The Slavonic god of farm animals is called Vlas or Volos and is definitely lurking behind the guise of St Vlasios. In Slavic areas, it is traditional to eat goat or mutton (from animals slaughtered in front of the church) and wheat cooked in butter and honey. In Aetolia, women are not supposed to carry firewood and Vlasios Cattlestrangler will drown any beasts of burden that are carrying loads on this day.
Celebration of Ivan Kupala has three important points. On this day, "bury" the spring - Yarilо - and meet the summer - Dazhdbog. Yarilo, in accordance with the Slavic tradition, burn. What is being built a big fire.