Seems my opinion isn't wanted here...so be it.
But don't you wonder why you have problems when you bring in new cattle?
You see FH, I had the same problems you did when I started...I purchased registered cattle...put them in the same herd, same pasture as my father-in-law's commercial cattle. His cattle bred at close to 100%...mine 60%. His calves dominated the top end of the calves each year...I had many of the same problems you did with my calves. We dewormed twice a year, vaccinated everything, used insecticides...fed loose mineral years round, hay in the winter or when needed, supplemented with range meal or licks, and even did some pasture rotation. I finally got tired of dealing with all the problems I had and started culling everything I had to help to do their job. I changed my genetic source to someone that ran their registered operation like commercial cattle...selling everything that didn't wean a good calf every year. I credit those genetics for fixing my herd and the fact that I have run a closed herd since 2001. It has made me a believer in what Jim Lents has said...when you bring in outside genetics, you reshuffle your genetic deck.
Don't be fooled into believing that minerals will solve all your problem.
Y'all have a good day.