Download Why Species of Grazing Animal is Important

Why Species of Grazing Animal is Important
Based on: Grazers and Browsers: How Digestive Morphology Affects Diet Selection. 1999.
By Lisa Shipley. Available at: www.cnr.uidaho.edu/range/pubs/Behavior/Shipley.pdf
The species of grazing animal determines:
 What the animal is likely to eat
 Grasses/Roughage (Grazers)
 Browses (Browsers)
 Mix of Grass, Forbs, and Browse (Intermediate Feeders)
 The animal’s ability to use terrain
 Transmission of disease between species
 Amount of water needed and frequency
Start by knowing if the critter in question eats meat of plants:
Herbivore Species - Page 1
Mammalian Digestive System– Makes the difference
o
Digestive system anatomy:
 Rumen - site of fermentation (absorb Volatile Fatty Acids and Ammonia)
 True Stomach (abomasum in ruminants) - secrets enzyme for digestion
 Small Intestines - absorption of nutrients
 Cecum - site of fermentation (absorb VFA's and Ammonia)
Can The Animal Digest Cellulose? – An important distinction
Carnivore
NO
o
↔
↔
Omnivores
SOMEWHAT
↔
↔
Herbivores
NO
Limited Cellulose Digestion- Monogastrics:
 Swine, birds, reptiles
 No rumen or large cecum-colon for cellulose fermentation
 Get energy from simple CHO's (sugars) and starch.
o
Cellulose Digestion:

Enlarged Fermentation Organ

Which houses microbes (bacteria and protozoa)


These microbes break to bonds of cellulose and release VFA's (volatile fatty
acids) as a byproduct. The VFA's are absorbed through the rumen or cecum wall
where they are transported to the liver and converted to "things" that can be used
for energy by the animal (glucose, acetyl coA, oxyacetyl acid and fat).
Foregut Digestion: including Ruminants and Camilids

For Example: Cows, sheep, deer, bison, elk, pronghorn

Have a rumen for fermentation
Herbivore Species - Page 2



Even the crop of some birds can facilitate fermentation

How foregut fermentation works:

Food entering gut is immediately fermented by microbes into Volatile Fatty Acids
(VFA’s, energy-rich byproducts )

Microbes use energy in cell solubles and cell wall, herbivore absorbs VFA’s to
use for its energy

Microbes also use protein in cell solubles, herbivore digests microbe bodies that
escape the rumen for protein

Microbes synthesize vitamins

Extent of cell wall digestion depends on time spent in foregut
Hind-Gut Fermenters:

For Example: Horses, rabbits, and some rodents.

Have enlarged cecum for colon for fermentation

How hindgut fermentation works:

Food enters stomach first, digested by HCl & pepsin, and directly absorbed

Cell wall goes through to intestines, some is routed through cecum for microbial
fermentation, some fermentation in sacculated colon

VFA’s absorbed, vitamins synthesized in cecum

Much cellulose is not digested, and microbial energy & protein eliminated from
body
Similarities and Differences between Foregut and Hindgut Fermenters:

Fermentation process is basically the same (i.e., cellulose ------> VFA's)

Rumen is before small intestines. Cecum is after small intestines. This means
ruminants have microbe bodies that can be digested in stomach for energy and
protein (particularly important for amino acids - practically eliminates need for
exogenous amino acids).

Hind-Gut fermenters (i.e., horses) have greater rate of passage, therefore can
survive on lower quality food.
Herbivore Species - Page 3
o
How plants and meat differ as a source of nutrients and energy:
o
Diet Selection Strategies - How animals meet nutrient needs.

Grazers or Roughage Feeders –
 Eat mostly grass which isn't as nutritious as forbs but is more abundant. Have to be
big in order to have a rumen or cecum to process roughage.


Intermediate Feeders
 Flexible in diet habits. May choose all grass when it is young and nutritious and then
switch to forbs or shrubs latter in season. Can handle a lot of roughage but generally
choose a high quality diet.


Sheep, goats, elk (usually medium sized ungulates)
Concentrate Selectors
 All monogastrics are concentrate selectors - cannot digest cellulose so must choose
a high quality diet.


Cattle, musk oxen, bison (usually large ungulates)
Deer, giraffe, rabbit - Choose to select high quality diet. This strategy requires
special harvesting skills like a small nose/mouth so the animal can chose only the
leaves of a shrub not the stems or select a small forb plant without getting a mouthful
of dead grass.
Partially determined by body size - smaller animals typically have higher metabolic rates
(require more energy/ unit of body weight).
 Therefore, smaller animals must eat higher quality diets.
 Whereas, large ungulates can subsist on high fiber diets.
 Whereas, large ungulates can subsist on high fiber diets.
Herbivore Species - Page 4
From: Hofmann, R. R. 1989.
Evolutionary steps of
ecophysical adaptation and
diversification of ruminants:
A comparative view of their
digestive system. Oecologia
78:443-457.
Herbivore Species - Page 5