Avian digestion and nutrition Flashcards
Why is metabolism high in birds?
high energy demands of flight
Describe the variation of the GIT of seed eating/green leaf eating birds
Large caeca where fermentation of fibre rich material occurs
Describe the variation of carnivorous birds such as birds of prey
relatively simple digestive tracts with small or absent caeca
Describe the composition of the beak/bill of birds
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
What muscles close the jaw in avian species?
adductor mandibulae externus
adductor mandibulae posterior
pterygoideus
What muscle open the jaw in avian species?
depressor mandibulae
What is larger in avian species to allow wide opening of jaw?
Quadrate bone
Describe the internal anatomy of the avian mouth
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
Describe the mechanics of eating in avian species
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
Describe the mechanics of drinking in avian species
immerse beak in water
water moved caudally by tongue
tip head back => water enters oesophagus
What is the clinical relevance related to avian oesophagus?
Heavy metal poisoning e.g., Pb, leads to paralysis
What happens to food in the crop?
degradation of starch by salivary amylase
bacterial fermentation
What is sour crop?
overgrowth of candida spp with swollen mucous membranes and impacted feed
How can you use the crop to assess eating habits in birds?
Food is stored in the crop
If food is available but crop is empty - not eating
What stimulates the crop to empty?
Emptying of the proventriculus
How is crop milk produced?
prolacting production increases whilst incubating eggs
=> increase in fatty cells in crop which slough off when chicks hatch - resulting liquid = crop milk
What is the function of the proventriculus?
produces HCl and pepsinogen from oxynticopeptic cells for chemical digestion
Epithelial cells produce mucous
What is the isthmus in birds?
thin, non-glandular wall between proventriculus and gizzard
What is kiolin and what is its functino?
tough lining of the gizzard
protects mucosa
formed from mucosal cell secretions
composed of protein and carb
Describe the function of the gizzard
protein digestion
mechanical food breakdown
smooth muscle
chemical digestion continues as transit time from proventriculus to gizzard is rapid
What happens to ingesta when the thin muscles of the gizzard contract?
small particles move into duodenum (prograde)
large particles move into proventriculus (retrograde) or are regurgitated (carnivores)
What is egestion in birds?
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
What is the function of grit in the gizzard?
aid mechanical digestion
if high in calcium carbonate will need replenishing as it will dissolve in acidic conditions
Why is grit not fed to broiler chickens and what is the implication of this?
damages gizzard harvesters in processing plant
may increase incidence of enteritis
Where is the gall bladder found in birds?
within the right lobe of the liver
Why is the SI short in birds?
to facilitate high metabolic rate
What is Merkel’s diverticulum?
vestige of the yolk sac that makrs the boundery between ileum and jejunum
What happens to the yolk sac after birth in chicks?
persists in the first few days to nourish the hatchling
Describe the anatomy and physiology of the avian small intestine
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
What enzymes can be found in the avian SI?
amylase and esterase
no need for lactase
What are Peyer’s patches in birds?
lymphoid nodules in the lamina propria - provide lymphatic drainage
What are the caeca?
paired, blind ending sacs at the iliocaecocolic junction
What is the function of the caeca in birds?
contain gram +ve bacteria and protozoa
digest cellulose
ferment carbs digested in the SI
What are caecal tonsils?
abundance of lymphoid materia, at the proximal end of the caeca
How does chyme enter the caeca?
antiperistaltic movements
Selective - small particles in chyme are retained, coarse fibre material is excreted
caeca emptied a few times a day (faecal droppings)
What is the function of the large intestine in birds?
reabsorbs water and electrolytes
reabsorb glucose and amino acids
what are the compartments of the cloaca in birds?
copradeum
urodeum
proctodeum
what occurs in the compartments of the cloaca in birds?
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
What adaptation allows water and electrolytes from urinary waste to be reabsorbed in birds?
some urinary excretions in cloaca become incorporated with ingesta which moves in a retrograde manner into the caeca
Why is the calculated nutritional value of prepared seed mixes for birds often not accurate
Calculated based on whole seeds, birds often dehull the seeds
