Lecture 3 - Vitamins, Minerals and Water

1. Vitamins — basics

Vitamins are organic compounds required in small amounts for normal growth and maintenance. They are involved in or mediate biochemical pathways.

There are 2 main groups:

• Fat-soluble vitamins: A, D, E, K

• Water-soluble vitamins: B complex and C

Provitamins = vitamin precursors that must undergo a chemical change to become active vitamins. Example: β-carotene → retinol (vitamin A).

Vitamin availability depends on food availability, storage/processing losses, environment, health status, stress, production/growth requirements, and vitamin–mineral interactions.

2. Vitamin A

What to know

• Active form = retinol

• Stored/accumulates in the liver

• Plants contain precursors called carotenoids

• β-carotene is the most important carotene and a major vitamin A source for farm animals.

• Carotene → retinol conversion ranges from 3:1 to 12:1.

• Vitamin A/carotenoids can be lost through oxidation, drying, prolonged storage, metals and heat processing.

• Cats have very low activity of the enzyme needed to convert β-carotene into vitamin A, so they depend on preformed dietary vitamin A.

Functions

Two major roles:

1. Vision → involved in rhodopsin

2. Cellular differentiation → formation/protection of epithelial tissues and mucous membranes → important for growth, reproduction and immunity

Deficiency

Can cause:

• night blindness

• keratinization of skin/cornea

• increased susceptibility to infection

• infertility

Excess

Hypervitaminosis A, particularly from excessive raw-liver feeding in cats, can cause:

• deforming cervical spondylosis

• during pregnancy → potentially fatal malformations in kittens.

3. Vitamin D

Forms and sources

Two important forms:

• D2 = ergocalciferol

• D3 = cholecalciferol

Precursors can be activated by UV light.

Vitamin D is relatively uncommon in plants except sun-dried roughages. Vitamin D3 occurs in some animal tissues and is especially abundant in some fish; cod-liver oil is a rich source.

Important: cats and dogs do not obtain vitamin D through sunlight exposure. They need dietary sources.

Dietary sources include:

• egg yolk

• liver/cod liver

• animal/fish fat

Pet food generally contains added D3 (cholecalciferol).

Main function

Vitamin D regulates:

• intestinal absorption of calcium (Ca) and phosphorus (P)

• Ca and P reabsorption involving the kidney and bone

Deficiency

In young animals → impaired Ca/P deposition → weak/easily broken bones + bowed legs → rickets.

Excess

Too much vitamin D → increased Ca/P absorption → hypercalcemia, potentially causing:

• calcification of soft tissues

• azotemia

• renal failure. 

4. Vitamin E

• Vitamin E represents a group of related compounds.

• α-tocopherol = most biologically active and widely distributed form.

• Not stored in large amounts → requires a regular dietary supply.

• Widely distributed in food.

• Young grass/greens = good sources.

• Vitamin E activity can decline substantially during storage of moist grain in silos.

Main function: ANTIOXIDANT

Vitamin E:

• protects cells from free-radical oxidative damage

• prevents oxidation of PUFAs

• works with the selenium-containing enzyme glutathione peroxidase

• contributes to immune-system development and function.

Deficiency

Vitamin E deficiency → muscle degeneration/myopathy, particularly in ruminants and horses.

In cattle, nutritional myopathy/muscular dystrophy can be associated with low vitamin E + selenium. 

5. Vitamin K

Main function = blood clotting.

Vitamin K is required for synthesis of prothrombin in the liver.

Animals cannot synthesize the relevant vitamin-K compounds themselves, but plants and bacteria can.

Deficiency is uncommon under normal conditions in ruminants, horses, cats, dogs and pigs because bacterial synthesis in the gastrointestinal tract generally supplies sufficient vitamin K

6. B-complex vitamins

• Water soluble

• Components of coenzymes

• In ruminants → synthesized by rumen microorganisms

• Can be secreted into milk, providing a source for suckling animals.

• Important natural sources include animal foods, particularly liver.

• Vitamin B12 / cobalamin

  B12 acts as an intracellular cofactor for 2 essential enzymes.

  For absorption:
  Intrinsic factor (IF) + B12 → absorption in the ileum via specific receptors

  In dogs:

  • exocrine pancreas = main source of intrinsic factor

  • exocrine pancreatic insufficiency (EPI) can therefore cause low B12

  • chronic small-intestinal disease can also cause low B12

  • damaged ileal mucosa → fewer cobalamin receptors → reduced B12 absorption

7. Minerals — basics

Minerals are inorganic elements essential for metabolic processes and represent approximately 4% of an animal's body.

Major functions:

• activate enzyme-catalysed reactions

• skeletal support → especially Ca + P

• nerve transmission

• muscle contraction

• components of transport proteins and hormones

• maintain water/electrolyte balance.

• Macro vs micro

  Macrominerals occur in appreciable quantities and account for most mineral content.

  Lecture examples:
  Ca, P, Mg, S, Fe, Na, K, Cl

  Microminerals / trace elements occur and are required in very small amounts.

  Examples:
  Zn, Cu, I, Se, Mn, Fe. 

  Note: the lecture itself lists iron (Fe) in both groups, so keep that in mind if you're being tested specifically on the slides

8. Mineral interactions

Minerals interact with each other, affecting absorption, metabolism and function.

Important examples:

High Ca → can reduce trace-element bioavailability

High Zn → ↓ copper absorption

Phytic acid → ↓ mineral/trace-element bioavailability

Phytic acid occurs in products such as soy.

Zinc dermatosis type II

Associated particularly with growing large/giant-breed dogs.

Can cause skin lesions.

Risk factors:

• poorly digestible diet

• low Zn

• high Ca

• high phytate from soy/grains/legumes → ↓ Zn absorption

9. Excess mineral supplementation

⚠ Minerals are not automatically safe because they are nutrients.

Excessive amounts can cause illness or death.

Particular toxicity concerns:
Cu, Se, Mo, F, V, As

Copper is a cumulative poison because the body cannot excrete it efficiently.

Minerals should be added through a premix and thoroughly mixed to avoid concentrated “hot spots” that could cause toxicity.

10. Common mineral supplement sources

Know these associations:

Mineral	Common source
Ca	Limestone
P	Dicalcium phosphate
Na	Common salt
Mg	Calcined magnesite
Se	Sodium selenite

Minerals can be supplied as blocks or premixes.

For grazing animals, free-access mineral blocks can be used, but intake varies with season, weather, block location/number, competition and water availability.

Trace elements can also be sprayed onto pasture or incorporated into fertilizer to increase their concentration in herbage.

11. Low calcium

The important sequence shown in the lecture is:

Chronic low dietary Ca → low plasma Ca → hyperparathyroidism → osteoclast activation → bone matrix resorption + increased Ca absorption from the digestive system.

12. Water — extremely important

Water = the most essential nutrient.

For most species, loss of 10–15% of body water → death.

Exception highlighted in the lecture:
camels can withstand ~30% loss.

Sources of water

Three main sources:

Drinking + feed + metabolic water

Water content of feeds:

• dry feed → 10–15%

• ensiled feed → 40–60%

• lush green grazed forage → up to 90%

Metabolic water = ~5–10% of total water, produced during metabolic reactions/body-tissue catabolism.

Interesting example: kangaroo rats never need to drink because metabolic water can exceed water losses.

13. Water in the body

Most tissues contain 70–90% water.

Important examples:

• muscle cells → ~80%

• adipose tissue → 5–10%

• blood → >90%

Major functions:

• solvent

• transports nutrients and metabolites

• transfer of light/sound

• regulates ionic concentrations

• regulates body temperature

• maintains cell shape

• lubrication → e.g. synovial fluid

• cushioning of nervous system → cerebrospinal fluid

• participates in chemical reactions

14. Water balance

Inputs

• drinking

• feed

• metabolic water from oxidation/body-tissue catabolism

Outputs

• urine

• feces

• sweat

• milk. 

Additional losses occur through evaporation from lungs/skin.

Water losses can increase with:

• high ambient temperature

• lactation

• pregnancy

• vomiting

• diarrhea

• severe burns

• open wounds

• diuretic use. 

15. What affects water intake?

Important factors:

• digestive system → ruminants > non-ruminants

• environmental temperature/humidity

• age

• physiological function → lactation, work

• disease → fever, diarrhea

• water quality

Example from the lecture — mature cattle:

No heat stress → 5–6% body weight/day

Heat stress → >12% body weight/day

16. Water requirements — numbers worth knowing

These are given as litres of water per kg of dry matter intake (DMI):

Animal	Water requirement
Lactating cow	4–7 L/kg DMI
Cattle	3–5
Young calves	6–8
Horses	2–3
Hard-working horse	10–12
Poultry	2–3
Swine	2–2.5

⭐ Highest-yield things to memorize for your quiz

A = vision + epithelial tissue; deficiency → night blindness
D = Ca/P; deficiency → rickets; excess → hypercalcemia
E = antioxidant + Se; deficiency → myopathy
K = prothrombin/blood clotting
B vitamins = water-soluble coenzymes
B12 + intrinsic factor → absorption in ileum
Minerals = inorganic; macro vs trace minerals
High Zn ↓ Cu absorption; high Ca/phytate can ↓ trace-mineral absorption
Water = most essential nutrient; 10–15% loss can be fatal
Water inputs = drinking + feed + metabolism; outputs = urine + feces + sweat + milk.