Epigenetic plasticity during early development in mammals is influenced by environmental cues. This leads to the apposition of epigenetic marks that support the Developmental Origins of Health and Disease. In horses, maternal nutrition, age and parity as well as reproductive technologies have been shown to affect offspring birthweight, post-natal growth, metabolism, testicular maturation, juvenile osteoarticular pathologies and performance (Chavatte-Palmer et al. 2017; Palmer et al. 2018). These observations have prompted changes in broodmare management recommendations in order to optimise fetal programming (Robles et al. 2021). The placenta, of foetal origin, is a key organ at the interface between dam and foetus. In response to maternal environment, modifications in placental function, whether in gene expression or cellular organisation, affect materno-foetal exchanges. These changes lead to foetal adaptation that will modify offspring long-term phenotype (Robles et al. 2022). Although epigenetic mechanisms were demonstrated to underlie developmental programming in many species, it has not yet been demonstrated in horses. There is an urgent need to explore the interactions between genome, epigenome, and environment in equine species, so as to develop complementary strategies to combine with genetic selection to produce offspring with optimal phenotypic capacities. Indeed, additional epigenetic information could improve phenotype prediction obtainedfrom genotype alone, as already demonstrated in cattle for bull selection (Costes et al. 2022). In terms of age, the economic and ethical need of longevity of sport horses could also benefit of epigenetic programming strategies during development for adult health. References: Chavatte-Palmer, P., Peugnet, P., Robles, M. 2017. Developmental programming in equine species: relevance for the horse industry. Anim Front. 7:48-54 Costes, V., Chaulot-Talmon, A., Sellem, E., Perrier, J.P., Aubert-Frambourg, A., Jouneau, L., Pontlevoy, C., Hozé, C., Fritz, S., Boussaha, M., Le Danvic, C., Sanchez , M.P., Boichard, D., Schibler, L., Jammes, H., Jaffrézic, F., Kiefer, H. (2022) Predicting Male Fertility from the Sperm Methylome: Application to 120 Bulls with Hundreds of Artificial Insemination Records. Clinical Epigenetics 14:54. Palmer, E., Robles, M., Chavatte-Palmer, P., Ricard, A. (2018) Maternal Effects on Offspring Performance in Show Jumping. Journal of Equine Veterinary Science 66:108 Robles, M., Hammer, C., Staniar, B., Chavatte-Palmer, P. 2021 Nutrition in broodmares. Vet Clinics of North America: Equine Practice 37:177-205 Robles, M. Loux, S., de Mestre, A. Chavatte-Palmer, P. 2022 Environmental constraints and pathologies that modulate equine placental genes and development. Reproduction 163:R25-R38