CHAPTER TWO
2.0 LITERATURE
REVIEW
2.1 Problem
of Poultry Production
The problem of protein deficiency in Nigeria is
evidenced by the fact that an average Nigeria consumes about l0g per day of the
minimum daily protein intake of 35g recommended by Food and Agricultural
Organization (FAO, 1997). Ani and Adiegwu (2005) had attributed the low protein
intake to low level of animal protein production and high cost of animal
products, and suggested the intensification of the production of highly
reproductive animals with short generation intervals such as poultry, pigs and
rabbits (Fielding, 1992; Serres, 1992; Smith, 2001).
However, the major factor
militating against intensive animal production in Nigeria is the high cost of feed
and feed ingredients like maize, soybean cake and groundnut cake (Obioha, 1992)
The ever increasing cost of poultry feeds with the attendant increase in the
cost of chickens and eggs shows that there is need to explore the use of
alternative feed ingredients that are cheaper and locally available such as
cassava peel meal, bambara nut waste, maize chaff etc.
2.2 Bambara
Nut Waste
Bambaranut (Vigna
Subterranean (L) verdc) waste is
widely cultivated in the Northern and Southern States of Nigeria where the
seeds are processed into flour and consumed as moi moi (Enwere 1998). The processing
of the seeds into flour results in the production of the waste which contains
16.40% crude protein (Okeke 2000). Bambara nut waste has been used in feeding
of poultry and rabbits (Okeke, 2000; Ani and Okafor, 2004; Ani; 2006, Ani; 2008).
However, its use in the feeding of monogastric animals is limited by the
presence of such anti-nutritional factors, as protease inhibitors,
haemoglutinins, tanins, cyanogenic glycosides and flatulence factors in the raw
bean (Doku and Karikari, 1981; Esminger, 1996; Enwere 1998).
Besides antinutritional factors,
another limitation is its high fibre content. Poultry cannot fully utilize high
fibre diets because they lack the digestive framework that can elaborately
digest large amount of fibre. It becomes imperative, therefore, to incorporate
exogenous enzymes into their diets in order to enhance the breakdown of the
non-starch po!ysaccharides (NSPs) present in fibre.
2.3 Production and Nutritional Value of Roots
and Tubers (Cassava)
Cassava is cultivated as staple
food crops. They are efficient in producing cheap food energy. More than 228
million tons of cassava was produced world wide in 2007, of which Africa accounted
for 52%. In 2007, Nigeria produced 46 million tons making it the world’s
largest producer (Table 1). The yields of sweet potato was 15-20 tonnes per
hectare and cocoyam give 25-30 tonnes per hectares of corms depending on
planting density
Table
1: Nutritional value of roots and
tubers (cassava) in different
countries
Year
Countries 2006 2007 2008* 2009**
Nigeria 45721 34410 42770 45000
Congo,
Dem Rep. of 14989 15004 15020 15036
Ghana 9638 9650 9700 10000
Angola 8810 8800 8900 9000
Mozambique 6765 5039 8400 9200
Tanzania,
United 6158 6600 6700 6500
Rep.
of 6158 6600 6700 6500
Uganda 4926 4456 4942 4500
Malawi 2832 3239 3700 4000
Madagascar 2359 2400 2405 2000
OtherAfrica 15,251 15,354 15923 16233
Africa 117 104 118 121469
449 952 461
Latin
America 36311 36429 37024 36606
Asia 70465 75882 77631 83715
World 224 217 233 242069
483 536 391
The roots, tubers and their
by-products are valuable sources of nutrients (Table 2). They share a number of
nutritional characteristics that constitute serious limitations for their
practical use in poultry, pig and fish feeding, if they are compared with the
cereals which are feed ingredients. The most important of these limitations are
as follows:
i.
All of them are
succulent materials with low content of dry matter (25-32 percent).
ii.
This makes the
preservation, transport costs and general handling more difficult.
ii. All
of them have starch being the major component with low protein (2.7-7.9
percent) that obviously needs adequate protein supplementation
iii. Root
and tuber by-products (peels, leaves and vines) are high in crude fibre
(12.1-16.0%). With such high level, the use of appropriate exogenous enzymes to
degrade the fibre is required for improved utilization by non ruminants (Longe,
2006)
iv. Some
of them contain toxic/anti nutritional factors (Table 3) such as cyanogenic
glycosides (lineation and lotaustralin) in cassava which cause bitter taste and
reduce palatability of the roots. Cocoyam contains irritating/ acidity
substance that causes burning sensation. The undesirable substances must be
eliminated through some kind of processing such as fermentation, grating, boiling
or sun-drying before being fed to animals to reduce the risk of toxicity.
v. Microbial
contamination due to high moisture content. Sun-drying of these materials in a
humid environment, especially during a bad weather, results in the
proliferation of microbial organisms in the feed materials. It is imperative to
have driers and silos to reduce deteriorative changes and contamination.
vi. Dustiness
of the dried roots and tubers flour can cause irritation of the respiratory
tract unless feed is pelletized or palm oil is added.
2.3.1 Anti Nutritional Factors
Foods are complex substances that contain many
chemical compounds, many of which are required to nourish the body. These
nutrients include water, protein, lipid, carbohydrate, minerals and vitamins.
Most plant foods consist of natural compounds or anti-nutrients that appear to
function generally in defense against herbivores and pathogens. Anti-nutrients
are potentially harmful and give rise to a genuine concern for human and animal
health in that they prevent digestion and absorption of nutrients. They may not
be toxic as such, but can reduce the nutritional value of a plant by causing a
deficiency in essential nutrients or preventing thorough digestion when
consumed (Prathibha et al., 1995).
The most commonly known and studied anti-nutritional factors in roots and
tubers include cyanogenic glycosides, saponin, phytate, oxalate, enzyme
inhibitors and total alkaloids (Table 3). They must be inactivated or removed
before they are suitable for non ruminants or fish (Bhandari and kawabata 2004;
Agbor-Egbe and Mbome 2006).
The cyanogenic glycosides or
cyanogens are glycosides of 2-hydro xynitriles that are synthesized and stored
in cassava and are widely distributed among plants (Rosenthal and Berenbaum
1991; Bisby et al, 1994). The peel
component has the highest concentrations of cyanogenic glycosides in cassava
(Table 3). In cocoyam tubers, Abdulrashid and Agwunobi (2009), Olajide et al., (2011) reported wide variation
(2.10-11
17.13mg/bOg)
in the level of these undesirable substances. Hydrolysis of cyanogenic
glycosides releases hydrogen cyanide (HCN), which inhibits several enzyme
systems, depress growth through interference with certain essential amino acids
and utilization of associated nutrients (Tewe and Egbunike 1992, Okafor, 2004).
Cytochrome oxidase is the primary site of action for ingested cyanide, an
effective inhibitor of many metalloenzymes (Enneking and Wink, 2000).
The enzyme cytochrome oxidase in the mitochondria of
cells is inactivated by hydrogen cyanide binding to the Fe2+/Fe3+
contained in the enzyme. This results in a reduction of oxygen usage in the
tissues (Vetter, 2000) and oxygen starvation at cellular level, due to the
effects of cyanide poisoning, resulting in death. Respiratory failure is
therefore the cause of death since the respiratory centre nerve cells are
extremely sensitive to hypoxia (Okolie and Osagie, 1999). Other diseases
associated with dietary cyanide intake include (1) Konzo Cliff et al., (1997), a paralytic disease;
(ii) tropical ataxic neuropathy (TAN) Onabolu et al., (2000), a nerve damaging disorder that renders a person
unsteady and uncoordinated: (iii) goiter and cretinism (Delange et al., 1994). (Sheeba and Padmaja,
1992; Okafor, 2001) observed that the palatability and shelf life of cassava
products may be prolonged by processing. The levels of cyanogenic glycosides
and hydrogen cyanides are also reduced to safer limits by processing (peeling, slicing,
boiling, fermentation) before consumption (Sheeba and Padmaja, 1997, Feng et al., 2003).
Table 2: Composition of roots, (% dry matter) tubers, their by-
products and
cereals
Roots tubers and
|
Dry matter
|
Cruse protein
|
Crude fibre
|
Fat
|
Ash
|
Starch
|
Gross energy
(kcal/kg)
|
Cassava
root
|
31.90
|
2.70
|
3.10
|
0.80
|
3.70
|
76.5
|
3909.40
|
Cassava
root ensiled
|
43.50
|
2.00
|
2.90
|
0.50
|
3.4
|
74.10
|
3010.18
|
Sweet
potato tuber
|
30.10
|
2.50
|
1.53
|
0.60
|
1.0
|
72.40
|
4061.00
|
Cocoyam
tuber
|
24.90
|
7.90
|
1.90
|
0.70
|
5.20
|
77.9
|
3474.60
|
Root and tuber by products
|
|||||||
Cassava
peel (dry)
|
94.90
|
8.20
|
12.50
|
3.40
|
5.40
|
-
|
2460.00
|
Sweet
potato vines (dry)
|
86.60
|
23.10
|
16,00
|
5,30
|
4,02
|
-
|
2269.58
|
Cassava
leaves (dry)
|
92.20
|
29.00
|
14.90
|
6.70
|
11.6
|
-
|
2532.37
|
Cocoyam
leaves
|
8.20
|
20.60
|
12.10
|
11.70
|
12.10
|
-
|
2314.60
|
Cereals
|
|||||||
Maize
|
87.0
|
10.0
|
1.3
|
4.0
|
2.0
|
71.8
|
4096.5
|
Guinea
corn
|
88.4
|
9.9
|
2.9
|
2.4
|
2.1
|
74.6
|
3940.9
|
Apata
et al., 1999, Bradbury and Nixon
1998, Oyenuga 1968, Olajide et al.,
2011.
Table 3: Symptoms and Mode of Elimination of Toxic
Components
of Roots, Tubers and their by-products
Roots, tubers and
by-products
|
Toxic/anti-nutritional
factor
|
Typical levels
|
Primary assistant symptoms
|
Mode of elimination
|
Fresh
cassava root
|
Hydrocyanic
acid
|
233-1150(mg/kg
DM)
|
Vomiting,
dizziness
|
Fermentation,
boiling
|
Fresh
cassava peel
|
Hydrocyanic
acid
|
1300-2250(mg/kgDM)
|
Vomiting,
dizziness, diarrhea, death
|
Sun-drying.
|
Dried
cassava root
|
Hydrocyanic
acid
|
14-65(mg/kg
DM)
|
Vomiting,
dizziness, diarrhea, death
|
Sun
–drying
|
Dried
cassava waste
|
Hydrocyanic
acid
|
57.2(mg/kg
DM)
|
||
Fresh
cassava leave
|
Hydrocyanic
acid
|
2650-7200(mg/kg
DM)
|
||
Cocoyam
tuber
|
Irritating/acidity
substance
|
-
|
Irritation/burning
sensation
|
Cooking
heating and fermentation
|
Apata et al., 1999, Olajide et al.,
2011, Nwokolo 1990a, Tewe et al.,1976.
Phytic acid, which is
hexaphosphate of myo-inositol, is very common in the plant kingdom (Chan et al., 2007). Phytic acid is the
primary storage compound of phosphons in plants, accounting for up to 80
percent of the total phosphorus (Raboy, 2001, Steiner et al., 2007). Phytic acid has been found in cassava root
(Panigrahi et al., 1992) and cocoyam
tuber (Olajide et al., 2011) up to
levels of 62.4 and 1.75g/l00g respectively. (Josefsen et al., 2007) reported to the negatively charged phosphate in
phytic acid strongly binds to metallic cations (e.g. Ca, Fe, K, Mg, Mn and Zn)
and forms a mixed salt called phytin or phytate.
Phytate forms insoluble complexes because they are
negatively charged under physiological conditions. These complexes cannot be digested
or absorbed in the gastrointestinal tract of monogastric animals owing to the
absence of the intestinal phytase enzyme (lgbal et al., 1994). Deficiencies of phosphorus and nutritionally
important minerals in monogastric animals can be as a result of cations bound
in the phytic acid salt and of low bioavailability of phosphorus (Apata and
Olog hobo 1989).
2.3.2 Use of Cassava in Diets for Poultry
Poultry feed constitutes more
than 90 percent of all commercial livestock feeds produced. The use of cassava
as a substitute for maize will therefore make its greatest impact if it can be
incorporated into commercial poultry feeds. Certain precautions need to be
taken to achieve satisfactory performance of stock on cassava based diets.
These include removal of cyanide, higher protein supplementation with fish
meal, soybean, groundnut cake or methionine in its pure form and the prevention
of microbial activity during sun-drying as well as overcoming dustiness. Most
of the present studies indicate that satisfactory growth response has been obtained
for growing chicken at 10% incorporation of cassava flour (lafun) or cassava
peel into the diet: 40% inclusion of cassava flour or 20% inclusion of cassava
peel in layer’s diet is satisfactory for egg production (Tewe and Egbunike,
1992). Combination of cassava root and leaves in ratio 4:1 could replace maize
in poultry diets and reduce feed cost without a loss in weight gain or egg
production (Tewe and Bokanga, 2001). Feeding cassava chips supplemented with Moringa Oleifera leaf meal at5% and 10% levels
showed that cassava chips replacing maize at 55-56 and 83.33% in the diets of
broilers had no negative effect on productivity and hematology (Olugbemi et al., 2010).
2.3.3 Use of Cassava Peel in Poultry
Diets.
Cassava peel can be used to cut down the cost of
production and lead to an active and sustainable development in livestock
production (Olorede et al., 2002).
Some workers (Osei and Duodu, 1998; Agunbiade et al., 2001; Salami et al.,
2003) recommended the inclusion of fermented cassava peel up to 15% in broiler
diets with no adverse effects. For a reasonable performance of animals fed
cassava-based diets, the rations must be nutritionally balanced and with
protein source that contain sufficient sulphur-containing amino acids (Tewe,
1992).
In the study on the influence of protein
source on the performance and hematology of broiler chicken on cassava
peel-based diets using fishmeal and groundnut cake, Egbunike et al., 2009) reported that broilers
could be raised on cassava peel-based diets using groundnut cake as protein
source without any adverse effect on performance indices. Also, Sogunle et al., (2009) studied the inclusion of
cashew nut reject and cassava peel meal in the diet of growing pullets and
concluded that combination of 10% cassava peel meal and 30% cashew nut reject
meal was appropriate for enhanced performance of growing pullets.
2.3.4 Precautions in using Cassava as
Poultry Feed stuff
Although there is presence of a cynogenic glucoside,
which on hydrolysis yields the poisonous HCN, results from various studies have
shown that this could be removed to tolerable levels by adopting different
processing methods (lgwebuike and Okonkwo, 1993). Udedibe et al., 2000) reported no deleterious effect utilizing sun-dried
cassava tuber based ration for egg and broiler productions. (Oke, 1996; Nweke
and Ezuma 1998) reported that sun-drying, heating and or soaking in water for
3-5 days eliminated 80-95% of cyanide in cassava.
2.4 Maize Chaff
Maize is a cereal crop that is grown widely throughout
the world and generally consumed by Nigerian’s than any other grains (IITA,
2009). It can be eaten after cooking or smoking and can also be converted into
animal feeds. The wastes of maize which are left behind after harvest include
the hooks, chaff, stocks and the leaves (Oseni and Ekperigin 2007). Maize chaff
constitute of 25.55% moisture content, 1.03% ash, 3.72% fibre, 0.61% protein,
1.48% fat and 75.85% carbohydrate (Oseni and Ekperigin 2007).
2.5 Nutrient Requirements of Poultry
For maximum growth and good health, intensively reared
poultry need a balanced array of nutrients in their diet. The nutrients
required by birds vary according to species, age and the purpose of production.
Whether the birds are kept for meat or egg production
(Lesson and summers 2001). Table I provides a summary of recommended minimum
levels of selected nutrients for meat chickens of different ages and for
layers. To meet these specific needs, different classes of poultry have to be
fed different types of diets (NRC 1994). These recommendations should only be
considered as guidelines and used as the basis for setting dietary nutrient
concentrations in practical diets. Historically, recommendations on nutrient
requirements have been based on available literature and data from expert
groups (NRC 1994), currently, however, because each specific genotype has it’s
own requirements, most commercial feed formulations use minimum requirements
recommended by the breeding companies that supply the chicks.
Poultry require nutrients to
maintain their current state (Maintenance) and to enable body growth (weight
gain) or egg production (Leeson and Summers, 2005). Birds need a steamy supply
of energy, protein, essential amino acids, essential fatty acids, minerals,
vitamins and, most important water (NRC, 1994). Poultry obtain energy and
required nutrients through the digestion of natural feedstuffs, but minerals,
vitamins and some key essential amino acids (lysine, methionine, threonine and
tryptophan are often offered as synthetic supplements (Scanes et al., 2004).
Table 4: ecommended Minimum Nutrient Requirements of Meat
Chickens and
Laying Hens, as Percentages or Units per Kilogram of diet (90 percent dry
matter).
Meat chickens
|
Laying hens
|
||||
Nutrient Metabolizable energy
|
Unit kcal/kg mj/kg(%)
|
0-3 weeks 3200 13.38
|
3-6 weeks
3200 13.38 20
|
6-8 wks
3200 13-38 18
|
2900 12.13 15
|
Amino
acids
|
%
|
||||
Arginine
|
%
|
1.25
|
1.10
|
1.00
|
0.70
|
Glycine
+ serine
|
%
|
1.25
|
1.14
|
0.97
|
-
|
Histidine
|
%
|
0.35
|
0.32
|
0.27
|
0.17
|
Isoleucine
|
%
|
0.80
|
0.73
|
0.62
|
0.65
|
Leucine
|
%
|
1.20
|
1.09
|
0.93
|
0.82
|
Lysine
|
%
|
1.10
|
1.00
|
0.85
|
0.69
|
Methionine
|
%
|
0.50
|
0.38
|
0.32
|
0.30
|
Methionine
+ cysteine
|
%
|
0.90
|
0.72
|
0.60
|
0.58
|
Phenylalanine
|
%
|
0.72
|
0.65
|
0.56
|
0.47
|
Phenylalanine
+ tyrosine
|
%
|
1.34
|
1.22
|
1.04
|
0.83
|
Threonine
|
%
|
0.80
|
0.74
|
0.68
|
0.47
|
Tryptophan
|
%
|
0.20
|
0.18
|
0.16
|
0.16
|
Valine
|
%
|
0.90
|
0.82
|
0.70
|
0.70
|
Fatty
acid
|
|||||
Linoleic
acid
|
%
|
1.00
|
1.00
|
1.00
|
1.00
|
Major
minerals
|
|||||
Calcium
|
%
|
1.00
|
0.90
|
0.80
|
3.25
|
Chlorine
|
%
|
0.20
|
0.15
|
0.12
|
0.13
|
Non–phytate
phosphorus
|
%
|
0.45
|
0.35
|
0.30
|
0.25
|
Potassium
|
%
|
0.30
|
0.30
|
0.30
|
0.15
|
Sodium
|
%
|
0.20
|
0.15
|
0.12
|
0.15
|
Trace
minerals
|
|||||
Copper
|
Mg
|
8
|
8
|
8
|
-
|
Iron
|
Mg
|
80
|
80
|
80
|
45
|
Iodine
|
Mg
|
0.35
|
0.35
|
0.35
|
0.04
|
Manganese
|
Mg
|
60
|
60
|
60
|
20
|
Selenium
|
Mg
|
0.15
|
0.15
|
0.15
|
0.06
|
Zinc
|
Mg
|
40
|
40
|
40
|
35
|
National
Research Council, 1994.
2.6 Energy Requirement
Poultry can derive energy from simple carbohydrates,
fat and protein (Esminger, 1990). They cannot digest and utilize some complex
carbohydrates, such as fibre, so feed formulation should use a system based on
available energy (Scott 1991). Metabolizable energy (ME) is the conventional
measure of the available energy content of feed ingredients and the
requirements of poultry. This takes account of energy loses in the faeces and
urine (Esminger, 1990).
Birds eat primarily to satisfy their
energy needs, provided that the diet is adequate in all other essential
nutrients. The energy level in the diet is therefore a major determinant of
poultry’s feed intake (Rose 1997). When the dietary energy level changes, the
feed intake will change and the specifications for other nutrients must be
modified to maintain the required intake. For this reason, the dietary energy
level is often used as the starting point in the formulation of practical diets
for poultry (Lesson and Summers, 2005).
Different classes of poultry need
different amounts of energy for metabolic purposes, and a deficiency will
affect productive performance. To sustain high productivity, modern poultry
strains are typically fed relatively high energy diets (Esminger et al., 1990). The dietary energy levels
used in a given situation are largely dictated by the availability and cost of
energy rich feedstuffs. Because of the high cost of cereals, particularly
maize, the use of low-energy diets for poultry feeding is not uncommon in many
developing countries.
2.7 Protein
and Amino Acids Requirements
The function of dietary protein is to supply amino
acids for maintenance, muscle growth and synthesis of egg protein (Ravindran and
Bryden, 1999). The synthesis of muscle and egg proteins requires a supply of 20
amino acids, all of which are physiological requirements. Ten of these are
either not synthesized at all or are synthesized too slowly to meet the
metabolic requirements, and are designated as essential elements of the diet.
The balance can be synthesized from other amino acids; these are referred to as
dietary non-essential elements and need not to be considered in feed
formulations (NRC 1994). From a physiological point of view, however, all 20
amino acids are essential for the synthesis of various protein in the body. The
essential amino acids for poultry are lysine, methionine, threonine,
tryptophan, Isoleucine, leucine, histidine, valine, phenylalanine and arginine.
In addition some consider glycine to be essential for young birds, because they
can be synthesized from methionine and phenylalanine respectively (NRC 1994).
Of the ten essential amino acids, lysine, methionine and threonine are the most
limiting in most practical poultry diets (Ravindran and Bryden, 1999).
Poultry do not have a requirement
for protein per se. However, an adequate dietary supply of nitrogen from
protein is essential to synthesize non-essential amino acids (Scanes et al., 2004). This ensures that the
essential amino acids are not used to supply the nitrogen for the synthesis of
non-essential amino acids. Satisfying the recommended requirements for both
protein and essential amino acids therefore ensures the provision of all amino
acids to meet the birds physiological needs. The amino acidrequirements of
poultry are influenced by several factors, including production level,
genotype, sex, physiological status, environment and health status (Ravindran
and Bryden, 1999). For example, high levels of lean meat deposition require
relatively high levels of lysine (Scott and Dean 1991). High levels of egg
output or feather growth require relatively high levels of methionine (Leeson
and Summers, 2001).
However, most changes in amino
acid requirements do not lead to changes in the relative proportions of the
different amino acids. There is therefore an ideal balance of dietary amino
acids for poultry, and changes in amino acid requirements are normally
expressed in relation to a balanced protein or ideal protein (Ravindran and
Bryden, 1999).
2.8 Fat and Fatty Acids Requirements
Because of the greater energy
density of fat compared with carbohydrates and protein, poultry diets usually
include fats to achieve the needed dietary energy concentration. Fat accounts
for about 3 to no more than 5 percent of most practical diet (Leeson and
Summers, 2005). Other benefits of using fats include better dust control in
feed mills and poultry houses, and improved palatability of diets (Erminger et al., 1990). Poultry do not have a
specific requirement for fats as a source of energy, but a requirement for
linoleic acid has been demonstrated (Rose, 1997). Linoleic acid is the only
essential fatty acid needed by poultry, and its deficiency
has
rarely been observed in birds fed practical diets (Leeson and Summer, 2005).
Linoleic acids main effect in laying birds is on egg size.
2.9 Mineral
Requirement
Minerals are needed for formation
of the skeletal system, for general health, as components of general metabolic
activity, and for maintenance of the body’s acid base balance (NRC, 1994).
Calcium and phosphorus are the most abundant mineral elements in the body, and
are classified as macro-minerals, along with sodium potassium, chloride,
sulphur and magnesium. Macro-minerals are elements required in the diet at
concentrations of more than 100 mg/kg.
Calcium and phosphorus are
necessary for the formation and maintenance of the skeletal structure and for
good egg-shell quality (Scott and Dean 1991). In general, 60 to 80 percent of
total phosphorus present in plant-derived ingredients is in the form of phytate
phosphorus. Under normal dietary conditions, phytate phosphorus is poorly
utilized by poultry owing to the lack of endogenous phytase in their digestive
enzyme (Leeson and Summers, 2005). It is generally assumed that about one-third
of the phosphorus in plant feedstuffs is non-phytate and is biologically
available to poultry, so the phosphorus requirement for poultry is expressed as
non-phytate phosphorus, rather than total phosphorus (Leeson and summers,
2001). A ratio of 2:1 must be maintained between calcium and non-phytate phosphorus
in growing birds’ diet, to optimize the
absorption
of these two minerals. The ratio in laying birds diet is 13:1, because of the
very high requirement for calcium for good shell quality
(NRC,
1994).
Dietary proportions of sodium
(Na), potassium (k), and chloride (Cl) largely determine the acid-base balance
in the body for maintaining the physiological pH (Leeson and Summer, 2001). If
a shift occur towards acid or base conditions, the metabolic processes are
altered to maintain the pH, with likely result of depressed performance. The
dietary electrolyte balance is described by the simple formula (NA++
K+-Cl-) and expressed as MEq/kg diet (Hunton, 1995).
Prevention of electrolyte imbalance needs careful consideration, especially in
hot climates. Under most conditions, a balance of about 250mEq/kg of diet
appears satisfactory for optimum growth, (Scanes et al., 2004). The overall balance among these three minerals, and
their individual concentrations are important. To be effective, the dietary
levels must each be within acceptable ranges, not deficient and not excessive.
Birds exposed to heat stress consume more water, and are better able to
withstand heat when the water contains electrolytes (Leeson and Summers, 2001).
The replacement of part of the supplemental dietary sodium chloride with sodium
bicarbonate has proved useful under these conditions (Leeson and Summers,
2001).
Trace elements include copper,
iodine, iron, manganese, selenium, zinc and cobalt, function as components of
large molecules and as co- factors of enzymes in various metabolic reactions
(NRC, 1994). These are required in the diet in only very small amounts (Table
1). Practical poultry diets should be supplemented with these major and trace
minerals, because typical cereal-based diets are deficient in them (Leeson and
Summers, 2005). Organic forms of some trace minerals are currently available,
and are generally considered to have higher biological availability than
inorganic forms.
2.10 Vitamins Requirements
Vitamins are inorganic substance
required in small amount in the diets for maintenance of normal body reactions
and health (Olomu, 1995). Consequently the functions of vitamins are
enhancement of digestion, absorption, metabolism, maintenance of weight, egg
production. Generally, vitamins are classified as fat soluble (Vitamin A, D, E
and K) and water soluble (vitamin B complex and vitamin C). All vitamins,
except for vitamin C, must be provided in the diet. Vitamin C is not generally
classified as a dietary essential as it can be synthesized by the bird (NRC
1994). However, under adverse circumstances such as heat stress, dietary
supplementation of vitamin C may be beneficial (Leeson and Summers, 2001). The
metabolic roles of the vitamins are more complex than those of other nutrients.
Vitamins are into simple body building units of energy sources, but are
mediators of or participants in all bio-chemical pathways in the body.
2.1.1 Water Requirements
Water is the most important, but
most neglected nutrient in poultry nutrition. Water has an impact on virtually
every physiological function of the bird. A constant supply of water is
important to
i.
the digestion of feed
ii.
the absorption of nutrients
iii. the excretion of waste products and
iv.
the regulation of body temperature
(NRC, 1994).
Water constitutes about 80 percent
of the body (NRC, 1994). Unlike other animals, poultry eat and drink all the
time. If they are deprived of water for even a short time, production and
growth are irreversibly affected (Leeson and Summers, 2001). Water must
therefore be made available at all times. Both feed intake and growth rate are
highly correlated with water intake. Precise requirements for water are
difficult to state, and are influenced by several factors, including ambient
conditions, and the age and physiological status of the birds (Scanes et al., 2004). Under most conditions,
water intake is assumed to be twice the amount of feed intake. Drinking-water
temperatures should be between 10 and 25°C. Temperatures over 30°C will reduce
consumption (Leeson and Summers, 2001).
The quality of water is equally
important. Quality is often taken for granted, but poor water quality can lead
to poor productivity and extensive
economic
losses (Hunton, 1995). Water is an ideal medium for the distribution of
contaminants, such as chemicals and minerals, and the proliferation of harmful
microorganisms (Rose, 1997). Water quality for poultry can be a major issue in
arid and semi-arid regions where water is scarce. In particular, underground
water in these areas can have high levels of salt. Saline drinking water
containing less than 0.25 percent salt is tolerated by birds, but can cause
sodium toxicity if water intake is restricted
(NRC,
1994)