Sometimes you have a problem and don't know it - toxo and EA (Chlamydia) are the two most common causes of abortion is sheep, but they also cause embryo loss and week lambs.
It's lifetime protection not an annual vaccination. We do ours every second year - so gimmers and ewe lambs one year, nothing the next. Helps use up the bottle; we also coordinate with another local sheepkeeper to spread the cost.
Toxovax and Enzovax. Live vaccines so need to be given aboutfour weeks before you put in the tup as they will cause abortion in pregnant sheep (obviously).