ANSC 433 Lecture Notes - Lecture 12: Vitamin K Deficiency, Vitamin A Deficiency, Carotene
23 May 2018
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12. ANSC 433: Animal Nutrition & Metabolism Chantal Coutu
1
Fat-Soluble Vitamins
Vitamins
Vitamins are organic compounds that are required in small amounts for normal growth and maintenance of animal life.
They are not structural; they are metabolic pathway mediators. They are classed in 2 categories: lipid-soluble vitamins (A, D, E,
and K) and water-soluble vitamins (8 B vitamins and vitamin C). Lipid-soluble vitamins are hydrophobic compounds that are
absorbed efficiently with lipids and are more likely to accumulate in fat stores of the body. This build up can reach
concentrations that could be toxic if it gets too high. Water-soluble vitamins are hydrophilic compounds that dissolve easily in
water and are not readily stored, are excreted from the body in urine and there must have constant supply.
Unique Aspects of Vitamins
Some compounds only function as vitamins after being converted into their active form, like β-carotene and certain
sterols. These compounds are described as vitamin precursors, or pro-vitamins. International units (IU) are used to account for
the different active forms and potencies of vitamins and their precursors.
Vitamins are stabilized during storage since they are prone to oxidation, destroying them. This makes them sensitive to
light, heat, moisture and some metals. This feature determines how much vitamins are in a feed for animals and it changes the
way the feeds are processed and stored.
Vitais ehae the ualit of the aial’s poduts ad ipoe thei health. To aoid defiieies, soe itais ae
added at a higher amount than needed to maintain homeostasis in the body. For chickens, they use a lot of calcium and vitamin
D to produce egg shells, thus they need excess to ensure good shell quality while still having enough for their own bones and
other normal functions. Also, vitamin E in steer improves carcass quality by preventing carcass oxidation. Vitamin A is added to
improve animal health due to its role in immune and epithelial integrity.
Vitamin A
Vitamin A is a β-ionone ring with an unsaturated side chain. It can occur as an
alcohol, aldehyde or acid, each with a different name: retinol, retinal, retinoic acid,
respectively. The R group determines its name. It can exist as isomers, either all-trans
form, all-cis form or as a mixture of cis and trans forms. Cis means the double bond
makes the molecule bend and fold in the opposite direction whereas trans means the
double bonds make a straight chain. The all-trans retinol has 100% biological activity;
these are used as the reference form.
Beta-Carotene
Vitai A does’t eist i plats ut it’s used as a peuso (pro-vitamin) for carotenoids. Carotenoids can be divided
into two categories:
1. Xantophylls – most cannot be converted to vitamin A
2. Carotenes – β-Carotene main source of vitamin A for farm animals
β-Carotene is composed of two vitamin A molecules joined head to head, thus cutting β-carotene would yield 2 vitamin A
molecules (i.e. its active form). Cleavage of β-carotene to vitamin A happens in the intestinal mucosa or liver of the animal
Sources
Vitamin A accumulates in the liver and this organ is likely to be a good source. Marine oil sources, such as cod and halibut
livers, are very rich sources of vitamin A. Forages can contain substantial amounts of β-carotene. Typically, grasses are
preserved as hay, which can have vitamin A. However, the fresh form would have 20x more vitamin A than in hay, i.e. showing
ho uh is degaded hagig the gass’s fo. Most grains and grain by-products are practically devoid of β-carotene
since there are a lot of double bonds. This makes them more prone to oxidation, destroying vitamin A activity, thus are
sensitive to light, heat, heavy metals and moisture. Vitamin A can be manufactured and obtained in pure form. Egg yolk and
ilk fat also ae usuall ih soues, although the otet depeds o the aial’s diet.
Factor Affecting its Bioavailability
β-carotene and vitamin A are degraded in the rumen. Steers need up to 60% supplemental vitamin A. Conversion of β-
carotene takes place in the intestinal mucosa. The theoretical efficiency is 1 β-carotene converts to 2 retinols. Species vary in
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Document Summary
Vitamins are organic compounds that are required in small amounts for normal growth and maintenance of animal life. They are not structural; they are metabolic pathway mediators. They are classed in 2 categories: lipid-soluble vitamins (a, d, e, and k) and water-soluble vitamins (8 b vitamins and vitamin c). Lipid-soluble vitamins are hydrophobic compounds that are absorbed efficiently with lipids and are more likely to accumulate in fat stores of the body. This build up can reach concentrations that could be toxic if it gets too high. Water-soluble vitamins are hydrophilic compounds that dissolve easily in water and are not readily stored, are excreted from the body in urine and there must have constant supply. Some compounds only function as vitamins after being converted into their active form, like -carotene and certain sterols. These compounds are described as vitamin precursors, or pro-vitamins.
