Poultry Husbandry Chapter VI: Hatching Eggs and Incubation

The Breeder Flock

Healthy chicks come from good breeders. Breeder nutrition, uniformity and the vaccination program are critical.

Breeder Flock Health, Age and Nutrition

A healthy breeder flock, females with a good rate of lay mated to vigorous males, will usually produce highly fertitle eggs that hatch well under good incubation practices. Hatching eggs from new breeder flocks (just starting to lay) do not hatch as well as eggs from those that have been laying for three to four months. Hatchability of eggs from old breeders nearing the end of their laying period also declines. A hatching ration should be fed to breeders for about three weeks prior to saving eggs for incubation. The extra vitamins and minerals that it contains, as opposed to a laying ration, are essential for good hatchability. Sometimes, poor hatching results occur when a lower priced laying ration is used. The nutritional requirement of the breeder hen must be adequate for optimum hatching and good chick quality.

Clean Eggs are Important

Breeder house sanitation, nest box sanitation and hatching egg care are important to the production of healthy chicks. Nest material must be clean and dry and free of contamination. It should be cleaned daily (remove dirty material and droppings) and replenished or changed weekly. Para-formaldehyde pellets (20-25 g per nest, per month) will improve nest-box sanitation. Breeder farms require a clean area where eggs can be cleaned, selected for quality and placed large end up on hatching trays. The temperature of this room should not be less than 21BC. If eggs are stored on the farm, temperature and humidity must be controlled.

Selection and Care of Hatching Eggs

Set only clean eggs. If eggs are soiled, it is preferable to clean them with sandpaper & egg brush. If hatching eggs are washed, the temperature of the water must be 43 to 44BC. The eggs should be spray washed with detergent, sanitized and fan-dried. Improperly washed eggs may rot or explode during the incubation period. Dirty eggs can be reduced if the eggs are gathered four or five times daily from nests supplied with fresh, clean nest material and if the litter in the breeding pens is kept dry so the hens feet are clean. Do not set floor eggs. Collect eggs with clean hands onto clean flats. Select hatching eggs that are uniform in size (recommended minimum 52g for meat-type), shape and colour, with good sound shells. Do not set malformed, porous-shelled, doubled-yolked eggs or eggs with cracks. Shells that have a mottled appearance upon candling are not considered to have poor shell quality and can usually be set with good hatching results. Since smaller eggs hatch in less time than large eggs it is recommended that eggs be separated by size and that small eggs be put in the incubator 8-18 hours after the larger eggs are set. The hatching percentage will be the highest if eggs are held at a temperature of 16 to 17BC for not more than one week before setting. Higher temperatures initiate embryo growth. Storage temperature should be reduced to 13BC if eggs are being held for two weeks or longer. Eggs may sweat when moved to warm, humid areas. This allows bacteria to penetrate the shell. Turning eggs during the holding period is not beneficial. It has been shown that eggs held for more than 2 weeks hatched better when stored small end up (contrary to the accepted traditional large end-up postion). Relative humidity should be maintained at approximately 80% in the egg holding room. Higher humidity encourages mold growth. Prior to placing eggs in the incubator, they may be removed from the egg storage room and warmed to room temperature for approximately 6 hours.

The Incubator Room

In the selection of a successful incubator room, factors such as heating, humidity, ventilation, and sanitation should all be considered. Optimum results can be expected if the temperature can be maintained at between 24 and 27BC, with uniform humidity below the level that is required in the incubator. Tropical climates (heat & humidity) make it difficult to maintain good incubator room conditions. Good ventilation and a constant supply of oxygen to remove excess carbon dioxide from the environment surrounding the incubating eggs is necessary for the developing embryo. High altitude reduces available oxygen. An incubator should not be placed near an outside wall or window in cold climates or in direct sunlight.

Incubators

Incubators are the most important equipment in the hatchery process. Many kinds of incubators are manufactured; however, the general principles of all modern machines for commercial hatchery production are the same. Incubator setting capacity ranges from approximately 14,000 to 100,000 eggs. During incubation, the hatching eggs are set vertically, with the large ends up in trays or flats in a setter and turned mechanically until about three days prior to hatching (setting period). The eggs are then transferred to a hatcher (hatching period) in a horizontal position and not turned during the hatching process. Both setters and hatchers have forced-draft air circulation, automatic temperature, humidity and cooling controls. For small backyard poultry operators, there are small, still-air machines. Capacity of these incubators varies from 12 to 200 eggs. The eggs are set in a horizontal position and are usually turned manually. This type of incubator may be used for the entire incubation period for any kind of eggs. The source of heat is a thermostatically controlled heating element or light bulb. Humidity is supplied in most cases by water in a pan below the eggs, and ventilation controlled by small air vents or holes. Most still-air machines have transparent plastic domes through which the incubation process can be observed.

Incubation Time for some Common Avian Species
Chicken	- 21 days
Turkey	- 28 days
Japanese quail	- 17 days
Guinea fowl	- 26 days
Pheasant, Partridge	- 24 days
Duck	- 28 days
Muscovy duck	- 35 days
Goose	- 28-32 days
Egyptian goose	- 35 days

The Principal Factors in Incubation

The five main factors affecting incubation, listed in order of importance are: temperature, humidity, ventilation, position, and turning of the eggs. Some factors to consider before purchasing an incubator: 1. Any incubator will produce better results when operating at capacity. Egg capacity is a factor; 2. How long the incubator will last and cost of all replacement parts; 3. Service and availability of parts; 4. Accuracy of controls, to keep temperature and humidity fluctuations to a minimum; 5. The amount of labour involved in operating the machine and carrying out a thorough sanitation program; 6. The guarantee.

Temperature

Hatching eggs may be warmed to a temperature of 25 to 30BC, prior to setting. The normal development of the embryo is dependent on the heat being held within a very narrow range in the incubator. In small still-air incubators, the temperature of the upper surface of the egg is higher than on the lower surface, while in large incubators, the air movement maintains the same temperature over the entire surface. For this reason, a still-air incubator must be operated at a higher temperature than a forced-draft incubator. In small still-air incubators, a constant temperature of 39BC is considered satisfactory to produce good hatching results. The temperature may vary between 37.5 and 39.5BC without hurting the embryos as long as the temperature does not remain at either extreme. These readings should be taken with the bulb of the thermometer level with the upper surface of the eggs, but not in contact with the egg shell. A standing thermometer will give a more reliable reading than a hanging thermometer and the thermometer must be accurate. The temperature may rise one degree at hatching time without causing any reduction in hatch percentage. In large incubators, the temperature, humidity, and speed of air movement are very closely dependent on each other, and since air speed varies in different incubators, it is impossible to state an exact operating temperature for all large machines, but generally it is around 37.5BC for a setter and 37BC for a hatcher. Follow the manufacturer's instructions closely with regard to temperature and ensure that instructions are for the model in use. High temperatures even for a very short period of time during any part of the incubation period will cause more harm than low temperatures.

Numerous factors may contribute to high or low incubator temperatures.

high or low room temperatures or floor temperature under the incubator affect the operating temperature of both large and small incubators. A large incubator placed near an outside wall may have one section operating at a lower or higher temperature than the other. These problems and those listed below will result in one group of eggs hatching earlier or later than the others, increased embryo mortality or cause leg deformity in chicks & poults. floor temperature variation because of drains causing cold or heat under the incubator.  an incubator thermometer not reading correctly.  the failure of automatic equipment such as thermostats, cooling coils or automatic dampers. improper air circulation leading in turn to a rise in temperature in part of the incubator, because of: a decrease in fan speed, usually caused by low voltage or a slipping fan belt; incorrect spacing of filled egg trays in a partially filled incubator. overloading an incubator for any one setting of eggs.

Humidity

During the incubation or setting period, eggs should lose 11 to 12% of their weight (another 3 to 4% in the hatcher, after day 18), due mainly to a loss of moisture. The amount of moisture (humidity) in the incubator controls the rate of evaporation from the egg. The evaporation rate is also related to temperature, air speed, shell thickness, and size of eggs; the smaller the eggs, the greater percentage of moisture loss. Too great a moisture loss from the egg in the early stage of incubation will cause the embryo to adhere to the shell, causing death. Insufficient evaporation may cause death from lack of oxygen because of a small air cell, since just prior to pipping the shell, the embryo pips into the air cell and starts to breath air. The best guides to the correct amount of humidity in an incubator is the weight loss and the size and enlargement of the air cell during incubation, or the position at which the chick pips the shell. The degree of enlargement of the air cell should be determined by candling several eggs and estimating the averagee evaporation. The amount of moisture in an incubator may be referred to as "relative humidity", which is a percentage of the moisture in the air at any given temperature. This can be measured by a wet-bulb thermometer. The relationship between dry-bulb air temperature, wet-bulb readings and relative humidity is shown in Table 1. A wet-bulb reading is based on air movement, and for this reason, a wet-bulb thermometer cannot be used to determine the amount of humidity in a still-air incubator. The relative humidity for small incubators is usually stated as 60%. Other inexpensive but less accurate equipment is available to measure relative humidity. A level water pan on the floor of the incubator under the eggs during the entire incubation period will generally supply sufficient moisture to give good hatching results, provided the moisture content of the air in the environment is neither too high or too low. Percent egg weight loss during the setting period can act as a guide to the correct humidity. This can be done by weighing some eggs at the start of incubation and the same eggs again on the 7th and 18th day, and calculating the loss that occurred (write the weight on the shell with a pencil). Chicken eggs should lose approximately 4.5% and 11.5% during the first 7 and the first 18 days of incubation respectively. Eggshells thicker than 0.34 mm are too thick and humidity should be reduced to increase moisture loss. Below 0.31 mm is too thin. Normal would be 0.33 to 0.34 mm at the beginning of production. Shell thickness decreases with age of breeder hen with 0.31 mm normal at 60 weeks. In large incubators, the temperature, air speed and humidity are intimately related, and the manufacturer’s instructions should be followed closely. Better hatching results may be obtained if the temperature is lowered and the humidity raised at hatching time (only if separate hatching compartments are available). Lowering the air temperature will provide an additional increase in relative humidity to keep shell membranes moist during the hatching process.

TABLE 1. PERCENT RELATIVE HUMIDITY AT DIFFERENT WET-BULB READINGS
Wet-bulb Reading	Relative Humidity (%) at Air Temperature of
(BC)	37.2BC %	37.8BC %
32.2	70	68
31.7	67	65
31.1	65	63
30.6	62	60
30.0	59	57
29.4	56	54
28.9	53	51
28.3	51	48
27.8	48	46
27.2	45	43
26.7	43	41

Incorrect humidity may be due to a number of factors, the more important of which are listed below:

1. High environmental humidity in tropical countries. 2. A wet-bulb thermometer reading incorrectly. Remove the wick to determine whether the thermometer is reading the same as the dry-bulb thermometer. 3. Dust and dirt on the wet-bulb wick. Change wicks often and use only distilled water in the reservoir. 4. In small incubators with humidity supplied by water pan evaporation, ensure that there is always an adequate amount of water in the pan, as the rate of evaporation is dependent on the humidity in the room. The lower the humidity in the room, the higher the evaporation and vice versa. During hatching fluff settles on the surface of the water producing a film that causes a reduction in the rate of water evaporation necessary for optimum hatchability. Clean the water pan daily and replace with clean, lukewarm water. 5. Ventilating an incubator to control temperature will lower humidity in a dry environment unless automatic humidifiers are being used in the incubator room. 6. If airflow in incubators is not uniform humidity may be different from bottom to top or side to side.

Ventilation

The free movement of oxygen, carbon dioxide and water vapor through the pores of the shell is important, since the developing embryo must be able to take in a constant supply of oxygen and release carbon dioxide and moisture. Oxygen content of 21% (present in air at sea level) and a carbon dioxide content not exceeding 0.5% in the air are considered optimum for good hatching results. Room temperature, room humidity, the number of eggs set, the period of incubation, and the air movement in the incubator all influence ventilation requirements. Ventilation problems are not the same in small incubators as they are in large incubators, where a large number of eggs are set in a very small space. During the early part of the incubation period, ventilation in small incubators may be held to a minimum. However, during the hatching period additional ventilation must be supplied to reduce the carbon dioxide in the incubator. It is advisable not to increased ventilation until half of the hatch has been completed, since ventilating too soon will reduce the humidity. In large incubators, the manufacturer's directions should be followed, however, ventilating recommendations may not be applicable to every locality and every room condition. If ventilation is used to control either temperature or humidity in the incubator, the control of the same factors in the incubator room are important. At a room temperature below 18 C, ventilating an incubator will reduce both temperature and humidity. In a room with high humidity, (tropical countries) the primary concern is to maintain the correct temperature. The main ventilation consideration may be summarized as follows: 1. Ventilation is more important in large incubators than in small incubators. 2. The amount of ventilation required may be altered by atmospheric conditions. 3. Ventilation is very important in any incubator at hatching time. Insufficient ventilation may result in embryo or chick death. 4. Ventilation in excess of the recommended amount may be applied to reduce temperature or humidity. 5. The appearance of chicks panting in a hatcher at normal temperature is an indication of a rise in the carbon dioxide content of the hatcher air. Under such conditions chicks must breathe faster to obtain the required amount of oxygen and to eliminate the exceses carbon dioxide. If excessive panting occurs, increase the airflow in the hatcher.

Position and Turning of Eggs

In small incubators, the eggs are maintained in a horizontal position during the entire incubation period. In large incubators eggs should be placed in a vertical position, large end up, during the hatching period. In small incubators, the eggs are moved when turned, while in large incubators they remain in a stationary position on the incubator tray and the egg tray is turned through an angle of not less than 90 in opposite directions with each turning. The objective is the same in both types of incubators; namely, to prevent the embryo from sticking to the shell membranes. Turning also ensures a complete contact of the embryonic membranes with the food material in the egg, especially in early stages of incubation. In small incubators, the eggs should be turned at least four times daily. It is advisable to leave some space on the tray to allow for moving the eggs forward a 1/2 turn on one turn and back a 1/2 turn on the next, thus making sure that all the eggs move. Eggs should not be turned in a complete circle, as this has a tendency to rupture the allantois sac with resultant embryonic mortality. Wash hands carefully before turning eggs to avoid bacterial contamination of the shell. In large incubators, the trays are usually turned hourly with all the egg trays moving at one time. For good hatchability, eggs should be turned to a position at least 45 from vertical, then reversed in the opposite direction to a similar position. In the most recent models of incubators, eggs are turned through an arc of 150 and in a few models they are turned as far as 180 . The introduction of these newer methods of turning eggs has been an important aspect in improving hatchability. Eggs should not be turned in either large or small incubators during the hatching period. The greatest benefit from turning eggs is during the first week in incubation.

Other Factors Affecting Incubation

Egg Selection

Poor quality hatching eggs do not hatch as well as eggs of good quality. The term "quality" refers to the condition outside the shell, the condition of the shell itself and that of the contents. Eggs with inferior characteristics, as discussed in "Selection and Care of Hatching Eggs," should not be set.

Sanitation

Eggs used for hatching should be clean and stored in clean containers in a sanitary egg holding room. Eggs contaminated with bacterial organisms usually do not hatch well and this poor quality is reflected in the chicks that do hatch.

Egg Handling

Rough handling of hatching eggs before they are set will increase the number of dead embryos, with mortality occurring between the 4th and 13th day of incubation. Also, jarring eggs during incubation may result in the rupture of the egg shell membrane and thereby lower hatchability. Large fluctuations in temperature and humidity during storage will have a major adverse affect on hatchability. Refer to "Selection and Care of Hatching Eggs" for proper egg storage procedure.

Toxicity

If the interior of an incubator is painted or varnished, or if the trays are varnished, the percentage of hatch will be reduced, possibly by as much as 25%. This adverse effect disappears in about 30 days, suggesting that the ill effect is eliminated by oxidation of the paint. This problem may be overcome without any reduction in percentage of hatch if the incubator is fumigated with formaldehyde gas at the concentration recommended for proper hatchery fumigation. The gassing should be done as soon as the paint is dry and with the incubator operating at recommended temperature and humidity for incubating eggs.

Automatic Equipment

The addition of automatic equipment has eliminated many of the problems with incubators, however, such hazards may occur when automatic devices fail. During hatching all automatic devices, such as cooling coils, automatic dampers, tray turners, alarm bells, etc., should be checked at regular intervals. Electrical failure may require that automatic equipment be reset. After an incubator is purchased, it is important to know how every part operates.

Egg Candling

Candling chicken eggs on the 7th and 18th day of incubation, may be recommended for small poultry producers. Egg candling will detect infertiles and early dead germs. Therefore, problems within the hatching flock can be identified without waiting until the incubation period is completed.

Improper Fumigation

Closely follow instructions outlined in "Fumigation Procedure". Excessive and improper fumigation can result in high mortality in developing embryos.

Fumigation of Incubators

The killing of bacterial organisms by formaldehyde gas is based on the concentrations of the gas, exposure time, temperature, and humidity of the incubator. The chemicals potassium permanganate and formalin (which is 40% formaldehyde gas) have proven to be the most effective method of destroying bacterial organisms in the hatchery. To accomplish the proper release of the gas, one and one-half parts (by volume) formalin is added to one part (by weight) of potassium permanganate. This will release the formaldehyde as gas or fumigant. When the reaction is complete, a dry, brown powder will be left. If the residue is wet, not enough permanganate was used; if the residue is purple, too much permanganate was added.

Concentration

The recommended concentration for effective fumigation is 53 mL of formalin added to 36 g of potassium permanaganate per cubic metre of space to be fumigated, or 1 1/2 mL of formalin added to 1 g of potassium permanganate per cubic foot of space to be fumigated. Caution: Never add the permanagante to the formalin. Heat is generated when the two chemicals are combined, and care should be taken. Formaldehyde gas is generated quickly. Do not allow the fumes to get into the eyes. Personnel should use a respirator or wear a mask to avoid unnecessary exposure. Ventilate the incubator room to remove fumes that escape from the incubator.

Time

It is not recommended to fumigate setters with hatching eggs in them, but if such treatment becomes necessary, embryos between 24 and 96 hours of age should not be exposed to the above concentration of formaldehyde. Hatching compartments should be fumigated after the eggs are transferred from the setter to the hatcher, again after the hatch has been taken off and before the refuse has been removed from the trays, and finally after the hatcher has been thoroughly cleaned. Do not fumigate chicks with this concentration of formaldehyde gas. Small still-air incubators should be fumigated after the chicks have been removed and prior to discarding the refuse from the tray and again after the incubator has been thoroughly cleaned.

Fumigation Procedure

1. Make sure the temperature and humidity of the incubators are at normal operating conditions. 2. Measure the inside volume of the machine in cubic feet or cubic metres (length x width x height). 3. Close the ventilators, but leave the fans on. 4. Weigh the required amount of potassium permanganate into a wide enamelware or earthenware vessel large enough to accommodate the boiling and splattering action experienced when the formalin is added. Place the vessel and the permanganate in the area to be fumigated; then add the formalin. 5. Close the door immediately and leave closed for 20 minutes. 6. After 20 minutes, open the ventilators. 7. Open the doors of the machine for five minutes, leaving the fan on to allow more of the formaldehyde gas to escape, or neutralize it with a 25% solution of ammonium hydroxide equal to one-half the amount of formalin used. The hydroxide should be thrown directly on the floor of the machine and the doors closed. The formaldehyde gas will quickly be neutralized.

Continuous Fumigation of Hatcher

The greatest increase in bacterial organisms occurs during the hatching period. These can be reduced, but not completely eliminated, by slow release of formalin in the hatcher during the last 48 hours of the hatching period. For continuous fumigation to be effective, hatching eggs should also be fumigated at transfer time with the recommended concentration. Place formalin in pan about 25 mm in depth, allowing 58 cm2 of pan for each cubic metre of hatcher space, or a pan about 1 in. deep, allowing 30 in2 of pan for approximately 1000 ft3 of hatcher space. Do not use permanganate. The pan should be placed in the open area of the hatcher in direct line with the airflow. Place the pan of formalin in hatcher 48 hours prior to hatch completion. To overcome fluff deposited on the formalin, add more formalin about 24 hours before hatch is complete to increase evaporation. If the fan stops (mechanical failure etc.) and reduces the airflow, remove the pan of formalin immediately. If hatchers are only partially full, continuous fumigation is not recommended, as a reduction in airflow will create an excessive build up of formalin in the hatcher.

Effects of Fumigation

1. Properly carried out, fumigation should not affect hatchability. 2. Fumigation will only kill bacteria that are present on the surface of hatchery refuse. Fumigation will not kill bacteria inside unhatched or pipped eggs. It is important to dispose of hatchery refuse carefully to minimize hatchery contamination. 3. The hatchery room must be separate from the tray dumping room and from the chick processing area. Air flow and traffic must be controlled to prevent contamination of the chick processing and holding areas. 4. Efficient fumigation along with other sanitary measures should control navel infection (omphalitis). 5. Fumigation is not intended to replace a thorough cleaning program.

HATCHERY DESIGN

Hatchery layout is important to a good sanitation program. Arrange the hatchery so there is a one-way flow of material from the point where the hatching eggs are brought in to where the processed chicks go out. Hatcheries should be designed so the flow of eggs, chicks and personnel does not spread contamination from one room to the next. Doors, including one-way doors, help stop cross contamination between rooms. Positive air pressure prevents contamination through an open door. Workers should change outer clothing and wash hands before moving from one work station to another.

SUMMARY OF SOME IMPORTANT FACTORS
1. Feed breeder flock hatching ration that is well fortified with essential nutrients.
2. Use healthy breeding stock.
3. Provide good egg-holding facilities.
4. Avoid holding eggs in storage for more than one week.
5. Prewarm eggs for 6 to 8 hours at incubator room temperature.
6. Set clean, good quality eggs. Delay setting small eggs (those more than 10% less than average ) for 8 to 16 hours.
7. Maintain correct incubation temperature, humidity and ventilation. Make sure air intake does not draw contaminated air into the incubator.
8. Turn hatching eggs frequently.
9. Maintain incubator room temperature between 21 and 24BC with good ventilation and relatively high humidity.
10. Fumigate regularly.
11. Clean vaccinating and beak trimming equipment. Newly hatched chicks may pick up contamination and infection in the hatchery from vaccinating and beak trimming equipment. This equipment requires a very rigid sanitation schedule.
12. Practice strict sanitation; cleanliness is very important for successful hatching operation. Make sure belts, equipment and workers hands used to move eggs or newly hatched chicks are kept clean.