SELECTED ARTICLES
THE EXPLOITATION OF STRAW FOR FOOD
By MAJOR G. WILLIAMSON,* O.B.E., Royal (Dick) Veterinary College, Edinburgh
(Reproduced from The Journal of the Royal Army Veterinary Corps, Vol. 12, No. 4, August 1941)
IN normal times, or at least in times of peace
cereal straws are used as food for animals to an
important extent only in the backward agricul-
tural areas of the world ; elsewhere the main func-
tion of straw in agricultural economy is to form a
basis for the production of manure. It thus hap-
pens that those who are the chief users of straw as
forage are in no position to exploit modern know-
ledge in an endeavour to realize its full potentiali-
ties, while to those who could do so the subject
generally is of little importance because they have
easy access to richer sources of nourishment. When
these sources are denied to them and when perhaps
because of difficulties of transport and an urgent
demand for fats, the handling of material with a
high oil and protein content is undertaken more
readily than is that of the more carbonaceous foods,
then the latter, being at hand, has its value much
enhanced, while the deficiency of protein with
which it may be associated and which in normal
times makes it economically worthless, is then of
less moment. It is, in fact, such conditions, or the
possibility of such conditions, that have turned the
attention of nutritionists to a study of the means
of extracting from straw its maximum use as
food.
A glance at the table below is sufficient to show
the nature of the problem involved :
Composition of the cereal straws
Straw
Oats (Winter) . .
Oats (Spring) . .
Barley . . .
Wheat (Winter) .
Wheat (Spring) .
Chemical composition
Pro-
tein
1.9
2.9
3.3
2.1
2.9
Oil
1.5
1.9
1.8
1.3
1.3
Carbo-
hydrates
Solu-
ble
43.1
42.4
42.4
40.7
39.8
Fibre
34.6
33.9
33.9
36.6
35.9
Digestible constituents
Pro-
tein
0.5
0.9
0.7
0.5
0.5
Oil
0.5
0.6
0.6
0.4
0.4
Carbo-
hydrates
Solu-
ble
19.8
19.4
22.5
15.0
14.7
Fibre
19.7
18.3
18.3
18.3
18.0
Ash
4.9
4.9
4.6
5.3
6.1
Starch
equiva-
lent
21
20
23
13
13
First, one sees how comparatively rich the straws
are in carbohydrates but how poorly these car-
bohydrates are utilized by the animal and how
that low digestibility applies not only to fibre but
also to the soluble carbohydrates. Again, one sees
immediately that little of the protein and fat is
digestible, but that at any rate the quantity of
these constituents is so small that they have little
significance from a feeding point of view. The
amount of ash is of some importance and more,
important still is the amount of silica which it
contains. Although the total amount of minerals
in straw is somewhat less than that contained in
hay, its nature is very different because silica
generally forms a quarter to a third of the straw
ash, that is 1 to 2 per cent of the total composition,
while the quantity of lime and phosphoric acid in
it is negligible.
Straw thus can be made useful as a food only
when the digestibility of the carbohydrates can be
very considerably raised. To do that it is neces-
sary to appreciate the conditions which account for
their low digestibility. In the first place, as the
analysis shows, more than half of the carbohydrates
is composed of crude fibre. This crude fibre con-
sists primarily of cellulose and other complex poly-
saccharides, the most important of which are lignin
and cutin. The lignin and cutin envelop and
impregnate the cellulose, forming as it were a
vegetable skeleton as well as a protective covering.
The crux of the question lies in the manner in
which these substances are dealt with in the intesti-
nal tract, for if they are not broken down the
material which they enfold must remain unaffected
by the digestive juices.
Pure cellulose is comparatively well digested by
herbivora but not so by other types of feeders
because its digestion depends not upon the action
of intestinal enzymes as does that of other car-
bohydrates but on the action of the enzymes of
* At present Animal Husbandry Commissioner with the
Government of India
62