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.
Because calcium absorption depends on an adequate level of vitamin D in your body, be sure to include vitamin D-rich foods in your diet. The RDA for calcium is 1,000 milligrams for adults through age 50. For women older than 50 and men older than age 70, the RDA for calcium is 1,200 milligrams.