Page 77 - Speedhorse June 2019

Green grass is an excellent source of carotene, which is converted to vitamin A in the intestinal wall. The greener the color, the more carotenes.
proteins and then can be distributed through- out the body.
“Some vitamin A is recycled in the body and some is used up, so there always needs to be some vitamin A in the diet to replace what is used.”
THE ROLE OF THE LIVER
The liver stores extra vitamin A and dispenses it as needed in the body, thus regulating the amount that you find in the bloodstream. “There can be a high buildup
of vitamin A in the liver, but you can’t take a blood sample and be able to see the levels in the liver because it is controlling the amount of vitamin A released into the bloodstream.
It is limited by the amount of retinol-binding protein in the liver to carry it out of the liver through the bloodstream to the cells that need it,” says Crandell. Not until there’s a huge amount of vitamin A would you see toxicity. Most symptoms of toxicity stem from liver damage – when the liver isn’t able to function properly to regulate the amount of vitamin A circulating in the body.
FUNCTIONS OF VITAMIN A IN THE BODY
One of the many important roles played by vitamin A is to help facilitate vision. This is obvious from the term used for vitamin
A once it is in the body; it becomes retinol. The retina is one of the major structures of the eye. “Vitamin A is crucial to the whole function of the eye as it receives light, and is thus very important in vision,”
says Crandell.
“Vitamin A is also important to health of epithelium cells, which includes skin, the
lining of the intestinal tract, lungs, reproduc- tive tract, and the eye.”
Since vitamin A affects so many things, deficiency (or extreme excess) of this vitamin can have serious repercussions, and the effects are similar. “The skin doesn’t have normal turnover of skin cells, so there is thickening of the skin,” she says. “There will also be thick- ening of the intestinal wall, which interferes with absorption of nutrients.
“Vitamin A is important for immune function. It helps with the differentiation of various immune cells and production of lym- phocytes and macrophages (blood cells that combat pathogens in the body). Carotene also helps with immune function, but in a little different way. Vitamin A also helps inhibit the growth of tumors.
“It is also important for growth and for remodeling of bones. Vitamin A helps control the two types of bone cells: osteoblasts, which are the bone cells that are growing; and osteoclasts, which are the bone cells that break down,” says Crandell. “There must always
be some bone cell turnover to have healthy growth of bones. If there is not enough vita- min A, or an excessive amount of vitamin A, the osteoclasts don’t work properly and this results in thickening of the bone – but not in a healthy way like increasing bone density. The bone just becomes shorter and thicker.
“Vitamin A also helps with degradation of aminoglycans and synthesis of proteo- glycans, which affect cartilage. For healthy cartilage, a young, growing horse needs adequate vitamin A.
“This vitamin also affects growth hormone regulation, which is also important for the
Vitamin A is important to the health of epithelium cells, which includes skin. Vitamin A deficiency
– or an extreme abundance – can have serious repercussions, such as a thickening of the skin that can interfere with the absorption of nutrients.
Once in the body, vitamin A becomes retinol which helps facilitate vision and is crucial to the function of the eye as it receives light.
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EQUINE HEALTH