I'm going to just give him Ivermectin because I'm pretty sure that is what was given to him last late march/early winter. My schedule is every 6-8 weeks (meaning I gave him the last one late january, now he's getting it early april). My barnowner worms his horses once a month! I think that's too much. Not sure!
6-8 weeks is took much too, or too little. After deworming with Pyrantel products, you wait 4-6 weeks. After deworming with Ivermectin, you wait 8 weeks. After deworming with Moxidectin, you wait 10-12 weeks. Those are the only three products I will use, as they are the most effective.
Here in Arkansas, we have wet summers and off-an-on freezes during the winter, so our chance for parasites never diminishes. My gelding is also more prone to worms, so I keep both horses on a tight schedule. My schedule is as follows. It works very well for me and my horses stay healthy looking all year round, with negative fecals.
Jan 1: Ivermectin + Praziquantel
Mar 1: Pyrantel, double dose (Exodus Multi Dose or TapeCare+)
Apr 15: Moxidectin
July 1: Ivermectin
Sept 1: Pyrantel, double dose (Exodus Multi Dose or TapeCare+)
Oct 1: Moxidectin