Nutrient digestibility

Question 1

DEFINITION

Answer 1

Digestible nutrients: proportion which is not excreted by the faeces;
Expression:
1. Digestibility coefficient (E.g. 0.85),
2. Digestibility in % (E.g. 85%).

Question 2

Characterization of feeds

Answer 2

1. Nutrients (CP, EE, CF, NFE);
2. Digestibility: calculation of the digestibility coefficients;
3. Digestible nutrients (DCP, DEE, DCF, DNFE) = nutrients * digestibility coefficients;
4. Digestible nutrients ➔ DE
5. Digestible nutrients ➔ TDN ➔ NE(l).
   TDN = Total Digestible Nutrients.

Question 3

2.1 Faecal Digestibility

Answer 3

measure of feed intake and total collection of faeces are required
Apparent Digestibility:
= (nutrient intake−nutrient output)/ nutrient intake
aka (absorbed nutrients/nutrient intake)
E.g. digestibility of the CP content of corn fed to swine; Fi (feed intake): 6000 g DM;
FE (faeces output): 2500 g DM;
CPf (CP content of feed) : 9%;
CPfe (CP content of faeces) : 4%
(CP intake) − (CP output)/(CP intake) =
(60000.09) − (25000.04)/(6000*0.09) =0.8148 (coefficient)

Question 4

2.2. In vitro enzymatic methods

Answer 4

Pepsin Digest Residue (PDR)
Pepsin-Pancreatin Digest (PPD)
liberation of amino acids by enzymes/total amino acid content
− prediction of the protein digestibility,
− prediction of the protein damage (e.g. heat damage).

Question 5

3. Digestible nutrients = nutrients * digestibility coefficients

Answer 5

CP(extr. soybean meal) = 480 g/kg,
Dig. Coeff. of CP(extr. soybean meal0 = 0.8,
Digestible Crude Protein (DCP)(extr. soybean meal) = 480*0.8 = 384 g/kg

Question 6

4. Digestible nutrients ➔ DE

Answer 6

Prediction of the DE content of extracted soybean meal (MJ/kg)
DEpig (MJ/kg) = 0.0242DCP + 0.0394DEE + 0.0194DCF + 0.0170DNFE

Question 7

5. Digestible nutrients ➔ TDN ➔ NEl

Answer 7

I. TDN = DCP + 2.25DEE + DCF + DNFE;
II. DE = 0,01845TDN;
III. Corrected DE = DE(1-2df);
IV. NEl = 0.6032corrected DE – 0.502.

Question 8

Apparent digestibility vs. true digestibility

Answer 8

Apparent Digestibility: CP intake − CP output/CP intake
True Digestibility:
CP intake − CP output + endogen CP /CP intake.

Question 9

INDICATOR METHOD

Answer 9

measure of feed intake and collection of faeces are not required, only sample takings are needed
Indicator - indigestible substances (e.g. Cr2O3, Fe2O3, SiO2, Mn, Lignin)
Calculation (e.g. CP digestibility):
(indicator/CP in the faeces − indicator/CP in the feed) / (indicator/CP in the faeces)