Science can be very dry and digging into the detail of trials and experiments can be time consuming and taxing. So it is great to find a relatively easy to read review paper. We have highlighted the key bits that support our views that:

• Typical horse diets almost always have enough magnesium
  
  
• Getting a horse into a magnesium deficient state is actually really hard
  
  
• Absorption of magnesium is not affected by the Calcium : Magnesium ratio
  
  
• Artificial magnesium sources have a different impact than natural sources (described as organic in this paper)
  
  
• The more magnesium you feed the more builds up all over the body
  
  
• The homeostatic control system for magnesium is weak
  
  
• Drawing conclusions about horses from human studies is potentially very misleading

Here is the paper "Magnesium disorders in horses" Allison J Stewart. Vet Clin Equine 27 (2011) 149–163