Micronutrients

Vitamins

• Organic compounds with a carbon skeleton.

• Can be:

  • Fat-soluble

  • Water-soluble

• Perform many functions:

  • Metabolic regulation

  • Coenzymes

  • Antioxidants

• May or may not be considered essential, depending on the species.

Fat-Soluble Vitamins

The fat-soluble vitamins are:

Vitamin A

• Retinol

• Retinal (retinaldehyde)

• Retinoic acid

• Retinyl esters

• Beta-carotene (provitamin A carotenoid)

Vitamin D

• D2: Ergocalciferol

• D3: Cholecalciferol

Vitamin E

• Tocopherols

• Tocotrienols

Vitamin K

• K1: Phylloquinone

• K2: Menaquinone

• K3: Menadione

Vitamin A; functions

• Vision

• Growth

• Tissue maintenance

• Immune function

• Embryonic development

Biologically Active Forms

• Retinol

• Retinal

• Retinoic acid

Storage Forms

• Retinyl ester

  • Comes from animal products

  • Stored in the liver

• Beta-carotene

  • Mostly comes from plant products

  • Associated with red/orange pigmentation

Vitamin A and Vision

Retinal + opsin → photoreceptor

Rhodopsin

• Found in rod cells of the retina

• Black-and-white vision

• Dim-light/"night" vision

Iodopsin

• Found in cone cells of the retina

• Colour vision

• Bright-light vision

Vitamin A: Toxicity & Deficiency

Hypervitaminosis A

• Caused by excess preformed Vitamin A

• Not caused by beta-carotene

Deficiency

• Fetal abnormalities

• Impaired growth

• Night blindness

Vitamin A: Species Differences

Preformed Vitamin A is essential for:

• Felids

• Marine birds

• Most carnivorous mammals

These animals lack sufficient quantities of 15,15'-dioxygenase.

Not essential for:

• Canids (foxes, coyotes, wolves)

• Most herbivores

• Most omnivores

These animals can readily convert beta-carotene → Vitamin A.

Vitamin D; functions

• Homeostatic regulation of calcium (Ca) and phosphorus (P)

• Growth

• Bone remodeling

• Eggshell formation

Vitamin D2 – Ergocalciferol

• Very few natural sources

• Foods are often fortified with D2

Vitamin D3 – Cholecalciferol

• Sunlight / UV-B exposure

• Phytoplankton

• Zooplankton

• Marine fish

Vitamin D Activation

D2 and D3 are biologically inactive.

Vitamin D3 pathway:

UV-B → Vitamin D3 → Calcidiol → Calcitriol

steps

1. UV-B reaches the skin.

2. UV-B converts 7-dehydrocholesterol → Vitamin D3.

3. Liver converts Vitamin D3 → 25-hydroxyvitamin D3 (calcidiol).

4. Kidney converts calcidiol → 1,25-dihydroxyvitamin D3 (calcitriol).

5. Calcitriol is the active form that regulates Ca/P.

Remember:

Calcitriol = active Vitamin D = regulates calcium & phosphorus

Vitamin D: Species Differences

Vitamin D3 is essential for:

• Amphibians

• Birds

• Reptiles

They cannot use Vitamin D2.

Mammals can use:

• Vitamin D2

• Vitamin D3

Vitamin D is only required in the diet for mammals with insufficient sun exposure, such as:

• Polar regions

• Fossorial/subterranean animals

• Nocturnal animals

Vitamin D: Toxicity & Deficiency

Toxicity

Hypervitaminosis D

• Causes hypercalcemia

• Calcium builds up in soft tissues and organs

Deficiency

• Rickets: soft bones in young animals

• Osteomalacia: brittle bones in adults

Vitamin E; Function

Antioxidant

• Inhibits/prevents oxidative damage

• Scavenges free radicals

  • Free radicals = unstable/reactive atoms

Sources/Forms

Tocopherols

• Alpha

• Beta

• Gamma

• Delta

• Alpha-tocopherol = most active form

Tocotrienols

• Alpha

• Beta

• Gamma

• Delta

Vitamin E: Toxicity & Deficiency

Toxicity

Hypervitaminosis E

• Can counteract Vitamin K

• This affects blood coagulation

Deficiency

• Muscular dystrophy

  • Muscle weakness

  • Paralysis

• Nerve damage

• Infertility in rats and birds

Vitamin K; Function

• Blood coagulation (clotting)

Forms & Sources

K1 – Phylloquinone

• Leaves of green plants

K2 – Menaquinone

• Animal tissue

• Gut bacteria

• Animals/bacteria convert K1 → K2

K3 – Menadione

• Synthetic precursor

• Inactive in synthetic form

• Plants and bacteria can activate it

• Animals cannot activate it

Vitamin K: Toxicity & Deficiency

Toxicity

• K1 and K2: innocuous, even in very large amounts

• K3: can be toxic

  • No longer used as a supplement

Deficiency

• Risk of hemorrhage/excessive bleeding

Water-Soluble B Vitamins

Main Function

B vitamins act as:

• Coenzymes for cell metabolism

• Or precursors to coenzymes

B1 – Thiamine

Deficiency

Beriberi

• Edema

• Heart problems

B2 – Riboflavin

Deficiency

Ariboflavinosis

• Skin disorders

• Edema

B3 Complex – Niacin

Forms:

• Nicotinic acid

• Nicotinamide

• Can be synthesized from tryptophan

• Synthesis is poorly efficient

Deficiency

Pellagra

• Skin disorders

• Dementia

• Diarrhea

B5 – Pantothenic Acid

• Precursor for coenzyme A

• Coenzyme A is a critical component for the TCAC

Deficiency

• Rare

B6 Complex

Forms:

• Pyridoxine

• Pyridoxamine

Deficiency

• Dermatitis

Function

• Involved in amino acid metabolism

• Carnivores have an elevated requirement

B7 – Biotin

• Can be synthesized by gut bacteria

• May not be essential for ruminants

• Deficiency

  • Anemia

  • Hair loss

B9 – Folate (Folic Acid)

Function

• Coenzyme for cell metabolism

• Can act as a precursor to coenzymes

Other

• Can be synthesized by gut bacteria

• May not be essential for ruminants

Deficiency

• Folate deficiency anemia

B12 – Cobalamin

Function

• Coenzyme for cell metabolism

Other

• Synthesized by gut bacteria

• All animals depend on microbially synthesized B12

Deficiency

• Severe and irreversible:

  • Brain damage

  • CNS damage

Vitamin C – Ascorbic Acid

Water-SolubleFunctions

• Antioxidant

• Collagen formation

• Hormone synthesis

• Iron absorption

Deficiency

Scurvy

• Skin disorders

• Impaired wound healing

• Increased risk of hemorrhage

Vitamin C: Species Differences

Nonessential

• Reptiles

• Amphibians

• Some birds

  • Mostly non-passerine birds

• Most mammals

Essential

• Bats

• Many passerine ("perching") birds

• Osteichthyes ("bony" fish)

• Guinea pigs

• Capybara

Choline & Inositol Water-Soluble "Vitamins"

Both are involved in:

• Structure of cellular membranes

Choline

• Phosphatidylcholine

• Lipid transport and metabolism

Inositol

• Phosphatidyl-inositol

• Neurotransmitter synthesis

Choline – "Vitamin B4"

• Conditionally essential

• Synthesized during methionine metabolism

• Synthesis can be slow and potentially insufficient during:

  • Growth

  • Geriatric phases

Inositol – "Vitamin B8"

• Non-essential

• Synthesized from glucose

• Synthesis can be slow and potentially insufficient during:

  • Growth

  • Geriatric phases

Minerals

• Inorganic compounds

• Have no carbon skeleton

• All minerals are essential

  • Animals and plants cannot synthesize them

• Must be obtained from the diet

Sources

• Plants: accumulate minerals from soil

• Animals: accumulate minerals by eating plants/animals

• Free water

Important

The environment strongly influences mineral availability.

Macrominerals

Required in amounts > 5 g

• Sodium

• Potassium

• Chloride

• Sulfur

• Calcium

• Phosphorus

• Magnesium

Micro/Trace Minerals

Required in amounts < 5 g

• Iron

• Zinc

• Chromium

• Fluorine

• Selenium

• Iodine

• Copper

• Manganese

• Molybdenum

• Cobalt*

*Cobalt is essential for ruminants only.

Other minerals can also be found in the body, including:

• Arsenic

• Nickel

• Silicon

• Boron

Functions of Minerals

1. Skeletal structures

2. Maintenance of osmotic pressure

3. Regulation of acid/base balance.

4. Components of enzymes

5. Activators of enzymes

6. Components of biological units

Nutritionally Organic Minerals

• Minerals chelated/bound to a carbon-containing compound

• Example: amino acid

• Generally more bioavailable

Nutritionally Inorganic Minerals

• Elements or molecules without carbon

• Generally less bioavailable

Calcium

Main role

Formation of:

• Bone

• Teeth

• Antlers

• Eggshells

• Milk

Sources

• Milk

• Eggs

• Bone

• Vegetation

Phosphorus

Main roles

• Bone formation

• ATP

• Phospholipids

Sources

• Animal tissue

• Milk

• Grains

• Vegetation

Important: In plants, much of the phosphorus may be present as phytate.

Phytate

• Inositol hexaphosphate (InsP₆)

Calcium : Phosphorus

Requirement

Ca:P is considered as a ratio.

Ideal Ca:P ratio = 1:1 – 2:1

Deficiency

• Rickets → young animals

• Osteomalacia → metabolic bone disease/adults

Minerals – Electrolytes

Electrolytes help maintain intracellular and extracellular fluid balance.

Main role

• Create osmotic gradients

• Regulate body fluid status and movement

Cations

Positively (+) charged ions

"Pawsitively charged = Cations"

Examples:

• Ca²⁺

• Mg²⁺

• Na⁺

• K⁺

Anions

Negatively (-) charged ions

Examples:

• Cl⁻

• PO₄³⁻

Important electrolytes

Ca²⁺, P (PO₄³⁻), Mg²⁺, Cl⁻, Na⁺, K⁺

Electrolyte Imbalance

Can cause:

Chronic

• Cardiovascular issues

Acute

• Fatigue

• Emesis

Trace Mineral – Cobalt (Co)

Cobalt (Co)

• Essential mineral for:

  • Ruminants (foregut-fermenting species)

  • Some monogastric hindgut-fermenting species

Function

• Needed for synthesis of Vitamin B12 (cobalamin)

Remember:

Co → B12