Avian digestion and nutrition

Question 1

Why is metabolism high in birds?

Answer 1

high energy demands of flight

Question 2

Describe the variation of the GIT of seed eating/green leaf eating birds

Answer 2

Large caeca where fermentation of fibre rich material occurs

Question 3

Describe the variation of carnivorous birds such as birds of prey

Answer 3

relatively simple digestive tracts with small or absent caeca

Question 4

Describe the composition of the beak/bill of birds

Answer 4

consists of bone, vascular dermis with a modified keratinised, germinal layer
covered in leathery keratin
epithelium has thick stratum corneum which makes beak hard
High density of mechanoreceptors

Question 5

What muscles close the jaw in avian species?

Answer 5

adductor mandibulae externus
adductor mandibulae posterior
pterygoideus

Question 6

What muscle open the jaw in avian species?

Answer 6

depressor mandibulae

Question 7

What is larger in avian species to allow wide opening of jaw?

Answer 7

Quadrate bone

Question 8

Describe the internal anatomy of the avian mouth

Answer 8

No soft palate, oral cavity or pharynx - have an oropharynx
Choana - connection between nasal cavity and oropharynx in the midline of the hardpalate (closes when swallowing)
Infundibular cleft - just caudal to choana - common opening for pharyngotympanic tubes (eustachian tube equivalent)
No teeth
hyoid apparatus supports keratinised tongue

Question 9

Describe the mechanics of eating in avian species

Answer 9

Papillae in oropharynx point caudally to move food in conjunction with tongue and gravity (tip head upwards)
No soft palate or pharyngeal muscles => no peristalsis to facilitate swallowing

Question 10

Describe the mechanics of drinking in avian species

Answer 10

immerse beak in water
water moved caudally by tongue
tip head back => water enters oesophagus

Question 11

What is the clinical relevance related to avian oesophagus?

Answer 11

Heavy metal poisoning e.g., Pb, leads to paralysis

Question 12

What happens to food in the crop?

Answer 12

degradation of starch by salivary amylase
bacterial fermentation

Question 13

What is sour crop?

Answer 13

overgrowth of candida spp with swollen mucous membranes and impacted feed

Question 14

How can you use the crop to assess eating habits in birds?

Answer 14

Food is stored in the crop
If food is available but crop is empty - not eating

Question 16

What stimulates the crop to empty?

Answer 16

Emptying of the proventriculus

Question 17

How is crop milk produced?

Answer 17

prolacting production increases whilst incubating eggs
=> increase in fatty cells in crop which slough off when chicks hatch - resulting liquid = crop milk

Question 18

What is the function of the proventriculus?

Answer 18

produces HCl and pepsinogen from oxynticopeptic cells for chemical digestion
Epithelial cells produce mucous

Question 19

What is the isthmus in birds?

Answer 19

thin, non-glandular wall between proventriculus and gizzard

Question 20

What is kiolin and what is its functino?

Answer 20

tough lining of the gizzard
protects mucosa
formed from mucosal cell secretions
composed of protein and carb

Question 21

Describe the function of the gizzard

Answer 21

protein digestion
mechanical food breakdown
smooth muscle
chemical digestion continues as transit time from proventriculus to gizzard is rapid

Question 22

What happens to ingesta when the thin muscles of the gizzard contract?

Answer 22

small particles move into duodenum (prograde)
large particles move into proventriculus (retrograde) or are regurgitated (carnivores)

Question 23

What is egestion in birds?

Answer 23

egestion of bones once nutritious components of prey has been digested
During reflux, gastric motility is inhibited and the pellet is expelled by oesophageal antiperistalsis

Question 24

What is the function of grit in the gizzard?

Answer 24

aid mechanical digestion
if high in calcium carbonate will need replenishing as it will dissolve in acidic conditions

Question 25

Why is grit not fed to broiler chickens and what is the implication of this?

Answer 25

damages gizzard harvesters in processing plant
may increase incidence of enteritis

Question 26

Where is the gall bladder found in birds?

Answer 26

within the right lobe of the liver

Question 27

Why is the SI short in birds?

Answer 27

to facilitate high metabolic rate

Question 28

What is Merkel’s diverticulum?

Answer 28

vestige of the yolk sac that makrs the boundery between ileum and jejunum

Question 29

What happens to the yolk sac after birth in chicks?

Answer 29

persists in the first few days to nourish the hatchling

Question 30

Describe the anatomy and physiology of the avian small intestine

Answer 30

thin walled and narrow
consist of mucosa, submucosa, circular and longitdunial muscle and serosa
has a higher pH than gizzard due to pancreatic and gall bladder secretions

Question 31

What enzymes can be found in the avian SI?

Answer 31

amylase and esterase
no need for lactase

Question 32

What are Peyer’s patches in birds?

Answer 32

lymphoid nodules in the lamina propria - provide lymphatic drainage

Question 33

What are the caeca?

Answer 33

paired, blind ending sacs at the iliocaecocolic junction

Question 34

What is the function of the caeca in birds?

Answer 34

contain gram +ve bacteria and protozoa
digest cellulose
ferment carbs digested in the SI

Question 35

What are caecal tonsils?

Answer 35

abundance of lymphoid materia, at the proximal end of the caeca

Question 36

How does chyme enter the caeca?

Answer 36

antiperistaltic movements
Selective - small particles in chyme are retained, coarse fibre material is excreted
caeca emptied a few times a day (faecal droppings)

Question 37

What is the function of the large intestine in birds?

Answer 37

reabsorbs water and electrolytes
reabsorb glucose and amino acids

Question 38

what are the compartments of the cloaca in birds?

Answer 38

copradeum
urodeum
proctodeum

Question 39

what occurs in the compartments of the cloaca in birds?

Answer 39

copradeum:
- rectum empties
- absorption of water and ions
Urodeum:
- where ureters and genital ducts empty
Proctodeum:
- empties contect of cloaca into vent on relaxation of the external anal sphnicter

Question 40

What adaptation allows water and electrolytes from urinary waste to be reabsorbed in birds?

Answer 40

some urinary excretions in cloaca become incorporated with ingesta which moves in a retrograde manner into the caeca

Question 41

Why is the calculated nutritional value of prepared seed mixes for birds often not accurate

Answer 41

Calculated based on whole seeds, birds often dehull the seeds