NUTRITION
BIO102 INTRODUCTORY ZOOLOGY
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ELEMENTS OF NUTRITION
⚫ Nutrition: supply of substrates for energy
metabolism and precursors for biosynthesis
(building and maintaining cellular and metabolic
machinery and growth and reproduction)
⚫ feeding: acquisition of food
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ELEMENTS OF NUTRITION
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ELEMENTS OF NUTRITION
⚫ digestion: breaking down of highly
complex compounds that constitute food
⚫ Include mechanical and chemical
digestion
⚫ While mechanical digestion involves
physical movements, such as chewing
and muscle contractions, chemical
digestion uses enzymes to break down
food making it easily absorbed by the
body
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ELEMENTS OF NUTRITION
⚫Nutritional requirements and dietary
requirements different
⚫ However, nutritional requirements nearly
the same for all animals
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ELEMENTS OF NUTRITION
⚫ dietary requirements: provide components
of body, and material for biosynthesis,
provide energy
⚫ depend on metabolic pathways used to
provide energy and biosynthetic
requirements e.g., all animals require water,
dietary requirement of water varies also
glucose is essential to metabolism but
amounts needed differ e.g. large amounts
toxic to cows but not to man
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Digestion in omnivores
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Villi in the inner surface of ileum
⚫ Site of digestion
completion and
nutrients
absorption
⚫ Villi are lined
with microvilli
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Digestion in Herbivores
⚫ maybe hindgut or foregut (ruminant)
fermentors
⚫ include mouse, rabbit, zebra, elephant,
rhino, dassie etc.
⚫ three dietary groups:
1.roughage eating grazers: high fibre
cellulose content of diet e.g. elephant,
buffalo, cow
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Elephant (Loxodanta africana)
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Elephant:
Loxodonta africana
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⚫ 2. intermediate feeders: leaves and
growing shoots e.g. eland, impala
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Impala: Aepyceros melampus
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Kudu:Tragelaphus strepsiceros
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Gemsbok/oryx: Oryx gazella
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Digestion in Herbivores
3. concentrate selectors: eat young
leaves, buds, growing shoots, seeds
i.e. the high energy/nutrient content
parts of the plants which also have a
low cellulose content e.g. goats, giraffe,
small antelopes, hare
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Pygmy mouse: Mus minutoides
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Giraffe: Giraffa camelopardalis
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Scrub
Hare:
Lepus
saxatillis
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Scrub Hare: Lepus saxatillis
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Digestion in Foregut Fermentors
⚫ amount of cell wall in diet determines
digestibility of food - cellulose relatively
very stable so difficult to break down
⚫ and cellulose once broken down yields
high energy products
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Digestion in Herbivores
⚫ protein, lipid digestion occurs in stomach and small
intestine, absorption in small intestine
⚫ the main energy source is fermentation of
carbohydrates (amylolytic - starch and cellulolytic
cellulose)
⚫ cellulolytic pathway is very important as it releases
cell contents for digestion and assimilation
⚫ microbes carry out digestion (anaerobically)
products include fatty acids, heat, methane,
ammonia, microbial proteins and some amino
acids and vitamins
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Digestion in Herbivores
⚫ microbes maybe anaerobic bacteria, fungi,
protozoa (bacteria are the most important and
there are over 200 species)
⚫ in foregut fermentors/ruminants - food passes
down the oesophagus into the rumen
(microbes reside here) and returns to the
mouth for re-chewing (rumination)
⚫ then passes into the reticulum - grain and
other concentrates go directly into the
reticulum - the food while being digested is
moved progressively into the omasum,
abomasum and small intestine - progress
depends on size of the particles
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Digestion in Herbivores
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Digestion in Herbivores
Rumen - paunch
Reticulum- honeycomb
Omasum - many plies
Abomasum - true stomach
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HINDGUT
FERMENTORS
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Digestion in Hindgut fermentors
⚫ non-ruminants/hindgut fermentors have microbes
in the caecum (chamber off the small intestine just
before large intestine) for example, rabbit
⚫ foregut fermentors have advantage in that
products of fermentation pass through intestine for
further digestion and absorption, mechanical
digestion goes much further here (regurgitation)
⚫ urea easier to recycle here
⚫ rabbits (hindgut fermentors) resort to coprophagy
(eat faeces) i.e. products of hindgut fermentation
are passed out as special faeces then taken in
again for further processing and absorption
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