PLEASE do not use Fenbendazole (Panacur Safeguard et al) as a single dose wormer except in the first case with a ten day old foal.
I worm first at ten days with Fenbendazole (all brands are the same it is the CHEMICAL that counts)
Then at a month with Ivermectin and for the next three months with |Ivermectin.
At weaning I do the five day course of Fenbendazole.
A also, now, Tapeworm at this time just to be sure.
Then they go on the normal schedule and, since there is no known resistance to Ivermectin and hence no reason to "rotate" chemicals, they stay on this every two months with the exception of:-
Autumn.
Five day Fenbendazole followed by Ivermectin ten days after the last dose coupled with Praziquantel for Tapes.
Spring- the same as Autumn- the actual time of tape worming and five day course differs with the area you live in so I do not give a specific month for this- consult a local land agent, your Vet may well not know.
Rotating wormers at random may well help build up a worm burden.
Latest research shows an alarming resistance due to daily wormers.