Understanding Vitamins: Requirements, Sources, and Functions in Horses

1. Lecture 12 Vitamins

2. Vitamins • What Affects Requirements? • Age • Stage of Production • Variety of stresses including: • Gastrointestinal Infections • Intense Muscular Exercise

3. Vitamins • Need for supplemental vitamins depends on what? • Type and quality of diet • Amount of microbial vitamin synthesis in the digestive tract • Extent of vitamin absorption from the site of synthesis • Horses grazing high-quality pastures • Need little or none • Forages are a rich source of most • Fat and water-soluble vitamins

4. Fat-Soluble Vitamins • A, D, E, and K • Generally expressed in International Units (IU) • Diseases that interfere with fat absorption also • Affect these vitamins • Mineral oil may also affect undesirable losses

5. Vitamin A • β-carotene • Biologically active molecule • Important for: • Vision • Epithelial cell development • Bone remodeling in the growing horse • Highest concentrations found in: • Green forage and yellow corn

6. Vitamin A • Carotenes slowly destroyed by: • Light and heat • Therefore, sun-cured hay is lower than fresh forage • Stored hay gradually • Declines in carotene concentrations • Pasture provides tremendous more carotenes than • U.S. #1 hay • Conversion of carotene to Vitamin A occurs in • Small Intestine

7. Vitamin A • Requirements are uncertain • Good quality pasture and/or hay should • Meet requirements • Deficiencies include: • Night blindness • Hyperkeratinizationof the cornea and skin • Anorexia • Poor growth • Respiratory infections

8. Vitamin D • Two primary active compounds found in nature: • D2 (ergocalciferol) • Result of ultraviolet irradiation of ergosterol • Synthesized by plants • Only found after they have been cut and exposed to sunlight • D3 (cholecalciferol) • Result from the UV irradiation of 7-dehydrocholesterol • Synthesized by the tissues of the horse • Present in the skin

9. Vitamin D • Maintains calcium homeostasis • Requirements have not been established • Deficiencies unlikely • Supplements have shown to ↑Ca and P absorption • Excesses can cause: • Calcification of blood vessels • Bone abnormalities and soft tissue calcification

10. Vitamin E • Generic Descriptor for α-tocopherol • ~ 8 found in nature • α-tocopherol most biologically active in horse • Interrelationship with: • Selenium – glutathione peroxidase • Helps to prevent myopathies • Located primarily in the lipophilic parts of the cell: • All have high concentrations of glutathione peroxidase

11. Vitamin E • Grinding and storage of grains decreases E • Exercise may increase requirements • Difficult to determine deficiency differences between • E and Selenium • Signs of toxicity have not been produced

12. Vitamin K • Compound found in plants is • K1 or phylloquinone • Bacteria are able to synthesize in the hindgut • Ca ion and K interactions aid in blood clotting • Requirements not determined • Deficiency could lead to hemorrhage • Toxicity has not been seen

13. Water Soluble Vitamins • B vitamins, except B12 are usually • Supplied in adequate amounts in good-quality forage • Microbial synthesis of B12 can • Typically meet the nutritional needs • Synthesis of other B vitamins • Also takes place • Mare’s milk provides necessary • B vitamins to the foal

14. Thiamin • Synthesized in the S.I., cecum, and L.I. • May still require dietary thiamin • Important in metabolism • Some plants as well as • Coccidostats(amprolium) may tie up thiamin • Requirements range from 3 to 5 ppm • Deficiencies would include anorexia and loss of weight • Toxicity is unlikely • Research has indicated may create a calming effect

15. Riboflavin • Synthesis in S.I., cecum, and L.I. • Requirements ~2ppm • Invovled: • ATP synthesis • Drug metabolism • Lipid metabolism • Antioxidant defense mechanisms • No reports of deficiencies or toxicities

16. Niacin • Generic term for: • Nicotinic Acid • Nicotinamide • Thought to be synthesized by tryptophan • Also synthesized in G.I. tract • No requirements have been established • No deficiencies or toxicities have been reported

17. Pantothenic Acid • Also synthesized in G.I. tract • No dietary requirements • No deficiencies or excesses have been reported

18. Vitamin B6 • Generic term for: • Pyridoxine • Pyridoxal • Pyridoxamine • Synthesized in the G.I. tract • No dietary requirements • No deficiencies or excesses reported

19. Biotin • Synthesized in G. I. Tract • No dietary requirements • Reports of improved hoof health • When fed 10 to 30 mg/d • Deficiencies may lead to • Poor hooves • No excess levels reported

20. Folacin • Generic term for Folic Acid • Synthesized in G.I. tract • Deficiencies and excesses have not described

21. B 12 • Cyanocobalamin • Synthesis with presence of • Cobalt by microflora • Deficiency has not been described

22. Ascorbic Acid • Also known as • Vitamin C • Thought to be synthesized from glucose • In the body of the horse • No reports of deficiencies or excesses