Agriculture Reference
In-Depth Information
Table 3.2.
Nitrogen excretion and utilization in poultry (Poulsen
et al
., 2012).
Type of poultry
Duration
Nitrogen excretion (kg)
Nitrogen utilization (% of intake)
1000 broilers
30 days
34.0
58
1000 broilers
32 days
39.2
57
1000 broilers
35 days
47.7
55
1000 broilers
40 days
64.8
53
1000 broilers
81 days, organic
126.6
33
100 female turkeys
a
112 days
48.1
37
100 geese
a
91 days
56.1
22
100 ducks
a
52 days
17.3
34
100 layers hens, batteries
1 year
69.3
34
100 laying hens, free living
1 year
82.9
29
100 laying hens, organic
1 year
101.1
25
a
The production of these birds is limited in Denmark and the calculated excretions are only indicative.
Phosphorus Utilization
and Efficiency
is shown in Table 3.3. Phytic acid is able to form
complexes with minerals (as shown in Fig. 3.8)
but also with proteins and other components
present in seeds. InsP
6
is mainly deposited in
the protein bodies of the aleurone or cotyle-
dons in cereals and seeds. During germination
and early growth, InsP
6
is degraded and phos-
phate molecules are gradually released turn-
ing the InsP
6
into InsP
5
, InsP
4
and so forth.
Unfortunately, monogastric animals do not
possess sufficient capability to digest phytate
whereby phosphate could be released in a simi-
lar way. Therefore, feed for monogastric ani-
mals has, as mentioned, been supplemented
with phosphate of non-vegetable origin (meat
and bone meal, bone meal or inorganic phos-
phates from mines).
Since the early 1990s, when the first
reports on the effects of supplementing micro-
bial phytase to feeds for monogastric animals
were introduced (Simons
et al
., 1990), the use
of the enzyme has expanded globally. The rea-
son for this is that the degradation of phytate
is stimulated by phytase whereby the release
of phosphate molecules is increased. This
results in increased P absorption in pigs and
poultry when feed contains phytase. For more
than 20 years, the effects of phytase have been
studied in hundreds of experiments with pigs
and poultry. At the same time, different com-
panies have developed different phytases
that are able to dephosphorylate InsP
6
.
Comprehensive reviews have been presented
(Jongbloed, 2012) or published recently (e.g.
Selle and Ravindran, 2007, 2008).
Many minerals are essential dietary components
for all animals but they are only required in very
small amounts, macro-minerals in grams per
kilogram and trace minerals in parts per million
(mg kg
−1
) or less. The functions of the minerals
are diverse and range from structural functions
in the body to regulatory components of sub-
stances and enzymes in tissue and blood.
Phosphorus interacts with calcium and conse-
quently plays a major role in the development
and maintenance of the skeleton in all animals.
Moreover, P is substantial in many other pro-
cesses such as the metabolism of energy and cell
replication. It is well known that animals fed
P-deficient diets develop a soft skeleton that is
incapable of keeping the animals healthy and in
a standing position. Therefore, for decades, it has
been common practice to add inorganic miner-
als to diets consisting of cereals and protein
sources of plant origin. Previously, bone meal or
meat and bone meal was also widely used, but due
to restrictions in the use of animal by-products
this use is not currently allowed in some areas
(e.g. within EC). Thus, inorganic P sources are
still commonly used to ensure a sufficient die-
tary P content to cover the animals' P need.
Most P in cereals and seeds is present as
phytate, the salt of phytic acid that consists of a
ring of six carbon atoms (
myo
-inositol) to which six
phosphate groups are attached (Erdman, 1979).
Phytate is referred to as
myo
-hexakisphosphate
or InsP
6
and the presence in different feedstuffs
