The lead cow takes everyone to the best hay or grazing. If you sell the lead cow another cow will take her place and do exactly the same thing. The lead cow only loses credibility if she tells the herd you are coming with feed and it turns out you are not. Credibility doesn't mean a lot to cows and forgiveness comes easily. Mother cow will scold her calf when she returns, if the calf has moved.
Time is probably better spent worrying about stray dogs and hogs when it comes to baby calves.
Lead cows like to make you think the whole herd is hungry. A baby hawk on the ground in the pasture can stir the deepest and most fearful emotions in a herd. The herd not understanding the beast in distress, will gather around and stomp and bellow the poor beast into the ground. Cattle work that involves a flow of blood should be saved until all other herd work is done. Cattle react very similar to elephants and get very upset and confused at the smell of blood from the injury of a fellow herd member.