Looking for something effective, but budget friendly
Horsetech sells a straight magnesium supplement that is very cost effective. Their customer service is great as well.
I’m really a fan of Uckele’s Seroquine. It’s cheapest at Horse.com or Stateline Tack–check both, including shipping. I’ve found it more effective that straight up mag for giving my reactive horses a moment to think before hitting mach 10.
Perfect Prep in tube or powder works well.
I use a supp called Ulc- R- Aid. Around $20 for a tub that lasts quite a while. Usually nervous ponies have nervous tummies too. It contains magnesium along with calcium, brewers yeats, etc. I give a small scoop everyday and double the dose on days of travel. I trailer regularly for lessons with a guy who hates trailering and hes done a lot better since we started.
Another supp that’s good is called Ex Stress. It contains all of the same ingredients except the calcium for stomach issues.
If magnesium is all you’re looking for, most feed stores sell magnesium oxide (“Mag-Ox”) in 30-50# bags for $20-30.
MVP 5000 is reasonably priced.
