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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 :.

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Chapter 18 nutrition l.jpg
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 l.jpg

  • Nutrition is the science that deals with food and the nutrients it contains, to include:

    • Water

    • Carbohydrates

    • Lipids

    • Protein

    • Vitamins

    • Minerals

The nutrients water l.jpg
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

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The Nutrients: Carbohydrates

  • 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

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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

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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

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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

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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

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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”

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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

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Essential Amino Acids:

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aspartic acid



glutamic acid




serine (may be essential for poultry)

glycine (may be essential for poultry)

Nonessential Amino Acids:

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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

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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

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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)

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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

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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)

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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

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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%

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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

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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

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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)

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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