At his south texas ranch near LaPryor, TX (about an hour from the border) my dad developed a herd that produced huge cattle, and enormous profit.
He started in the 80's buying 15 registered longhorns for dirt cheap prices. He bred them, along with some 10 limousin, and some pure brahma to a monster of a limousin bull. The whole of the group was bred in central texas and then when he bought the ranch in the late 80s he trucked his herd down there to "the mesquite desert" as i like to call the whole area.
Well long story short there has been 2 brangus bulls in that herd for 8 years now, and there are some of the most monstrous, bad-ass beef cattle that we truck out of that place every year or two.
We did not feed them (besides some hay in the winter, hardly though)
The herd count was probably 60-80 last summer before we started rounding them up (the problem, as they were wild as be nice, but we got it done w/o horses, dogs, or help from outside, just had to use tricks and occasionally tackle a few in the pens)
They developed down there by themselves without our intervention, and only the strongest survived, and were not skinny by any means. This method definately worked and we have never given a vaccine or shot or medice to any of our animals.
Nature knows best and always wins, so might as well listen to it.