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 is essential to the proper absorption of calcium. Vitamin D allows calcium to pass from your gut into your bloodstream so that your body has access to the mineral. Without sufficient vitamin D, your body cannot absorb calcium, regardless of how much you consume. You can increase the amount of vitamin D in your body by taking in more vitamin D-rich foods, such as salmon, mackerel, sardines, fortified milk, egg yolks, enriched cereals and fortified orange juice.