animals are kept for breeding Both males and females may be used for reproduction until they become elderly. The aim of this review is to evaluate the horse as a model to study human reproduction and to improve ART considering that (1) selection is not based on reproduction capacity [3,11], (2) infertility seems to impact a large number of stallions and elderly. Comparative Anatomical, Physiological and Pathological Aspects of Reproduction in Mares and Women
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