I realized one of my retired mares (18) was not placed on CS when I selected her barn in the Vet's Office. When I searched for her in the drop-down of individual mares, she didn't come up. I did implant one of her embryos before trying to place her on CS, though, so that might be why. That's the only reason I can currently think of as to why she isn't eligible for it this month.

https://horseeden.com/horse.php?id=39820802

Once a mare is a senior, she no longer has her cycle because she's unable to have foals. So I would assume there's no cycle to suppress :)

I've been able to place other senior mares on cycle suppressant before, including mares that I've created embryos with for their final breeding season, like this mare