By Dr Colin Walker BSc, BVSc, MRCVS, MACVSc (Avian health)
A swollen tummy in a bird is a surprisingly common reason for its presentation to an avian vet.
Often, the first response of an aviculturist, when he walks into an aviary and sees a sick-looking bird, is to catch the bird and examine it. A not unusual finding is to discover that the bird’s abdomen appears swollen. To many, a swollen abdomen means egg binding and because of this my nurses often receive phone calls from clients seeking advice on what to do with an egg-bound bird. Questioning often reveals that the bird has been unwell for some time. As egg-binding is an acute condition, it makes this diagnosis unlikely. What the bird owner really means is that the bird has a swollen abdomen. In fact, many conditions in addition to egg binding can cause a bird’s abdomen to swell. The causes can be grouped into six categories. The abdomen can become distended either due to fluid, fat, a hernia, organ enlargement, a tumour or an egg.
When abdominal distension is found in a bird that is in otherwise good condition, then as a general rule, this tends to indicate an acute (short-term) problem, while if the bird is in poor condition, this indicates a longer-term problem. Delays in diagnosis and treatment give the condition more of a ‘head start’ and are less likely to lead to a successful result.
And so how does an avian veterinarian go about actually diagnosing the problem and what are the likely outcomes?
There are five or so different types of fluid (depending on how they are categorized) that can accumulate in a bird’s abdomen. These form under different conditions and so examination of the fluid helps in diagnosis. A sample of fluid can be drawn with a needle directly through the abdominal wall into a syringe. The two main classifications of fluids are transudate and exudate. For detailed testing, the collected fluid sample can be sent to a lab, but often just visual examination of the fluid in the clinic gives the avian vet an idea of what is going on. Transudates tend to not smell, do not clot and are clear. They form as a result of problems that lead to circulatory disturbances, such as heart failure and low protein levels in the blood. Exudates, on the other hand, usually form in response to infection. They contain high levels of cells and protein and are therefore more viscous, smell and clot on exposure to air.
Although examination of the fluid gives an idea of the nature of the process we are dealing with, this is rarely diagnostic. In order to reach an accurate diagnosis, further tests usually need to be done. The other common tests are x-rays and blood testing. Drawing blood from unwell birds for biochemistry (organ function tests) and haematology (red and white blood cell parameters) testing is relatively routine these days. Blood is usually drawn from the right jugular (which is larger than the left) vein. Unless the bird is severely debilitated, 1% of the bird’s weight in grams can be drawn in milliliters. This means that we can draw 4 ml of blood from a 400 g galah or 0.25 ml from a 25 g budgerigar. A sample of 1 ml (i.e. all birds over 100 g) enables all common tests to be done reasonably accurately. Below this, the blood has to be diluted significantly, which does introduce some errors but results are usually sufficient to show diagnostic trends. Blood collection in birds does have its own peculiarities when compared to animals such as dogs and cats, which can at times present special problems for avian vets. Unlike mammal red blood cells, bird red cells have a nucleus. This means they really are alive and actively metabolizing. Because of this, certain blood readings such as calcium will continue to change after collection. Therefore, bird blood needs to be tested very quickly. This is okay, however, because most of the bigger city labs offer fairly quick turnaround times. My local lab in Melbourne can get results back to me in less than 3 hours. In only 3 hours from the blood being collected from the bird, a courier has collected the blood, the blood has been analysed and the results faxed back to me. Another potential problem is that bird blood clots really quickly after collection. In mammals, clotting factors are actually in the blood stream. However, in birds these factors are in the tissues around the blood vessels. During blood collection, some of these almost invariably come into contact with the blood, initiating the clotting cascade. Collected blood therefore needs to be quickly drawn into the syringe and placed in the correct testing tubes to prevent clotting. Avian blood is considerably more fragile than dog and cat blood and so this also needs to be done more gently. The other factor to consider when collecting blood from birds is that it needs to be collected correctly first time. Unlike dogs and cats, birds are not a bottomless pit as far as blood is concerned. 1 – 2 ml of blood from a dog is enough to run all tests. If collected incorrectly, more blood can simply be drawn. As birds only have a certain amount of blood available for collection, if this is messed up there has to be a time delay before more blood can be safely drawn. Not a good situation for a vet to find himself in if the bird is getting sicker and he needs that diagnostic information.
Having said all that, avian blood collection and processing in experienced hands is routine. Testing laboratories are now geared to handle it and the results are of great value to the vet, bird owner and bird.
The other common test, as mentioned earlier, is radiography (x-rays). Most birds are sufficiently small that two views can be taken on the average small-animal x-ray plate. Usually the bird is laid on its back and then its side. The resultant two images enable us to get a reasonable three-dimensional impression as to what is going on in the bird’s abdomen. Sometimes, abnormalities elsewhere in the bird’s body can also be coincidentally picked up too. Frustratingly, fluid behaves a bit like a tissue on x-ray in that it is radio-dense (appears white) and as such it can conceal detail. Sometimes fluid is described as having a ‘ground glass’ appearance because of the way it is whitish in the middle where it is thickest and fades out to gray around the edges where it starts to thin. An x-ray of fluid is, however, useful because even if the fluid does conceal detail, the x-ray helps to confirm that any swelling is in fact fluid and it also helps to localize just where the fluid is.
This may sound strange, but an abdominal distension due to fat can, at times, be hard to diagnose. Usually, if the bird has fat in its abdomen, it is generally fat elsewhere, although this is not always the case. Racing pigeons, for example, are particularly prone to a type of fat-based tumour called a mesenteric lipoma. These are benign fat-based tumour that can become as big as a cake of soap, weighing as much as 50 g (in a 400-g pigeon) and grow in the fat around the intestines. Often these birds otherwise are in normal condition.
Often clinical examination of the bird and palpation of the abdomen suggest that the bird is just fat. However, blood tests are often useful. Often, overweight birds are on a dry seed diet and so the blood results are often consistent with this. Low total protein, low calcium and high cholesterol values are typical. Sometimes the liver values will change, associated with fat infiltration of the liver. Interestingly, parrot cholesterol levels should be similar to our own, i.e. between 3.5 and 5.5. At our clinic, we have had cockatoos on dry seed diets with cholesterol readings as high as 45! Blood testing and also x-rays are useful when a diagnosis of obesity is suspected if for no other reason than to rule out other more serious causes of abdominal distension.
An abdominal hernia is a split in the abdominal muscles so that the abdominal wall no longer offers its proper support to the abdominal cavity. Although the term hernia is often used, it is somewhat of a misnomer in birds. Although hernias do occur, more often than not the muscle does not actually split but rather stretches and becomes thin. The end result, however, is a bulging of the abdominal wall, which allows prolapse of abdominal contents into the resultant pouch. True hernias do occur in racing pigeons, particularly in older hens, often starting at the navel. For avian vets, however, the most common presenting syndrome involving a ‘hernia’ involves older pet female cockatoos. These birds often have a history of intermittent chronic egg laying. Testing often reveals long-term low-grade oviduct infections, cystic oviducts, impacted soft-shelled eggs, or a combination of these things. The resultant infection and inflammation lead to fluid formation. This increasing fluid pressure, together with an increase in oviduct size, results in an increase in abdominal pressure. Often compounded by a dry-seed diet, and inactivity, the abdominal wall distends, resulting in the characteristic hernia-type appearance. In the short term, antibiotics, drugs to suppress further ovulation, dietary change and fluid drainage (if breathing is compromised) will help, however, only surgery involving removal of the oviduct and hernia repair offers a cure.
Blood profiling is always useful and x-rays are of particular value in diagnosing a hernia because they enable visualization of the abdominal wall outline and sometimes the abnormal position of organs in the hernia itself.
It is important to remember that egg laying is a normal avian phenomenon and just like the mammalian birth process some variation in the time and difficulty associated with laying an egg can occur from species to species and individual to individual. This means that a bird presented with an egg palpable in the abdomen is not necessarily egg bound. Having said that, however, there should be steady movement of the egg along the oviduct and the egg should be laid within a time regarded as normal for that species. A diagnosis of egg binding is tentatively made when neither of these things occurs. As a general rule, small birds such as canaries and finches lay their eggs quite quickly (usually in just a few hours) compared to bigger birds such as cockatoos and pigeons where 24 hours is fairly normal.
Egg binding initially causes abdominal pain with affected birds attempting to relieve this by adopting a horizontal posture. Often birds are short of breath due to the physical size of the egg interfering with the distension of the abdominal air sacs. As the condition becomes more chronic, obstruction of the bowel and ureters can lead to constipation and an inability to urinate. These combined with other changes can lead to shock and death.
Diagnosis of egg binding in birds displaying the above symptoms is relatively straight forward because more often than not the egg can be palpated within the abdomen. If there is doubt that the abdominal distension may not be an egg, an x-ray can be taken where a normally mineralized egg becomes immediately obvious. Soft-shelled (undermineralised eggs) are more difficult to see and any radiographs taken need to be thoroughly examined.
The degree of intervention with a case of egg binding needs to correlate with the severity of the problem. Essentially this relates to how long the bird has been egg bound for. Sometimes intervention in aviary birds, which are not used to handling or confinement, can exacerbate the bird’s symptoms. Also, in valuable species, it is particularly important that an attempt be made to save the egg and that in all birds the hen be given the opportunity to lay in her box so that parent-rearing remains an option.
Many early cases of egg binding in otherwise well birds respond to oral calcium supplementation. I use Calcivite Plus™ 0.2 ml per 100 g bodyweight via crop tube every 8 hours. The provision of heat is also useful. If the hen still does not lay, placing her in a darkened brooder set at 30 – 35°C and continuing with oral calcium supplementation every 8 hours will often result in the passage of the egg. As it is more likely to be a later egg in the clutch that becomes bound, once passed the hen can be returned to the aviary and the egg placed with the others in the nest box.
Failure to pass the egg within 24 hours or the hen becoming distressed means that it is time to call the avian vet. Such birds can be starting to go into shock and so as vets we often try to stabilize this before addressing the actual egg binding. As a result, fluids (e.g. lactated Ringers) can be given by injection, some vets also give corticosteroids, and often antibiotics are indicated for any complicating infection. Egg bound birds are more likely to be on a dry- seed diet and as such are multideficient. Calcium can be continued by injection and sometimes also multivitamin injections are given, in particular those containing vitamin E, vitamin D3 and selenium. A constant warm environment is provided.
If the bird continues to fail to pass the egg, a variety of drugs that stimulate oviduct contraction are available for the vet to use. All have side effects and must be used with care. Sometimes if the egg is in the last third of the oviduct, lubrication of the cloaca and gentle digital pressure on the egg can deliver it. This is best done under anaesthesia. If the egg has adhered to the oviduct or cloaca, a needle can be passed through the egg shell, the egg contents aspirated and the egg imploded. Once done, the bird is immediately more comfortable and is more likely to pass the collapsed shell. The bird must be monitored, however, to ensure this happens and care must be taken not to lacerate the oviduct wall. If all fails, the egg can be delivered through the avian equivalent of a caesarian operation or in pet birds the entire oviduct, together with the egg, can be removed.
After a severe egg binding episode, in order to give the bird a chance to recover, a number of medications are available to suppress further ovulation.
Despite the best of care, every bird keeper is going to get the odd bird with egg binding. However, if several birds over a short period of time develop the condition, then the birds’ environment, general management and in particular diet need to be reviewed. Egg binding is one of the conditions in aviculture, like so many others, where veterinary intervention can solve the problem but unless the underlying causes are addressed ongoing problems will be experienced. Adequate exercise, together with a diet rich in calcium, providing the correct levels of vitamins and containing an adequate level of protein for breeding, do much to minimize problems.
All of the abdominal organs have the potential to enlarge. These include the kidneys, pancreas, spleen and liver. Of these, it is the liver, and to a lesser extent the spleen, that are likely to increase to the point where the abdomen is noticeably enlarged. In health, the liver in birds extends to the rear edge of the sternum or keel. When enlarged, it can sometimes be felt as a firm ‘wedge’ extending beyond this. In addition, in small birds, with their translucent skin, any enlargement can actually be seen as a deep purple mass extending beyond the keel. This is made even easier if the skin is made wet. Organs can enlarge as a result of cancers (e.g. leucosis in chickens), changes induced by diet (e.g. fatty liver in cockatoos, hypervitaminosis A in lorikeets), infection (e.g. polyoma virus and Chlamydia in parrots), changes in circulation and exposure to toxins.
The liver is particularly vulnerable to enlargement for a number of reasons. The liver filters blood and in doing so actively filters out organisms and toxins that have the potential to infect and damage it. Also, birds have a portal vein (the only vein in the body that does not return blood to the heart) which takes blood from the bowel to the liver. This means that for many potential pathogens, such as Salmonella, the liver is the first ‘port of call’. Some organisms, such as Chlamydia, retrovirus and polyoma virus, particularly target the liver. Also, its normal role as metabolic regulator makes it vulnerable to problems such as iron storage disease and fatty liver syndrome.
Blood tests help to localize not only which organs are involved but also the nature of the process involved. X-rays enables the organ enlargement to be quantified. Many of these cases, however, end up having an organ biopsy collected under anaesthesia. This can either be collected as part of a laparotomy procedure (where the abdomen is opened) or through a ‘keyhole’ using an endoscope (the same instrument used for surgical sexing). This becomes necessary because an x-ray may show that the abdominal distension is due, for example, to the liver being enlarged, and blood tests may confirm that this organ is inflamed and not working well but a biopsy is needed to identify what the actual process is that is damaging the liver.
Today, with our safer anaesthetics and more refined surgical procedures, a diagnosis of abdominal cancer does not necessarily equal euthanasia. Frustratingly, however, we are still not able to do as much for some of these patients as we would like. Clinical examination, x-rays and blood tests, usually allude to the problem. However, many of these cases end up at surgery. This not only enables us to accurately diagnose the problem but also places us in the situation to do something surgically if in fact this is appropriate. Cancer of the testes, ovary and kidney are considerably more common than most people realise, while cancer is a principle cause of liver enlargement. Some of these cancers can affect even young and middle-aged birds. Of all the species that we see, budgerigars seem particularly prone to a variety of tumours. The reason for this, however, remains unclear. Most tumours affect unlucky individuals at random in the same way that a tumour may affect a dog or cat, but there are some infectious causes of cancer in birds, e.g. herpes virus can induce tumours of the bile duct in parrots, and retrovirus can induce cancer in a variety of species.
Accurate diagnosis, even if it results in euthanasia, means that the euthanasia is an informed one, knowing that nothing can be done for the bird.
Recognition by the aviculturist of abdominal swelling in one of his birds and the prompt presentation to an avian vet, make a successful outcome more likely. Diagnostic testing can be expensive and sometimes the amount of diagnostic work done has to be determined by the owner’s means and the value of the bird. Obviously, the more diagnostic work that is done, the more fully the whole biology of the health problem can be understood, the more effective any prescribed medication is likely to be and the more prepared the vet can be if the bird does require an operation. Even if an individual bird is lost, understanding the problem fully can have long-term beneficial spin-offs for the aviculturist so that further losses can be prevented or reduced in the aviary.