water

  1. Classification: Macronutrient, inorganic, essential nutrient (metabolic water is not sufficient for most animals).

  2. Significance: Basis for all body fluids (blood, lymph), required for hydration, digestion (mixing food, hydrolysis reactions), nutrient transport (dissolving water-soluble nutrients in blood), metabolism (reactions), excretion of byproducts.

  3. Thermoregulation: Critical function, helps maintain constant body temperature. Two key properties:

  4. High Specific Heat Capacity: Water can absorb large amounts of heat without significant temperature change.

  5. High Latent Heat of Evaporation: Evaporating a small amount of water removes a large amount of heat (sweating, panting).

  6. Body Pools: Majority of body water is intracellular fluid (inside cells, ~2/3), rest is extracellular fluid (~1/3), including interstitial fluid (between cells, ~22%) and vascular fluid (blood). Small percentage in transcellular fluid (inside organs like eye, brain).

  7. Body Water Content: Negatively related to body fat content. Males typically have more body water than females due to less body fat. Older animals have less body water (more fat) than young animals. Fetus is ~90% water, infant ~80%, decreasing with age to ~55% in elderly.

  8. Water Inputs:Water in Feed: Moisture content of feed contributes to water intake.

  9. Drinking Water (Free Water): Not bound to feed.

  10. Metabolic Water: Produced during oxidation of carbohydrates, fats, and proteins. Oxidation of fat produces significantly more water than carbohydrates or protein. Metabolic water is typically only 5-10% of total requirement for most animals, making drinking water essential. Some desert animals (e.g., kangaroo rat, camel) and migratory birds rely heavily on metabolic water. Camel humps store fat, which yields water and energy when metabolized.

  11. Water Outputs:Water in Feces: Amount varies.

  12. Evaporation: Sweating (from sweat glands) and panting (exhaling moisture). Animals use these methods in different degrees to dissipate heat (horses/donkeys mostly sweat, pigs/dogs mostly pant). Pigs lack sweat glands.

  13. Water in Urine: Predominant water loss. Factors affecting urine output: dietary salt/sodium and protein intake (high levels increase urine production to excrete waste products like urea from protein metabolism), ambient temperature (high temp can decrease urine output to conserve water), physiological states (pregnancy increases urination), animal origin (animals from dry areas conserve water by producing less urine; animals from wet areas produce more urine).

  14. Water Quality: Important for animal health. Parameters:

  15. Salinity: Total dissolved inorganic salts (Mg, Ca, Na, Cl). High levels can cause temporary diarrhea and be lethal (especially to poultry >5000 ppm).

  16. Hardness: Specifically calcium and magnesium salt concentration.