Animal Nutrition
Chapter 41
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Nutritional Requirements
Animals require food for fuel, carbon
skeletons, and essential nutrients
Animals are heterotrophs
- obtain nutrients by consuming other organisms - consumers
In contrast, plants and other photosynthetic organisms
synthesize organic nutrients from inorganic elements - producers
A Nutritionally Adequate Diet Provides Source of
...
Fuel (chemical
energy) - carbohydrates and others - used in production of ATP (cellular
respiration)
Carbon skeletons - biosynthesis of complex organic molecules
Essential nutrients - substances essential to life which organism cannot synthesize
from raw materials - must be obtained in diet
Essential Nutrients
Amino acids
- used in protein synthesis - 20 required - 8 essential
Fatty acids
- components of cell membrane and other functions - unsaturated
Vitamins -
coenzymes in key metabolic processes and other functions - 13 required
Minerals -
numerous functions - 17 required
Essential Amino Acids
Animals require 20 amino acids for protein synthesis -
8 essential (see Fig. 41.3)
Animal products tend to be complete - provide all
essential amino acids in proper proportions
Plant products incomplete - lack one or more essential
amino acids - variety of plant products may provide complete complement (see
Fig. 41.3)
Essential Fatty Acids
Animals can synthesize most of the fatty acids they
require
Several unsaturated fatty acids essential -
e.g., linoleic acid involved in
synthesis of phospholipids
Most diets provide ample quantities of essential fatty
acids - deficiencies rare
Essential Vitamins
Variety of functions - 13 essential (see Table 41.1)
Required in small amounts - 0.1 to 100 mg per day -
dependent on particular vitamin
Water soluable vitamins - B complex and C
Fat soluable - A (incorporated into visual pigments), D (calcium
absorption & bone formation), E (antioxidant), K (required for blood
clotting)
Essential Minerals
Variety of functions - 17 required - (see Table 41.2)
Required in small amounts - 1 to 2,500 mg per day -
dependent on particular mineral
Examples - calcium (functioning of nerves &
muscles), iron (component of cytochromes and
hemoglobin), sodium & potassium (nerve function & osmotic
balance)
Nutritional Deficiencies
Undernourishment - diet deficient in calories
Malnourishment
- diet deficient in essential nutrients
Feeding Categories
Herbivores -
consume primarily plant material
Carnivores -
consume primarilyanimal matter
Omnivores -
consume both types
Most animals are opportunistic - will eat foods
outside their normal range when available
Feeding Adaptations
Bulk feeders
- consume relatively large items of food - e.g., snakes
Substrate feeders - eat while on or in their food source, e.g., leaf-miners (flies)
Fluid feeders
- extract nutrient-rich fluids from food source - e.g., mosquitoes
Suspension feeders - sift or trap relatively small food particles from water, e.g.,
whales
Stages of Food Processing
Ingestion -
consumption - act of eating
Digestion -
enzymatic breakdown (hydrolysis) of macromolecules into smaller units (e.g.,
monomers) - see Fig. 5.2
Absorption -
uptake of nutrients (monomers, etc.) by cell
Elimination
- undigested material voided
Intracellular vs Extracellular Digestion
Intracellular
- occurs within cell - food particles engulfed by endocytosis
- digested within food vacuoles - prevents damage to other cell parts
Extracellular - occurs
outside cell -enzymatic hydrolysis occurs within specialized
compartments - used by most animals
Digestive Tracts
Gastrovascular Cavities -
single opening for ingestion and elimination - function in digestion and
distribution of nutrients - occur in small organisms (e.g., cnidarians)
Complete Digestive Tracts - tract extends between two openings (mouth &
anus) - provides for compartmentalization - also allows additional food
to be consumed before earlier meals digested
Mammalian Digestive System -
Alimentary Canal
Upper digestive tract - oral cavity, pharynx, esophagus - food processing
initiated
Stomach
stores food & performs preliminary digestion - forms acid chyme
Small intestine
- main organ of digestion and absorption
Large intestine
- colon - water resorption and elimination of
undigested material
Upper Digestive Tract
Oral Cavity
- mouth - food pulverized - salivary amylase hydrolyzes starch and
glycogen - initial process of digestion
Pharynx -
junction that opens to both trachea and esophagus
Esophagus
conducts food to stomach by peristalsis - involuntary contractions of
smooth muscle tissue
Stomach
Primarily storage organ
Secretes gastric juice - high concentration of HCl (pH = 2) - contains pepsin involved in
hydrolysis of proteins
Pepsin
secreted in inactive form (pepsinogen) -
activated in lumen of stomach by HCl - activation and
mucous coating of lumen prevent self-digestion
Generates acid chyme
- nutrient rich broth
Small Intestine
Main organ of digestion and absorption
Acid chyme enters duodenum
- main site of digestion - villi and microvilli create large surface area - 300 m2 -
for absorption - blood enters hepatic portal vessel (to liver)
Jejunum and ileum
- function mainly in absorption of nutrients and water - absorb most of water
that has entered system
Large Intestine - Colon
Reclaims (absorbs) most of remaining water in system
Harbors rich microflora
(microorganisms) - colon absorbs vitamins produced by symbionts
- supplements diet
Elimination of undigested materials
Accessory Glands
Pancreas -
produces several hydrolytic enzymes & alkaline solution rich in bicarbonate
- acts as buffer
Liver -
produces bile - contains bile salts that facilitate digestion and absorption of
fats
Gallbladder
- bile stored until needed
Homeostatic Regulation of Cellular Fuel
Homeostatis - maintenance of constant internal environment
Carbohydrates and other nutrients used for ATP
production - excess stored as glycogen in liver & muscle cells
Pancreas & liver play key role in regulation of
blood glucose levels - homeostatic mechanism
Evolutionary Adaptations - Dentition & Alimentary
Canal
Dentition correlated with diet - teeth of herbivores
generally adapted to grinding - carnivores for cutting - omnivores equipped
with both types
Alimentary canal of herbivores generally longer than
carnivores - relates to difficulty in digesting plant material (cellulose)
Evolutionary Adaptations -
Digestion of Cellulose
Most animals do not produce enzymes that hydrolyze
cellulose - difficulty in digesting plant material
Many harbor symbiotic microorganisms which digest
cellulose - mutualistic relationship - both benefit
Ruminants -
cattle, sheep, etc. - harbor cellulose-digesting microorganisms in fermentation
chambers