Kerry find out more about the strong drench!
I know we had a woman on this forum that had her cattle drenched for 'Qld cattle tick' and the withholding for milking cows was the life of the animal. Who would have even considered something like that, I didn't until her.
The person she bought off considering them beef cattle that from memory only had a withholding of 40 something days but she was milking and giving to her little children, it was a real eye opener when we read up on that drench. Read everything and if anyone gives you something get the name, and google it.
We were using anipro (cattle supplement) last winter/spring and they're changed that by adding a new additive that is falvo (or something similar they call it), it's good for your cattle and they grow quickly blah blah... I read up and it's antibiotic, but nowhere do they call it that, it's off our list for the future now.
If you intend to milk or eat livestock always look thoroughly into what you put in them, because ultimately it goes into you.