The holiday of Predoi is typical for southern Bulgaria (Rhodope and Pirin mountains). It has managed to survive since pagan times, although it is usually timed to coincide with the feast of Saints Constantine and Helena. Therefore, it is celebrated by both Christians and Pomaks (Bulgarians who forcibly converted to Islam during the Turkish yoke). There is an assumption that this is an ancient Thracian holiday, but there is also a version that the Slavs brought the holiday with them, who came to the Balkans in the 5th-6th century.
In many ways, today's holiday is similar to Gergovden (St. George's Day), since the cult is centered on sheep and milk. The emphasis, however, is now somewhat shifted - on this day a real competition in milk yield is held.
The holiday usually begins at a cheese factory or at sheep pens far from the villages, where the shepherds went out with their flocks in early May. Already in the morning there begins a ritual milk yield. Usually each owner himself is engaged in this difficult work, passing the most thoroughbred white sheep first. This first increased milk yield of the year, as a rule, also gives the first true idea of the general condition of the herd.