In Parshas Mishpatim, one of the laws we learned was one of the three instances where it says “Lo Tevashel G’di BaChalev Imo,” Don’t cook a kid (young lamb) in its’ mother’s milk. Classically, the first teaches that we may not cook meat with milk, even if we do not intend to eat it. In this, people are sometimes not careful. The second teaches that we may not eat meat with milk. The third shows that we may not derive any benefit out of meat cooked together with milk – it may not even be given to one’s dog. (Hullin 115a)
Some insight into this decree has been shed and here is a Kabbalistic perspective: milk symbolizes life and meat symbolizes death, and combining the two creates a spiritual clash in the celestial realms both of your soul and in the worlds beyond us. Without delving into this, since it’s Kabbala, all we need to know is that that’s bad news.
Rabbi Yaakov Tzvi Mecklenburg ZT”L once explained a Chiddush that explains how this pertains to all meat, not just a kid. In “Lo Tevashel G’di BaChalev Imo,” “Gdi,” kid, can be explained in the Lashon of Meged, which means all delicacies, i.e. meat. Imo, “it’s mother,” can also be read as “Umo,” it’s species, after “Am,” nation. Therefore, it should rather be read as “don’t cook meat it with milk of any of it’s species.”