Newgrange, the Neolithic monument and centerpiece of the Brú na Bóinne UNESCO World Heritage complex, is a high-profile example of prehistoric societies’ observation of, and reverence for, solar events. Comparatively little is known about how these concepts were remembered by those using Newgrange over subsequent millennia. While excavations have uncovered large quantities of later material culture, debate continues about what these subsequent activities represent. We combine zooarchaeological, radiocarbon, and isotopic evidence to assess the nature and seasonality of human–animal–environment relationships at Newgrange. Results show a concentration of feasting activity, focused on pigs, dating to 2600–2450 BC and indicate that most pigs were slaughtered shortly after a period of rapid, pannage-fueled weight gain. This seasonal specificity indicates feasting likely occurred in the weeks around the winter solstice and suggests that, centuries after passage tomb construction ended, practices at Newgrange continued to focus on the general winter solstice timeframe. We also connect a unique isotopic signature for mast (tree nuts) with pannage husbandry, a pattern that should allow for reinterpretation of archaeological pig diets and human–woodland relationships across Europe.