Caring for Hatching Eggs Prior to Incubation

There are many factors which affect chick quality and percent hatchability from hatching eggs. As a general rule, other than fertility, conditions in the hatchery are considered to be more important to successfully hatching quality chicks than conditions on the farm. However, providing the proper temperature and environmental conditions for hatching eggs prior to incubation can be nearly as important as during incubation. As midday summer temperatures continue to rise both in, and around breeder houses, it then becomes even more critical to handle hatching eggs properly. To maximize the number of quality chicks hatched from these eggs, it is helpful to understand how the avian embryo develops and why maintaining a proper storage temperature of hatching eggs is so critical

Sperm storage in the hen

The avian reproductive system is somewhat unusual in that it allows the hen to store sperm in specialized sperm storage sites within the oviduct. After successful mating and insemination by the male, sperm cells deposited in the hen accumulate in these storage sites called sperm storage tubules, in the oviduct. These primary, long term sperm storage tubules are located in the lower portions of the oviduct, while additional short term storage sites are located in the upper portions of the oviduct closer to the site of fertilization. The domestic chicken hen can store viable sperm for 20 days or longer after a single insemination. Reports indicate that turkey hens have the ability to maintain viable sperm within their storage tubules for as long as 40 days. However, while these stored sperm cells may maintain their ability to fertilize an egg, eggs fertilized from sperm stored in the hen for longer than 12-14 days have increased incidences of early embryonic mortality (particularly in days 1-3 of incubation).

Fertilization and Embryo Development

Twenty to thirty minutes after a hen lays an egg, the next ovum (or yolk) is ovulated and this is the egg that will be laid the following day. The ovum that has just been ovulated must be fertilized within the first 5-10 minutes after it is released from the ovary. The addition of egg albumen around the yolk begins within these first few minutes following ovulation and will prevent fertilization from occurring. The addition of the egg albumen renders the sperm cells incapable of penetrating the outer layer of the ova thus preventing fertilization of the egg. As the yolk, or ova, moves down the reproductive tract, additional albumen is laid around the yolk, egg membranes are laid around the albumen then a shell is formed on the membranes to surround the entire package. This process requires approximately 24-26 hours from the time of ovulation to the time the egg is laid.

While the egg progresses down the oviduct, it is maintained at the hens body temperature of between 104° and 106° F (40° to 41.1°C). Although the ideal incubation temperature is near 100° F (~37.8°C), following fertilization of the avian egg, any temperature greater than 70°F (21.1°C) can allow for embryonic development. Obviously, the hen’s body temperature of 104-106°F is sufficient to allow for embryonic development in the 24-26 hours after fertilization and before the egg is laid. Therefore, at the time the egg is laid, the chicken embryo is composed of approximately 20,000 to 40,000 cells. What this really means is that from fertilization to hatching it requires approximately 22 days to complete development in the chicken egg and about 29 days for turkeys, with about 4.5% (in chickens) of this time occurring prior to the egg being laid.

Arresting Embryo Development

After the egg is laid, further development of the embryo can be carefully interrupted by lowering the temperature of the egg. This is natures way of allowing a hen to accumulate enough fertile eggs to form her clutch, which she will incubate and hatch. By bringing the internal temperature of the egg below the physiological temperature of 70° F, further development of the embryo stops. The longer the egg remains above approximately 70° F, the greater the potential for embryonic development to occur. If the embryo undergoes too much pre-incubational development prior to being cooled, the chick can hatch early and will dehydrate and weaken by the time the entire hatch is pulled out of the hatchers.

Additionally, if the internal temperature of the egg is allowed to oscillate above and below a 70 to 80 ° temperature range, the embryo may continue to start and stop development. It is not uncommon to see producers remove partial buggies of hatching eggs from the cool room to fill the remainder of the rack. This situation allows the eggs to oscillate above and below the physiological temperature of 70° F. When this happens, the embryo becomes weakened and there is a greater chance for the embryo to die in the first few days of development inside the setters. Obviously, when this happens there will be a decrease in the overall hatch of the eggs as well as a subsequent reduction in chick quality.

Egg storage prior to incubation

To maximize the chance of fertile eggs developing properly into healthy chicks, hatching eggs should be handled with care. Hatching eggs should be removed from the hen house as often as possible and placed in the cool egg storage rooms to avoid unnecessary pre-incubation development. Frequent gathering of eggs becomes more and more important as the midday summer temperatures continue to rise. Houses equipped with mechanical nests provide an opportunity to remove eggs from the houses more frequently and more rapidly as compared to conventionally equipped houses. Houses which rely completely on manual egg collection generally expose the hatching eggs to elevated temperatures for extended periods of time.

Once the eggs are removed from the breeder house, they should be stored between 50-70° F (65 - 68° F recommended) with a relative humidity of 75% if possible for no more than seven days. This temperature will safely arrest embryo development and the humidity will prevent excessive egg moisture loss from the eggs. Storage of eggs for longer than seven days will result in significant reductions in hatchability. Turning eggs during storage is generally not necessary when stored for less than seven days, but if done, won’t hinder normal embryonic development. When eggs have been placed in the cool egg storage environment, they should not be allowed to warm up above the physiological temperature until they are ready to be placed in the incubator. Pre-warming of eggs is gaining popularity and is beneficial as a method to slowly bring the arrested embryo back into active development. Remember, eggs already contain a live developing embryo and any added stress negatively effects their development and reduces the number of quality chicks hatched.

Summary

During the hot days of the summer, increase frequency of egg collections times, particularly in the afternoon hours. This should be done in an effort to get hatching eggs into the cool room as soon as possible. This is much more important in older houses not equipped with many of the modern environmental control systems. Once eggs have been placed in the egg storage room, do not remove them unnecessarily. Once embryo development is arrested, it should not be allowed to proceed until the eggs are ready to be placed in the setters. Remember that poor egg handling on the breeder farm can reduce both overall egg hatchability and chick quality.

By R. Keith Bramwell, Extension Reproductive Physiologist
Center of Excellence for Poultry Science, University of Arkansas
Avian Advice newsletter - University of Arkansas Poultry Science Extension

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Caring for Hatching Eggs Prior to Incubation