INVESTIGATING EGGS THAT DONT HATCH
By Dr Colin Walker BSc, BVSc, MRCVS, MACVSc
Eggs are commonly taken for incubation for a variety of reasons, but one of the most frustrating things that can happen to an aviculturist is, after getting an egg from a good pair, to lose it during the incubation process. Despite the best of care, the odd egg is going to be lost, but in a recent episode at the clinic, a client failed to hatch 13 of 14 Macaw eggs. Absolutely heart breaking. And so, how should we investigate such problems?
It is the bird that produces the egg that goes into the incubator and so basically the problem can only lie in one of these three areas, i.e. either the incubator, the egg or the parents. I find it easiest to look at each of these separately and go through a check list of potential problems.
1. Poor quality incubator
Incubators can be divided into two types depending on whether or not a fan is used to circulate warm air. In the first, or fan-forced, type, a fan is used to circulate warm air throughout the incubator. In the second type, air is simply heated. As a general rule, a fan-forced incubator is preferred over a still-air type as they are better at maintaining a steady temperature through the incubator. Thermostats also vary. Solid-state thermostats are more precise and accurate than wafer-type thermostats. Better quality incubators have more sensitive thermostats, even air flow, a gentle turning mechanism and a smooth-opening incubator door to minimize vibration (which can be associated with early embryonic death).
2. Incorrect incubator settings
As a general rule, most parrot eggs are best incubated between 37.2°C and 37.5°C and at a humidity of approximately 56%. Temperature, particularly in the first third of incubation, is critical. Too high a temperature at this time can kill chicks. Towards the end of incubation, temperature is less critical because the chick to some extent can thermoregulate. Too high a temperature then may just lead to an early hatch. If the temperature is a bit high all through incubation, the chick is generally weakened and either dies towards the end of incubation or alternatively hatches small and weak. Too low a temperature leads to inadequate fluid loss. Those that survive to hatch resemble those that have been incubated at too high a humidity and have swollen, fluid-filled bodies. Hatching may be prolonged and delayed.
Humidity is not as critical as temperature for proper incubation. The embryo has some ability to compensate for differences in humidity, particularly in the last third of incubation. If the humidity is too low and the chick risks dehydration, it can swallow amniotic fluid and any remaining albumin to compensate for excessive moisture loss. However, persistent or excessive low humidity in late incubation can lead to dehydration and kidney failure due to decreased perfusion of the kidneys with blood. Low humidity in the first third of incubation interferes with the mobilization of calcium from the egg shell to form the growing chick’s skeleton and can lead to a stunted embryo. On the other hand, increased humidity levels during incubation mean that insufficient moisture is lost from the egg. This results in eggs with small air cells and swollen chicks. This in turn interferes with yolk sac resorption and sealing of the navel. Embryonic death can result from inadequate space in the air cell for pipping.
3. Problems with the actual temperature and humidity in the incubator
Faulty thermostats and poor quality incubators can lead to a failure to deliver the required temperature and humidity. A fluctuation of just 0.2°C can result in decreased hatchability. Both thermometers and hygrometers can be placed around the incubator and in particular near the eggs. They should be checked and calibrated frequently.
4. Poor incubator hygiene
In the absence of disease from the ovary or oviduct, the egg is essentially a sterile package. The warm humid environment in the incubator is the perfect setting for harmful organisms to flourish and so the risk of introduction must be kept to a minimum. The incubator can be cultured to check for bacterial and fungal infection. Hands should be washed prior to touching eggs and ideally clothing worn around other birds should be removed. Regular candling picks up early deaths and therefore eggs can be removed, giving infected eggs or egg debris less of a chance to contaminate the incubator or hatcher.
5. Incubator breakdown
Ideally, before artificial incubation begins, the incubator should be cleaned, set up and running for several weeks to make sure it are working properly.
6. Incubator location
The room in which the incubator is placed is important. It should be an area of low traffic, to minimize vibration, and temperature fluctuation. The area is best maintained at 20-25°C. It should not have windows as direct sunlight can quickly heat up an incubator. The incubator should be on a steady shelf. The room should be easily cleaned, ie no carpet.
One would think that the simple act of removing an egg from a nest box and placing it in an incubator would be fairly straightforward. There are, however, many potential hiccups during this time. The following factors should be considered.
1. Egg vibration
Particularly in the first third of incubation, excessive vibration is a common cause of embryonic death. Eggs should be handled carefully when being removed from the nest. The only movement an egg will experience in the nest is a gentle roll as the hen turns the egg. Jarring and bumping are unnatural and are potentially dangerous to its contents.
2. Egg cleaning
An egg is laid at the temperature of the hen. As it cools down, it draws in contaminants on the shell. Bacteria, fungi and viruses from a dirty nest box can all be drawn into the egg. Washing the eggs, if done properly, decrease contamination, if done poorly it can increase contamination. Washing of eggs, however, is controversial. It can lead to loss of the protective cuticle on the egg and bacteria find it easier to invade the pores of a wet egg. It is not usually recommended for parrot eggs. Washing can, however, be beneficial if there are large amounts of dropping on the egg shell. Often, however, a better approach is to let the droppings dry and sand them away. If washing is done, warm water (approx. 43°C) should be used.
3. Egg fumigation
In the past, some references recommended fumigating eggs. They generally recommended a formalin and potassium permanganate mixture. This was used shortly after the start of incubation to disinfect eggs and the incubator. Such procedures are no longer recommended. The resultant mixture was carcinogenic and if done later in incubation could harm the embryo. Some references suggest sanitizing eggs with warm (40°C) iodine solution.
4. Egg shell contamination
Apart from droppings and infectious agents, substances such as oil, insecticides, cleaning agents, and even the nicotine on a smoker’s fingers can all contaminate the egg shell. They all have the potential to either deform or kill the developing embryo. Hands and collecting baskets should be washed or disposable gloves worn. Consider using a plastic soup spoon to pick up eggs. They have rounded edges and can easily be sterilized.
5. Egg chilling
Common sense really, but particularly important if the parents have been allowed to incubate and chick development has commenced. Transfer to the incubator should not be delayed and if occurring on a cold day, the egg should be covered.
6. Egg storage
Sometimes eggs are stored to synchronize incubation and hatching or to produce even-aged chicks. Transport to an incubator sometimes necessitates storage. Eggs can only be stored if incubation has not commenced and as a general rule the longer eggs are stored the lower is the hatchability. For most species, the recommendation is that eggs be stored between 13 and 18°C and at a relative humidity of 75%. Cockatiel eggs can be stored at 12°C and 60% for 3 – 4 days before decreased hatchability is noted. In chickens, hatchability decreases by 2% per day when stored. Egg storage for more than one week is not recommended.
7. Egg setting
The position of the egg in the incubator affects chick survival. Parrot eggs are either incubated horizontally or with the air cell end slightly elevated. For comparison, chicken eggs are placed vertically with the air cell up.
8. Egg turning
Egg turning is important in preventing malpositioning of the developing embryo as it seeks to place its head near the enlarging air cell and to prevent sticking to membranes as the albumen becomes more viscous with increased moisture loss during development.
Artificial incubation is more successful if the eggs are left under their parents or fosters for the first 2 – 3 weeks and so it is obvious that the closer we can mimic the technique of the birds then the more successful artificial means are likely to be. There really are two issues here. How often the egg should be turned and how much should the egg actually be rotated. It is thought that parent birds turn eggs on average every 35 minutes. Most sources recommend that parrot eggs be turned at least three to five times daily with some people suggesting every 2 hours is preferable. More frequent turning, up to 24 times a per day, may improve hatchability in particular in embryos that are thought to be weak. Many automatic units turn eggs 12 – 48 times per 24 hours.
Most parrot incubators turn the egg 45° in either direction so that the egg actually turns through 90°. Some believe that this is inadequate and recommend that eggs be given an extra ¼ turn three times daily if incubated from day 1, or two times daily if naturally incubated for the first 1 – 2 weeks. Some turn eggs 180° four times daily with success. A mark can be made on the egg shell with a graphite pencil to monitor turning position.
It is also thought that the manner of the roll may be important. Some believe that a gentle roll with no jarring (more likely to occur with manual turning), mimicking more closely that found in nature, improves hatchability, while others believe that this makes no difference.
9. Weight loss
Eggs naturally lose weight during incubation due to the chick’s metabolism and evaporation of water. The correct amount of water loss is essential for normal chick development and to adequately enlarge the air cell ready for internal pipping. The average amount of weight lost is 13% with the normal range being 11 – 16%. Dr Crosti, the veterinary director of Loro Parque, states that Macaw eggs must lose at least 15% weight otherwise hatchability will be adversely affected. Usually 20% of total weight loss occurs during pipping (eg 12% during incubation, 3% during pipping, making a total of 15%). Weight loss is affected by egg shell thickness, egg pore size and number, temperature, humidity and air exchange. Air cell size, determined through candling, is proportional to weight loss and can be used to monitor weight loss. Various techniques have been described to control weight loss such as sanding eggs (to decrease thickness and increase weight loss), creating holes (that can then be closed again with tape), and covering a small part of the shell with paraffin. A technique is described where dehydrated eggs are placed in zip-lock bags with cotton balls dipped in sterile water. When large numbers of eggs are involved, running two or three incubators at different humilities to accommodate normal, dehydrated and wet eggs becomes essential to maximize hatchability.
1. Parental health
Most agents that infect eggs come from the cloaca, nest or environment. Birds carrying infections that are passed in the droppings such as Circo virus and E. coli contaminate the environment, exposing the eggs to a heavy pathogen load. In addition, certain agents such as Chlamydophila or Salmonella can infect the ovary and/or oviduct and be incorporated into the egg at its formation. This ‘vertical’ transmission can also occur with Circo virus and possibly Polyoma virus. Failing this, droppings from carrier birds containing these viruses can contaminate the egg shell during laying or in the contaminated nest. Such eggs are time bombs waiting to explode, providing a significant source of infection in the incubator, hatcher or hand-rearing facility.
Breeding birds whose eggs are to be incubated should undergo regular health checks and only eggs from healthy birds should be incubated. Disease introduced into the incubator can lead to the loss of the entire batch of eggs.
Nutritionally deficient hens can continue to lay but the low level of nutrients means that the eggs they produce are less likely to hatch. The yolk may be less nutritious for the growing embryo or the egg shell may not be properly formed. The age of embryonic death usually depends on the degree and type of deficiency. For example, a deficiency of folic acid can cause the spine not to develop properly, vitamin A deficiency directly results in decreased hatchability, riboflavin is used in albumin and a calcium or vitamin D deficiency leads to a thin shell.
Older birds are more likely to produce poor quality eggs and eggs with less nutritious yolks. It is interesting to note that mutations are more likely to be bred from older birds. If eggs are left with young pairs prior to starting artificial incubation, there may be inconsistent parental incubation or egg trauma in the nest due to reproductive inexperience.
3. Genetic problems
This seems to be much less of a problem in aviculture than in domestic species such as poultry. Lethal genes can be carried recessively. Examples include mating crested canaries together or almond tumblers (pigeon) results in death of the youngsters. Recessive (and often harmful) genes are much more likely to be exposed through inbreeding.
4. Recent medication
Some commonly used medications can adversely affect hatchability. Tetracycline antibiotics interfere with calcium absorption, Baytril (another antibiotic) has been associated with embryonic death, and Emtryl (for flagellate infections, such as canker) can interfere with sperm production for up to 6 weeks, resulting in ‘clear’ eggs.
5. General condition
Birds that are malnourished or obese are predisposed to secondary infections and more vulnerable to disease generally. Anatomical problems can interfere with the normal mating act being successfully completed.
Having said all that, in most well-managed aviaries, poor hatchability is usually associated with problems with either temperature, humidity or the rate of turning in the incubator.If these parameters seem fine working through the above check list should prove helpful. Monitoring the eggs through candling, weighing and with the newer heart monitors allows fertility, development and viability to be monitored. Early detection of dead eggs enables their quick removal. This decreases the risk of spread of disease and also provides an excellent opportunity for egg autopsy, so that the cause of the poor hatchability can be investigated further.