got a question for you cattlemen out there...

I work on a ranch that my dad operates we have right around 1000 head of 100% santa gertrudis cattle. I HATE THE SOB"S!! these cattle are fairly easy going in the pasture but as soon as you get them in a pen you have to watch your back at all times. they get plum crazy especially if they have a calf on the ground. hat being said if your gonna run them anyway i would say take the S.G. bull and charlais cows. our bulls seem to be alot more gentle wich we also spend more time around them also cause we pull them off the cows for 3 months of the year.
S.G. bulls do put out smaller calves at birth. that is one good thing with young heifers.
Your plan with selling the older heifers and keeping the calves from year to year is not gonna work so well money wise. it takes a heifer roughly 18-22 months to become mature enough to breed. therefor your looking at around 29-34 months between calving sessions. and also as stated previously heifers are a pain to get started calving especially if they are still not matured enough.
i would suggest starting out with some seasoned cows and a 2-3 year old bull. let the older cows breed and calve maybe keep a few heifer calves this year and breed your old cows again sale your calves that you dont keep save a few from the next calve crop breed cows and the heifers from the year befor and then maybe et rid of some older cows as you bring in the younger heifers. just repeat that year by year.
thats just how we run our operation here and this ranch went from 25 head to around 1000 were we have kept it for around 10 years. hope this helps