Digestibility by difference

INDIRECT METHOD - DIGESTIBILITY BY DIFFERENCE

Aim

To determine the digestibility co-efficient of nutrients present in concentrate feedstuffs (like grain, cake, bran etc).

Principle

In this method, two digestion trials are conducted; first with maintenance type of fodder and the second trial by feeding test concentrate feed along with maintenance type of fodder. Assuming that the digestibility coefficients of nutrients in maintenance type of fodder remain the same as was determined in the first trial, the digestibility coefficients of nutrients present in concentrate feed are determined by subtracting the amount of undigested nutrients in maintenance type of fodder from the total undigested nutrients voided in faeces in the second trial.

Requirements

  • Test concentrate feedstuff
  • Maintenance type of fodder
  • Experimental animals
  • All the apparatus required for conducting a digestion trial.

Procedure

  • First step is to conduct a digestion trial using maintenance type of fodder and to calculate the digestibility coefficients of all the nutrients (or nutrient in question) present in the fodder.
  • Conduct a second digestion trial by feeding the concentrate feed (for which the digestibility has to be determined) along with maintenance type of fodder (for which the digestibility of nutrients had been previously determined).
  • While conducting the second digestion trial, record the amount of maintenance type of fodder and concentrate feed consumed by the animal /day and also record the total quantity of faeces excreted by the animal per day.
  • Based on the data available from the second digestion trial, calculate the nutrient intake through maintenance type of fodder, nutrient intake through concentrate feed and the total nutrient voided in the faeces by the animal.
  • Based on the data available from the first digestion trial and assuming that the digestibility of nutrients of the maintenance type of fodder remains the same during the second trial, calculate the nutrient voided in faeces through maintenance type of fodder in the second trial.
  • Subtract the amount of nutrient voided in faeces through maintenance type of fodder from the total quantity of nutrient voided in faeces in the second trial so as to get the quantity of nutrient voided in faeces through concentrate feed.
  • Calculate the digestibility coefficients of all the proximate nutrients in the concentrate feed by using the formula
                                                   Nutrient intake – Nutrient outgo
Digestibility co-efficient = ------------------------------------------------ X 100
                                                               Nutrient intake
  • From the first trial, it was found that maize fodder had 60% digestibility for DM and 65% for CP. In the second trial, 25 kg of green maize and 1 kg of GNC were fed to the animal. The animal excreted on an average 22 kg of faeces. The following was the composition of green maize, GNC and faeces.

%Nutrient
Green Maize
GNC
Faeces
% DM
20
90
10
% CP
1.4
42
1.2

Solution
 
1. Calculation of DMI through Green maize:
Amount of green maize consumed = 25 kg
DM content in green maize = 20 %
Amount of DM consumed through green maize = 25 x 20 / 100 = 5 kg.
2. Calculation of DMI through GNC:
Amount of GNC consumed = 1 kg
DM content in GNC = 90 %
Amount of DM consumed through GNC = 1 x 90 / 100 = 0.9 kg
3. Calculation of DM excreted in faeces:
Amount of faeces excreted = 22 kg
DM content in faeces = 10 %
Amount of DM excreted through faeces = 22 x 10 / 100 = 2.2 kg
4. Calculation of DM excreted in faeces through green maize:
Based on first trial, dig. co-eff. Of DM of green maize = 60 %
ie. Un-digestibility of DM of green maize = 100 – 60 = 40 %
Amount of DM consumed through green maize = 5 kg
Assuming that the digestibility co-efficient of DM remains the same,
Amount of DM excreted in faeces through green maize = 5 x 40 / 100 = 2 kg
5. Calculation of DM excreted in faeces through GNC:
Total DM excreted in faeces = 2.2 kg
DM excreted through green maize = 2.0 kg
DM excreted in faeces through GNC = 2.2 – 2.0 = 0.2 kg
6. Calculation of amount of DM digested from GNC:
DMI through GNC = 0.9 kg
DM excreted through GNC = 0.2 kg
DM digested from GNC = 0.9 – 0.2 = 0.7 kg
7. Calculation of digestibility coefficient of DM of GNC:
                                                DM intake – DM outgo
Dig. coefficient of DM = ------------------------------------ x 100
                                                      DM intake
= {(0.9 – 0.2) / 0.9)} x 100
= 77.77 %
Last modified: Monday, 2 April 2012, 5:08 AM