This question came as an email:

Hi, Doughertys! A question:

One of our girls is lactating but only 2 of her quarters are fully functioning (which is fine with us for our purposes). One of the non-functioning quarters does produce milk, but the teat has a scar tissue buildup internally from some old injury or infection that makes effective milking impossible. Is it best to just leave that one alone and let it dry up on its own while I milk the other two? Will that cause mastitis? That was the vet’s recommendation and I was just curious what your thoughts are.

We would just leave that quarter alone.  The milk ducts still work, but you can’t get the milk out, so you want it to dry off. If you don’t use it, it won’t lactate (much); eventually it will stop making milk.  Yes, the quarter will probably get mastitic for a while, and yes, there is a small chance the mastitis could spread, even that the cow could get sick, but only a small chance. We’ve never had a blind quarter cause problems.