Agriculture Reference
In-Depth Information
thermal well-being, whereas animals kept in
thermo-neutral conditions have no extra need
for energy as the heat production is at a mini-
mum. In hot areas, the animal's capacity to get
rid of the heat generated by the metabolic pro-
cesses taking place within the body often reduces
feed intake (Tauson, 2012). Consequently, the
climate or housing conditions may have sub-
stantial impacts on feed intake affecting the
efficacy of turning feed into edible products.
Therefore, the concentration of nutrients
(protein, amino acids, minerals etc.) has to be ad-
justed to the energy supply in order to optimize
the intake to the animal's requirement. The
actual requirement for energy and nutrients
is dependent on the physiological stage of the
animal and therefore the use of phase feeding
where the feed composition is adjusted to the
changes in the nutrient and energy requirement
is widely practised (Kebreab et al ., 2012). This
means that several feed mixtures are used to
raise a broiler or a growing finishing pig.
Genetic selection programmes have led to a
substantial increase in the capacity for lean tis-
sue growth and decrease in the rate of fat deposi-
tion in monogastric animals (Jensen et al .,
2011). At the same time, the selection for lean
tissue growth (less deposition of fat) has also
improved average daily gain (ADG) and FCR, as
the feed amount needed to produce 1 kg lean
meat is much lower compared with the need for
producing 1 kg fat. A major tool to improve the
utilization of all nutrients and energy is there-
fore to minimize the amount of feed needed to
produce 1 kg of product. The goal is to reduce
both the maintenance requirements and the
number of days required to produce a pig or a
chicken to a minimum. The overall principles of
nutrient utilization are shown in Fig. 3.1.
Selection programmes for higher ADG and
lower FCR are widely applied (Jensen et al .,
2011). Animals have undergone selection for
productivity, which means that modern breeds
demand less feed for producing a unit of product.
Actually, the FCR is often as low as about 1.5 in
chicken (during the 30 days to reach a body
weight of 1.6 kg) and 2.6 in growing finishing
pigs (30-110 kg body weight) (Poulsen et al .,
2012). All things being equal, an improvement
in FCR has major impact on the general utiliza-
tion of energy and nutrients. The development in
FCR in growing finishing pigs is shown in Fig. 3.2.
Feed nutrients
Faecal excretion
Absorbed nutrients
Urinary excretion
Nutrients in products
Fig. 3.1. Conversion of nutrients in feed into
products and excretions.
As it appears later in this chapter, the dramatic
improvements during the 1980s and 1990s are
partly due to the more efficient protein utilization
and subsequent growth.
Growth is usually expressed in daily gain
but can also be expressed in protein retention,
which emphasizes that focus has to be put on
protein accretion to obtain lean growth. All
things being equal, this will also result in the
most efficient conversion of feed into edible
products for human consumption.
Protein, Amino Acids and Nitrogen
Utilization and Efficiency
Protein is an essential dietary component for all
animals, but it is not protein per se but the amino
acids as constituents of proteins that play a role
(Lewis and Southern, 2001). Basic knowledge
of the importance of amino acids in relation to
productivity (growth and reproduction) has
been critical for improvements in N utilization in
monogastric animals (Jensen et al ., 2011). It is
recognized that some of the 20 different amino
acids present in proteins have to be supplied by
the feed every day and are thus considered
essential amino acids, whereas others are non-
essential, i.e. they do not need to be provided as
they can be synthesized by the animals (Table 3.1).
Three of the amino acids are considered semi-
essential as they can only be synthesized from
essential amino acids (cysteine from methio-
nine (both contain sulfur) and tyrosine from
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