Agriculture Reference
In-Depth Information
of energy for ruminants. They include diverse compounds
classifi ed as monosaccharides (single sugar unit), such as
glucose, fructose, or polymers of monosaccharides, that is,
oligosaccharides (2-10 sugar units), such as maltose and
lactose, and polysaccharides, such as cellulose, hemicel-
lulose, and starch. Carbohydrates also are divided into two
main groups based on their availability for fermentation or
digestion: (1) nonstructural carbohydrates (NSC) being
found inside the cells of plants that are readily available
and fermented such as sugars and starch, and (2) structural
carbohydrates (SC) being present as plant cell walls that
resist digestion but are partially fermented in the rumen
and in the cecum/colon.
Nonstructural carbohydrates include sugars, starches,
organic acids, and other reserve carbohydrates such as
fructans. Starches generally comprise 50-100% of NSC in
most plants. NSCs are well digested and provide the main
source of energy for both ruminal microbes and the host
ruminant. Nonstructural carbohydrates typically are mea-
sured by enzymatic methods and differ slightly from non-
fi brous carbohydrates (NFC) that are calculated by
subtraction as NFC = 100
Lipids
Lipids are organic compounds defi ned by being soluble in
a nonpolar solvent like ether or chloroform. Lipids will
include long chain fatty acids (FA), triglycerides, phospho-
lipids, and other substances such as sterols and cholesterol.
Lipids are generally classifi ed as (1) simple lipids, mainly
neural fats and waxes; (2) compound lipids, including
phospholipids, such as lecithin, cephalins, and nonphos-
phorylated lipids, such as glycolipids and lipoproteins; and
(3) derived lipids, such as fatty acids and sterols. Fats are
lipids, but not all lipids are fats. For example, petroleum
products are lipids but are not fats. Fat generally refers to
stored, energy-rich compounds that have high concentra-
tions of long-chain fatty acids including triglycerides,
phospholipids, nonesterifi ed fatty acids, and salts of long-
chain fatty acids. Fats are dense sources of energy provid-
ing more than twice the energy per unit of weight of
carbohydrates and proteins with more than 85-90% of this
additional energy being available for metabolism. Fats also
provide fat-soluble vitamins such as A, D, and E that
rumen microbes are unable to synthesize in the rumen, and
the essential fatty acids such as linoleic acid and linolenic
acid. Fat is present in grains and forage at levels of 2-5%
of dry weight. In addition, fats often are added to diets
of ruminants in the form of oilseeds, animal or animal-
vegetable blends (with a saturated : unsaturated FA ratio
of 1 : 1), dry granular fat, or rumen-protected fat. Feeding
more than 6-7% of diet DM in the form of fat will decrease
intake and has been associated with depression in cellulose
digestion in the rumen.
(%NDF + % CP + % Fat + %
Ash). The difference between NSC and NFC includes
pectin and organic acids. Pectin is not included in NSC.
The levels of NSC in the diets of dairy cattle should not
exceed 30-40% of the ration dry matter while the maximum
level for NFC can be slightly (2-3%) greater. The optimal
concentration of NSC or NFC in the diet of dairy goats has
not been determined.
Structural carbohydrates separated from cell contents by
solubilizing away materials solvent in acid and base yield
crude fi ber (CF), or in a pH neutral detergent solution yield
neutral detergent fi ber (NDF), or an acid detergent solution
yielding acid detergent fi ber (ADF). Neutral detergent fi ber
represents much of the fi ber in the plant cell walls and
includes cellulose, hemicellulose, and lignin. Acid deter-
gent fi ber is equal to NDF minus hemicellulose. Generally,
ADF is less digestible than NDF, and ADF concentration
in a feed is negatively related to energy digestibility of that
feed. However, digestibility of NDF is affected by its
source (from forage or grain), and the proportions of its
components: cellulose, hemicellulose, and lignin. NDF
from nonforage and present in small particles is less
effective for maintaining rumen pH than NDF from
coarser forage particles. The recommended dietary require-
ments for dairy cattle for NDF to support optimum milk
production with no depression of milk fat is set at 25% of
diet dry matter with not less than 19% of NDF from forage
(NRC, 2001). There is no recommendation stated for dairy
goats.
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Proteins
Proteins are large molecular weight nitrogenous com-
pounds composed of amino acids. Proteins are vital to
living cells and play important roles (1) as enzymes,
hormones, and structural components of the cells, (2)
for immunity and heredity, and (3) for oxygen transport,
muscle contraction, acid-base balance, osmotic pressure,
and blood clotting. Proteins generally are classifi ed as
either (1) simple proteins that upon hydrolysis yield mainly
amino acids and their derivatives, (2) conjugated proteins,
or (3) derived proteins. Simple proteins are classifi ed based
on their solubility as globular proteins (albumin, globulin,
glutelins, and prolamines) or fi brous, less soluble proteins
(collagen, elastin, and keratin). Conjugated proteins are
simple proteins with an additional nonprotein prosthetic
group, such as nucleoproteins, glycoproteins, metalopro-
teins, etc. Derived proteins include peptones and metal-
loproteins. Globular proteins are present in all feeds,
whereas fi brous proteins are more abundant in feeds of
