Lecture 3- Digestibility

Question 1

Digestibility:

Answer 1

• Measure of the fraction of a specific nutrient (or of energy) that is extracted by the GI tract
• Calculated from the amount of nutrient in the diet and the amount appearing in the feces
• Represents a combination of nutrient release from the food matrix, microbial fermentation, and absorption
○ Absorption of some nutrients affects the absorption of other nutrients
Prevents deficiency and ensures essential nutrients are available to the organism

Question 2

Total Collection Method:

Answer 2

• Allow animal to adapt to diet over a 7-21 day period
• Isolate animal for quantitative analyses
• Measure intake over a 3-10 day period
• Collect and weigh all feces
Analyze for nutrient of interest

Equation

Question 3

Limitations of the Total Collection Method:

Answer 3

• Accuracy in measuring food intake (spilled food…etc)
• Metabolic cages creates anxiety in animals, which may then behave abnormally
○ Metabolic cages accurately determine intake/out take of food (spilled food, put it back in food bowl)
• Labour intensive
• Animals confined in costly equipment
Not feasible for captive wild animals

Question 4

Indicator Method:

Answer 4

Also referred to as the “Marker Technique”
• Adapt animal to test diet (which contains marker)
• Collect feed and fecal sample (don’t need all of it, just a sample)
• Analyze each for marker and nutrient of interest relative to the indicator
○ Looks at ratio between nutrient of interest and marker
• Less labour intensive, ideal for wild animals

Equation

Question 5

Marker

Answer 5

○ Internal- natural component of the feed
○ External- component added to the feed
○ Non absorbable
○ Must not affect or be affected by GIT (can’t be broken down, or make the animal sick which might affect the digestive tract activity)
○ Must mix easily with food (want it to be consumed by animals, don’t want them to know it is there or it might change how much they eat)
○ Easily and accurately measured in a laboratory setting
i.e. ferric oxide, silica, lignan

Question 6

Apparent vs. True Digestibility:

Answer 6

• Apparent digestibility underestimates true digestibility, doesn’t account for
○ Endogenous secretions
§ Epithelial cells converted into fatty acids (cell membranes made of lipids)
○ Bacterial growth in gut
§ Nutrient synthesis -> biotin
○ Digestive enzymes
§ Protein secretion (constantly secreted from cell to break down food, ends up in feces)
○ Vitamin synthesis
Bacteria produces vitamins not taken up by host, passed through feces

Question 7

Measuring True Digestibility:

Answer 7

• Perform digestibility study using test diet
• Switch to diet containing none of the nutrient of interest
○ If interested in protein, zero nutrient diet will have no protein
• Analyze feces after test diet is cleared
Subtract level of nutrient in feces of animals fed zero nutrient diet from test diet

Equation

Question 8

Factors That Affect Digestibility:

Answer 8

• Over 50 factors that can influence digestibility
• Feed intake
○ Composition of food can affect digestibility
• Particle size
○ Smaller molecules move more quickly, less time for them to be absorbed
• Chemical composition
○ Structure of compounds affect digestibility
• Climate
○ Hotter climates increases digestibility
• Age
○ Some organisms improve digestibility with age
§ Accumulate bacteria with age (sterile at birth- no bacteria)
Set bacteria levels reached at adulthood