XEROSIS IS A COMMON CAUSE OF FEATHER DESTRUCTION BEHAVIOUR IN ECLECTUS AND OTHER PARROTS.
Rob Marshall,* B.V.Sc., M.A.C.V.Sc (Avian health)
Tailai OBrien BBus (HRM & BMGT), Cert IV Assessment & Workplace Training, Cert III Captive Animal Management
Carlingford Animal Hospital, Sydney, Australia
* Corresponding author
SESSION NUMBER #2001
KEY WORDS: xerosis, epidermal lipids, cutaneous water loss, dry skin, feather destruction behaviour, eclectus parrot
Xerosis is an abnormal dryness of the skin. Any condition that interferes with the two key functions of skin, namely permeability barrier homeostasis and stratum corneum integrity and cohesion, will lead to dry skin. Essential fatty acid deficiencies especially involving linoleic acid contribute to dry skin problems in eclectus parrots (Eclectus roratus) as they upset the function of epidermal lipids (skin oils) that protect the skin from dehydration. Stressful episodes (physical, physiological and emotional) are often implicated in dry skin problems as they inhibit the synthesis of epidermal lipids. Birds with vitamin D and calcium deficiencies are also likely to experience dry skin during excessively dry weather. Understanding the dietary, environmental, health and bathing requirements of eclectus parrots for proper barrier function and skin permeability homeostasis and circumstances that interfere with it are instructive when organizing treatment plans for those birds exhibiting feather destruction problems associated with dry skin.
Xerosis is the medical term used to describe abnormal dryness of the skin. There are many causes of xerosis. Treatment varies according to the particular cause. Eclectus parrots are particularly prone to dry skin probably because they have evolved in a rainforest environment of high humidity and stable temperatures.1 Their wild diet is nutritionally and functionally sound. They bathe regularly. Their breeding is seasonally restricted. These natural conditions are responsible for keeping their skin moist and supple. Dry skin is a frequent problem in eclectus parrots living outside the tropics where weather conditions are more drying, changeable and seasonally variable. Nutritional imbalances and digestive disturbances are common due to feeding incorrect diets. Bathing frequency is significantly reduced in the captive setting especially during cold weather. Indoor heating is often used in winter and air conditioning in summer. Abnormal sexual behaviours are also prevalent in captive birds. It is a combination of these factors that predispose eclectus and other parrot species to the irritation of dry skin that may trigger feather destruction episodes.
Eclectus and other parrots will usually show signs of dry skin irritation when the air becomes exceedingly dry. Sneezing is the first obvious sign of dry skin. Short bursts of sneezing are heard as the bird wakes and overgrooms in an effort to relieve the irritation of dry skin. In relatively healthy birds the symptoms will disappear with a return of normal environmental humidity conditions. In the lowland rainforests where eclectus parrots live humidity at its lowest is around 70% in the middle of the day but reaches 100% at night. The skin of eclectus parrots is prone to dryness when humidity suddenly drops below 60%. Under these circumstances the skin of birds with underlying health problems (e.g. digestive upset, hormonal imbalance) or emotional upset (e.g. separation anxiety, sexual frustration and aggression) will not re-establish proper skin barrier function. The dry skin of these birds may become inflamed and uncomfortable which may initiate feather destruction behaviour.
Epidermal Lipids & Skin Hydration
Maintaining a healthy epidermal lipid layer function is key to preventing dry skin problems as it controls water loss through the skin. The epidermis is the outer of two skin layers, the inner being the dermis. Lipids, protein and cells within the stratum corneum (SC), which is the external layer of the epidermis, prevent the loss of body fluids and form a barrier against injurious agents.2 Layers of epidermal lipids facilitate evaporative cooling by controlling cutaneous water loss (CWL). Evaporative cooling is essential as birds lack sweat glands. This alternative method of thermoregulation helps birds overcome rising body temperature generated by flight and during hot weather.2 Dry skin develops when the epidermis loses moisture faster than it is replenished, which stems from a failure of epidermal lipids to adequately control CWL.
In birds, the SC serves as the primary barrier against water loss through the skin. “A bricks and mortar” arrangement of impervious flattened dead skin cells (keratinocytes) embedded within a layered matrix of lipids forms a tough and facultative waterproofing barrier. The lipid layers regulate SC integrity and cohesion.3 These extracellular lipids are thought to serve as the primary barrier against CWL.3 They contain ceramide, free sterols, essential and non-essential fatty acids, and cholesterol.4 Of these fatty acids, ceramides and cholesterol are the most important lipid groups. They must be present in the correct quantity and proportion for normal skin barrier function. Dry skin is a consequence of a “leaky” lipid layer barrier caused by deficiencies or faulty ratios of any one of these principal lipids.4 Amongst the fatty acids, linoleic acid (LA) is structurally the most important. Cerebrosides, which are ceramide-type waxy lipid molecules, play a prominent role in reducing CWL in birds.5 They are thought to be absent in mammal skin.5 The mosaic of different lipid layers and skin cells modulates CWL whilst at the same time resisting the entry of external water. The lipids have antimicrobial properties and contain sterol precursors for vitamin D. Their full functional significance continues to be unraveled.5
A major bodily function is skin repair. The epidermal barrier is a highly organised tissue that responds efficiently and rapidly to a changing environment in order to maintain a state of homeostasis, or perfect balance. Once the epidermal barrier is disturbed, either by penetration by foreign material or dehydration, signals are sent by the lipids to replenish the lipid barrier system and remove any foreign material.16
Specialised skin cells called sebokeratinocytes produce the epidermal lipids.5 The essential fatty acids (EFAs) LA and arachidonic acid (AA) are involved in the proper function of these cells. These two fatty acids must be provided by the diet as they are not produced by skin cells.6 Dietary deficiencies in these fatty acids may cause dry skin because they interfere with lipid layer function involving permeability barrier homeostasis.6 Epidermal lipids also regulate the enzymes involved with detachment of dead skin cells (desquamation) from the epidermis. Deficient or altered ratios of epidermal lipids result in dry skin desquamation defects that release clumped fragments of adhering sloughed skin scale.6 The abnormal detachment of the dead skin cells is a source of irritation.
Essential Fatty Acids & Dry Skin Problems
LA and AA are considered the most important essential fatty acids for skin health as they play unique and important roles in maintaining skin barrier function and keratinocyte homeostasis.5 LA and AA are abundant in bird skin.7 They are considered essential nutrients because they cannot be synthesised by the body or skin. Birds have a capacity to store LA in their bodies for extended periods.7 It follows that EFA deficiencies in free-living birds are probably rare. Deficiencies are more likely in captive birds as adequate supply depends upon sufficient dietary intake and efficient intestinal absorption. Mild deficiency of LA is enough to cause dry skin in humans.8 Nuts are a natural food source of LA for many parrots. An intolerance of captive Eclectus to fatty foods suggests nuts are not part of their wild diet.9 Their source of LA comes from the pulp and seeds of a variety of rainforest fruits,9 which may account for their increased incidence of dry skin problems compared to parrots like macaws whose wild diet is enriched with nuts.
Human research shows that dietary deficiencies in LA and AA lead to abnormalities in skin barrier function, resulting in dry skin (scaly dermatitis) due to water permeability defects.8 Birds with EFA deficiency may be inclined to dry skin problems for similar reasons.10 The EFA composition of human skin is significantly modified by diet. Accordingly, dietary supplementation with LA and AA can be used to correct a deficit or incorrect ratio of epidermal lipids in birds with EFA deficiency and in doing so relieve the irritation of dry skin.
Pathogenesis of Dry Skin Problems
Properly hydrated skin is smooth, healthy and pliable. It is devoid of scaling or dryness.11 Dead skin cells (keratinocytes) are shed as individual cells that are not visible to the naked eye. The degradation of corneodesmosomes by hydrolytic enzymes is impaired with desiccation of the SC.11 This results in a tendency of keratinocytes to “clump” before shedding causing visible scaling and flaking. In humans, dry skin is scaly, rough, dull in appearance and often uncomfortably itchy. In eclectus parrots, large broad flakes of adhered dried skin scale are a cause of intense irritation. Eclectus and other parrots will pluck the feathers from these irritated areas. Slight disturbances to barrier function usually only affect the superficial epidermis.11 In otherwise healthy well-nourished birds, mild symptoms of dry skin (e.g. occasional sneezing episodes) will often pass quickly because the disruption of epidermal barrier activates a rapid metabolic response directed towards recovering epidermal homeostasis and re-establishing normal keratinocyte differentiation. An increase in the synthesis of epidermal lipid (cholesterol, ceramides and fatty acids) allows the SC to quickly recover its full permeability function.4 Conditions that cause a deterioration of ceramide synthesis of the SC such as ongoing dry air, significant cold or heat stress, unresolved digestion problems, dietary deficiencies and so on tend to perpetuate the dry skin cycle by disrupting the lipid layer structure, inducing dysfunctional keratinocyte differentiation and amplifying the inflammatory response.
Predisposing Factors to Dry Skin
Poor diet is an important predisposing factor to dry skin.6 Nutritionally balanced and functionally healthy diets guarantee the correct nutrition is available to maintain healthy skin barrier function (epidermal homeostasis). Even slight nutritional deficiencies (e.g. fatty acid deficiencies) can give rise to dry skin.8 `Digestive disturbances that give rise to intestinal malabsorption causing nutritional deficiencies act in a similar fashion.
In humans, vitamin D promotes the integrity of the permeability barrier by regulating ceramide synthesis.13 Vitamin D is also anti-inflammatory.13 We have noted that birds with little exposure to direct sunlight and no dietary vitamin D supplementation are more likely to develop and be irritated by dry skin flakiness.
Calcium plays a crucial role in keratinocyte differentiation and regulation of epidermal permeability barrier function.14 Females eclectus that are allowed to breed continuously over consecutive years often experience feather destruction episodes during winter as a result of dry skin problems due to hormonally induced calcium deficiencies. The moisture from bathing helps with the desquamation process (i.e. healthy shedding of dead skin cells).15 Eclectus parrots will not bathe when it is too cold, or if they are unwell, overtired or disturbed in any way. A reluctance to bathe will predispose them to the irritation of flaky dry skin.
Studies have shown that testosterone has negative effects on epidermal barrier function and can slow down barrier development and recovery.17 Sexually overstimulated male Eclectus develop dry skin problems due to prolonged testosterone secretion.
Human studies demonstrate that stress (mediated by increased endogenous glucocorticoids) may cause dry skin problems.18 Stress rapidly inhibits epidermal lipid synthesis and subsequently leads to abnormalities in permeability barrier homeostasis and stratum corneum integrity and cohesion. The inhibition of epidermal lipid synthesis occurs not only in the basal state but is even more profound following barrier disruption.18 Replenishment of epidermal lipids by dietary supplementation or topical treatment reverses these abnormalities and represents a potential therapeutic modality to reduce the irritation caused by dry skin.11 This therapeutic approach implies that feather destruction behaviour associated with dry skin is a direct result of abnormal epidermal barrier function initiated by a stressful event (physiological, physical or emotional) rather than being the direct result of abnormal behaviours (e.g. boredom, redirected foraging behaviour or other psychological problems). Therefore, treatment plans for managing feather destruction behaviour initiated by dry skin should aim to restore normal epidermal permeability barrier homeostasis rather than following a psychotherapeutic approach.
Physical exercise stimulates skin vasodilation and increases the level of skin blood flow thereby increasing the transfer of nutrients and oxygen to the keratinocytes. Poor circulation due to lack of exercise predisposes to desquamation defects and dry skin irritation.4 Physical fitness is another useful means for reducing the likelihood of dry skin problems in eclectus parrots.
These many predisposing factors need to be investigated when formulating a treatment plan for parrots exhibiting symptoms of xerosis.
Munoz-Garcia A. Developmental plasticity of cutaneous water loss of desert sparrows. PNAS. 2008; 105:15611-15616
Giminez-Arnau A. Standards for the protection of skin barrier function. Curr Probl Dermatol. Basel, Karger. 2016; 49:123-134.
Elias PM. An integrated view of the epidermal environmental interface. Derm Sinica. 2015; 33:2:49-57
D.Barco. A dysfunctional state of the epidermal barrier. Actas Dermosfiliogr. 2008; 99:671-82
Menon GK. Avian epidermal lipids: Functional considerations and relationship to feathering. Int. Comp Biology. 2015; 40:540-552.
Basavaraj K. Diet in dermatology: Present Perspectives Indian J Dermatol. 2010; 55:205-210.
Scott RC. The influence of skin structure on permeability. J Invest Derm. 1990; 6:921-925.
Rawlings AV. Stratum corneum moisturization at the molecular level. J Invest Derm. 1994; 5:731-740.
Marshall R. Exploring the wild diet to solve functional digestive disorders in eclectus parrots. Int. Conf Av Herpet Exotic Proc. 2017; 3:497-506.
Rajchard J. Biologically active substances in bird skin: a review. Veterinarni Medicina. 2010; 55:413-425
Denda M. Environmental conditions markedly influence epidermal structure and function. J Invest Dermat.1998; 111:5:858-863.
Del Rosso J. Clinical relevance of Maintaining the Functional Integrity of the Stratum Corneum. J Clin Aesthet Dermatol. 2016; 4:22-42.
Russell M. Assessing the relationship between vitamin D3 and stratum corneum hydration for the treatment of xerotic skin. Nutrients. 2012; 4:1213-1218.
Weimann BI. Studies on wound healing: of calcium on the migration, proliferation and protein synthesis of human dermal fibroblasts in culture. Int. J Vitam Nutr Res. 1999; 69:113-9.
Thune P. Evaluation of the hydration and water binding capacity in atopic skin and so-called dry skin. Actas Derm Veneereol. 1989;144 Suppl:133-4.
Huang C. Skin Aging. J Aesthetic Surgery. 2007; 27:4: 402-412
Kao JS. Testosterone perturbs epidermal permeability barrier homeostasis. J Invest Dermatol. 2001; 116:443-451.
Elias P. Mechanisms by which psychological stress alters cutaneous permeability barrier and SC integrity J Invest Dermatol. 2005.124:587-595.
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