Vitamins

Expressed in:

International Units (IU); different “strengths” of different forms of vitamins

Origin of vitamins

 Feeds

 Supplements

 Tissue synthesis - vitamin D

 Microbial synthesis in hindgut - Vitamin K

Considerations

 Essential vs. non-essential needs

- Pro-vitamins (ß-carotene) vs Active vitamins (Retinol)

 Stability

 Storage in feeds; Storage in tissues

Best expressed as a function of

metabolic BW kg instead of whole BW kg

Fat-Soluble Vitamins

• Properties:

- essential for vision, immunity, bone health, and acting as antioxidants

- don’t require daily consumption

- require dietary fat for absorption

• Site of absorption - small intestine

• Can be toxic - yes, stored in liver and fatty tissues (accumulating in excess)

Vitamin A

• Functions: vision, night vision, cell differentiation; immunity, reproduction

• Forms: Retinol; β-carotene (G.I. tract)

Vitamin A REQ:

• 30 iu/kg BW for maintenance

• 45 iu/kg for growth and exercising

• 60 iu/kg BW for broodmares

Vitamin A Source:

High quality forage; fresh, green is best! Concentrates fortified with Vit A

 There are seasonal variations as well as storage

losses from forages

 Horses are very efficient as storing Vit A

Vitamin A Deficiency

 Reduced feed intake, diarrhea, slow growth, poor fertility, dull hair, anemia, night blindness, tearing

 What minimum req. is based on

Vitamin A Toxicity

Same as deficiencies; brittle bones, DOD in young horses

Vitamin D

• Function: Ca Absorption, Ca & P reabsorption and Bone Integrity

• Forms: Cholecaciferol (D3) Skin-UV rays, Ergocalciferol (D2) dried leaves

• Active form: 1,25(OH)2 D3 or Calcitriol

Vitamin D REQ:

• 6.6 iu/kg BW: all mature horses

• 22 iu/kg BW: foals-yearlings

• 13 iu/kg BW: growing horses

Vitamin D Source:

High quality forages (legumes); sun-cured best!

• Horses are not likely to need supplementation if exposed to sunlight or fed high quality forages; horse can make active form of Vitamin D in body (cholecalciferol-D3)

Vitamin D Deficiency

• Rickets?

• Ponies deprived of daylight (study duration = 5 mo )

- Reduction in bone mineral density

- Difficulty standing

Vitamin D Toxicity:

• Most common of vitamin toxicoses (Cumulative toxicity…not overnight effect!)

• Overdosing, consumption of specific plants (….WILD JASMINE)

• Calcification of heart, blood vessels, other soft tissues

Vitamin E

Functions: Immunity, Anti-oxidant

• Oxidation of phospholipids

• Functions with selenium

• Role with Vitamin C - crucial antioxidants to combat oxidative stress, protect cell membranes, and boost immune function

Forms: α-topcopherol

Vitamin E REQ:

1.0 iu/kg BW: mature horses

• Fat-added diets will have added α-topcopherol

Vitamin E Source:

Good quality forages - FRESH is best! Concentrates if supplemented.

• Hay only diet=likely need to supplement. What group of horses might be on a hay-only diet? - easy keepers, ones with metabolic disorders

Vitamin E Deficiency symptoms

Nutritional Muscular dystrophy “white muscle”

• Can occur in young and adult horses

Other diseases related to decreased vitamin E status

Equine Motor Neuron Disease (EMND) 2 yr olds and older; quick onset

• Muscle wasting

• Recumbency

• Trembling

• Seen following a prolonged period of Vitamin E deficiency

Vitamin K

Functions: co-factor for Gla-proteins; blood clotting, bone formation, circulatory system

Forms: Phylloquinones (Vit K1), Menaquinones (Vit K2)

Vitamin K REQ:

no dietary requirement known

Vitamin K Source:

Plants/Hindgut microbes

Vitamin K Deficiency:

Not seen in horses, though sweet clover poisoning may cause impaired blood coagulation.

• Clinical signs can occur quickly

Water Soluble Vitamins

• Ascorbic Acid (Vit C) and 8 B-complex Vitamins

• Toxicity: low risk

• B vitamins are important in energy metabolism in the body

• High quality forages provide adequate B vitamins

Thiamin (B1)

• Thiamin(e) or B1 was the first water-soluble to be discovered (early 1900’s)

• FUNCTION: Required by pyruvate dehydrogenase, others in CHO metabolism

• Active form: Thiamin Pyrophosphate

Thiamin (B1) May need to be added in diets of heavy working horses-WHY?

energy metabolism

Thiamin (B1) REQ:

.06 mg/kg body weight for maintenance horses

Thiamin (B1) Source:

Good quality forages, cereal grains

• Manufactured by hindgut microbes

• may need supplementation on low quality forage

Thiamin (B1) Deficiency:

Rare, though if clinical:

• Anorexia, bradycardia, fasciculation of muscles, ataxia, decreased feed intake, diarrhea, blindness

Riboflavin (B2), Niacin (B3) & Pyridoxine (B6)

Functions: co-enzymes in CHO, fat metabolism

Riboflavin -

FAD and FMN

Niacin –

NAD and NADP

Pyridoxine -

works with B2 and B3

Riboflavin (B2), Niacin (B3) & Pyridoxine (B6) REQ:

B2: 0.04 mg/kg BW

• not established; adequate if consuming good forage for microbes

Riboflavin (B2), Niacin (B3) & Pyridoxine (B6) Sources:

Microfloral in hindgut

Riboflavin (B2), Niacin (B3) & Pyridoxine (B6) Deficiency:

not known in the horse; but if it was…..clinical signs? - impaired energy metabolism, poor skin/coat, reduced appetite, and neurological issues

Pantothenic Acid

Functions: CHO and fat metabolism

• Acetyl-CoA functions

Forms: Co-enzyme A

Pantothenic Acid REQ:

no dietary requirement established

Pantothenic Acid Source:

In all feedstuffs

Pantothenic Acid Deficiency:

Not known

Cobalamin (B12)

Functions: Required for methionine synthesis; folate absorption (cell replication); DNA synthesis

Forms: Only made by microbes

Cobalamin (B12) REQ:

Not established; but needs cobalt to function

Cobalamin (B12) Source:

Microbes in hindgut

Cobalamin (B12) Deficiency:

Not known if good quality forage is provided

Folic Acid

Functions: Needed for DNA synthesis, RBC synthesis, cell replication

• (growth & development!)

• Works with Cobalamin B 12

Folic Acid REQ:

not established

• Exercising/Gestating horses may need supplementation

Folic Acid Source:

Good quality forages

Folic Acid Deficiency:

Unknown; likely issues with fetal growth

Biotin

Functions: co-enzyme for carboxylation/decarboxylation ReDox

• Gluconeogenesis, fat synthesis, NT factors, DNA, RNA synthesis

Biotin REQ:

Not established

• only B-vitamin that has clinical effect with supplementation

Biotin Source:

Good quality forage

Biotin Deficiency:

Not understood in the horse; abnormal hoof growth

• other species: skin lesions, impaired growth, anemia

Biotin Research Study Conclusions:

supplementation with 15 to 30 mg / d biotin may benefit both hoof growth and integrity after 5 months or more of feeding to horses that have poor hoof wall integrity

Biotin Mechanism of action?

• Keratin synthesis

• lipogenesis

Vitamin C: Ascorbic Acid

Function

• Collagen synthesis

• Antioxidant

• Role for maintenance of joints??? - essential for the structural integrity of joints, tendons, ligaments, and cartilage

Horse can synthesize

vitamin C

• At present time, not considered dietary essential for horses