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.
Your body has no way to create vitamin molecules itself, so the vitamin molecules must come in through food that you eat. The human body is known to need at least 13 different vitamins: Inside the body, vitamins are used in many unique ways. For example, one of vitamin A's main roles is in the production of retinal. Retinal is used within the rods and cones in your eyes to sense light. There is no way for your body to produce retinal without vitamin A, and without retinal you cannot see.