There are three designated dates for the maaser of animals: fifteen days before Pesach, fifteen days before Shavuos, [and] fifteen days before Succos; these are the words of R’ Akiva. Ben Azzai says: [The three periods are] on the twenty-ninth of Adar, on the first of Sivan, on the twenty-ninth of Av. R’ Eliezer and R’ Shimon say: [The three periods are] the first of Nissan, the first of Sivan, and the twenty-ninth of Elul. Why did they say the twenty-ninth [of Elul], instead of saying the first of Tishrei? Because it is a holiday and it is impossible to separate maaser on a holiday; they therefore advanced it to the twenty-ninth of Elul. R’ Meir says: The first of Elul is the beginning of the year for the maaser of animals. Ben Azzai says: Those born in Elul are tithed by themselves.