The process of incubation is a wondrous process, and nature has provided the perfect incubator, the bird. However, for many reasons, aviculturists may choose to artificially incubate eggs. There are many different types of incubators, but the success of artificial incubation depends more on the knowledge and skills of the person using the equipment than of the sophistication of the incubation equipment.
It is important to have a basic understanding of the egg to successfully artificially incubate eggs. The egg must contain all of the nutrients necessary to sustain a growing embryo until hatching. The shell contains pores that allow respiration of moisture and gasses through the egg. These pores can also allow bacteria and other pathogens into the egg under certain conditions. The shell contains three layers: the cuticle, the testa and the mammillary layer.
Eggs have two shell membranes, the inner and outer shell membranes. At the area of the air cell, these two membranes are separated. If the egg is opened during an assisted hatch over the air cell, the inner shell membrane will be visible covering the chick.
The egg white, albumen, consists of three proteins. Thick and thin albumen and the chalazae, which are two strands of thick albumen, connect to the shell membranes. These act to keep the yolk in the center of the egg.
The yolk provides the main source of nutrition for the growing embryo. The yolk has four membranes and blood vessels develop around the membranes to carry nutrients to the embryo. At hatch, the twitching of the muscles of the embryo help pull the remaining yolk into the celoem, where it is utilized during the first few days of life.
The germinal disc is the nucleus of the female egg. If the egg is fertile, it is the blastoderm, and if infertile, the blastodisc.
In most psittacines, the reproductive tract of the hen includes only the left ovary and left oviduct. The parts of the oviduct include the infundibulum, magnum, isthmus, uterus and vagina.
The embryo actually begins to develop before oviposition. The egg may be candled to assess fertility after it is laid, and in some cases, it may show development within a few days of being laid. Fertility is ascertained by the development of blood vessels within the egg. The developing embryo is subject to damage by chilling or jarring (addling). For best hatchability, it is best to leave eggs under the hen for at least 14 days, to ensure the health of the developing chick, but this is not always possible or economically advisable. By pulling eggs for artificial incubation, many birds can be induced to lay more eggs than would normally occur, this increasing productivity. Optimum temperatures that simulate those of the natural parents will produce the healthiest chicks.
It should go without saying that the production of healthy, viable baby birds requires a healthy flock. Breeder birds should be examined, tested and treated for any disease uncovered. The entire facility should be evaluated periodically, to uncover any management problems that may contribute to disease in the aviary.
Aviculturists must develop an egg numbering system. Records are extremely important. By keeping accurate records, the avicultural veterinarian and aviculturist can more easily assess trends in production. Incubators should be set up and running for several weeks prior to incubating the first egg to insure that they are operating normally. It is preferable to run three incubators, but this is not always possible. The incubator should be set initially at 99.1 - 99.2 degrees F. Some species require slightly different incubation temperatures. The wet bulb temperature should stay between 80-82 degrees F. At a high altitude, the wet bulb reading may need to be increased slightly.
The room in which the incubator is kept should be maintained between 70-74 degrees F. The incubator should be routinely disinfected. If possible, the incubator should be placed in a room by itself with minimal traffic and should not be kept in the nursery.
Eggs should be moved to the hatcher when the internal pip (or drawdown) occurs. Many aviculturists use their old incubators as hatchers, and many keep their hatcher in the nursery. Hatching actually begins three to four days prior to the expected hatch date. The hatcher should be set at 98.5 degrees F, or approximately one degree less than the incubator. The humidity should be high enough to prevent the hatching chick from sticking to the membranes and drying out. The wet bulb temperature, which measures humidity, should read 92-94 degrees F or higher. The hygrometer wick must be kept wet to give an accurate reading. As chicks hatch in the hatcher, the humidity will naturally rise.
Candling eggs is a very important skill. Eggs should be candled immediately after removal from the nest to check for fertility. The size of the air cell should be noted. Any shell abnormalities should be noted and corrected, if possible. Within 24-48 hours of pip, the egg will undergo drawdown, as the air cell changes shape. At this time, it is a good idea to candle the egg every 6-8 hours, and to place the egg in the hatcher, as turning is no longer required.
Damaged eggs can be easily repaired. If cracked eggs are not repaired, the egg will lose too much moisture during incubation, resulting in dead-in-shell (DIS) embryos, or the egg may become infected. Repaired eggs require special monitoring during hatch, as the repaired area may prevent the chick from hatching normally. Thin cracks can be repaired with water-soluble white glue. Several coats are usually required. Bite or toenail holes should be repaired. If the defect is too large to be corrected by glue alone, tissue paper may be used to cover the defect, using several coats. Repaired eggs should be hand-turned, and weighed frequently.
Recognizing DIS embryos by candling is an important skill. Early embryo death is easy to diagnose by the presence of a blood ring. Older embryos that die turn very dark as the blood supply recedes. Blood vessels indicate a viable embryo. If no active blood vessels are seen, or if patches of the shell are devoid of vessels, then that indicates DIS.
Embryos begin developing at about 97 degrees F and will continue to develop up to about 102 degrees F. The higher the temperature, the faster the chick will develop, up to a certain point. Chicks incubated at the incorrect temperature will be weak hatch chicks, if they survive at all. Lower temperatures will cause the embryo to develop too slowly. For most psittacine eggs, the incubator temperature should be between 98.5 and 99.7 degrees F.
Incubators may have several different temperature areas within the same compartment. Incubators with a glass window may have a temperature reading of several tenths of a degree lower near the glass. It is a good idea to measure temperatures in several different locations in the incubator.
Eggs should be weighed when pulled, and then weight loss should be monitored periodically, preferably daily. Eggs should lose between 9-20% of their day one weight by the time of internal pip. Egg weight loss varies with the different species. For example, a Moluccan cockatoo should lose between 16-20% and an eclectus parrot should lose between 14-17%. The wet bulb reading should be adjusted based on individual egg weight losses during incubation. Factors affecting weight loss include the size of the egg, thickness of the shell, altitude, size of pores of egg shell, stress lines on egg shell, damaged areas to shell, and ambient humidity in the incubator. For eggs losing too much weight, it is possible to create a higher humidity environment within the incubator by placing an egg in a sealed plastic bag, with a few holes punched in it, in which a gauze pad soaked in sterile water, is placed. Bags should be opened up daily and aired out.
Eggs are giving off gasses when respiring, especially carbon dioxide. Therefore, ventilation is very important in the incubator. Incubators used as hatchers can have problems with increased levels of ammonia when eggs hatch. Supplementation with oxygen should not be necessary in the average, well-ventilated incubator, but supplying oxygen to weak hatch neonates can be beneficial. Actually, in some species of birds, such as pheasants, eggs will benefit from the administration of carbon dioxide during hatching.
Psittacine eggs should be incubated in the horizontal position. Ratite eggs are usually incubated vertically, with the air cell (large end) up.
Eggs should be turned every two hours during a 16 hour day. Eggs should be turned an odd number of times per day. Eggs should be turned 180 degrees at least once per day, and one-quarter to one-third turn each other time. Eggs should be rolled gently and slowly.
Abnormally shaped or sized eggs tend to have more incubation problems. If possible, these misshapen eggs should be pulled for artificial incubation, since the aviculturist will have more control of factors that may affect development.
Drawdown occurs when the air cell changes shape as the embryo, using the egg tooth, punctures the inner shell membrane and enters the air cell. The egg is designed to allow ease of exit from the egg, and the egg tooth is used to begin unzipping the egg shell in a circular manner, usually at the larger end of the egg.
The initiation of hatch occurs partially from the increased carbon dioxide level in the egg. This causes the embryo to begin twitching it's muscles, allowing the inner shell membrane to be punctured by the egg tooth. The chick then begins breathing the air in the air cell. As the carbon dioxide level begins to rise again, the muscularia complexus (the pipping muscle) at the base of the neck begins twitching again, facilitating the hatch. Abdominal muscles also begin twitching, which helps draw the yolk sac into the celoem. Leg muscle twitching helps strengthen the legs.
The Pipping Muscle
Assisting the hatch is a difficult decision, and in this author's experience, many aviculturists will do more harm than good by assisting the hatch. Normally the chick will hatch 24-48 hours after drawdown has occurred. By making a pin hole in the egg shell over the air cell, the carbon dioxide level will drop, actually slowing the hatch. Making a pin-hole or opening the air cell end of the egg should only be done if the vocalization level of the hatching chick is decreasing or other signs indicating that the chick is in trouble are evident (for example, if the chick does not pip into the air cell).
The problems related to DIS are quite complex and are beyond the scope of this manuscript. DIS eggs should be examined by an avian veterinarian to determine the cause of death. This author strongly believes that every DIS egg or dead bird is valuable, both to the avicultural veterinarian and to the breeder, because the cause of death may pinpoint management areas or sub-clinical disease in the aviary, incubator or nursery.
Incubation and hatching are two areas of avian medicine that are not easy to consult aviculturists on, unless you, the veterinarian, have a good, working knowledge of theriogenology. It may be worthwhile for you to consider purchasing an inexpensive incubator, and actually go through the process of incubating and hatching some cockatiel eggs for the experience. Theriogenology is a fascinating and very rewarding area of avian medicine that deserves further study.
Copyright © 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
All Rights Reserved
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