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 A is best absorbed when taken with oil or fat. It occurs in animal tissues as retinol but in plants as carotene, a precursor of vitamin A. Vitamin D works synergistically with vitamin A. It plays a role in absorbing and regulating calcium and phosphorus. This vitamin helps the body synthesize protein.