I do not know about foals and the "gold" ivermectin, zimectrin and equimax (all the same active ingredients but in different concentrates).
For my weanlings-18mos old, I deworm with ivermectin every month. For my adults, I deworm with ivermectin every 6-8weeks. In the spring, I deworm with a "gold" product.
If I had sucklings to deworm, I'd just call the vet and ask if the gold is okay, or should I use Safeguard / Strongid, etc.