I would treat the thyroid first. If only the T4 was checked and that's low, I bet his free T3 and free T4 is out of wack and the total T4 can no longer compensate.
I would immediately run a full panel on the thyroid. Thyroid aggression and behaviour problems associated with the thyroid often occurs when the thyroid is low-normal, not necessarily low.
You can always experiment for yourself by adding some kelp and seeing what that does, though if there is an autoimmune component it will make it worse, and you'll have to wait longer to retest the thyroid.
Any recent rabies vaccines? They can trigger autoimmune thyroid problems.
I would immediately run a full panel on the thyroid. Thyroid aggression and behaviour problems associated with the thyroid often occurs when the thyroid is low-normal, not necessarily low.
You can always experiment for yourself by adding some kelp and seeing what that does, though if there is an autoimmune component it will make it worse, and you'll have to wait longer to retest the thyroid.
Any recent rabies vaccines? They can trigger autoimmune thyroid problems.