lecture quiz 11: chemical & biological evaluation of feeds

Question 1

specialized analytical chemical methods

Answer 1

1. gross energy analysis
2. AA analysis
3. mineral analysis
4. vitamin analysis
5. fatty acid analysis

Question 2

bomb calorimetry

Answer 2

• first thing in diet formulation is balancing for energy
• gross energy (heat of combustion) measured by burning sample of feed in a bomb calorimeter & measuring heat produced
• calorie (cal) = basic unit of heat energy → amount of heat required to raise the temp of 1g of water 1ºC (use kcals for livestock)

Question 3

proximate analysis: ether extract (EE)

Answer 3

• supposed to represent the lipids (fats) in a feedstuff
• method: reflux sample w/ boiling ether (C₄H₁₀O) to remove the fat
  
  • ether & hexane (C₆H₁₄) = organic solvent ∴ can dissolve fats/lipids (water = inorganic solvent)
  • uses soxhlet extraction apparatus
  • aka solvent extraction (as opposed to cold extraction that uses pressing/mechanical)
• calculation: %EE = (residue after evaporation of ether)/(sample weight) x 100
• implication of [EE]: ↑ EE% implies that feed has ↑energy
• limitations: crude fat contains true fat in addition to non-nutritive EE components (e.g. chlorophyll & other pigments) ∴ may overestimate fat content
• automated soxtec extraction system uses same mechanism (repeated boiling/condensing/washing → evaporate ether)

Question 4

proximate analysis: N-free extract

Answer 4

• supposed to determine non-structural carbohydrates → readily digestible carb portion (e.g. sugars & starch)
• not determined directly, determined by diff in calculation
• %NFE = 100 - (%H₂O + %CP + %EE + %CF + % ash)
• any errors in those calculations adds together to make big error in % NFE (accumulated errors)
• rarely used by nutritionists

Question 5

gross energy

Answer 5

1. gross energy doesn’t give much direct value in evaluating feedstuffs
2. don’t use gross energy to compare energy value of feedstuffs for animals
3. used as starting point in feed energy evaluation systems

Question 6

near-infrared spectroscopy (NIRS)

Answer 6

• rapid & cost-effective alternatives to traditional wet chemistry analysis of feed samples (not as precise)
• NIR light is shone at sample & measures reflection (compares w/ internal library of feedstuffs)
  
  • works well for forages → have good library
  • good for dealing w/ indiv feedstuffs (not as accurate for TMR or mixed ration)
  • not used in research
• estimates most likely values for moisture, DM, fat, protein, NDF, ADF, ash, & energy content, & some minerals
• disadvantages:
  
  1. only as accurate as database & calibration
  2. not accurate for mixed feeds or uncommon unique ingredients

Question 7

biological evaluation

Answer 7

• use of animals to measure utilization of nutrients from a given feedstuffs or diet
• all involve feeding
• common methods for biological evaluation of feeds:
  
  1. feeding trial determines palatability of feedstuffs & their effect on feed intake & animal performance (e.g. growth & weight gain, milk yield, egg production, etc.)
  2. digestion or metabolism trial
  3. feed energy evaluation systems

Question 8

feeding trials

Answer 8

• measure feed intake & output produced (e.g. weight gain, quantity of milk/eggs)
• used to measure efficiency of feed utilization
• beef, swine, fish, & poultry industries use feed efficiency (feed to gain ratio) as a bench mark for profitability
• feed to gain ratio (aka feed conversion ratio (FCR)) = feed consumption➗body weight gain
  
  • lower # is better
  • for every pound of weight gain animal consumed x amount of feed

Question 9

calorie (cal)

Answer 9

basic unit of heat energy → amount of heat required to raise the temp of 1g of water 1ºC

Question 10

gross energy in water

Answer 10

0kcal/g

Question 11

gross energy in minerals/ash

Answer 11

0 kcal/g

Question 12

gross energy in carbs

Answer 12

4.2 kcal/g

Question 13

gross energy in fats

Answer 13

9.45 kcal/g

Question 14

gross energy in protein

Answer 14

5.7 kcal/g

Question 15

implications of [EE]

Answer 15

↑ EE% implies that feed has ↑energy

Question 16

limitations: crude fat

Answer 16

contains true fat in addition to non-nutritive EE components (e.g. chlorophyll & other pigments) ∴ may overestimate fat content

Question 17

limitations of N-free extract

Answer 17

• not determined directly, determined by diff in calculation
• any errors in those calculations adds together to make big error in % NFE (accumulated errors)

Question 18

what do beef, swine, fish, & poultry industries use as a bench mark for profitability

Answer 18

feed to gain ratio → evaluates feed efficiency