Feed Strategy - June 2018 - 43
FeedStrategy ❙ 43
Fava beans are a global legume that deserve
a second look as a valid protein source for
animals. Elena Schweitzer | Dreamstime.com
contain less protein but more oil/energy than soybean
meal - but it is soybean meal that is being used extensively as protein feed. Such possibility does not
exist with fava beans, as their oil content is negligible.
Thus, by replacing soybean meal with fava beans, the
concentration of the latter will have to be higher -
roughly 1.7 kg of fava beans are needed to replace 1
kg of soybean meal (on a protein alone basis, which is
not correct in terms of modern feed formulation, but
it serves to illustrate the point of this discussion).
And, here is where the problems begin.
Anti-nutritional factors in fava beans
Nutrient profile of fava beans used as
There are two major types of fava beans: those from
white-flower varieties and those from colored-flower
varieties. Their chemical composition and nutritive
value is about the same with 25 to 27 percent crude protein, 7 to 8 percent crude fiber, 1 to 2 percent crude fat,
and about 10 and 13 MJ/Kg metabolizable energy for
poultry and pigs, respectively. Compared with soybean
meal, the major difference is in the amount of crude
protein (44 to 48 percent in soybean meal), whereas the
rest of the nutrients and energy concentration are rather
similar. Even the amino acid profile is quite similar with
soybean meal having 6.1 grams lysine per kg protein,
whereas fava beans contain slightly more at 6.5 percent.
Digestibility values do not differ much either.
In practical terms, it is the absolute lower value in
crude protein concentration that places fava beans in
disadvantage to soybean meal. Here it merits mentioning that we have been comparing a whole fruit
(legume), that of fava beans, to a by-product of soybean oil extraction, that of soybeans. Whole soybeans
June 2018 ❙ www.WATTAgNet.com
Most, if not all, legumes contain a plethora of antinutritional factors. These compounds have a wide array of functions within the plant, but when consumed
by animals they inhibit the normal use of nutrients in
legumes and other ingredients. They are not toxins but
rather impediments to normal digestion and metabolism. For example, a well-known anti-nutritional factor
is that of trypsin inhibitor activity (TIA) compound.
This factor inhibits the action of trypsin, an enzyme
secreted during protein digestion. As such, the organism either suffers from lower protein digestibility or it
is forced to secrete higher amounts, leading again to a
net protein loss as enzymes are proteins too.
In the case of soybean meal, the majority - but
not all - of anti-nutritional factors are denatured
and thus neutralized to a great degree by the process
of heat treatment. This is why raw soybeans are not
being fed to monogastric species. Of course, soybeans have other issues too, but this is not relevant to
our discussion. In contrast, fava beans are not being
cooked, and even when they can be treated by some
form of heating (for example, extrusion), this has never been sufficient enough to destroy the majority of
anti-nutritional factors. As such, this problem limits
the usage of fava beans, although some recent efforts
have demonstrated that partially dehulling can create
a form of a fava bean meal that contains relatively
few anti-nutritional factors - but this remains a most
recent development that requires much evidence to
support practical application.