Bercy is a prehistoric village sited by the Seine river (Paris, France), whose main period of occupation was dated to the very beginning of the 4th millennium BC. The animal subsistence economy relied heavily on cattle husbandry, complemented by other species including sheep. Cattle and sheep isotopic history (δ¹³C, δ¹⁸O) was investigated at the seasonal scale, through sequential sampling in tooth enamel, providing new insights into seasonality of birth and diet. Sheep were lambing in mid-spring, only slightly later than expected from what is observed nowadays in temperate Europe at similar latitude. Cattle were born over a period spanning approximately six months, which was an unexpected result compared with a two to three months calving period in free-ranging cattle populations. The extension of the calving period might have been related to seasonal food supplementation. Some cattle and some sheep fed on a ¹³C-depleted resource in winter, potentially leafy fodder. A direct consequence of an extended calving period would be the availability of cow milk, which would have covered the whole year at Bercy. This is important information in a context where the exploitation of cattle milk by the human community was highly suspected from the demographic management of the herd.