Digestibility

Question 1

Purposes of digestibly

Answer 1

1. Evaluate and quantify available nutrients from individual feed ingredients
2. Evaluate and quantify available nutrients from diets
3. Partition digestion of nutrients in different compartments of the digestive tract
4. Quantify the available energy concentration of feedstuffs and or feeds

Question 2

two approaches used to measure digestibility

Answer 2

1. Animal assessment
   - in vivo
   - in sacco

2.Lab assessment
-in vitro
- in sacco

Question 3

Define internal markers

Answer 3

• Non absorbable, non-toxic, indigestible, easy to
  analyse in feed and faeces
• Used to determine feed intake
• E.g. iNDF
• naturally occurring components within the feed

Question 4

Define external markers

Answer 4

• Chemicals (e.g. Cr2O3, TiO2)
• Used to determine faecal output

Question 5

Assumption made in an in sacco digestibilty trial

Answer 5

Disappearance of substrate from synthetic porous bags in rumen = actual substrate
degradation by rumen microbes

Question 6

stages in vitro rumen digestibility/degradability.

Answer 6

One-Stage Procedure

• Method: Feed is incubated with rumen fluid and a buffer solution for 48 hours.

• First Stage: Similar to the one-stage procedure, feed or feed ingredients are incubated with rumen fluid and a buffer for 48 hours.
• Second Stage: Hydrochloric acid is added to lower the pH, followed by the addition of pepsin, and the mixture is incubated for another 48 hours.

• Stage 1: Rumen fermentation, similar to the initial 48-hour incubation with rumen fluid and buffer.
  -Stage 2: Gastric digestion involves adding hydrochloric acid and pepsin.
  -Stage 3: Intestinal digestion includes adding enzymes such as trypsin, chymotrypsin, amylase, lipase, and bile to complete the digestive process.

Question 7

factors that influence digestibility

Answer 7

1. Ruminal pH
   - Digestibility decreases by approximately 3% for every unit drop below pH 6.2.
2. Physiological Stage of the Animal
   - Digestibility is generally a characteristic of the feed itself rather than the specific animal consuming it.
3. article Size and Processing
   - The size and processing of feed particles affect their digestibility.
4. Feed Source and Composition
   - The interaction between different feedstuffs can affect digestibility. The overall matrix of the diet may differ from the digestibility of individual feed components.
5. Level of Intake
   - Higher intake levels are directly related to an increased rate of passage through the digestive system.
6. Rate of Passage
   - Slower Passage Rate: Allows for more exposure to microbes and digestive enzymes, potentially increasing digestibility.
   - Faster Passage Rate: Results in less exposure to microbes and digestive enzymes, potentially decreasing digestibility.

Question 8

Explain why there is an overestimation of the digestible carbohydrates and energy content of feeds.

Answer 8

• Methane is produced as a byproduct of fermentation in the rumen.
• This methane is eructed (belched) by the animal and not absorbed into the body.
• Essentially, some of the energy that could have been used by the animal is lost as methane gas, making the feed appear more energy-rich than it actually is.

Question 9

Why is it not sufficient to consider that all feaces is equivalent to undigestible feed residues ?

Answer 9

-Fecal material also includes enzymes secreted into the gut and cellular material shed from lining of gut
- it contains :
* nitrogen derived from the body = metabolic nitrogen
* substances and some minerals from metabolic origin
- this can lead to an underestimation of digestible protein content of feed