Mammalian Physiology BIOAP 4580
The broadest view of animal nutrition includes feeding strategy, diet and gastro-intestinal
The details of GI-physiology are profoundly influenced by the diet and feeding
behavior and consideration of one without understanding of the other is fraught with peril.
For example, animal diets can be broadly divided into those based primarily on plant matter
versus those based on animal matter.
For the overwhelming majority of animals, diet is a
matter of evolutionary development, not choice. Since the nutritional content of different
foods varies considerably, the effective utilization, ingestion, digestion, and assimilation of
nutrients require behavioral, physiological, and biochemical adaptations.
By the standards of what animals require for development and maintenance, grass – even
good grass – is relatively nutrient poor.
Those animals that survive on a diet consisting
largely of grasses have evolved mechanisms for utilizing plant material that are absent in
For example, to realize the caloric value of indigestible cellulose – what we
consider fiber – cattle have a 4 part stomach.
One part is the rumen, a fermentation vat
where symbiotic micro-fauna break the cellulose down into various nutrients that can be
absorbed by the intestine.
In addition, the fermentation vat really acts like a bio-reactor,
where the growing microfauna become an important source of protein.
considered fore-gut fermenters and the potential for them to harvest the micro-fauna is a
significant advantage to their feeding strategy.
Horses and rabbits also eat a diet high in
grasses and other leafy matter but they are monogastric, not ruminant.
However, they also
use symbiotic micro-fauna to aid in the digestion of cellulose.
Their fermentation vat is in
the colon and/or caecum. Alas, “hind-gut” fermenters do not have the ability to digest the
But nutritionally challenged horses and rabbits can be observed to feed
on excrement, known as “copraphagy”, where first a soft stool is passed and then re-ingested
to claim its nutrient value (and proteins) and later a hard stool is passed for its excretory
Well nourished, i.e., grain fed, horses may not exhibit copraphagy.
All of the nutrient requirements for the development and maintenance of the animal are
obtained through the diet, either directly or as precursors.
Dietary requirements are those
nutrients that must be obtained in the diet because the animal lacks the ability to synthesize
from precursors. Humans have a dietary requirement for 8 (or 9) amino acids
from which all other nutritionally required amino acids can be derived by available metabolic
Members of the
(cats) have a dietary requirement for taurine.
not available from any plant source, making the
taurine is an intracellular osmolyte that participates in the regulation of cell volume.