Chapter 18: Nutrition

1. 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

2. Nutrition: • Nutrition is the science that deals with food and the nutrients it contains, to include: • Water • Carbohydrates • Lipids • Protein • Vitamins • Minerals

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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”

10. 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

11. lysine tryptophan phenylalanine leucine isoleucine threonine methionine valine arginine histidine Essential Amino Acids:

12. alanine aspartic acid cysteine cystine glutamic acid hydroxyproline proline tyrosine serine (may be essential for poultry) glycine (may be essential for poultry) Nonessential Amino Acids:

13. 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

14. 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

15. 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)

16. 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

17. 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)

18. 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

19. 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%

20. 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

21. 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

22. 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)

23. 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