Vitamins Flashcards
Fat soluble vitamins
A,D,E,K
- stored in liver and then moved to target tissue
- if fat levels are insufficient –> vitamin absorption is impaired
- potential for toxicity –> build up and accumulation –> calcification of soft tissues
Water soluble
B1 = thiamin B2 = riboflavin B3 = niacin B5 = pantothenic acid B6 = pyridoxine B7 = biotin B9 = folic acid B12 vitamin C - excreted in urine - don't have to be as concerned about toxicity
What is the major site of vitamin absorption?
SI
What is the major site of vitamin K and B production?
LI and cecum
Where is vit C produced?
liver
Where is vit D produced?
skin
What is the vitamin A conversion factor?
33% beta carotene –> vitamin A
- beta cartoon isn’t toxic but vit A is
- horses can regulate how much is converted
- beta carotene susceptible to oxidation (increased by UV and heat) –> initial 80% loss then 6-7%/month
Functions of vitamin A
- vision
- maintenance of epithelial membranes
- reproduction
where is most vitamin A received?
pasture and good quality hay
What does vitamin A deficiency lead to?
- night blindness
- excessive tear production
- reproduction problems
What does vitamin toxicity result in?
- lethargy
- hair loss
- elevated bone fragility
Dietary sources of vitamin A
- vitamin A –> supplements and fortified feeds
- beta carotene –> green grass, hay, coloured plants
- content affected by species, climate, leaf to stem ratio, maturity
Why is vitamin A important in the performance horse?
- supports mucosal integrity an immune system (exercise can alter GI tract permeability and resistance to infection)
Vitamin D3
Cholecalciferol
- made in skin
Vitamin D2
Ergocalciferol
- plant form
Vitamin D conversion in the liver
vitamin D3 + D2 –> 25-hydroxyvitamin D = calcidiol
Vitamin D conversion in the kidney
25-hydroxyvitamin D –> 1,25 hydroxyvitamin D = calcitriol = active vitamin D metabolite
What is the marker of vitamin D status
25-hydroxyvitamin D (calcidiol)
How are vitamin D requirements met?
- covered with pasture access
- generally met –> small amount produced in skin, feed/supplement, pasture
When is vitamin D especially important?
young horses –> growth (0-6 months)
Vitamin D toxicity
soft tissue calcification –> often fatal
Vitamin D deficiency
- stiffness
- rickets/osteoporosis
What’s a better source of vitamin D - hay or pasture?
hay
- pasture exposed to UV
- less in artificially dried hay
- more leaves = more
What affects vitamin D stability in feed?
heavy metals, UV, oxygen, alkaline components
- 10-30% loss during 4-6 months of storage at room temperature
What are the functions of vitamin E?
- antioxidant
- protects cell membranes (by trapping peroxides)
- DNA synthesis
- gonad function
- immune function
Vitamin E body stores
90% in adipose, liver, muscle
- measured through blood alpha-tocopherol levels
- vitamin E supplementation can mask vitamin A deficiency
When should horses be supplemented vitamin E?
horses with no pasture access (as amounts in hay can be low)
- amounts are variable (depending on time of harvest: younger = higher vitamin E)
Vitamin E toxicity
relatively non-toxic
What is the result of vitamin E deficiency?
- white muscle disease in foals (Se or vitamin E) –> treated with high doses
- tying up
- equine degenerative myeloencephalopathy = degeneration of myelin sheath surrounding nerves
- equine motor neuron disease
- levels dependent on Se levels = both low –> worse symptoms
Vitamin E dietary sources
Forage
- generally high in young green plants
- levels in hay/haylages can be very low
- depends on growth stage, harvest time, genetic variety, processing, storage
Feed/supplements
- highest in wheat germ + vegetable oils
- typically low in cereal grains
- no difference in bioavailability between forages + grains
Effects of storage on vitamin E
Forages
- harvesting results in 70% loss and will continue to decrease with storage
Feed + supplements
- synthetic form = less bioavailable compared to natural form
- highly susceptible to processing - sensitive to oxidation, heat, moisture and grinding
- refining oils –> relative small losses
- addition of oils –> increased absorption
Why do foals + weanlings have lower vitamin E levels compared to adults?
- low transfer of mare’s vitamin E concentration into milk (
Why is vitamin E important in the performance horse?
Higher levels of oxidative stress; higher energy (fat) = higher vitamin E requirements
- most important lipid soluble antioxidant
What are the functions of vitamin K?
- blood coagulation
- vascular health
- bone health?
What are the different forms of vitamin K?
- menaquinone = produced by gut microbes
- phylloquinone = synthesized by plants
- menadione = synthetic form
Sources of vitamin K?
Forages
- found in leafy, green plants (may be low bioavailability)
- generally low in hay (susceptible to oxidation)
Feed + supps
-cereal grains have lower amounts than forages
When might supplemental vitamin K be required?
prolonged antibiotic use or poor nutrition
Symptoms of vitamin K deficiency?
- impaired blood clotting
Toxicity of vitamin K
not known orally but injection can cause renal damage and death
Functions of thiamin
- carb metabolism
- functions of nervous system
Deficiency of thiamin
- anorexia
- bradychardia
- ataxia
- convulsions
- neural dysfunctions
- associated with intake of thiaminases (found in certain plants)
Thiamin toxicity
not described in horses
Sources of thiamin
Forages
- generally lower than grains
feeds + supps
- high concentration in cereal grains, protein supps, grain by-products
- highest is brewer’s and bakers yeast
Why is thiamin important in the performance horse
- elevated carb metabolism
Function of riboflavin
precursor for enzymes involved in ATP synthesis and lipid metabolism
Riboflavin deficiency
not reported in horses
- reduced protein synthesis and growth in other species
Riboflavin toxicity
unlikely
Functions of biotin
- needed for enzymes involved in fatty acid synthesis
- gluconeoegenesis
- AA metabolism
Biotin deficiency
- poor skin, coat, hoof quality in other species
- rare in horses (but could be a factor for poor hoof health)
Biotin toxicity
rare
Why is biotin important for the performance horse?
hoof quality and growth support
When is folacin supplementation necessary?
in horses with no pasture access
Function of vitamin C
- antioxidant
- prevents free radical damage
- regenerates vitamin E
Is hepatic synthesis of vitamin C sufficient to meet horse’s requirements?
should be
vitamin C deficiency
not described in horses
vitamin C toxicity
- no symptoms in horses
- GI disturbances, allergic reactions, decreased hepatic synthesis in other species
Why is vitamin C important in the performance horse?
to help deal with effects of exercise on plasma concentrations (antioxidant function)
When would vitamin C supplementation be most beneficial?
During
- hot weather
- increased stress
- rapid growth
- high level performance
- any interference with hepatic synthesis
What vitamin supplementation would a hard working horse most benefit from and why?
Vit E, as it acts as a antioxidant with selenium. Oxidation from exercise generates free radicals that cause muscle damage, therefore performance horses would benefit. Vitamin E is also involved in fat metabolism, and helps hard working horses utilize fat in their diet.
