Our calves get whole milk, but we wean them at 30 days, been doing it that way for 20+ years. IMO if the calf gets a good dose of high quality colostrum right away you'll have 90+% of your calf problems licked.

We used to blood test cows for Johne's, now DHI offers milk testing so that's what we've been doing the last couple years. Milk testing doesn't work very well with a bull, I've been told(smirk).

I've heard the theories about SCC being 'too low' but I think the immune system is always ready. The cleanliness that gets you to a low SCC will also keep you from having too many immune challenges, so IMO it's all good.