One of the best-known roles of vitamin D3 is its function in calcium and phosphorus absorption.  These two minerals are essential for bone growth, so it naturally follows that vitamin D is key to skeletal health.

However, vitamin D3 is also necessary for proper hormone function.  In this role, it helps regulate immune response, insulin secretion, and blood calcium levels.

Two other important functions of vitamin D are carbohydrate metabolism and gene expression, which translates into embryonic growth.

The most common use of supplemental vitamin D3 in livestock is to prevent rickets and other bone deformities.  Recent research, however, suggests that this vitamin also has great potential as a substitute for or complement to antibiotics.  It can help animals combat a wide array of both bacterial and viral diseases, most notably mastitis.  Careful supplementation may also prolong the lives of dogs with congestive heart failure.

Two other interesting uses of vitamin D3 are enhancing reproductive performance and increasing meat tenderness when fed before slaughter.