It depends . Have you already established that your horse is deficient in magnesium and this is what's causing the spooky behaviour, or are you wanting to rule it out using the Pro Hoof?
If using straight MgO to rule out Mg deficiency, I'd feed 25g which would provide about 12.5g of Mg. Pro Hoof provides 6g of Mg, so I'd be looking to feed an extra 12g of MgO to provide an extra 6g of Mg - if you decide you want to add more.
yep currently on magnesium, all spooky behaviour and nonsense stopped once established on it.
i know i cant overdose him.on magnesium but i dont want to waste my money buying it if i dont need to.
pro hoof will be fed as a supplement for his hooves and my mare too...its funny shes the same with or without magnesium but the young ones like a different horse!