Usually a painkiller injection is done during or right after the OP
. I know at school that for females we did one more injection 4 hours after waking up but that was horrible : they were usually still a bit under ketamine influence and completly mad at us
, we had to fight to give that injection and I'm not sure they wouldn't have been better left alone... (now when working you don't do that, but also you don't spend half an hour looking for the ovaries and moving organs this way and that !
).
Anyway we only did one injection for males, even at school
, and no worries ^^ (it was morphine at school and now we usually give AINS like tolfenamic acid but the effect is still ok
).
Painkillers are only given later as tablets when the animal has undergone a really painful OP (bone surgery for eg.). That's also when we give morphine during the OP...