Transcript Chapter 1: Animal Agriculture

Chapter 18: Nutrition
• Chapter overview:
– Chapter 18 presents the principles of nutrition,
to include:
• composition of plants and animals
• definition of the nutrient classes
• feed and food analysis procedures
Nutrition:
• Nutrition is the science that deals with food
and the nutrients it contains, to include:
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Water
Carbohydrates
Lipids
Protein
Vitamins
Minerals
The Nutrients: Water
• Water is the most abundant and important
constituent in plant and animal tissues
– An embryonic calf is 90% water and a market
steer is 40+% water
– Sources of water are:
• drinking water
• ingested as a component of feed and food
• metabolic water arising from metabolism in tissues
The Nutrients: Carbohydrates
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Organic compounds composed of C-H-O
Most abundant organic compounds in plants
Formed by photosynthesis in plants
Generally provide 50 to 75% of dry matter
of food animal diet
Carbohydrate Classification:
• Monosaccharides - simple sugars (5 to 6 C’s)
• Disaccharides - two molecules of simple
sugar linked together
• Polysaccharides - many molecules of simple
sugars linked together
– Starch - polysaccharide that is readily digestible
– Cellulose - polysaccharide that is only digested
by microbes such as those in the rumen
The Nutrients: Lipids
• Organic compounds composed of C-H-O
• Higher proportion of C-H than carbohydrates
• “Fat” is the main energy providing lipid
– Composed of a glycerol backbone and 3 fatty
acids
– Provide 2.25 times as much energy as
carbohydrate when metabolized
Fat Classification:
• Saturated fats
– Solid at ordinary room temperature
– No double bonds within carbon chains of the
fatty acids
• Unsaturated fats
– Liquid at ordinary room temperature
– Double bonds exist within carbon chains of the
fatty acids; “polyunsaturated” have multiple
double bonds
Other Lipids:
• Lipids of importance, but not providing
energy to the diet include:
– Sterols such as ergosterol (pre-vitamin D) and
cholesterol
– Carotenes such as the precursor to vitamin A
– Essential oils that give plants flavor and odor
– Phospholipids such as lecithin
The Nutrients: Protein
• Proteins are primarily composed of C-H-O-N
with lesser amounts of sulfur and phosphorus
• Proteins constitute the active protoplasm in
plants and animals
• Amino acids are the individual units of
protein; chains of amino acids form proteins
• Amino acids not produced in animal tissues
are termed “dietary essentials”
Amino Acid Classification:
• Based upon need in the diet, because all
amino acids are needed at the tissue level
– Essential - not synthesized in the animal body
at a rate adequate to meet demand; the list is
dependent on species, age, and level of
productivity
– Nonessential - synthesized in the animal’s body
at a rate adequate to meet demand
Essential Amino Acids:
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lysine
tryptophan
phenylalanine
leucine
isoleucine
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threonine
methionine
valine
arginine
histidine
Nonessential Amino Acids:
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alanine
aspartic acid
cysteine
cystine
glutamic acid
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hydroxyproline
proline
tyrosine
serine (may be
essential for poultry)
• glycine (may be
essential for poultry)
Protein and Ruminant Animals:
• Adult ruminants do not require dietary
essential amino acids
– Rumen microorganisms synthesize amino acids
– Microorganisms convert nonprotein nitrogen
and inferior proteins to their own body proteins
– Rumen microorganisms flow to the abomasum
and small intestine to become a high quality
protein source for the host
The Nutrients: Minerals
• Many inorganic minerals are dietary
essentials for specific metabolic functions
and bone structure
– Macrominerals: those required in larger
amounts, for example 0.5% calcium in some
diets
– Microminerals: those required in minute
amounts, for example 40 mg/kg (0.004%) iron
in some diets
The Nutrients: Vitamins
• Vitamins are
– Organic substances required in very small
amounts in the diet
– Composed of C-H-O-N, and vitamin B12 also
contains cobalt
– Not closely related in chemical formula
– Divided into two groups: fat soluble (A, D, E, K)
and water soluble (B complex and C)
Unique Comments on Vitamins:
• Some are required by all animals while
others may be required by only a few
• Some are synthesized by microbes in the
rumen and large intestine
• Some are converted from precursors
– Example: vitamin D is converted from a sterol
by sunlight action on the skin in some animals
Analysis of Feedstuffs:
• Dry matter - for comparison of feeds on a
standardized basis, dry matter is determined
by drying a sample in an oven until constant
weight is attained
• Crude protein - feeds are analyzed for
nitrogen and “crude” protein is estimated
based upon protein being approximately
16% nitrogen (%N x 6.25 = % CP)
Analysis of Feedstuffs:
• Crude fat - fat (lipid) is soluble in ether;
therefore ether extraction is used to
determine a “crude” fat value by weight loss
• Crude fiber - fiber is estimated by
successive boiling of sample in dilute acid
and alkali to give a “crude” fiber value by
difference
Analysis of Feedstuffs:
• Mineral matter - though not very useful in
practical nutrition, a total mineral value called
“ash” is determined by burning a feed sample
• Digestible carbohydrates - the estimation of
digestible carbohydrates (called nitrogen-free
extract) was historically calculated by
subtracting all of the previous analytical
results from 100%
Digestibility of Feeds:
• Chemical analysis of feeds cannot
determine the extent of digestibility
• Digestion trials can give reasonably
accurate results for complete feeds and
components of complete feeds
• Feeds are analyzed and fed to an animal;
feces are collected and analyzed;
digestibility is estimated by difference
Determination of Feed Energy:
• Energy is necessary for animals to perform
productive processes, such as weight gain
• Comparison of feeds on an energy basis
leads to estimation of impact on productive
processes
• The “net energy” system gives various
levels of information about energy loss and
availability for maintenance and production
Steps to “Net Energy” Value:
• Gross energy (GE) = heat of combustion of
a feed sample
– Next: measure energy loss in feces (FE)
• Digestible energy (DE) = GE minus FE
– Next: measure energy loss in urine (UE) and
rumen gas (GPD, ruminants only)
Steps to “Net Energy” Value:
• Metabolizable energy (ME) = DE minus
UE and GPD
– Next: measure heat resulting from digestion and
absorption (heat increment, HI)
• Net energy (NE) = ME minus HI
– Net energy can be further subdivided into
maintenance energy and energy for production,
such as growth or milk production