Agriculture Reference
In-Depth Information
Fortunately, the occurrence of industrially
produced amino acids (crystalline amino acids)
on the market gave rise to reductions in crude
protein content by inclusion of crystalline
amino acids. Importantly, the dietary crude pro-
tein can, concurrently with the supplementa-
tion of crystalline amino acids, be lowered by
less inclusion of e.g. soy protein (Fig. 3.6).
This combined action has been the major
feeding measure contributing to the lowered N
excretion that has been observed over the last
decades (Fig. 3.7). From 1985 until 2012, the
excretion of N has been reduced 51% in grower-
finisher pigs.
The first commercially relevant crystalline
amino acid was lysine, but now other amino
acids such as methionine, threonine, trypto-
phan and valine are widely used in the feeding of
monogastric animals (Fig. 3.6). The use of crys-
talline amino acids depends largely on the need
to reduce N excretion, which especially in live-
stock-dense regions or countries is of major con-
cern, because in those areas, regions or countries
strict demands have been defined politically. For
instance, the European Community (EC) intro-
duced directives to alleviate the risk of leaching
of nitrate to prevent pollution of groundwater
and soft water ecosystems 20 years ago (Oenema
et al
., 2011). However, the costs for the replace-
ment of soybean meal, canola, rapeseed etc.
with the crystalline amino acids greatly affect to
what extent these amino acids are used in practi-
cal feeding situations.
The actual utilization and excretion of N in
poultry is shown in Table 3.2. The utilization of
protein is high in broilers whereby the N excre-
tion is less than 50% of the intake, but the utili-
zation is highest in the youngest broilers and
decreases with age. Broilers raised organically
have a much lower protein efficiency compared
with conventionally raised broilers, whereby the
N excretion is much greater in organically raised
birds. Laying hens have a high excretion and low
utilization of N compared with broilers, with the
poorest efficiency in organically raised laying
hens (Table 3.2).
Recently, political focus has also been on
the emissions of ammonia in agriculture. This
also calls for actions in livestock farming, espe-
cially in areas with intensive animal production.
Therefore, restrictions on manure application
and on-farm handling of manure have been
CP retained: 38%
CP in urine: 44%
CP intake: 100%
CP in faeces: 18%
Fig. 3.3.
Retained protein and excreted (faecal
and urinary) nitrogen, percentage of intake in
growing-finishing pigs.
N is excreted in urine (Jensen
et al
., 2011).
The overall principles of N utilization are
shown in Fig. 3.3.
Protein or its constituent essential amino
acids must be supplied on a daily basis in amounts
equivalent to the animal's requirement. The need
for protein/amino acids therefore varies during
the animal's life with the highest percentage of
dietary content in early life. During reproduc-
tion, the percentage of protein and amino acids is
higher in diets fed to lactating sows compared
with diets for pregnant sows.
Historically, the first challenge in pig and
poultry production was to feed protein-
sufficient diets to the animals (protein balanced
feed), which resulted in increased production
and N efficiency because the maintenance require-
ment was lowered due to the higher daily per-
formance (Jensen
et al
., 2011). Nowadays, focus
is on feeding the animals a diet that is balanced
according their amino acid requirement. All
feedstuffs contain crude protein but the
concentration varies (Fig. 3.4). Unfortunately,
cereals and protein feedstuffs not only contain
essential amino acids but also an overload of
non-essential amino acids in relation to the
animals' requirements. Especially, the protein
in cereals contains large proportions of the
amino acid glutamine, which is a non-essential
amino acid. The contents of essential amino
acids also differ between feedstuffs, illustrated
in Fig. 3.5 by the concentrations of lysine and
valine. One way to improve the N efficiency
and reduce the excretion of N is to formulate
diets consisting of low levels of protein supple-
mented with essential amino acids in amounts
sufficient to cover the animal's amino acid
requirement (Nørgaard, 2012).
