Agriculture Reference
In-Depth Information
animal origin. Seed proteins are rich in glutelins and
prolamines, whereas leaf protein is primarily albumin.
Feedstuffs also contain NPN compounds, peptides, free
amino acids, nucleic acids, amides, amines, and ammonia.
Grasses and legumes have the highest and most variable
content of NPN (nonprotein nitrogen, typically being any
protein that is not precipitated by a protein precipitant like
tungstic or trichloroacetic acid). The NPN content of fresh
forage is mainly short peptides, free AA, and nitrates,
whereas fermented forage is rich in free AA, ammonia,
and amines but lower in peptides and amines.
80-85% and MP is estimated to be between 60-64% of
CP.
N
ITROGEN
R
ECYCLING
The liver synthesizes urea from ammonia in blood.
Ammonia in turn is absorbed through the rumen or intes-
tinal wall or is produced during nitrogen metabolism by
tissues. In goats, some 18-85% of blood urea is recycled
to the rumen either via saliva or directly via diffusion
through the rumen wall (NRC, 2007). The intakes of rumi-
nally degradable intake protein and available fermentable
carbohydrates regulate the degree to which intake or recy-
cled urea is used whereas salivary fl ow and rumen pH
infl uence the extent to which urea is recycled and to which
ammonia is retained within the rumen. Recycled nitrogen
(urea) contributes to rumen microbial protein, fecal nitro-
gen, and urine nitrogen. The metabolizable protein repre-
sents the proportion of protein that is digested (DP) and
absorbed and not eliminated by the kidneys. Nitrogen recy-
cling by ruminants is a signifi cant survival tool that helps
conserve protein when quality of feed is marginal.
However, urea recycling may be simply a fortunate side
benefi t of adaptation to a desert environment. Through
recycling N, excretion of urine is reduced and this in turn
reduces the need for water, a factor important for survival
under desert conditions.
M
ETABOLIZABLE
P
ROTEIN
Metabolizable protein is used for maintaining and repair-
ing body tissues, tissue gain, conceptus gain, and milk
or wool production. The goal of feeding protein to rumi-
nants is to provide amino acids to complement the micro-
bial protein and supply dietary protein that escapes
destruction within the rumen and to reach the small intes-
tine to be digested therein and provide AA for absorption.
The crude protein and digestible protein systems com-
monly were used in the past as indices of ruminants'
protein needs. These have been displaced through the
metabolizable protein (MP) concept that should defi ne
requirements more accurately. True MP supply is the total
of microbial protein synthesized in the rumen plus the
amount of dietary protein that escapes fermentation (UIP)
that in turn is supplied by the diet and by recycled nitrogen.
Microbial protein synthesis in the rumen requires both a
nitrogen source and available energy. Most cellulolytic
bacteria require ammonia for growth while amylolytic bac-
teria may require amino acids. Protozoa meet their nitro-
gen need from digestion of bacteria, feed, or fungal protein.
Outfl ow of microbial protein from the rumen is associated
with both liquids and solids. Faster rates of rumen outfl ow
will increase microbial yield by reducing the time that
microbes spend in the rumen and thereby the amount of
energy bacteria used for maintenance. Protozoa have a
slower generation rate and limited outfl ow from the rumen
and thereby have a very low effi ciency for production of
microbial protein. Passage rate also can affect how much
of the intake protein is degraded in the rumen. Although
dietary protein is divided into two fractions, degradable
intake protein (DIP) and undegradable intake protein
(UIP), extent of degradation of DIP will vary with time
available for degradation that in turn is altered by level of
feed intake. This in turn infl uences the amount of MP
available. In the small intestine, amino acid absorption rate
appears more variable for UIP than that for microbial
protein. Small intestinal protein digestion is assumed to be
Minerals
Minerals are essential components of a diet and play mul-
tiple major roles in the body. Collectively they are assayed
as and thereby called “ash” and comprise the inorganic
portion of the diet. Minerals do not yield energy or produce
protein for the animal, but their presence is crucial for
nutrient metabolism. Minerals also provide structure with
bone and teeth formation; play signifi cant roles as electro-
lytes in acid-base balance and body fl uid volume regula-
tion; maintain osmotic pressure, membrane permeability,
and nervous transmission; regulate cell replication and
differentiation; and act as coenzymes or cofactors in
metabolic activities and body immune function. Fourteen
different mineral elements have been identifi ed as required
in the diet of goats.
Minerals generally classifi ed based on the quantities
required as either (1) macrominerals or major minerals that
are needed in “gram per day” quantities and include
calcium, phosphorous, sodium, chloride, potassium, mag-
nesium, and sulfur or (2) microminerals or trace minerals
that are needed in very small amounts as “mg per kg” and
include cobalt, copper, iodine, iron, manganese, selenium,
and zinc. Additional trace elements that may be needed
