lecture quiz 12: biological evaluation Flashcards

1
Q

feed to gain ratio

A
  • aka feed conversion ratio (FCR)
  • FCR = (feed consumption)/(body weight gain)
  • lower # is better ➔ produce more with less feed
  • for every pound of weight gain/milk/eggs prod animal consumed x pounds of food
  • well balanced diet imrpoves FCR
  • industries selected chx w/ lower FCR
  • FCR measures feed efficiency for meat animals
  • higher for ruminants than chx/pigs b/c fed lower quality diet
    • can only compare using human-edible food
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2
Q

digestibility

A

proportion of feed that is not excreted & assumed to be absorbed by amimal (%)

  • looking for ways to improve digestibility of feedstuffs (e.g. processing/grinding)
  • can be calculated for DM, organic matter, & various nutrients (& energy)
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3
Q

apparent digestibility

A

= (amount consumed − amount feces)/amount consumed x 100

  • assumes all DM in feces is from undigested feed
  • there are substances in feces not arising directly from feed = metabolic fecal products (MFP)
    1. intestinal cells & mucosa
    2. enzymes secreted in GI
    3. microbial mass
  • MFP mainly important for proteins, but have lipids (e.g. cell membranes)
  • underestimates digestibility (always lower than true digestibility)
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4
Q

true digestibility

A

= [amount consumed − (amount feces − MFP)]/amount consumed

  • accounts for metabolic fecal products
  • MFP can be quantified by measuring fecal output of fasted animals (only for non-ruminants)
  • always higher than apparent digestibility
  • for fiber: apparent always = true (animals cannot make)
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5
Q

feed energy evaluation systems

A
  • gross energy has little direct value ∴ energy systems evaluate “available” energy content
  • 2 energy systems:
    1. total digestible nutrients (TDN)
    2. caloric system
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6
Q

caloric system

A
  • uses gross energy as a start to get energy values of feedstuffs using bomb calorimetry
  • helps convert gross energy system to usable energy values to formulate diet
  • accounts for energy losses
  • if you don’t meet energy requirement animal loses weight
    • surplus energy ➔ weight gain
  1. digestible energy (DE)
  2. metabolizable energy (ME)
  3. net energy (NE)
  4. maintenance energy (NEm)
  5. productive or recovery energy (NEp)
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7
Q

digestible energy

A

DE = GE − FE

  • FE = fecal energy
  • accounts for energy lost in feces
  • represents energy absorbed by animal but not necessarily available for usage
  • some energy lost along metabolic processes
  • burn feces in bomb calorimeter
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8
Q

metabolizable energy

A

ME = DE − UE (− MtE)

  • UE = energy lost in urine
    • bomb calorimetry (must be freeze-dried first)
  • MtE = energy lost in gases
    • account for in ruminants (non-ruminants also have but negligible)
    • anything you can burn has energy
    • don’t account for CO2 b/c non-combustible
    • measure methane production in respiration chamber
    • apply heat of combustion (~212.5 kcal/mol)
  • represents portion of ingested gross energy left over after accounting for losses in feces, urine, & methane gas
  • still does not represent total energy available
  • used for energy evaluation of horses
  • ME available for most species
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9
Q

main indicator of whether or not you’re meeting energy requirements is…

A

body weight gain or body weight loss

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10
Q

net energy (NE)

A

NE = = GE - UE - MtE - HI

  • accounts for heat loss via heat increment (HI)
  • most accurate energy value you can get
  • portion of GE in diet that animal can readily use for maintenance, growth, lactation, & production
  • not available for all feeds & species
    • used for beef cattle & dairy cows ➔ more energy losses for ruminants
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11
Q

heat increment (HI)

A
  1. heat of nutrient metabolism
  2. heat of fermentation (from the rumen, cecum, & colon)
  • useful in winter for animals raised in a non-confinement system
  • could be harmful in summer under hot envir conditions
  • dietary protein > dietary carbs > dietary fats
  • forages > grains
  • dietitians can alter diet to modify HI depending on envir conditions
  • hard to measure
    1. estimate values using equations
    2. bottom-up approach = adding maintenance energy + productive energy
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12
Q

bottom up approach to net energy

A

NE = heat energy (from maintenance) + NEp (productive energy retained in tissues, milk, conceptus, etc.)

  • whenever energy is used for maintenance there is heat generated
  • no heat associated w/ production/weight gain
  • heat energy (HE) can be directly measured by isothermal calorimetry
    - during fasting: ant heat generated must be from maintenance
    - during fasting: HI = 0
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13
Q

maintenance energy (NEm)

A

energy required for:

  1. basal metabolism
  2. voluntary activity
  3. thermal regulation
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14
Q

productive or recovered energy (NEp)

A

energy used for:

  1. gain / growth (muscle, fat)
  2. lactation
  3. egg production
  4. conceptus
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15
Q

energy values

A
  • DE, ME, NE
  • species-dependent
  • too laborious to measure routinely
  • estimations come from chemical composition
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16
Q

net energy values efficiency

A
  • not all NE is used w/ same efficiency for every purpose
  • most efficiently used for maintenance
  • least efficiently used for weight gain
  • efficiency of net energy for lactation is relatively high (almost as efficient as maintenance)
  • must meet energy requirement for lactation, gain, etc.
17
Q

physiological fuel values

A
  • calories listen on human label
  • not GE
  • equivalent of ME
  • calculated by subtracting energy lost in excreta (feces & urine) from GE