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                                               Energetics Exercise

1. Animals and humans usually consume exactly enough food to meet their energy requirements for growth
   and maintenance unless bulkiness of the diet prohibits food intake first. Intake of a woman when pregnant
   or lactating would probably be (lower than) (higher than) (equal to) food intake before pregnancy. (Go to
   question 2 next).

14. 4, 4, 9 kcal/g carbohydrate, protein, and fat.

    Deduction of fecal energy from “gross energy” yielded “digestible energy” values; deduction of urinary
    energy yielded “metabolizable energy” values. Because urinary energy deduction is made in the PFV,
    physiological fuel values are therefore estimating (gross) (digestible) (metabolizable) energy.

27. heat increment; net energy for maintenance.

    This heat is useful to keep humans or animals warm if the environmental temperature is (below) (above) the
    comfortable or “critical” temperature.

40. (625)3 = (25)3 = (5)3 = 5 x 5 x 5 = 125

    At the energy expenditure for resting maintenance of 77 kcal per day for each kilogram of metabolic body
    size, this equals ________ Mcal daily for Annabelle and Zelda.

    Metabolizable energy.

                                                                        _____ energy
                       Digestible----                                   Heat increment losses
    Gross ----                                Urine and gases

66. downward.

    This is why sheep are sheared in the (fall) (spring) of the year.

2. higher than – She has greater energy needs and therefore greater food intake.

   Energy density of nutrients differ, with carbohydrate and protein contributing 4 kcal metabolizable energy/g
   dry matter and fat with ____ kcal/g dry matter. (Go to question 3 next).

15. metabolizable.

    The deduction from “gross energy” to yield “digestible energy” is the energy lost in _______.

28. Below

    The environmental temperature below which the body must expend extra energy to keep warm is called the
    “_________” temperature.

41. 9.625 Mcal per day net energy for maintenance.

    This, together with heat increment of 13 and 26 Mcal daily, means that _____ and _____ Mcal must be
    disposed of.

54. net energy
                                               Net energy---
                            Metabolizable---                        Net energy for maintenance
             Digestible--                      Heat increment
    Gross-                  Urine and gasses

67. spring

   Air movement and “wind chill” will shift these points (downward) (upward) in temperature and explains
   why protection from wind in cold climates is necessary.

3. 9 kcal/g

   If food intake of an adult hamster to meet energy needs was 10 g of starch (a carbohydrate) daily, intake of
   casein (a pure protein) would probably be _____ g per day and a fat, _____ g per day. (Go to question 4.)

16. feces

    The deduction from “digestible energy” to yield “metabolizable energy” is energy lost in ________.

29. critical

    Above the critical temperature, heat from the heat increment or net energy for maintenance is (useless)

42. 22.6 and 35.6 Mcal heat/day.

    If 40% of this is to be dissipated by evaporating water from the lungs, with .575 kcal per g water
    vaporized, how much water must be expired? _____ and _____ liters

55. net energy for gain

   To keep burning, a candle oxidizes wax, the fire consumes oxygen and forms carbon dioxide and water.
   Similarly animals to stay alive oxidize carbohydrate and fat to produce _____, ________ and ______.

68. upward.

   Since extra energy must be expended to keep warm or cool outside the comfort zone, the amount of food
   energy that can be used for work or production of milk, meat, eggs or wool would be greatest (below)
   (within) (above) the comfort zone temperatures.

4. 10 g; 4.44 g (Not true if amino acid excesses depress intake.)

   The combustible energy of a feed is subdivided in a specific fashion by animals or humans. First we will
   divide energy, then determine how much energy is used by an animal for various functions. Energy is
   measured in calories, kilocalories or megacalories. A kilocalorie, the amount of available heat in ¼ gram of
   most foods, is the amount of heat necessary to raise the temperature of _____ g water _____oC.
   (Remember your high school physics?) Go to question 5.

17. urine

    In addition, losses as methane are added to urinary energy and deducted at this point as gaseous energy
    loss. Urinary energy loss is only observed with (carbohydrates) (fats) (proteins). The exception to this
    occurs in a ketogenic diet such as an all meat diet when ketones derived from (carbohydrate) (fat) (proteins)
    are excreted in urine.

30. useless

    Food intake has a marked influence on efficiency of use of energy from a food. For example, consider two
    dairy cows. Annabelle eats 10 kg and Zelda eats 20 kg of feed daily having 4.20 kcal gross energy per
    gram. Gross energy intakes are _____ and ____ megacalories (careful! A megacalorie is 1,000 kcal).

43. 15.72 and 24.8 liters of water

    The amount of net energy left for production, from the initial 18.2 and 36.4 Mcal daily net energy with 9.6
    Mcal daily deducted for maintenance is ____ and ____ Mcal daily.

56. heat, carbon dioxide and water.

    Protein oxidation by mammals will yield ______ as well.

69. within

    Heat production by an animal can be measured by placing it in a chamber and measuring heat output
    directly. This is called “direct calorimetry.” Heat production can also be determined indirectly by
    calculations from CO2 output and O2 uptake, a procedure called “_______________________.”

5. 1,000 g, 1oC

   “Gross energy” is the amount of heat released when a substance is completely oxidized. It represents
   (enthalpy) (entropy) (enthalpy and entropy) of the material. (Go to 6)

18. proteins; fats are the source of ketones

    This means for carbohydrate and fat, in general “metabolizable energy” equals “_____________ energy”

31. 42; 84 megacalories of gross energy.

    Digestibility is 80% which means digestible energy intakes are ____ and ____ megacalories per day.

44. 8.6 and 26.8 Mcal per day net energy for production.

    In each kg of 3.5% butterfat milk, how many Mcal gross energy are present? Milk contains 3% protein (at
    gross energy of 5.14 kcal/g), 3.5% fat (at 9.4 kcal/g) and 5% lactose (at 4.15 kcal/g).

57. urea (product of nitrogen metabolism)

    Poikilotherms (cold-blooded animals) have body temperatures that fluctuate with the environment.
    Because most chemical reactions of life processes double with every 10oC temperature rise, food intake,
    metabolism and growth rate of a fish will be (higher) (lower) in Mississippi than in Minnesota.

70. indirect calorimetry

    As more CO2 is produced or O2 is consumed, heat production has (increased) (decreased).

6. enthalpy

   The “gross energy” of average proteins, fats and carbohydrates are 5.65, 9.40 and 4.15 kcal/g. A man
   consuming 1 kg of a 20% protein, 5% fat, 60% starch diet is consuming _______ kcal gross energy.
   (Go to 7).

19. digestible

    Birds excrete uric acid as an end product of protein digestion, and bird urine contains about 8.7 kcal/g
    nitrogen as compared to 7.45 for mammals. This means that that the urinary energy loss from protein is
    (higher) (lower) (the same) for birds than for mammals.

32. 33.6; 67.2 Mcal of digestible energy.

    Assume these feeds contain 12.5% protein or ____% nitrogen.

45. 0.69 Mcal/kg milk.

    This amount of net energy must have been used in production of milk. If the cows are not raiding body
    energy stores, Annabelle can produce _____ kg milk and Zelda _____ kg milk from the 8.6 and 26.8 Mcal
    net energy.

58.higher (This is why outdoor fish farming is not economical in colder states).

    Hibernating animals have body temperatures that drop seasonally. The polar bear, a hibernator, would
    require (higher) (lower) energy reserves for survival during winter than a non-hibernating, non-eating fox
    of equal weight.

71. increased

    Below the critical temperature then, CO2 output would be (lower) (higher) than for the animal in the
    comfort zone.

7. 4,090 kcal (4.09 kcal gross energy per g feed x 1,000 g).

   The „digestible energy” of food or feed deducts the fecal (indigestible) energy from the gross energy. For
   example, if 10% of the gross energy of the above feed appears in feces, the digestible energy content of the
   feed is _________ kcal/g feed. (Go to 8).

20. higher

    In turn, “ metabolizable energy” per gram protein for birds is (higher) (lower) than for mammals.

33. 2% nitrogen (Proteins are 16% N)

    This means that the total nitrogen intake by Annabelle (fed 10 kg) is ________ g and by Zelda (fed 20 kg)
    is ___________g.

46. 12.5 kg milk and 38.8 kg milk.

    Note that Zelda‟s food intake was twice that of Annabelle‟s (100% higher) whereas milk production was
    _______% higher.

59. lower

    Homeotherms maintain a constant body temperature. To maintain body temperature, homeotherms must
    oxidize (less) (more) energy reserves if environmental temperatures fall below temperatures within a
    “comfort zone” or “zone of thermoneutrality.”

72. higher

    CO2 output alone is often used to measure metabolic rate. But carbohydrate and fat produce different
    amounts of energy per unit of carbon present, the more energy dense material, (carbohydrate) (fat),
    producing more heat.

8. 3,681 kcal digestible energy per gram.

    For humans, the digestion coefficient for most proteins is 91%. Therefore, of the 5.64 kcal gross energy/g
    protein, only ______ kcal is digestible. (Go to 9)

21. lower

     Not all the “metabolizable energy” of food can be used for productive functions. As glycolysis and the
     Krebs cycle cannot convert all food energy into ATP, but loses 40 to 50% as heat, this heat loss or “heat
     increment” must be deducted from “____________energy” to yield “net energy”.

34. 200 g; 400 g nitrogen

     Assume 50% of nitrogen consumed is deposited in tissue or milk and 50% is excreted as urinary nitrogen.
     With 7.45 kcal/g nitrogen excreted, this totals a loss of _____ Mcal and _____ Mcal for the two cows in

47. 210%.

     This illustrates that food intake markedly influences efficiency by which feed energy is converted into
     animal products. Doubling food intake increase product yield (<100%) (=100%) (>100%).

60. more.

     The temperature point below which an animal must expend extra energy to keep warm is called the
     “critical” temperature. The critical temperature is therefore a point (at the low extreme) (midway) (at the
     high extreme) of the comfort zone.

73. fat.

     Fat will also consume more oxygen per unit of heat produced, so measurement of both CO2 and O2
     exchange will show total heat production. The rate of CO2 produced to O2 consumed (will) (will not)
     indicate whether fat or carbohydrate is being oxidized.

9. 5.13 kcal digestible energy/g protein.

   Of energy in fats and carbohydrates fed to nonruminants, about 4% appear in feces. Fibrous feeds will be
   much less digestible. If 4% of these components is not digested, they have 9.4 and 4.15 kcal gross energy/g
   of these two nutrients, their digestible energy content is _____ and _____ kcal per gram.

22. “metabolizable energy”

    Following this “heat increment” deduction, the remainder, like the income tax calculations, is called “____”

35. 0.745; 1.490 Mcal.

    In addition, gaseous methane losses are about 5% of digestible energy values. This means that urine and
    gaseous losses reduce the digestible energy intakes of 33.6 and 67.2 Mcal to ______ and ______ Mcal daily
    of metabolizable energy.

48. > 100%

    Let‟s review these figures:
                                                    Annabelle             Zelda
    Food intake                                     10 kg                 20 kg
    Gross energy of feed                            4.20 kcal/g           4.20 kcal/g
    (a) ____ energy intake                          42 Mcal               ___ Mcal
       Fecal energy (20%)                           8.4 Mcal              16.8 Mcal
    (b) ____ energy intake                          33.6 Mcal             ___ Mcal
       Urinary energy
        (7.45 kcal/g N)                             0.7 Mcal              1.5 Mcal
       Gaseous energy
        (5% of dig.)                                1.7 Mcal              ___ Mcal
   (c) ____ energy intake                           31.2 Mcal             ___ Mcal
       Heat increment
        1.3 Mcal/kg fed                             13.0 Mcal             ___ Mcal
   (d) ____ energy intake                           18.2 Mcal             ___ Mcal
       Net energy for maint.
        [77 kcal x (kg)3/4]                         9.6 Mcal              9.6 Mcal
   (e) ________________ intake                      8.6 Mcal              ___ Mcal
   Milk production
       (at 0.69 Mcal/kg milk)                       12.4 kg               ___ kg

61. low extreme

    Homeotherms also must expend extra energy to keep cool by such processes as sweating or panting when
    temperatures rise above the ________ zone range.

74. will

    The mole ratio of CO2 produced to O2 consumed is called the “respiratory quotient” or, for short, RQ. For
    oxidation of carbohydrate, what is the RQ? Chemical reaction: C6H12O6 + 602  6CO2 + 6H2O.

10. 9.02 kcal digestible energy per gram fat; 3.98 kcal digestible energy per gram carbohydrates.
     (100 – 4 = 96%; 96% of 9.4 and 4.15 = 9.02 and 3.98 kcal/g)

       For these two nutrients, these figures are rounded to the nearest whole numbers and represent the
    “Physiological Fuel Values” of these two nutrients for humans. The PFV values for fat and carbohydrate
    are therefore ______ and ______ kcal/g.

23. net energy.

    Like net income, some energy can be saved and is called “net energy for production” for work or products
    like milk, meat, eggs and wool, but some must be used to maintain the animal, so is called “net energy for

36. 33.6 - (33.0) (.05) - (.745) = 31.2 Mcal metabolizable energy
    67.2 - (67.2) (.05) - (1.490) = 62.4 Mcal metabolizable energy

    Heat increment is about 1.3 Mcal per kg feed fed or _____ Mcal total for Annabelle and _____ total for

49. a. Gross                   84 Mcal
    b. Digestible              67.2 Mcal
        Gas                    3.3 Mcal
    c. Metabolizable           62.4 Mcal
        Heat increment         26.0 Mcal
    d. Net                     36.4 Mcal
     e. Net energy for
        production             26.8 Mcal
       Milk                    39 kg milk

   (Go to #50)

62. comfort zone or thermoneutral zone.

    The lowest temperature point at which this extra energy to keep cool is expended is called the “point of
    hyperthermal rise”. On the graph below, this is ________.


              Animals                       100
              heat production
              (kcal/ kg3/4 day)               50

                                                    10       20       30

                                            Environmental temperature (oC)
              CO2          6
75. RQ =               =       = 1.00
                  O2       6

    For oxidation of a typical fat, palmitic acid, what is the RQ? Chemical reaction:
       CH3 (CH2)14 COOH + 2302  16CO2 + 16H2O
11. 9 and 4 kcal/g

    For protein, the energy excreted with nitrogen in urine must be deducted as this energy is not available for
    use. For every gram nitrogen in urine, 7.45 kcal combustible energy is present as nonoxidized organic
    matter. This means for every 100 g protein (or 16 g N) excreted in urine, ______ kcal is excreted.

24. “net energy for maintenance.”

    To determine the amount of “net energy for work or products”, one must deduct ____ and ____ from
    “methobolizable energy.”

37. 13 Mcal and 26 Mcal heat increment daily.

    Of the 31.2 and 62.4 Mcal metabolizable energy, this leaves ______ Mcal and ______ Mcal net energy for
    maintenance and production.

50. In summary, the combustible energy in a feed is called “________energy”.

63. 26oC

    On this graph, the critical temperature is ______oC and the comfort zone is _____ to _____ oC.


               Animals                       100
               heat production
               (kcal/ kg3/4 /day)             50

                                                    10       20       30

                                                    Environmental temperature (oC)
               CO2         16
76. RQ =               =        = 0.70
               O2          23

    If the RQ is 0.85, halfway between the RQ for carbohydrate (1.0) and fat (0.7) this means that (fat and
carbohydrate are being metabolized equally), (no fat is being metabolized), (no carbohydrate is being

12. 119.2 kcal urinary energy per 100 g protein.

   With protein 91% digested, this means ____ kcal must be deducted per g protein fed. This reduces the
“metabolizable energy,” content from 5.13 kcal digestible energy per g protein.

25. heat increment; net energy for maintenance.

    Because the net energy for maintenance is used for essential functions such as circulation, respiration and
    replacement of body tissues, this energy is eventually released from the body as (light) (chemical) (heat)

38. 18.2 and 36.4 Mcal net energy daily.

    Consider net energy requirement for maintenance is equal to 77 kcal per day for every kilogram “metabolic
    body size”, which is kilograms body weight raised to the three quarter power. Lets figure metabolic body
    size. First, if Annabelle and Zelda each weigh 1,375 pounds, they each weigh _______ kg.

51. Gross energy
                                                                             _________ energy
    Divisions of energy is as follows: Gross energy ---
                                                                             Fecal energy
      o     o          o
64. 13 C; 13 C to 25 C

    Name the points a and b and zone

    a. __________________

    b. __________________                                 Heat           a       b
                                                          production         c
    c. __________________

77. Fat and carbohydrate equally metabolized.

    The following RQ‟s are typical for animals fed carbohydrate diets. At 2 hr. after feeding, the main energy
    source is _____ but this shifts to _____ from stored reserves as the animal reaches the post-absorptive state.


                           2     4   6    8   10     14

                           Fed           time (hr)

13. 1.08 kcal/g; 4.05 kcal/g protein, which is rounded to 4 kcal/g.

    This gives us the “physiological fuel values” or “Atwater values” for dietary food nutrients for humans of
    ___, ___ and ___ kcal/g carbohydrate. (Go to question 14)

26. heat

    The total heat loss from the body is the sum of ___ and ___.

39. 625 kg

    This to the ¾ power (the square root of the square root multiplied by itself three times) is ____ kg.

52. digestible energy

                                                             __________ energy
    Gross--                                                  Urine and gaseous energy

65. a. Critical temperature

    b. Point of hyperthermal rise

    c. Zone of thermoneutrality or comfort zone

    Insulation from hair, wool or clothing on surfaces would shift all these points (upward) (no change)
    (downward) in environmental temperature.

78. carbohydrate; fat

    Congratulations and take a break. You have finished the exercise.


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