Lecture 11 - Digestibility

Question 1

Definition of digestibility

Answer 1

the proportion not excreted in feces, and so assumed to be absorbed by the animal

Question 2

Digestibility can be calculated by:

Answer 2

DIGESTIBILITY = (NUTRIENT INTAKE – NUTRIENT IN FECES) : NUTRIENT INTAKE
commonly expressed in term of dry matter as a coefficient or percentage
e.g. a 0.56 digestibility coefficient means that the dry matter is 56% digestible

Question 3

What are the 3 methods to measure digestibility?

Answer 3

1. Digestibility trials
2. Indicator methods
3. Lab methods

Question 4

1. Digestibility trial aim and its 3 periods

Answer 4

Food under investigation is given to an animal in a known amount and the faecal output is measured.
3 periods:
-adaptation
-maintenance
-collection

Question 5

2. Indicator methods

Answer 5

Uses Internal or External indicators known to be completely indigestible
(INDICATOR IN FECES G/KG DRY MATTER – INDICATOR IN FOOD G/KG DM) : INDICATOR IN FECES (g/kg DM)=quanta dry matter è stata digested and absorbed

Question 6

3. Lab methods

Answer 6

in vitro pepsin and HCl that mimic the activity of GI tract

Question 7

APPARENT VS TRUE DIGESTIBILITY

Answer 7

TRUE nutrients digestibility considers also endogenous faecal nutrients, like metabolic fecal nitrogen in monogastric animals
ruminants, they lose methane by eructation
TRUE NUTRIENT DIGESTIBILITY = (NUTRIENT INTAKE – ENDOGENOUS FECAL NUTRIENT) : NUTRIENT INTAKE

Question 8

6 FACTORS AFFECTING DIGESTIBILITY OF FOOD

Answer 8

• chemical composition
• Positive or negative associative effect (ratio)
• processing
• enzyme supplementation
• animal factors
• level of feeding

Question 9

How do you obtain a kjoule from a kcal?

Answer 9

kcal x 4.184

Question 10

Relationship between gross and chemical energy

Answer 10

Energy is stored in chemical components of food as chemical energy, and the amount of chemical energy in food is measured by converting it to heat.
The amount of heat produced by burning the food and its complete oxidation is known as gross energy value

Question 11

degree of oxidation

Answer 11

(carbon + hydrogen) : oxygen

important bc more oxydizable elements = higher gross energy content

Question 12

Which has the highest gross energy content amongst carbs, proteins and fats?

Answer 12

Fats: 9300kcal/kg DM
Proteins: 5600kcal/kg DM
Carbs: 4100kcal/kg DM

Question 13

bomb calorimetry function

Answer 13

used to calculate the gross energy content of all food
strong steel vessel called bomb resting in an insulating bucket of water
measure water temp before and after burning

Question 14

Gross energy formula

Answer 14

GROSS ENERGY DIGESTIBILITY = (GROSS ENERGY INTAKE - GROSS ENERGY EXCRETED) : GROSS ENERGY INTAKE

Question 15

Metabolizable energy formula

Answer 15

METABOLIZABLE ENERGY = DIGESTIBLE ENERGY - ENERGY LOST IN URINE AND IN COMBUSTIBLE GASSES
so to measure it similar to digestibility trials but feces, gases and urine must be collected as well

Question 16

NET ENERGY

Answer 16

energy actually available to animal for useful purposes

obtained by subtracting food heat from metabolizable energy