Q. What is the reason for eating a meal of milk sources on Lag Baomer?
A. The reason given by our Sages is that during Sefira days, before the completion of the seven weeks, the Jewish Nation is considered to be still in a state of tumah or impurity similar to a nidda, (menstruating woman) seeking purification. The final tahara is to be achieved at the time of receiving the Torah on Shavuos.
Since the dam (blood) of a nidda is related by our Sages and by medical science experts to the human milk production, the process is alluded in the eating of milchig food on the day we receive our Holy Torah.
Horav Shlomo Miller’s Shlit’a opinion is that each person should maintain the traditions and minhogim of his family and community.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a