NATURAL INCUBATION
The broody hen chosen for natural incubation should be large (to cover and thus keep more eggs warm), healthy and preferably vaccinated, with a good brooding and mothering record. Signs of broodiness are that the hen stops laying, remains sitting on her eggs, ruffles her feathers, spreads her wings and makes a distinctive clucking sound. Brooding may be induced with dummy eggs or even stones.
Eggs usually become fertile about four days after the rooster has been introduced to the hens. A maximum of 14 to 16 eggs may be brooded in one nest, but hatchability often declines with more than ten eggs, depending on the size of the hen. Feed and water provided in close proximity to the hen will keep her in better condition and reduce embryo damage due to the cooling of the eggs if she has to leave the nest to scavenge for food.
The hen keeps the eggs at the correct humidity by splashing water on them from her beak. This is a further reason for providing her with easy access to water. In very dry regions, slightly damp soil can be placed under the nesting material to assist the hen in maintaining the correct humidity (between 60 and 80 percent). Fertile eggs from other birds are best added under the brooding hen between one and four days after the start of brooding. In Bangladesh, it has been reported that local broody hens will even sit on and hatch a second clutch of eggs, often losing considerable weight in the process (especially if insufficient attention is paid to the provision of food and water).
The incubation period for chicken eggs is 20 to 21 days, and increases up to 30 days for other poultry. After sitting for some days, a broody hen can be given some newly hatched chicks and, if they are accepted, the original eggs can be removed and replaced with more chicks. Thus hens with a better record of mothering can be better utilised for their abilities.
Eggs initially need a very controlled heat input to maintain the optimum temperature of 38°C, because the embryo is microscopic in size. As the embryo grows in size (especially after 18 days), it produces more heat than it requires and may even need cooling. Moisture levels of 60 to 80 percent Relative Humidity (increasing during the incubation period) are important to stop excess moisture loss from the egg contents through the porous egg shell and membranes. Factors to consider for successful natural incubation include the following:
Feed and water should be close to the hen.
The broody hen should be examined to ensure that she has no external parasites.
Any eggs stored for incubation should be kept at a temperature between 12 and 14 °C, at a high humidity of between 75 to 85 percent, and stored for no longer than seven days.
Extra fertile eggs introduced under the hen from elsewhere should be introduced at dusk.
The eggs should be tested for fertility after one week by holding them up to a bright light (a candling box works best. If there is a dark shape inside the egg (the developing embryo), then it is fertile. A completely clear (translucent) egg is infertile.
A hatchability of 80 percent (of eggs set) from natural incubation is normal, but a range of 75 to 80 percent is considered satisfactory. Setting of hatchings is best timed so that the chicks to be hatched are two months of age at the onset of major weather changes, such as either the rainy (or dry) season or winter/summer. A plentiful natural food supply over the growing period of the chicks will ensure a better chance for their survival. Successful poultry species instinctively lay and incubate their eggs at a time of the year when newly hatched chicks will have a better supply of high protein and energy food provided by the environment. For example, guinea fowl will only lay eggs in the rainy season. However, seasonal changes in weather patterns are also times of greater disease risk.
ARTIFICIAL INCUBATION (PARCHED PADDY RICE AND RICE HUSK TECHNIQUES)
There are many commercial artificial incubators of varying capacities. Most depend on electricity, but some use gas or kerosene for heating. All use a thermostatic switching device to keep the temperature constant within one Celsius degree. The correct humidity is usually maintained by having a pre-determined surface area of water appropriate for each incubator chamber.
Turning the egg several times each day is important to prevent the embryo from sticking to the shell membranes. With hand-turning systems, an odd number of times turned per day (five to seven times) will ensure that during successive overnight periods the egg is always oriented the opposite way from that of the previous night.
The broody hen carries out all of these incubation tasks instinctively, and artificial incubation attempts to duplicate these tasks. Traditional artificial incubation techniques have evolved over thousands of years in many parts of the world. One such technique, developed for hatching duck eggs in China, is the parched (heated) rice technique. It is based on the use of heated paddy rice and embryo-generated heat. It is still used in China and Bali, Indonesia, with hatchability results of up to 80 percent (Smith, 1990). The objectives of artificial incubation are met equally well using either parched rice or rice husks, and a hatchability of 65 to 75 percent is common. By candling the eggs between days 5 and 7, infertile eggs can be detected as “clears” (as the light is not obscured by the growing embryo). These eggs are still suitable for sale for human consumption, which improves the economic viability of this system.
As duck eggshells are less brittle than chicken eggs, the system was never adopted for chicken eggs in China. The original Chinese system used 80 duck eggs per bundle. However, with extra care, and fewer eggs per bundle (25 to 30 compared with 40 duck eggs), chicken egg incubation was found to be equally successful in Bangladesh when adapted there in the 1980s. The number of duck eggs per bundle was reduced to 40, which gave better hatching results as well as fewer breakages than 80 per bundle.
The artificial parched rice or rice husk incubation process is started by heating the eggs, either in the sun or in an insulated warming room equipped with a heat source. On sunny days, approximately 25 to 30 chicken eggs or 40 duck eggs, (presumed fertile, and carefully dated and labelled) are placed in the sun on pieces of padded cloth for about 30 minutes and turned occasionally to raise the temperature of the eggs to the required 37 to 38 °C. This temperature can be judged by the appearance of water droplets on the shell or by touching the egg to the eyelid. On sunless days, eggs must be placed on a cloth in a shallow bamboo basket and put on racks in a heated warming room to slowly achieve the same temperature. This usually requires approximately one to three hours. Any slow-burning fuel is suitable, and kerosene and charcoal are commonly used. In Egypt, dried beanstalks were used for thousands of years for their characteristic slow-burning property, and are still used today in the Fayoumi district (from where the well-known chicken breed of the same name originates). A well-vented stove will prevent any toxic fumes affecting the embryo. In Bangladesh, slightly heated (to 38oC) sand or wood-ash, covering the eggs for approximately one minute, is also effective in warming the eggs. Human clinical thermometers, now readily available, can be used to assist training in using the eyelid’s sensitivity to temperature. If the humidity drops below 70 percent, 60 percent, 50 percent or even 40 percent (particularly in typical progressively drier months), a wet (and slightly warm) cloth should be placed over the eggs with a frequency corresponding to the above humidities of one, two, four or six times daily. This will raise the humidity of the egg so that the embryo will not dry out.
The unhusked (paddy) rice is heated (parched) and continuously stirred until it reaches a temperature of 60°C, to provide heat for the eggs for the first two weeks of incubation. About 2.5 to 3.0 kg of the heated rice is enclosed in a cloth pillow and placed into the egg basket. The pillows have the same diameter (40 cm in the Bangladesh example) as the basket, and should be about 8 cm thick. Where rice-husk is used, pillows can be made with black-coloured material, which easily absorb the sun’s heat. When the temperature of the pillow has dropped to about 40°C, a loosely bunched bundle of 40 duck (or 25 to 30 chicken) pre-warmed eggs are placed on top of the warm rice. The bundle is made from a square piece of cloth about 45 cm on each side. A soft duster cloth with pinholes is suitable. Alternating pillows of warm rice and egg bundles are added until the basket is full, finishing with a pillow of rice. The basket is then covered with padding to conserve as much heat as possible. This procedure is repeated until all the eggs are placed in baskets, leaving one basket empty to allow the addition of freshly warmed rice. The incubating baskets are cylindrical in shape (50 cm in diameter and 80 cm in depth in China, and 40 cm in diameter and 70 cm in depth in Bangladesh and are made of woven bamboo strips. In China, a few layers of bamboo paper are pasted on the inner surface of the sides and bottom to seal the gaps against temperature loss through convection.
In warmer parts of southern China, rice husk is substituted for paddy rice, and the pillows containing the husks are made from black-coloured material, which easily heat up in the sun. Rice husks also provide very good insulation against loss of heat from the older eggs, which is instead transferred (by conduction) to younger eggs placed in contact with them in separate bundles. This rice-husk system was adopted on a large scale in Bangladesh after being introduced by poultry development projects in the 1980s. The system has evolved, and the cylindrical egg baskets are now set into larger bamboo frame setting boxes, with more insulating rice husk material placed between the cylinders and the walls of the enclosing setting boxes. The cylinder wall should be about 10 cm from the setting box wall and 8 cm from the next cylinder. With this greater insulation, there is less heat loss, thus less need to provide supplementary heat from costly fuels.
For the first three days, reheated paddy rice (or rice husk) is added three times a day at regular intervals. During days four to six, this may be reduced to twice a day. The object is to ensure that the eggs are kept at the temperature most suitable for embryo development. The spare basket is used to transfer eggs from an adjoining basket when adding freshly warmed rice or rice-husks. Thus the top layer of eggs becomes the bottom layer and the bottom layer ends up on top of the spare cylinder. The newly emptied basket is then ready to receive eggs from the third basket, and so the cycle continues.
In China, heat is provided for days 13 to 14 in summer and in the colder months also on days 18 to 19. After that, the developing embryos are able to produce enough heat to maintain the incubation process without further need of an outside heat source. Eggs set for the first six days are called "new eggs", those between days 6 to 13 (which neither need nor produce extra heat) are "in-between eggs" and eggs after day 13 (which give out excess heat) are "old eggs". Once a basket contains "old" and "in-between eggs", it is possible to use embryo-generated heat alone to incubate "new eggs", which are usually introduced at intervals into the basket and placed between layers of "old eggs". Even when outside heat is not added, the eggs in the baskets must be regularly turned and aired three to five times a day in the process of transferring them to adjoining baskets. In order to use the embryo-generated heat effectively (almost all year round), the layers of eggs in the baskets are organized to a particular pattern, a typical example of which is shown in Table 5.1.
The eggs are candled on days 5 and 13, both to identify infertile eggs and dead embryos and to assess the degree of embryo development; which is used as one of the guides in adjusting basket temperature. Placing the egg on the upper eyelid allows the egg temperature to be assessed. The temperature of the basket may be adjusted in the following ways:
by varying the proportion of eggs in a basket at different stages of incubation (for example, the temperature may be lowered by removing some of the bundles of "old eggs");
by varying the arrangement of eggs in a basket (for example, as heat dissipation from eggs near the sides of the basket is faster than from those in the centre; a bundle of "old eggs" can be placed in the centre core and bundles of "new eggs" shaped to enclose them); and
by changing the top covering of the basket using heavier padded material in cold weather and at the beginning of the incubation period, and a lighter covering if less heat retention is required.
Table 5.1 Arrangement of eggs in the incubation baskets prior to and after transfer to adjoining baskets
|
Incubation time (days) |
||||
|
Layer |
Before transfer |
Summer |
Winter |
After transfer |
|
1 |
A |
14-6 |
17-20 |
J |
|
2 |
B |
1-3 |
1-4 |
I |
|
3 |
C |
10-13 |
13-16 |
H |
|
4 |
D |
4-6 |
5-8 |
G |
|
5 |
E |
7-9 |
9-12 |
F |
|
6 |
F |
7-9 |
9-12 |
E |
|
7 |
G |
4-6 |
5-8 |
D |
|
8 |
H |
10-13 |
13-16 |
C |
|
9 |
I |
1-3 |
1-4 |
B |
|
10 |
J |
14-16 |
17-20 |
A |
Source: Fuan, 1987
Eggs in the advanced stages of incubation produce a lot of heat, so on days 13 to 14 in summer (days 18 to 19 in winter), the "old eggs" are transferred to hatching beds, where they are placed in a single layer for final development and hatching. The surface of the bed is covered with a thin layer of rice husks and then covered with a straw mat. The edges of the bed are lined with padding to protect the eggs. The covering for the developing eggs in the bed may be heavy or light cloth, depending on the degree of insulation required. The temperature in the hatching bed is maintained at 36 to 37 °C, slightly lower than that of the basket. The temperature can be adjusted by changing the thickness of the covering, varying the space between the eggs, and moving the eggs twice a day so that those on the perimeter change places with those at the centre. In very hot dry weather, the eggs are sprayed with a fine mist of water. They are kept in the bed until the chicks hatch out and dry.
The hatching bed should be two-storied (like a bed-bunk) and can be made of wood. An example hatching bed with a 500-egg capacity has a length of 90 cm and width of 68 cm. The height of the side wall on all sides should be 20 cm from the bed base level, with a 25 cm gap above the side wall for ventilation and ease of access.
