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.
Both human and animal studies show that a higher vitamin A intake interferes with bone metabolism. Specifically, excess vitamin A suppresses osteoblast (bone-building) activity, stimulates osteoclast (bone breakdown) formation, and interferes with vitamin Dâs role in calcium absorption and regulation.