Measurement of pasture consumption and its digestibilty

MEASUREMENT OF PASTURE CONSUMPTION AND ITS DIGESTIBILTY

Aim

  1. To determine the amount of pasture consumed by the animal on range.
  2. To determine the digestibility of the feed consumed by the animal on range.

Requirements

  1. Experimental animals on range
  2. External indicator (chromic oxide)
  3. Internal indicator (lignin)

Procedure

First method

Example

Amount of DM voided in faeces in 24 h = 2500 g
Digestibility of DM determined = 50 %
100 g DMI resulted in 50 g DM excretion in faeces
g of DM consumed for excretion of 2500 g of DM in faeces
                               = 2500 x 100 / 50 = 5000 g.

Second method

In this method, the DMI is determined by using an indicator. This indicator can be a natural indicator (present in feed) like lignin or an external indicator (mixed with feed) like chromic oxide (or) chromic oxide (green).

  • In this method, there is no need for harnessing the animal with faecal bags for quantitative collection of faeces.
  • In such cases, a grazing animal is fed a measured amount of an external indicator and grab samples (these are small samples of faeces removed from the rectum manually or collected at random from the pasture at various times during the day) of faeces are collected subsequently.

Pasture consumption

  • The total faecal DM output (g) can be determined by use of external indicator as shown in the formula given below.
                                                                          External indicator fed (g)
              Faecal DM output (g) = -------------------------------------------------------------- x 100
                                                         % external indicator in faeces grab sample DM
Note:
  • The DM consumed (g/day) can be determined by use of internal indicator as shown in the formula given below.
                                                   {Units of internal indicator {g of DM in
                                                       per g of dry faeces} x faeces per day}
DM consumption (g/d) = -------------------------------------------------------------
                                               {Units of internal indicator per g DM of forage}
The DM consumed (g / d) can also be determined from DM digestibility by use of internal indicator as shown below.
                                                                                   % indicator in feed         % nutrient in faeces
                    DM digestibility = 100 – {100 x -----------------------------x -----------------------------}
                                                                                 % indicator in faeces        % nutrient in feed
             Indigestibility of DM = {100 – Digestibility of DM}
                                                                 DM in faeces (g)
              DM consumed (g/d) = ---------------------------------- x 100
                                                            % indigestibility of DM
Example:
a. Fed – 10 g chromic oxide per day
b. Feed contained – 13 % lignin (DMD)
c. Faeces contained – 1.15 % chromic oxide (DMB)
22.6 % lignin (DMB)
Solution:
 
1. Calculation of DM voided in faeces (g/d):
                                                              External indicator fed (g)
Faecal DM output (g) = ------------------------------------------------------------ x 100
                                            % external indicator in faeces grab sample DM
                                     = (10 / 1.15) x 100
                                     = 870 g  
2. Calculation of DM consumed per day:
                                                    {Units of internal indicator {g of DM in
                                                       per g of dry faeces} x faeces per day}
DM consumption (g/d) = ------------------------------------------------------------
                                             {Units of internal indicator per g DM of forage}
                                        = (22.6 / 13) x 870
                                        = 1513 g 
3. Calculation of DM digestibility:
                                                              % indicator in feed         % nutrient in faeces
DM digestibility = 100 – {100 x ------------------------------x --------------------------------}
                                                              % indicator in faeces         % nutrient in feed
                                                        13      100
                          = 100 – {100 x -------x-------}
                                                      22.6    100
4. Calculation of indigestibility of DM:
Indigestibility of DM = {100 – Digestibility of DM}
                                    = 100 – 42.5 = 57.5 %
5. Calculation of DM consumed based on the indigestibility of feed:
                                                 DM in faeces (g)
DM consumed (g/d) = ------------------------------- x 100
                                            % indigestibility of DM
                                   = (870 / 57.5) x 100
                                   = 1513 g.
 
1. Calculate the DMI, DM digestibility and CP digestibility in an animal maintained on range conditions by using the following data.
a. Fed - 10 g chromic oxide per day
b. Feed contained - 14 % Lignin (DMB)
                         12 % Protein (DMB)
c. Faeces contained – 1.5 % Chromic oxide (DMB)
                        18 % Lignin (DMB)
                        9 % Protein (DMB)
42.5 %: Calculate the DM intake and DM digestibility of an animal maintained on range conditions by using the following data. Grab samples should be taken from each animal to keep error below 5 % and chromic oxide should be fed for atleast 10 days before the start of sampling. Faeces bags (if necessary) method: In this method, the animals are harnessed with faeces bags. An animal on range has voided 2500 g DM in faeces in 24 h. The digestibility of DM of pasture on range determined separately was 50 %. Calculate the amount of DM consumed by that animal.
  • The DM voided can be determined by collecting the total faeces in the faecal bags.
  • Simultaneously, the DM digestibility of the fodder available on range for grazing is determined by feeding the fodder to the animals in metabolism stalls.
  • If the DM digestibility of the feedstuff as well as the DM voided in faeces are known, the DM consumed can be determined.
Last modified: Wednesday, 4 April 2012, 5:22 AM