I used to supplement magnesium and recently stopped because I started my gelding on TC Gold Balancer and it has a good amount of magnesium in it. But I have a bag of unopened Uckele MagOx that I’ll use if I feel like he ever needs it again. I can’t remember what it cost, but it’s the powdered version and I think it’ll last me close to a year.
I started my guy on B1 a few months ago more for muscle relaxation and recovery (to see if it made any difference), and I think he’s been more chill and less reactive. I use the Horse Health brand (in the purple bucket with the race horse picture on the front). He only gets an ounce a day (500mg of B1). I get the smaller bucket because my storage space is limited, but they make a 20-lb. bucket that at 1 ounce would last 320 days. Less than $100 for that size.
I used to feed SmartCalm Ultra a few years ago, and it worked well too. 10g mag, I can’t remember how much B1, and some tryptophan as well. They have a 30-lb bag for around $270 that says it’s a 224-day supply.