The Biology of the Goat

The rumen and reticulum
The reticulum can be considered a sac of the rumen since feed stuff can travel freely between them.

Rumen
pH 5.5 to 7.0
temperature 38-40 deg C (100- 104 deg F)
volume 3 to 15 liters (1 to 4 gallons)

The Reticulum

The cells that line the reticulum are folded into a honeycomb structure.

The Rumen

The lining inside the rumen is covered with tiny papillae of different shapes and sizes.
There are more papillae in the lower half of the rumen than in the upper half.
The papillae have a rich supply of blood which absorbs the nutrients produced by fermentation.

When young goats suckle milk from their mother's udder or from a bottle,
the esophageal groove will close to form a tunnel so that the milk will go
directly into the omasum and abomasum, bypassing the rumen and reticulum.
If milk went directly into the immature rumen it would rot.

The freshest feed, once mixed with the microbes and fluids,
is formed by the cardia and rumen near the esophageal opening into a soft mass.
This bolus is regurgitated up the esophagus into the mouth as the cud.
The goat presses the fluid from the cud with the tongue, rechews it leisurely and thoroughly,
and mixes it well with saliva.
The cud is swallowed and since it is in smaller pieces will fall to the lower levels
of the rumen to be further processed by microbes.
The nutritional elements are absorbed through the rumen lining.

The Omasum

When food particles are small enough they pass through from the rumen into the omasum.
The round omasum is the smallest stomach chamber but because its interior has many folds
it has a large surface area.
Liquid and some fermentation products are aborbed through the lining of the omasum.
Contractions of the omasum push flakes of feed into the abomasum.

The Abomasum

The abomasum or fourth stomach chamber is similar to the stomachs of nonruminants except
that the ruminant abomasum secretes lysozyme, an enzyme which breaks down bacterial cell walls.
Hydrochloric acid is secreted which activates digestive enzymes to break down food particles
into large molecules.
Much of the goat's protein is supplied from rumen bacteria that migrate to the abomasum.

In young ruminants, the abomasum secretes chymosin (rennin) an enzyme that coagulates milk.
This is necessary to slow the passage of milk through the abomasum
so that digestive enzymes have more time to act on it.

Most of the protein in milk is casein.
There are four kinds of casein protein:
2 types of alpha casein (αs1 & αs2),
a beta casein (β) which has two types A1 and A2 (goat milk is mostly A2)
and a kappa casein (κ).

In fluid milk, casein proteins form small spheres called micelles.
Alpha and beta casein proteins are connected to each other by phosphate and calcium.

Kappa casein is a little different.
It prevents the alpha and beta casein proteins from combining with additional calcium.

The enzyme chymosin (also called rennin) secreted by the abomasum of young ruminants
acts on the kappa casein protein to change it.

The resulting para-kappa-casein is no longer able to prevent calcium and phosphate
from binding to the casein proteins.
Micelles clump together causing the milk to coagulate.

The Intestinal Tract

The duodenum secretes alkaline products produced by the pancreas and liver
which neutralizes stomach acids.
Digested food then travels to the small intestine where enzymes
break down protein, starch, sugars and fat and the products are absorbed into the blood system.
Any cellulose that reaches the small intestine cannot be metabolized in the small intestine.
It takes about 3 hours for feed to pass through the 36 feet of the small intestine.

The main function of the large intestine is to absorb water.
Some further fermentation occurs in the large intestine and some digestion end products are absorbed.
Movement is slow in the large intestine.
It takes about 18 hours for food to pass through the 6 feet of large intestine.
Undigested food is passed out as feces.