Reshit HaGez is a postive mitzvah to give the first shearing of the sheep’s wool to the kohen.  Although uncommon, some chassidim go ahead and do this mitzvah outside of eretz yisroel.

The mitzvah is written is sefer Dvarim;

 ראשית דגנך תירשך ויצהרך וראשית גז צאנך תתן לו

Dvarim

Chazal explains that the mitzvah applies only to sheep (and not goats), whether male or female.  The first shearing is the one given to the kohen and a sixtieth is to be given -which is enough to make at least a small garment.

Arba’ah turim writes that the mitzvah does apply outside the land of Israel (Yoreh Deah, ch. 333), but the majority didn’t keep up a minhag to implement it.

In Israel

Ever see the mitzvah happen? check it out;

[youtube=http://www.youtube.com/watch?v=pdrhZNUGu44&rel=0]