ANN 121: Applied Animal Nutrition-I (2+1)

In vivo method of deteriming digestibility - Direct Method

IN VIVO METHOD OF DETERMINING DIGESTIBILITY -DIRECT METHOD

• Digestibility of the nutrient is determined by conducting digestion trial in live animals, involving measurement of nutrient consumed and voided.

Materials Required

1. Experimental animals

• The experimental animals should be of similar breed, type, size or weight, same sex,age and healthy .
• Males are preferred over females because it is easy to collect faeces and urine separately in males. 
• Minimum of four animals are required for conducting the trial.

2. Animal Weighing balance

• A 1000 kg capacity weighing scale is required to weigh the animals before and after conducting the experiment with large ruminats and a 100 kg balance for small ruminants.

3. Metabolic stall or crate

• Metabolic crate is specially designed stall or pen for experimental animal to house in controlled condition during experimental period.
• It is designed to permit the collection of faeces and urine separately.
• The feed box is attached to the front and constructed in such a way to prevent scattering.
• In absence of any metabolic stall or crate, ordinary barn may be adapted to use for digestion experiment with minor modification in relation to manger and faeces collection arrangement.

4. Weighing balance

• 1, 5, 25 kg capacity for weighing feed, fodder and faeces.

5. Buckets or tubs with covers: for collection of faeces

6. Plastic bottles

• Of 2.5 litre capacity (or) buckets of 20 litre capacity are required for urine collection ( metabolism trial) in case of small or large ruminants,respectively.

7. Measuring cylinders

• Required to measure water intake and urine output.

8. Polythene smaple bags

• Required to aliquot faecal samples in dep frezer.

Procedure

1. Collection of test feed 

• Adequate amount of test feed should be available for feeding the animals throughout the thr trial period.
• In case of fodder, ensure regular supply at a particular stage of growth throughout the trial period.

2. Preliminary/Adjustment period

• It is essential that the collection period of a digestion trial be preceded by a preliminary period of 10- 12 days for ruminants.
• In this period, test feed is given in the same weighed amount daily as in the collection period.
• The purpose of this period is to remove all the residues of previous feeding regime in the digestive tract and establish a uniform passage rate of faeces as related to feed intake.

Recording of feed consumption and residual feed (both in the preliminary and collection period)

• Weighed quantity of feed is offered for the accuracy of digestion trial.
• Residual feed should be as minimum as possible, for achieving this feed intake, the pre-experimental feeding period should be regularized in such a way that very little or nothing is left as residual feed.
• Residual feed if any left out during experimental period should be collected and pooled for further analyses.
• The nutrient content of the feed offered and residue left out should be determined to ascertain the accurate amount of nutrient intake.
• The residue feed is often higher in moisture (due to spill over saliva), ash, fiber content and low in protein and NFE.

3.Collection period

• This is the actual experimental period. In this period accurate recording of feed offered, residue left out and faeces and urine voided should be done.
• The length of the collection period depends upon the species. In general, 7–10 days for ruminant .

Preparation of faeces sample

• Faeces from individual animal should be collected without any loss and weighed and then sampled for analyses.
• In cattle, 5 % aliquot is used as a sample for further analyses. In sheep or small animals all portion or major portion (50%) of the faeces may be stored in cans or polythene bags or wide mouth airtight glass jar and stored in refrigeration condition until the end of the collection period.
• At the end of the collection period, samples collected in each day are mixed thoroughly for each animal and composite sample representing the faeces for the entire period is taken for analyses.
• From the aliquot, two samples should be taken, one for crude protein (CP) estimation and other for dry matter (DM) and other nutrient analyses.
• Faeces for crude protein (CP) estimation should be preserved with 5ml of 3% H₂SO₄.

4. Body weight recording

• The experimental animals are weighed consecutively for 3 days just before the collection period at a fixed time in the morning before feeding and watering.
• The average body weight of the animal for 3 days will be considered as the initial body weight of the animal.
• The same procedure of weighing is repeated at the end of collection period to get the final body weight of the animal.

5. Recording of feed intake

• The time at which feed is offered is to be fixed during the preliminary period (for example say 8 a.m). During the collection period,weighed amount of feed will be offered every day at the same time (8.a.m). Simultaneously, a representative sample of feed offered is preserved in the laboratory for the determination of dry matter and other proximate nutrients.

6. Recording of residual feed

• Weight of residual feed is to be recorded on the next day (at 8.a.m.) and processed in a similar manner as in the case of feed offered.

7. Recording of faeces voided

• Faeces voided during a period of 24 h is collected,weighed and processed for preserving aliquots for nitrogen and dry matter determination. The aliquot of faeces to be taken for preservation will depend on the total quantity of faeces voided per day and it may range from 1/100 to 1/1000 part for nitrogen analysis and stored in a deep freeze in labeled polythene sample bags. At the end of collection period,the daily pooled samples are to be defrosted and aliquot taken for nitrogen analysis.

8. Recoding of urine excreted

• Urine excreted during 24 h period should be collected quantitatively and aliquot of 1/100th part is preserved in glass bottles by adding concentrate Sulphuric acid for nitrogen analysis and another 1/100th part is preserved in glass bottles by keeping in deep freezer for mineral estimations.

Calculation of Digestibility

           

                 

• Eg. If the digestibility coefficient of protein in soybean meal is 75 % and the protein content is 45% . The digestible crude protein content of soyabean meal is 45 x 75 /100= 33.75 %.
• Similarly digestibility of other nutrients are also calculated and the “Total Digestible Nutrient (TDN)” is calculated as follows.
• Calculation of Total Digestible Nutrients (TDN)

TDN (%) = % DCP + (% DEE x 2.25) + % DCF + % DNFE.