Avian and Exotic Pet Medicine, The University of Queensland, Gatton, QLD, Australia
Psittacine chicks have little in the way of compensatory mechanisms to cope with disease and consequently frequently present as acute emergencies. This presentation details the major problems facing a chick with an emergent condition, and their recognition and treatment by the clinician.
Most companion birds (e.g., parrots and passerine birds) are altricial (i.e., when hatched they are blind, deaf and not feathered, and therefore totally dependent on their parents or rearer. They go through a rapid growth phase, during which their size and weight increases to a level above that of their adult weight, before falling and then plateauing at their fledging weight. During this time their eyes and ears open, their feathers grow, the bones and internal organs mature, and their social skills and learned behaviours are shaped. This is obviously a period of rapid change, where small changes can have a big impact on their health and development.
Added to these rapidly-developing changes is the lack of awareness by the owner that a problem is present—and then a delay in seeking veterinary assistance—meaning that most chicks presented for health problems are often severely decompensated and are emergent cases.
What Are the Challenges of a Paediatric Case?
There are unique challenges the clinician faces when dealing with a paediatric case. These include:
1. Their small body size:
a. A large surface area to body mass ratio, sensitising them to temperature extremes (especially hypothermia).
b. Difficulty in accessing blood vessels for the administration of fluids and medications and collecting blood samples.
c. Small muscle mass, making intramuscular injections difficult to administer without causing significant bruising pain, and discomfort.
2. The lack of body fat makes:
a. Body heat retention difficult, contributing to hypothermia.
b. Coelomic radiography difficult to interpret due to the loss of contrast.
3. Immature physiology:
a. The ability to invoke compensatory physiologic responses (e.g., vasoconstriction and vasodilation) is limited.
b. Lack of white fat (for insulation) makes them reliant on brown fat (to a small extent) and metabolism to maintain their body temperature. This requires the frequent ingestion of a high energy, easily digested food.
c. The kidneys have poorly developed concentration and filtering capacity.
d. The digestive tract has a rapid transit time and is easily ‘stressed,’ leading to ileus.
e. The respiratory tract is immature, and the air sacs are compressed by the intestinal tract, giving a low respiratory reservoir.
4. Haematologic and biochemical differences from adults can make the use of diagnostic testing difficult. Compared to an adult of the same species, chicks generally have:
a. Lower PCV and higher WCC.
b. Lower total protein and uric acid.
c. Higher CK.
Evaluating the Sick Chick on Presentation
On initial presentation of the chick, a rapid but thorough evaluation needs to occur. This evaluation includes a history, physical examination, and finally diagnostic testing (performed after the chick is stabilised).
The history of the patient needs to include the:
1. Species and age of the chick?
2. Whether it was artificially or naturally incubated?
3. Whether it is been parent-reared or hand-reared?
4. What the parents were fed?
If it is been hand-reared, the following information must be ascertained:
1. From what age did the hand-rearing start?
2. What it’s been fed?
3. How has it been mixed?
4. How often and how much has the chick fed?
5. When it was last fed?
6. At what temperature the chick has been maintained?
It is also important to know what the exposure of the chick to other birds/chicks is, and whether there has been any problem with them. It is useful if there are records accompanying the chick, but these are often not available.
The physical examination needs to include:
1. Its body weight
2. Its body condition (best evaluated by examination of the toes and elbows)
3. Its posture and conformation
4. Its body colour and temperature
5. Its hydration status
6. Whether its crop has food in it
7. An evaluation of its droppings
If possible, a few drops of blood can be collected for a PCV, blood smear, TPP, and blood glucose.
This evaluation, while not exhaustive, can performed rapidly and assessment made as to the chick’s status using the four Hs.
The Four Hs
Regardless of the underlying aetiology, the majority of problems with sick chicks can be associated with the “four Hs”:
Other problems, such as beak abnormalities and angular limb deformities, are rarely present as emergent conditions and will not be discussed further in this paper.
Severe dehydration is common in chicks, usually associated with GI dysfunction (vomiting, diarrhoea, and ileus) or decreased intake (poor husbandry, refusal to eat). Respiratory loss due to panting when heat stressed can also lead to dehydration. Dehydration and hypovolaemia lead to decreased tissue perfusion and subsequent organ damage and even failure. As chicks appear to lack the ability to compensate for mild hypovolaemia to increase tissue perfusion (increased heart rate and contractility, and increased vascular tone), they are extremely sensitive to the effects of dehydration.
Clinical signs include:
1. Thickened mucoid saliva
2. Wrinkling of the skin
3. Decreased venous return (assessed by ‘blanching’ the basilic vein)
4. Decreased urine output and thickened urates
5. Crop stasis
If any uncertainty is present, it is usually safe to assume the chick is dehydrated and act accordingly.
Treatment requires the administration of warmed isotonic fluids. These can be given IV, IO or SC, but if the SC route is chosen the chick should be normothermic, as peripheral vasoconstriction will slow fluid absorption. IO catheters can be placed in the tibiotarsus or ulna, while IV catheters can be placed in the jugular, basilic or medial metatarsal veins. An initial fluid bolus of 3%–4% of the chick’s body weight can be given over 15 minutes and repeated based on the chick’s response. Ongoing fluid administration at 3 ml/kg/hour can then be initiated. Care must be taken to avoid fluid overload (often seen as a dyspnoea associated with non-cardiogenic pulmonary oedema). Once the chick is well hydrated the oral administration of fluids can be expected to maintain a suitable fluid balance.
Hypoglycaemia often arises due to either poor husbandry (inappropriate diet, infrequent feeding, diluted food, or insufficient volume of food) or severe systemic illness (particularly sepsis or those conditions leading to GI ileus or other GI dysfunction). When low dietary intake is combined with an immature gluconeogenic response and low body fat, the result can be severe hypoglycaemia. This in turn leads to CNS and cardiac disturbances (weakness, seizures, coma and death). In the early stages of hypoglycaemia, chicks may be constantly hungry, exhibited as excessive begging behaviour.
Chicks with severe hypoglycaemia should be treated with an IV/IO bolus of dextrose 250–500 mg/kg (50% dextrose, 0.5–1 ml/kg diluted 1:4) administered over 5 minutes. Repeat boluses can be given, based on response to treatment, and then once normoglycaemic the chick’s IV/IO fluids can be supplemented with 5% dextrose until the chick is eating.
Less severe hypoglycaemia may be effectively dealt with by an early return to feeding (or by feeding a more appropriate diet).
Hypothermia in chicks arises because of the effect of the following factors:
1. Low reserves of white (insulating) fat
2. Large surface area to body mass ratio
3. Lack of feathers to insulate the body
4. Reduced ability to vasoconstrict or shiver
5. Reduced activity (chicks are usually sleeping or eating)
When these factors are combined with inappropriate environmental temperatures or reduced food intake (decreased metabolic energy), the result can be profound hypothermia.
Hypothermic chicks are lethargic and poorly responsive to stimulus. Their limbs and bodies are cool to the touch. Peripheral vasoconstriction can be seen as a pallor to the skin. Left untreated cardiovascular function will be compromised, resulting in organ dysfunction and finally cardiac arrest.
Hypothermic chicks should be warmed before fluid resuscitation, but care should be taken to avoid peripheral vasodilation and possible hypotension. Warming can be achieved with warmed air or heat lamps but the chick must have the ability to move away from the heat source once it is normothermic, to avoid hyperthermia.
Hypoxaemia is common in chicks and can be associated with anaemia, the aspiration of hand rearing formula, infectious respiratory diseases (e.g., bacterial or fungal infections), or compression of the air sacs by distended loops of intestinal tract. Hypoxic chicks will have an increased respiratory rate and effort (mouth breathing, increased sternal lift and tail bobbing). Cyanosis can be seen but is usually difficult to appreciate. Pulse oximetry may be of benefit but—because of calibration difficulties with nucleated erythrocytes—trends, rather than absolute numbers, should be monitored.
Oxygen supplementation (via an anaesthetic induction chamber, flow-by oxygen or an intranasal oxygen line) should be administered when hypoxaemia is diagnosed or suspected Care must be taken to prevent oxidative tissue damage associated with 100% oxygen administered for prolonged periods of time.
Where to from Here?
Once the sick chick has been stabilised the clinician can then move on to determining the underlying reason for the problems that the chick was presented. The most common causes of disease in chicks are:
1. Infectious diseases (viral e.g., PBFD, APV; fungal e.g., Candida, Aspergillus; and bacterial)
2. Malnutrition (stunting syndrome, metabolic bone disease)
3. Scissor beak
4. Crop burns
But the diagnosis and treatment of these cases can only be performed once the chick is stabilised. Careful evaluation and examination are paramount in diagnosing and treating paediatric problems.
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