Ok-so I've been riding for 40 years, and teaching and training for 20. I have always based a horses' jump on his athletic abilities, scopiness, etc. I've seen the solid, 2'6 packers that can stretch to 3' but are better suited to the 2'6 job.
Bioactive vitamin D or calcitriol is a steroid hormone that has long been known for its important role in regulating body levels of calcium and phosphorus, and in mineralization of bone.
Vitamin D plays a key role in absorbing calcium, especially in the context of keeping bones healthy. Vitamin D is made in the skin and then travels through the blood to the liver and then the kidneys. In the liver and kidneys, vitamin D is converted to its active form, often known as 1,25 vitamin D, that then sets off the production of compounds needed to absorb calcium in the intestine. It also acts on bones to make sure they are properly maintained.