Farm Animal Metabolism and Nutrition

cereal grain. For instance, based on values
compiled by Sauer and Ozimek (1986), the
digestibility values ranged from 72.3 to
74.5%, 79.8 to 84.6% and 69.0 to 73.7% for
lysine, methionine and threonine, respec-
tively between barley and wheat. The rather
larger within than between variation in
cereal grains indicates that methodological
rather than other factors may be responsible
for a large proportion of this variation.

Protein supplements

Many studies have been carried out to
determine amino acid digestibility values
in protein supplements. These values were
summarized by Sauer and Ozimek (1986),
Knabe et al. (1989) and Knabe (1991).
There were large differences in ileal amino
acid digestibility values among samples of
the same protein supplement, although the
range of variation in protein supplements
is smaller compared with cereal grains.
The variation in ileal amino acid digesti-
bility values within the same protein
supplement was larger in cottonseed meal,
fish meal, meat and bone meal and ground-
nut meal, and smaller in blood meal
(except for isoleucine), canola meal, casein,
soybean meal and sunflower meal. For
example, the amino acids that showed a
relatively large variation in ileal digestibil-
ity values were lysine, methionine and
threonine within different soybean meal
samples, ranging from 80.1 to 90.7%, 74.5
to 96.7% and 70.7 to 82.2%, respectively.
However, isoleucine digestibility values in
blood meal and tryptophan in meat and
bone meal showed the largest differences,
ranging from 60 to 80% and 35 to 65%,
respectively (Sauer and Ozimek, 1986;
Knabe et al., 1989).
In addition to differences in processing
conditions, differences in amino acid
digestibility values between samples of the
same protein supplement (e.g. meals from
oil seeds, meat and bone meal and fish
meal) may also arise from other factors. For
example, differences in digestibility values
in canola meal may result from different
levels of fibre (e.g. Fan et al., 1996).

Last but not least, differences in amino

acid digestibility values for the same feed-

stuff, as reported by different research

groups, may result from differences in

methodology, which will affect, in parti-

cular, the limiting amino acids.

Legume seeds

Legume seeds, such as peas, field beans and

lupins, which can provide a rich protein and

energy source for swine diets, are increas-

ingly used, especially peas. The evaluation

of the nutritive value in pigs for these ingre-

dients is receiving much attention. The

apparent ileal amino acid digestibility values

in legume seeds, mainly in peas, were sum-

marized by Gatel (1992). There were also

considerable differences in ileal amino acid

digestibility values among different pea sam-

ples. Of the essential and semi-essential

amino acids, the differences were relatively

large for cysteine, methionine, threonine and

tryptophan, ranging from 44.0 to 85.0%, 58.0

to 80.7%, 56.8 to 92.1% and 46.6 to 78.0%,

respectively. As discussed by Gatel (1992),

differences in processing conditions, anti-

nutritional factors and other factors associ-

ated with variety and growing conditions

were only in part responsible for the large

variation.

Methodological Sources of Variation

As indicated previously, there are large

differences in the apparent ileal digesti-

bility values of amino acids among sam-

ples of the same feedstuff. These

differences decrease the sensitivity and

reliability of apparent ileal amino acid

digestibility values for assessing amino

acid availability between different feed-

stuffs and cause inaccuracy in diet formu-

lation for swine.

In addition, this variation may mis-

represent the real variation among samples

of the same feedstuff, as methodological

factors are most probably responsible for a

large proportion, whereas inherent factors

may only elicit relatively minor variations.

Methods for Measuring Ileal Amino Acid Digestibility 285