If a cow is over 8 months gestation, you can easily induce labour by using two injections together. Dexamethasone and PgF2alpha (I use estrumate) will cause calving in 40 hours according to the book. I find they calve in 30 hours in my experience. Ask your vet.
Side effects include retained placenta, insufficient colostrum if too early...
Good Luck
V