Poultry production &Technology - PowerPoint Presentation

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Poultry production &Technology

Formation

of

the Hen’s

Egg

By

Bnar

-F-

Sulaiman

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Formation of the Hen’s Egg

The

egg of the laying hen is the end product of a complicated series of processes. The first step is the ovulation of the yolk from the left ovary into the left oviduct. The right ovary and oviduct do not develop in the commercial laying hen

.

The yolk is captured by the infundibulum where the developing egg remains for about 15 minutes and it is here that the formation of the

perivitelline

membrane and chalazae occurs.

In

breeder birds, fertilization also occurs in this region of the oviduct. The egg then moves into the magnum where it remains for about 15 hours while the egg white (albumen) proteins are produced.

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Section of oviduct

Approximate time egg spends in this section

Functions of section of oviduct

 

1- Funnel (infundibulum)

 

15 minutes

Receives yolk from ovary. If live sperm present, fertilization occurs here 2- Magnum 3 hoursAlbumen (white) is secreted and layered around 3 -Isthmus 1 hourInner and outer shell membranes are added, as are some water and mineral salts   4- Shell gland (uterus)   21 hoursInitially some water is added, making the outerwhite thinner. Then the shell material (mainlycalcium carbonate) is added. Pigments may alsobe added to make the shell brown 5 -Vagina/cloaca less than 1 minuteThe egg passes through this section beforelaying.

Table 1:

 

Functions of various different sections of the hen's oviduct. The yolk

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Nutritional Importance of the Egg:

1-Chicken eggs, the most commonly eaten eggs, provide

155 

calories

 (

kcal

) of food energy and

12.7 g of protein in a 100 gram serving 2-Eggs are a rich source of protein that is of a high biological value. The protein quality of the egg is often the standard for measuring the quality of all other food proteins.3- Eggs are also an important source of essential unsaturated fatty acids (Iinoleic oleic acid), a monounsaturated fatty acid, iron, phosphors, trace minerals, the fat soluble vitamins A, D, E, and K and many of the water soluble B vitamins.

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Nutritional Importance of the Egg:

4-Eggs provide a unique,

well-balanced source of nutrients for persons of all ages

. Before the advent of present-day baby foods, hard-cooked egg yolk served as the major supplementary source of iron for young babies. Now iron-eroded, precooked baby cereals, strained meats, and canned egg yolks offer alternative and more convenient sources of iron. Therefore an excellent food for young children and teenagers.

5-Eggs are

good for any meal or as snacks

. They provide good nutrition, are satisfying, and have comparatively low calorie content, important for persons with weight problems.

6-Eggs are easily digested and absorbed to provide several essential nutrients.

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Chemical composition of egg contents

1.The

weight

and

composition

of a table egg is dependent on

heredity

, age, season, diet, and other factors. A typical White Leghorn egg usually weighs from 53 to 63 g with an average of 55 g. 2. In addition to water (74%), the main chemical compositions of hen egg are 11.8% lipids, 12.7% proteins, and small amounts of carbohydrates and minerals. 3. Most of the proteins are present in the egg white and the egg yolk, amounting to 50% and 44%, respectively; the eggshell contains the rest of the proteins. The yolk accounts for slightly over one-third of the edible portion, but it yields three-fourths of the calories and provides all or most of the fat in whole eggs.

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Chemical composition of egg contents

4. The yolk comprises

48% water, 16% protein, 32.6% fat, and some minerals and vitamins. The white consists of 88% water, 10% protein, and some minerals

. The amount of lipid in the egg white is negligible (0.01%) compared with the amount present in the yolk.

5.The shell makes up 11% of the weight of an egg, and approximately

98% of the shell consists of calcium

. Carbohydrates are a minor component of hen eggs. Their average content is about 0.5 g per egg, 40% of which is present in the yolk.

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Chemical composition of egg contents

6.

Carbohydrates

are present as free and conjugated forms which are attached to

proteins and lipids

.

Glucose

accounts for about 98% of the total free carbohydrate in the white. 7.The content of carbohydrate in egg yolk is about 1.0%; 0.7% of it consists of oligosaccharides bound to protein, composed of mannose and glucosamine; the remaining 0.3% is free carbohydrate in the form of glucose. 8.About 94% of the minerals are in the eggshell fraction; the rest are distributed in egg white and egg yolk. Most of the minerals are in conjugated form, and only a small portion is present as inorganic compounds or ions.

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Chemical composition of egg contents

9.Calcium represents over 98% of total mineral in the shell; other inorganic components include phosphorus, magnesium, and trace contents of iron and sulfur. Egg yolk contains 2% minerals, phosphorus being the most abundant.

10.More than 61% of the total phosphorus of egg yolk is contained in phospholipids. The major inorganic components of egg white are sulfur, potassium, sodium, and chlorine.

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Internal and external egg quality

Quality:

has been defined as the properties of any given food that have an influence on the acceptance or rejection of this food by the consumer.

Egg quality

is a general term which refers to several standards which define both internal and external quality

.

External quality is focused on shell cleanliness, texture and shape, whereas Internal quality refers to egg white (albumen) cleanliness and viscosity, size of the air cell, yolk shape and yolk strength.

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Internal

egg quality

involves

functional

,

aesthetic

and

microbiological properties of the egg yolk and albumen. The proportions of components for fresh egg are 32% yolk, 58% albumen and 10% shell.

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The egg white is formed by four structures

.

Firstly, chalazae, immediately surrounding the yolk, accounting for 3% of the white

.

Next is the inner thin layer, which surrounds the chalazae and accounts for 17% of the white.

Third

is the firm or thick layer, which provides an envelope or jacket that holds the inner thin white and the yolk. It adheres to the shell membrane at each end of the egg and accounts for 57% of the albumen. Finally, the outer thin layer lies just inside the shell membranes.

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Egg yolk

from a newly laid egg is

round and firm

. As the egg gets older, the yolk absorbs water from the egg white, increasing its size. This produces an enlargement and weakness of the

vitelline

membrane

.

 As soon as the egg is laid, its internal quality starts to decrease: the longer the storage time, the more the internal quality deteriorates. However, the chemical composition of the egg (yolk and white) does not change much.

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In a newly laid egg the

albumen pH lies between 7.6 and 8.5

.

During storage, the albumen pH increases at a temperature dependent rate to a maximum value of about

9.7.

Increases in albumen pH are

due to CO2 loss through the shell pores, and depend on dissolved CO2, bicarbonate ions, carbonate ions and protein equilibrium. Bicarbonate and carbonate ion concentration is affected by the partial CO2 pressure in the external environment.

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In newly laid eggs, the

yolk pH is in general close to 6.0

; however, during storage it gradually increases to reach

6.4 to 6.9.

The decrease in internal egg quality once the egg is laid is

due to the loss of water and CO2

. In consequence, the egg pH is altered, resulting in watery albumen due to the loss of the thick albumen protein structure. The cloudy appearance of the albumen is also due to the CO2; when the egg ages, the CO2 loss causes the albumen to become

transparent, compared with fresh eggs.

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To minimize egg quality problems

two things are important:

1-frequent

egg collection, mainly in the hot months

,

2-

rapid storage in the cool room. The best results are obtained at a temperature of 10 °C. There are six main factors affecting internal egg quality: disease, egg age, temperature, humidity, handling, and storage.

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External egg quality

Poor eggshell quality has been of major economic concern to commercial egg

producers.To

maintain consistently good shell quality throughout the life of the hen, it is necessary to implement a total quality management

programme

throughout the egg production cycle.

It has been always recognized that the hen has the most extraordinary method of obtaining and depositing calcium (

Ca) in the entire animal kingdom. An egg has an average of 2.3 g of calcium in the shell, and almost 25 mg in the yolk . Exterior egg quality is judged on the basis of texture, colour, shape, soundness and cleanliness according to USDA (2000) standards. The shell of each egg should be smooth, clean and free of cracks. The eggs should be uniform in colour, size and shape.

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There are five major types of shell problems in the egg industry:

cracks due to excess

pressure.

2. cracks due to thin

shells.

3. body-checks. 4. pimpled or toe holes. and 5. shell-less eggs.

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Factors affecting egg shell quality

1-Bird Strain:

As a result of genetic selection, different strains of laying hen vary significantly in egg shell quality, egg size and production . and there are clear differences between modern commercial birds and traditional breeds of laying fowl.

2- Bird Age

:

A number of studies have shown that egg shell quality

decreases as birds grow older . Egg size increases with increasing hen age at the same time as shell weight increases or stays the same.

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3- Nutrition :

Each egg shell contains up to 3- grams of calcium. Therefore, the diet of hens must contain adequate calcium in a form that can be utilized efficiently.

4- Water:

Quality may influence egg shell quality. Water containing high levels of electrolytes (saline drinking water) may have long-term negative effects on egg shell quality. The water supplied to birds must also be hygienic to ensure that disease is not transmitted by this route.

The

temperature of the water provided to laying hens is also important, especially during hot weather. It appears that hens reduce water intake or may even cease to drink, if the water gets too hot.

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5-Stress :

A-General Stress

:A range of types of general stress can affect egg shell quality.

B- Heat Stress :

The high temperatures experienced during the summer can result in smaller eggs and reduced shell quality via a number of physiological processes occurring within the bird Heat stress reduces feed intake and limits the availability of blood calcium for egg shell formation also induce delays in the timing of oviposit ion.

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6-Production System :

The type of production system may influence egg shell quality. Direct comparisons among the different types of production system (e.g. cage, barn, free range) have been made

diffcult

by the shortage of experiments in which all other variables have been maintained constant. Some of the problems with egg shell quality reported from free range systems. Some studies have found effects of cage density on egg shell quality.

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Factors affecting egg Internal quality(

Albumen quality )

:

1-Storage:

The effects of storage time and temperature on albumen quality are well documented.

Albumen height and

Haugh

units decrease with storage time and this decrease occurs more quickly at higher temperatures.2-Hen strain and age :The age of the hens is also important as albumen quality declines with bird age. Albumen quality is affected by the strain of bird and genetic selection.3-Induced Moult :Albumen quality in older hens has been shown to improve following an induced moult .

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4- Nutrition:

A number of nutritional factors have been reported to affect albumen quality.

5-Disease:

The main disease of laying hens that has been reported to affect albumen quality is

infectious bronchitis virus

which may cause a decrease in quality and more variable albumen quality.