Investigating DIS
By Bobbie Andleton SPBE Internet Chairperson

Frequently advice is given to breeders that the cause of dead-in-shell (DIS) can be detected by egg necropsy. This is only partly true. Egg necropsy must be performed within literally hours of the death of the embryo. The difficulty in detecting time of embryonic death is immense. Whether the egg is being incubated by parents or artificially incubated the naked eye cannot readily detect the status of an embryo. Therefore time of death is difficult to calculate.

There are many reasons for DIS conditions and each contributing factor should be thoroughly investigated by the breeder in cooperation with his/her veterinarian. Several conditions fall directly into the field of microbiology as the search for microorganisms causing DIS conditions begins.

If a breeder continually has DIS two simultaneous tests need to be run immediately. The first would be an oral and cloacal swab of both parents. Secondly various areas of the nestbox or incubator and hatchery should be cultured. Merely adding new strata to an old nestbox does not eliminate existing disease organisms already present in the box. This is one of the imminent dangers in constantly using the same nestbox repeatedly.

Merely washing a nestbox with soap and water between hatches will not destroy the organisms! Unless the nestbox is of metal or plastic construction it cannot be safely cleaned. Even painted wooden boxes can store unwanted organisms. Wooden nestboxes under constant use become natural harbors for a variety of harmful organisms including bacterial, viral and parasitic diseases. Ideally only one clutch should be hatched and raised in a wooden box and then a new box installed. Maximum length for use of a single wooden nestbox should never exceed one breeding season!

If the eggs are artificially incubated then the incubator and/or hatchery both need to be tested for the presence of bacterial, viral and parasitic organisms. Routine cleaning of all parts of the incubator should occur throughout the breeding season. One of the best products on the market is Vanodine. When breeding season is over, the incubator and hatchery should both be fumigated according to the manufacturer's recommendations. At the same time when either cleaning or fumigation occurs the egg cartons should be totally replaced The majority of egg cartons are made of a porous, paper fabric which quickly absorbs a variety of harmful organisms making cleaning impossible.

Several and/or consistent DIS from a variety of species can be a sign of low humidity, an airborne disease or a common carrier such as roaches. Roaches love the dark confines of nestboxes; they are excellent carriers of diseases.

Strata used in nestboxes can also be carriers depending upon the type of strata and its origin. Hay, straw, dead leaves and wild grasses might provide a more natural strata but each can be deadly to incubating eggs, the parents and young hatchlings. Many such materials are exceedingly prone to a variety of fungi and parasites which cause various respitory problems. Shredded paper products, especially ones containing ink and colorations are prone to causing other respiratory problems. The various manufactured stratas for birds have usually undergone some type of sanitizing making them safe for birds. Some of the same stratas are also manufactured for dogs, cats, rabbits, and the rodent family of pets. These should not be used with the birds.

Several species of birds will defecate within the confines of the nestbox. Hatchlings likewise defecate in the nestbox. Fecal and urine matter in the nestbox can contaminate all unhatched eggs causing DIS to occur. Merely removing clumped portions of strata formed by the fecal droppings does not necessarily remove unwanted organisms.

Even if an egg necropsy identifies the organism responsible for the DIS condition, the aviculturist working with the veterinarian still must uncover the contaminating source. Some disease are passed directly from parent to egg; other diseases arise during the incubation process from the parents' cloacal region; other diseases enter the egg from the parents oral cavity as the beak is utilized in the turning of the eggs. There are reasons for DIS. Finding that reason requires minute microscopic examination of many areas associated with the parents and the environment. Then must follow an eradication program and re-testing of all areas including parents to assure the breeder that the condition no longer exists.

Humidity is easily detected by placing a hydrometer in the breeding area. If low humidity is the problem then adding a humidifier can help correct the problem. Other ways to increase humidity would be adding an automatic misting system or daily misting birds and the exterior of the nestbox. Too high a humidity level can likewise cause incubation problems resulting in not only DIS but deformed chicks for those fortunate enough to hatch. In this case it might be necessary to add a dehumidifier or cease daily misting.

Certain species of parrots require different heat and humidity settings for artificial incubation and hatching. Using a community incubator and hatchery for mixed species can have detrimental affects on certain parrots. Research done by UC-Davis in the eighties showed that a slight deviation of one degree in temperature and humidity levels severely affected the growing embryo and among these was a pronounced increase in DIS incidences.

Another DIS cause is malpositioning of the embryo inside the egg. In order for pipping to occur successfully the head must be properly positioned for the beak to make it's circular cut (or pip) of the egg. When free movement and proper positioning of the embryo is not present the chick either cannot pip or it continues to pip in the same area. Unable to get out of the shell it becomes a DIS statistic.

One seldom discussed cause of DIS is the part genes might be playing. Sometime embryonic or neonate death and deformities are transmitted by human parents an other animals to their offspring. Birds have the same capability for transmission of these lethal genes. This is an area of scientific study which has only begun in a very elementary manner for the aviculture community. The advanced DNA studies required to determine the effect the avian parental combination of genes will have on their offspring is a costly and longitudinal undertaking. It is therefore not likely to become an imminent research area in parrots in the near future. For a variety of species which have developed mutations DIS becomes more frequent. Any mutation is always weaker than the nominate. When these mutant genes combine in a lethal manner DIS occurs. The more mutations contained in the parents' genotype the more subject the chick will become to lethal combinations. This is proving to be especially true with the Lutino mutations in some species.

As one can see the answer to DIS by its very nature is a much more detailed investigative process than merely having an egg necropsied at the proper time. The only guarantee that an egg necropsy may reveal is the appearance of an organism which might be responsible for DIS but it does not disclose how this organism arose within the egg. Therefore, the search for clues as to DIS situations must continue beyond the egg necropsy.

This bit of information was brought to you by:
Bobbie Andleton, SPBE