With respect to protein supplements
and legume seeds, most measurements of
apparent ileal digestibility values are made
with the direct method, whereas in the
case of some protein supplements or
legume seeds, some of which are of poor
palatability and/or have a high content of
anti-nutritional factors, the determination
is often carried out with the difference
method (Sauer et al., 1989).
The likelihood exists that the improper
use of determination methods may also be
partly responsible for the considerable
variation in apparent ileal digestibility
values of amino acids within the same
feedstuff. Few studies have been carried
out to compare methods.
Some of the methods for determination
of nutrient digestibility in assay diets and
assay feed ingredients have been described
by Schneider and Flatt (1975). The
principles of three methods to determine
nutrient digestibility in feed ingredients for
ruminants were described briefly by Giger
and Sauvant (1983).
Indicators (e.g. Cr 2 O 3 ) are widely used
in nutrient digestibility measurements, as
reviewed by Kotb and Luckey (1972) and
Van Soest et al. (1983), since they obviate
the need to measure the quantity of assay
diet input or ileal digesta or faeces output
(see Chapter 12). The digestibility values in
the assay diet are usually calculated by the
indicator technique (Equations 13.2 or
13.4) rather than by total collection
(Equation 13.1).DD= AD((IDAF)/IF) (13.4)
where DDis the apparent digestible content
of a nutrient in the assay diet (g kg^1 ), AD
is the nutrient concentration in the assay
diet (g kg^1 ), IDis the indicator concentra-
tion in the assay diet (g kg^1 ), AFis the
nutrient concentration in ileal digesta or
faeces (g kg^1 ) and IFis the indicator con-
centration in ileal digesta or faeces (g kg^1 ).Methods for Measuring Ileal Amino Acid Digestibility 291Table 13.4.The range of crude protein and amino acid contents (g kg^1 , on dry matter basis) in the assay
diets for the determination of apparent ileal crude protein and amino acid digestibility values in protein
supplements.
Soybean meala–m Canola mealc,i,k–m,oSunflower meale,g,j,k Threshold leveln
Protein supplements (n=15) (n=7) (n=6) (n=1)
Crude protein 120–193 157–202 111–196 171
Amino acids
Indispensable
Arginine 9.6–13.4 8.2–13.3 9.4–15.6 11.5
Histidine 3.2–5.1 4.8–6.9 3.1–4.5 4.3
Isoleucine 5.7–9.0 6.8–8.7 4.6–7.9 8.3
Leucine 9.8–14.5 12.6–13.9 6.7–12.0 13.3
Lysine 7.9–11.4 9.2–11.1 4.3–6.9 9.4
Methionine 1.8–2.6 3.2–5.0 2.7–4.2 2.4
Phenylalanine 5.6–9.6 6.9–8.4 4.9–8.2 8.2
Threonine 4.6–7.8 8.1–9.4 3.8–6.9 6.3
Valine 9.4–9.7 8.9–10.9 5.2–9.6 8.4
Dispensable
Alanine 4.9–8.4 8.0–8.9 4.6–8.1 6.9
Aspartic acid 14.3–17.9 13.4–16.1 10.1–17.3 17.1
Cysteine 1.8–2.6 3.0–5.3 1.9–3.1 2.4
Glutamic acid 23.7–32.2 30.6–36.5 21.5–38.9 23.1
Glycine 4.6–8.1 8.9–10.0 6.0–11.0 6.7
Serine 6.0–9.1 7.9–8.5 4.5–8.7 8.7
Tyrosine 4.7–5.6 3.7–4.9 3.0–4.9 6.2
aHolmes et al. (1974); bTanksley et al. (1981); cSauer et al. (1982); dRudolph et al. (1983); eJørgensen et al.
(1984); fLa Rue et al. (1985); gJust et al. (1985); hChang et al. (1987); iImbeah et al. (1988); jGreen and
Kiener (1989); kKnabe et al. (1989); lDe Lange et al. (1990); mFan et al. (1993); nFan et al. (1994); oFan et al.
(1996).