Avian Incubation and Hatching for the Practitioner

Many avian veterinarians quake at the thought of advising or helping an aviculturist with issues related to incubation and hatching. Once you learn the principles of artificial incubation and hatching, you should be able to offer competent assistance. If you are serious about becoming a good avian veterinarian, however, please consider purchasing an inexpensive incubator (or borrow one from a client or friend) and try to incubator-hatch a few eggs yourself. Cockatiels are a good bird to begin with. Do not attempt this with quaker parakeets, as incubator hatching them is quite difficult. You will learn more by hatching some birds yourself than from sitting in ten lectures on the subject!

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 coelom, 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 is it 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 diseases 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 ensure 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 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 areas 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 indicated 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. When just starting out, initially set the incubator temperature just above 99 degrees F. Rose-breasted cockatoos and Australian parakeets incubate best at about 98.7 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 egg should lose between 16-20% and an Eclectus parrot egg should lose from 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 1/4 to 1/3 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 eggshell 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 muscularis complexus (the pipping muscle) at the back of the neck begins twitching again, facilitating the hatch. Abdominal muscles also begin twitching, which helps draw the yolk sac into the coelom. Leg muscle twitching helps strengthen the legs.

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 doe not pip into the air cell).

Every DIS egg 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. There are many infectious diseases that can cause DIS eggs. Histopathology of a dead embryo will often prove diagnostic, however, on occasion, special stains, in situ DNA hybridization, or cultures may be necessary for a diagnosis.

There are many infectious organisms that can be transferred from the hen to the egg. In some cases, the infectious organism may infect the egg, yet the embryo may continue developing, and may even hatch, carrying the organism at hatch. Vertical transmission is used to describe the transmission of an infectious agent from a parent to an egg during fertilization, during egg development in the oviduct of the hen or immediately after oviposition. Once oviposition has occurred, some infectious organisms can pass through the eggshell upon contact with contaminated feces, urates or bedding. This is still considered vertical transmission if infection occurs immediately after laying. Transovarian transmission occurs from the ovary to the egg. Infectious organisms harbored in the oviduct can also be passed into the egg prior to shell formation, and organisms can infect the egg if contents from the cloaca contaminate the surface of the egg and then penetrate the egg. A Gram's stain of shell membranes, yolk or internal organs can be used as a screening test, followed by bacterial culture and sensitivity.

Chlamydophila can be vertically transmitted from an infected hen through the egg to the embryo. Depending on the pathogenicity of the strain and the number of organisms that are passed into the egg, the embryo may die during incubation or it may actually hatch as a baby bird already infected with Chlamydophila. Transovarian transmission of chlamydiosis has not yet been confirmed by researchers, so it may be that the eggs are contaminated by another vertical means of transmission. In my experience, if an egg or eggs have died part-way through incubation, and histopathology or DNA PCR testing of egg membranes or internal organs, shows infection with Chlamydophila, egg injections with long-acting injectable doxycycline may be instituted, after the eggs are removed to an isolation incubator. Neonates that hatch from these eggs should start on oral doxycycline therapy, as well as antifungal therapy (fluconizole, 100 mg. crushed and added to Nystatin, 100,000 U/ml, 20 ml., dosed at 0.5 ml per 1000 gm bw PO BID), and probiotics.

Bacterial contamination with Salmonella sp. can cause DIS, or if a very small number of bacteria infect the egg, the egg may continue to develop, resulting in a weak hatch neonate that dies shortly after breaking out of the egg. Bacterial infection may cause yolk material to coagulate in the egg, and dead embryos may show hemorrhagic streaks on the liver. The spleen and kidneys may show congestion. Pinpoint areas of the liver may be necrotic, and inflammation of the pericardium may be seen. Culture of the infected egg may be diagnostic. Salmonella are motile bacteria that can penetrate the eggshell and can be transmitted vertically.

Some Staphylococcus bacteria can kill embryos. The avian embryo can be resistant to some strains of staphylococci, but can be highly susceptible to other strains. Infected wounds on parent birds can infect eggs, as can staph infections found on the hands of aviculturists, if the egg comes into contact with lesions. Artificial incubators will grow staph readily, and it can spread horizontally in this manner. An embryo can die within 48 hours of exposure to some strains of staph, especially S. aureus. The older the embryo is at the time of first exposure, the less the chance of embryonic mortality. Hemorrhages may be found on the various internal organs. A laying hen can develop an ovary infected with Staph. faecalis, which can contaminate the forming egg. Contaminated eggs will have up to 50% mortality. Culturing the egg is important for diagnosis.

E. coli is commonly found in the GI tract of mammals and some birds. It can enter the egg from an infected reproductive tract of a hen. E. coli can also penetrate through the eggshell if the egg becomes contaminated with fecal material. E. coli commonly causes yolk sac infection, causing the yolk sac contents to appear watery and yellow-green or yellow-brown. Dirty nests and cages can serve as sources of contamination to eggs. The use of water bottles can reduce the amount of E. coli that builds up in the GI tract of birds. In my experience, aviaries that use a watering system and not water bowls will have fewer problems with sub-clinical bacterial infections in their breeder birds and their offspring.

Many embryos infected with E. coli will die late in incubation or shortly after hatching. If an E. coli infection is acquired during incubation, the hatchling may develop an umbilical and yolk sac infection (omphalitis) and they may have poor weight gains. Cracked eggs are more easily infected and may serve as a source of infection for other eggs in the incubator. Cracked eggs should be repaired as soon as the damage is discovered or they should be discarded, especially if signs of infection are present.

Mycoplasmatales

Mycoplasmatales are one order of organisms that replicate by binary fission. They have no cell wall but have a three-layer membrane. They are more primitive than bacteria, and must live and grow inside the host. In the environment, they live only for a short time. Although we have much to learn about Mycoplasma, they can be involved in problems with cockatiel conjunctivitis and respiratory infections, and also respiratory/eye problems in other species of pet and breeder birds. It is spread by respiratory excretions and by the gonads of both sexes, and infection in the air sacs can lead to contact transmission of the ovary and developing follicle. Transovarian transmission can occur. Mycoplasma can spread to the egg from an infected oviduct or from the semen of infected cocks.

It is possible to treat infected eggs. Tylosin is injected into the air cell at the start of incubation. A combination of lincomycin and spectinomycin is also effective for egg injections. Dipping the eggs in antibiotic solutions is effective in reducing the incidence of disease.

A third method of treatment has been useful in breaking the transmission cycle of Mycoplasma gallisepticum and M. synoviae. This involves elevating the temperature in a forced air incubator to 46 degrees C for 12-14 hours before incubating the eggs normally. This technique inactivates the organisms, but it will reduce hatchability by 8-12%.

Viral Diseases

Several important viral diseases are vertically transmitted in birds. PBFD has been demonstrated to be vertically transmitted, since the virus is found in the blood of infected birds. It has been shown that artificially incubated baby birds from PBFD-infected hens will consistently develop PBFD. So attempting to control PBFD by pulling eggs for artificial incubation is ineffective.

Avian paramyxovirus 1 (Newcastle's Disease or PMV 1) is one of a group of nine distinct serovars (with several more yet to be characterized) of the virus that are dangerous to birds. Although paramyxovirus is theoretically vertically transmissible, this mode of transmission is considered unlikely because infected hens will generally stop laying eggs when they are viremic. Eggs contaminated by virus-laden feces immediately after laying could contaminate an incubator, and can serve as a source of virus for recently hatched neonates.

Herpesviruses, most of which are very species-specific, include Pacheco's Disease virus, Amazon Tracheitis Virus, respiratory disease in Neophema sp. and Psittacula sp., wart-like or flat plaque-like lesions on the skin of psittacine birds, budgerigar herpesvirus, pigeon herpesvirus (infectious to budgerigars and cockatiels), falcon herpesvirus (infectious to budgies and Amazon parrots), Marek's disease (suggestive lesions in budgies). It has been theorized that some hens latently infected with Pacheco's Disease virus can pass the virus (as well as antibodies to the virus) to their eggs. The resulting neonates would be latently infected carriers that might not develop detectable levels of antibodies. Herpesvirus of European budgerigars causes feather abnormalities (referred to as "feather-dusters") and is thought to be egg transmitted, and has been demonstrated in dead-in-shell embryos and is considered a major cause of early embryonic death in affected flocks, resulting in decreased egg hatchability.

It has been my own personal experience that PDD may be vertically transmitted. Some adenoviruses, REO viruses and reticuloendotheliosis viruses can be vertically transmitted. Influenza A may also be vertically transmitted.

Parasites

Oddly enough, some parasites have been documented to occur within eggs. Adult ascarids have been found within eggs. The ascarids can get into an egg by moving from the cloaca up into the oviduct, where the shell is then placed around the aberrant parasite. The fluke, Prosthogonimus ovatus can be found in the oviduct of Galliformes and Anseriformes, and may also be trapped within an egg, but the flukes are more likely to result in abnormal shell formation.

Conclusions

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. Theriogenology is a fascinating and very rewarding area of avian medicine that deserves further study.

Recommended Reading

1. Wissman MA. Artificial Incubation. Proc Avicult Program 1996; 29-42.
2. Parsons BE, Wissman MA. Work-up for dead-in-shell psittacines. Proc Annu Conf Assoc Avian Vet 1993; 337-342.
3. Joyner K. Theriogenology. In: Ritchie BW, Harrison GI, Harrison L (eds). Avian Medicine: principles and application. Lake Worth, FL: Wingers Publishing Inc. 1994; 748-804.
4. Clubb S, Swigert T. Common sense incubation. In: Shubot RM, Clubb KJ, Clubb SL (eds). Psittacine aviculture. Loxahatchee, FL: ABRC, 1992.
5. Olsen GH, et al. A review of some causes of death of avian embryos. Proc Annu Conf Assoc Avian Vet 1990; 106-111.
6. Olsen GH. Problems associated with incubation and hatching. Proc Annu Conf Assoc Avian Vet 1989; 262-267.

Copyright © 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
All Rights Reserved
ExoticPetVet.net
www.exoticpetvet.net

Printer Friendly Page