Halocho #77 - What's special about a firstborn Kosher animal?

If a kosher animal that has never given birth - and belongs only to a Jew - gives birth to a male, the calf has Kedusha (some holiness) and needs to be given to a Cohen, even nowadays. This first-born animal may not be used for any work, and its wool may not be sheared, nor used if it fell off. In the time of the Bet Hamikdash (Temple) the animal would be brought as a sacrifice, with most of the meat being eaten by the Cohen. Nowadays the Cohen needs to keep it until it gets a permanent blemish, at which time anybody can help eat it. The Cohen may not blemish it. It's a Mitzva to sell part of all first-time pregnant kosher animals to a non-Jew so that the calf - if it's a male - will not have any Kedusha; avoiding the possibility of it not being treated properly. Source Kitzur Shulchan Aruch 177