The horse, as a domestic animal, had a strong impact on the organisation of ancient societies of the eastern steppes of Eurasia by enabling people to move faster and transport goods and people more efficiently. This newfound mobility was accompanied by profound changes in the expression of ritual practices, and horses are repeatedly found in funerary monuments of the Late Bronze Age in Mongolia. While recent advances in research have highlighted the link between the presence of horses in ritual monuments and their role in the pastoralist diet, little is yet known about their practical contexts – including the season in which the animals were slaughtered and the time of year when the funerary and ritual sites were visited. In modern Mongolia, horse meat is consumed during winter, but the antiquity of this practice is currently undocumented. Here, we use stable oxygen isotope variations (δ18O) recorded by developing molars of horses to estimate the season of slaughter of two horses deposited at the Late Bronze Age khirgisuur of Burgast (Bayan-Ölgii province, western Mongolia). The analysis of a modern reference set consisting of five horses from the same locality shows that it is possible to date the time of death with a resolution of the order of the season. Isotopic analysis of the two ancient horses suggests that they were slaughtered in early (November) and late (February) winter. Zooarchaeological evidence reveals that while the first horse was deposited shortly after death, the second was deposited several months after death, following open-air exposure. These preliminary results provide an important landmark to document the multi-dimensional aspects (economic, social, as well as cultural) of the role of horses in the ritual practices of Bronze Age Mongolia. They indicate that the timing of horse deposition is more complex than previously thought. They also demonstrate that winter slaughtering of horses dates back to the Late Bronze Age and was probably constrained by a combination of economic and practical decisions regarding meat preservation. © 2020 Elsevier Ltd