Avian Integument

Question 1

What does the avian integument consist of?

Answer 1

Skin
Scales
Beak
Cere
Feathers
Nails
Foot pads
Adopted appendages for defence and display (eg. Wattles, combs, snood, knobs)

Question 2

How is the avian epidermis different to the mammal, what three layers does it consist of?

Answer 2

The skin is similar to that of mammals however in comparison it is much thinner and contains feather follicles

The epidermis consists of three layers: the basal (germinative) layer, the intermediate layer and the outer cornified layer
Striated muscles in the epidermis move the skin

Question 3

What does the avian dermis consist of?

Answer 3

A superficial layer which varies in thickness depending on age and position and contains loosely arranged layers of collagen in interwoven bundles
A deep layer which contains fat, father follicles, smooth muscles that control the movement of the feathers and blood vessels/nerves.

Question 4

What does the avian subcutaneous layer consist of, what is different to mammals?

Answer 4

The subcutaneous layer of avian skin is formed mainly by loose connective tissue, it contains fat as a layer and discrete fat bodies. These areas are readily observed as yellow deposits underneath the skin and their position will vary by species (higher number in aquatic birds) and time of year (pre-migration deposition). Common areas of deposition are lateral to the pectoral muscles, the cloacal region and on the back.

Question 5

What is the effect of having a minimal dermis on skin? What does this mean clinically?

Answer 5

Skin with minimal dermis is not very elastic, this combined with the thin nature of bird skin means that sutures readily pull through and are not always idea.

Question 6

What is the podotheca?

Answer 6

This is the non-feathered areas of the leg and feet.
Scales are formed from raised, heavily keratinised epidermis separated by folds of less keratinized tissue
This area often shows a pimpled surface and this is normal

Question 7

What is bumblefoot?

Answer 7

Bumble-foot (podadermatitis) is a common disease of domesticated birds and shows balding and inflammation of the epithelium before ulceration and necrosis in the final stages.

Question 8

Do birds have sebaceous and sweat glands?

Answer 8

No

Question 9

What glands to birds have in their skin?

Answer 9

Uropygial gland, glands of the ear canal, pericloacal glands.

Question 10

What is the Uropygial gland?

Answer 10

The uropygial gland is a bilobed gland located dorsal to the cloaca at the end of the pygostyle, it opens through a caudally directed nipple. This holocrine gland is not present in all species of bird (parrots, finches and pigeons but not amazons).

Question 11

What is the function of the uropygial gland?

Answer 11

Its function is for maintaining feather condition by providing secretions for preening. It serves as waterproofing, and secretions contain a pro-vitamin D converted by UV light to vitamin D, the oil also affects light absorption and feather colouring as well as inhibiting the growth of microorganisms.

Question 12

What happens to the developing dermal cells in birds?

Answer 12

Developing dermal cells (keratinocytes) undergo metamorphosis from cuboidal or squamous nature, lose organelles, produce lipids and fibrous proteins (keratin), dehydrate and lyse

Question 13

Why do the KC’s lyse in birds?

Answer 13

This function is unique to birds and it is suggested that the lipid production makes the entire skin an oil producing gland.
When macaws and amazons are stressed they emit a musty smell that arises from the volatile fatty acids emitted directly from the rapidly lysing keratinocytes

Question 14

Is avian skin movable like a mammal?

Answer 14

The skin overlaying the head, extremities and sternum is firmly attached to underlying skeletal structure and thus is effectively non-moveable. Elsewhere in the body the skin is more loosely attached to the underlying muscles but still has limited motion.

Question 15

What are patagia?

Answer 15

The skin may be reflected into flat, membrane like structures called patagia in areas where the wings, legs and tail join the body.

Question 16

On the wings, there are 4 patagia that are responsible for wing stability and aid aerodynamics, what are they called?

Answer 16

Propatagium (wing web): Junction of the neck and wing
Postpatagium: Formed at the caudal angle of the carpi
Metapatagium: Caudal junction of the wing and thorax
Alular patagium: Interspace between the alula (bird thumb) and carpi

Question 17

What other patagia do birds have and what is their significance for vets?

Answer 17

Additional patagia include the cervical patagium (between neck and scapula) and the knee web which is formed from the skin connecting the knee to the paralumbar area although this is not a true patagium as its not always present
Patagia can be used for subcutaneous injections in birds

Question 18

What is the beak made up of?

Answer 18

These are the bones of the maxilla and mandible with a horny covering (rhamphotheca)

Question 19

How does the histology of the beak differ from that of the skin?

Answer 19

The histology is similar to the skin however the stratum corneum is very thick with abundant keratin and contains cell bound calcium phosphate and layered hydroxyapatite

Question 20

What is the bill tip organ?

Answer 20

The beak is very sensitive to temperature and pressure due to a high number of mechanoreceptors (Herbst corpuscles). This is histologically recognisable as papillae originating from the dermis and ending in crater like structures at the distal tip of the beak.

Location and degree of development varies among species, for example it is highly developed in birds that feed by pushing their beak into the dirt and absent in birds that feed by pecking

Question 21

What is the egg tooth?

Answer 21

A small pointed keratin eminence found on recently hatched neonates
Used to penetrate the air space within the eg and then the eggshell, it falls off after a few days
The Megapodes do not have an egg tooth but rather they kick their way out of the egg
The egg tooth is also present in many reptiles.

Question 22

What is the cere?

Answer 22

Situated at the base of the beak sits the cere, keratinised skin which often houses the nostrils.

Question 23

What influences the colour of the cere?

Answer 23

The colour of the cere is influenced by diet and hormones: in budgies the male has a blue cere due to testosterone and the female has a brown cere. In raptors, high levels of carotenoids will colour the cere yellow.
In male budgies brown hypertrophy of the cere may occur presumably due to changes in the sex hormones but it is commonly associated with testicular hormones.

Question 24

Is hypertrophy of the cere normal in laying hens?

Answer 24

Yes

Question 25

What is scaly face?

Answer 25

Hyperkeratosis of the cere, beak and surrounding tissue with associated honeycombing is diagnostic of knemidokoptics mite or ‘scaly face’

Question 26

In terms of feather distribution what two areas can the body be divided into?

Answer 26

In most birds the body is divided into areas that contain feather tracts (pterylae) and areas that do not have feather tracts (apteria).

Question 27

Does the jugular vein lie in an apteria or a pterylae?

Answer 27

Apteria on the RHS

Question 28

What is the calamus of the feather?

Answer 28

The short hollow tubular unpigmented end of the mature feather inserted into the feather follicle and thus present below the skin level

Question 29

What is the rachis of the feather?

Answer 29

The long solid tubular extension of the calamus above the skin. The rachis contains pith which is composed of air filled keratinised epithelial cells surrounded by a solid keratinised outer cortex

Question 30

What is the shaft of the feather?

Answer 30

Made up of the calamus and the rachis

Question 31

What is the vein or vexillum of the feather?

Answer 31

the portion of the feather that extends to either side of the rachis and is composed of barbs and other associated structures. The vane is either plumulaceous (soft and downy) or pennaceous (compact and closely knit) depending on the individual type of feather

Question 32

What are we looking for when we pluck and examine a feather?

Answer 32

Examination of plucked or moulted feathers can help diagnose the presence of Ectoparasites (some that live in the hollow of the rachis), the quality of the barbs and barbules which give an indication of the nutritional status of the bird, the calamus (when normal appears as rounded but when diseased shows as pinched off) and the presence of stress or fret lines.

Question 33

What are contour feathers?

Answer 33

predominant feather covering the body

Question 34

What are covert feathers?

Answer 34

small contour feathers of the wing and tail

Question 35

What are remiges feathers?

Answer 35

large stiff feathers of the wing

Question 36

What are retrices feathers?

Answer 36

large flight feathers of the tail

Question 37

What is the function of powder down feathers?

Answer 37

Down feathers can be found on adults and chicks as powder down, a specialized type of down feather that produces a powder (keratin) that is spread through the feathers during preening. They are found throughout the body among the down feathers and contour feathers

Question 38

A shiny beak can be indicative of…

Answer 38

a lack of powder down

Question 39

Feather follicles are formed by…

Answer 39

formed by invagination of the skin

Question 40

At the umbilicus of the calamus…

Answer 40

The dermis carries a hump of pulp into the tip of the calamus

Question 41

Is the feather well innervated?

Answer 41

The follicular wall has an abundant supply of sensory nerve fibres, and the papillae, pulp and feather muscles are also well innervated

Question 42

How can birds regulate body temperature using their feathers?

Answer 42

Smooth muscles at the base of the feather follicles help maintain feather follicles help maintain body temperature by increasing or decreasing the elevation of the feathers from the skin

Question 43

How do birds detect vibrations with their feathers?

Answer 43

Herbst corpuscles at the base of feather follicles are believed to detect subtle ground vibrations and changes in air currents

Question 44

What affects the colour of a birds feather?

Answer 44

Biochromes – colour pigments that are deposited at the time of feather development, these can be:
Naturally occurring, food derived carotenoids give a yellow red colour and colour intensity can be dictated by the availability of free carotenoids
Synthetically derived melanin’s (browns, greens and black) or psittacofulvins (pigment in parrots)

or structural properties of feathers that are placed on the feather after development so the feathers can scatter light.

Question 45

What can cause colour change to the birds feather?

Answer 45

Due to two types of mutation:
The genetic ability or inability to absorb, manufacture or deposit colour pigments
An alteration in the feather structure (usually at barbule level) creating a different reflective or absorptive light pattern

Question 46

Do birds moult?

Answer 46

The soft keratin structures such as scales, wattle and cere undergo a constant moult and replacement in a similar fashion to mammalian skin. The feathers moult by the growth of a new feather pushing out the old one (like teeth).

Question 47

How often do birds moult?

Answer 47

Moulting varies with age, species, time of year and sex and can be gradual (months), dramatic (weeks) or continual (seen in powder down)

Question 48

What controls the birds moult?

Answer 48

Circannual rhythms – changing temperature and photoperiod. Pineal gland-hypothalamic-pituitary and autonomic nervous pathways operate

Hormonal influences – oestrogens, progesterones, thyroid, catecholamines and prolactin

Nutrition – feathers make up around 10% of the body mass in small birds so it places a high metabolic demand on birds.

Question 49

What is the effect of nutrition on moulting?

Answer 49

The feathers consist of around 90% protein in the form of keratin, which contains a high amount of sulphur containing amino acids, methionine and cysteine, however a lack of any of these will not stop the moult. Inadequate nutrition during or pre-moult will result in the bird delaying or adjusting its moult by reducing the rate of feather production or sustaining the moult at the cost of other bodily functions, this often results in poor quality feathers.

Question 50

What are fret marks?

Answer 50

Fret marks on the feathers as clear breaks in feather colour as a result of an interruption in feather growth and malformation of the feather barbs.