lecture 10: proximate analysis continued

Question 1

crude fiber

Answer 1

measure of the quantity of cell wall fraction in a feed

Question 2

proximate analysis: crude fiber

Answer 2

• any feedstuff from plant origin has some fiber (incl byproducts & seed coats of grains)
• steps:
  
  1. boil sample in dilute acid (pH just below 7 e.g. H2SO4) ➞ breakdown proteins, sugars, starch
  2. boil sample in dilute base (e.g. NaOH) → saponifies fatty materials (remaining material = CWF + minerals)
  3. determine amount of ash (via burning in muffle funrace at 500ºC) & subtract out from material weight in step 2
  4. %CF = (crude fiber weight)/(weight of original sample) x 100

Question 3

the methods used in proximal analysis are:

Answer 3

gravimetric methods

Question 4

crude fiber limitations

Answer 4

• intent: measure of fiber (cellulose, hemicellulose, lignin) in feed
• reality: may recover only:
  
  • 10-15% of lignin
  • 15-20% of hemicellulose
  • 50-80% of cellulose
• does not accurately measure cellulose, hemicellulose, or lignin

Question 5

examples of feed byproducts

Answer 5

• wheat middlings
• almond hulls
• cottonseeds
• citrus pulp
• soy hulls
• wheat bran
• beet pulp

Question 6

detergent fiber methods (van soest methods)

Answer 6

• crude fiber = most important nutrient for ruminants & hind-gut fermenters b/c makes up major part of their diet
• more accurate than proximate analysis crude fiber method (can accurately separate cell wall components)
• primarily used for forage evaluation
• not part of proximal analysis
• neutral detergent fiber (NDF) = cellulose + hemicellulose + lignin (cell wall fraction)
  
  • boil sample in neutral detergent soln (pH 7.0) to remove plant cell contents to get remaining residue
  • remaining residue = NDF
  • reflects bulkiness of forage (higher NDF = more bulk)
• acid detergent fiber (ADF) = cellulose + lignin (& some lignified N = ingestible proteins)
  
  • boil in acid detergent to remove hemicellulose & cell wall N to get ADF residue
  • using new sample
  • reflects indigestible components of a forage

Question 7

↑NDF =

Answer 7

↓ intake for ruminants

• sample is bulky
• particle size restriction in ruminants due to reticulo-omaso orifice to get to next compartment (omasum)
• larger CWF takes longer to break down → stays in rumen longer giving full sensation
• similar relationship w/ horses but not same extent
  
  • horses have no particle size restriction (can see larger particles in feces)
  • can just consume more to make up for low quality

Question 8

what reflects indigestible components of a forage

Answer 8

acid detergent fiber (ADF)

Question 9

↑ADF =

Answer 9

less digestible → ferments to a lesser extent → provides less VFAs→ less energy

Question 10

fiber analysis apparatus

Answer 10

• uses crucible
• via reflux system: boil & condense repeatedly until all cell wall components are gone

Question 11

what happens to a plant’s cell wall as it matures

Answer 11

proportion of stems to leaves ↑ (↑CWF) → less digestible

Question 12

neutral detergent fibers (NDF)

Answer 12

cellulose + hemicellulose + lignin residues (cell wall fraction)

Question 13

acid detergent fibers (ADF)

Answer 13

cellulose + ligning residues (+ some lignified N)