We are also in a badly deficient area. We give our cows Mu-Se 30 days prior to calving, and we also give it during the second trimester. Our calves also get Bo-Se at birth.
I forgot to mention, if you use one of his offspring, be sure that he is tested PHA negative, and all club calf bulls should be tested for TH, also. You don't want to pass on these genes
50% of his calves will carry PHA. If your intend to use his offspring for breeding stock, you will have to have a DNA test done on each calf. PHA is a very ugly genetic defect. You will lose the calf and you could lose the cow.