The seizures may have been caused by dehydration or shock from being frightened by a predator. Restoring his glucose and electrolyte balances, he may recover quickly with no ill after effects.
If you determine the rooster has indeed ingested a toxin such as mold or coffee grounds, a flush would be a good idea. It will stimulate in a gentle way, diarrhea to clean out his digestive system. You can do it using Epsom salt solution or a molasses flush. Select one.
For the Epsom salt flush, mix a teaspoon of Epsom salt in a cup of water to dissolve it. Let the rooster drink as much as he will in lieu of his regular water.
If you choose to do the molasses flush, dissolve one teaspoon of molasses in a fourth of a cup of warm water and try to get him to drink it all.
There is a chance that the seizures are being triggered by tumors or a cardio issue. I'm afraid there is no help for that, and if this is the cause, your roo may soon die.
