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 promotes calcium absorption, and it is needed for bone growth. It also has a positive role in the function of the immune system and reduces inflammation. Women aged 19 to 70, pregnant or nursing are required to get 600 international units, or 15 micrograms, of vitamin D. After age 70, the RDA for vitamin D is 800 IU, or 20 micrograms.