It is always best to keep different nutritional requirement groups seperated. Yes, the cows will bully the heifers away from the feed. Cattle "like" to eat together. So, yes, the young stock will eventually get to eat (after cows are finished) - but they may not eat as long as they should because their instinct is to join the rest of the group. But, it's not a problem when they are out on grass.
Also, as manager, you can supply better quality feed to the younger stock.
It is definately more management. We keep replacement heifers seperate, and coming 2-3 year olds seperate from adult cows, and c/c pairs seperated from bred cows. This time of year, we have 6 groups of cattle. Yearlings, pregnants ready to calve, pregnants not immediately due, fall c/c pairs, 2 & 3 yr old c/c pairs, & mature c/c pairs. Sure was a bugger working all 6 groups thru the chute this past Sat. for spring work-up. Spring is coming, spring is coming, spring is coming!!!!! :banana: than all the groups will be together - except the weaned fall calves - which I'll wean in about 2 weeks.