UNIT 2: (FOOD/FEED COMPOSITION ANALYSIS) AND DIGESTIVE SYSTEMS - digestibility

Question 1

The fraction of a given nutrient of energy that is extracted from food matrix by given GI tract is…

Answer 1

measure of nutrient availability

Question 2

amount of nutrient extracted from food ingested =

Answer 2

overall digestibility

= nutrient released from food matrix via digestion, microbial fermentation, absorption

Question 3

What does total collection method and indicator method measure?

Answer 3

degree of bioavailability or digestibility

Question 4

What type of method is this:

• adapt 7-21 days
• measure intake 3-10 days
• collect and weigh feces
• analyze homogenized samples of food and feces for nutrient

Answer 4

Total collection method

• humans/pigs adapt 7 days, larger animals up to 3 weeks to adapt
• animals need to be isolated

Question 5

How are nutrients of interest measured after collecting with the total collection method?

Answer 5

Apparent Digestibility Coefficient. ADC

Question 6

(total intake - total feces) / total intake

Answer 6

= ADC
apparent digestibility coefficient
(for total collection method)

Question 7

What are limitations of total collection method?

Answer 7

• accuracy of measuring actual food intake (humans - leftovers, animals - play with food)
• metabolic cages -> anxiety

Question 8

What are characteristics of a good indicator?

Answer 8

• not absorbable and move through GIT
• does not alter GIT function
• mix well with food/feed
• easily/accurately measured in feed/fecal samples

Question 9

An indicator that is added to a component of feed is considered…

Answer 9

external indicator

- i.e. silica, ferric oxide

Question 10

Lignin is what type of indicator?

Answer 10

Internal indicator

- a natural component of feed

Question 11

If the digestibility of a wild animal’s diet were to be measured, what method would you use?

Answer 11

Indicator method

Internal Indicator - lignin content measured

Question 12

How do you calculate apparent digestibility coefficient (ADC) for the indicator method?

Answer 12

ADC = (ratio of nutrient/marker in feed - ratio of nutrient/marker in feces) / ratio of nutrient/marker in feed

• this measures the relative amounts of nutrient of interest and marker
• you need 4 things (nutrient intake, nutrient excrete, fecal marker intake/excrete)

Question 13

Total collection method and Indicator method are what measurements of digestibility?

Answer 13

Apparent

Question 14

What does “true” digestibility take into account of?

Answer 14

Endogenous secretions from:

• digestive enzymes
• epithelial cells

Question 15

What type of diet is used to measure true digestibility?

Answer 15

• zero nutrient diet

- if nutrients are found, then they are endogenous sources and can be subtracted from test diet

Question 16

True digestibility coefficient =

Answer 16

[ ratio of nutrient/marker in feed - (ratio of nutrient/marker in feces - ratio nutrient/marker in feces after zero nutrient diet) ] / ratio of nutrient/marker in feed]
[A - (B-C)] / A

Question 17

What are the 5 factors that affect digestibility?

Answer 17

1. feed intake: large meal decreases digestion efficiency
2. particle size: smaller particle = faster travel = less time for digestion
3. Chemical composition
4. Geography: digestibility is higher at higher altitudes (greater retention time)
5. Age of animal: may diminish with age, but mature animals can digest roughage than their young