Avian reproduction Flashcards
List the features of the male reproductive tract in the bird
- Gonads (testis)
- Epididymis
- Ductus deferens
- No accessory glands
- +/- phallus
Describe the testis of birds
- Paired
- Large compared to mammals
- Intra-abdominal
- Cranioventral to first kidney lobe, near abdominal air sac
- Can increase 300-500x when breeding
Describe the duct system in male birds
- Epidydimis and ductus deferens
- E is small
- DD highly coiled, terminates in urodeum on papilla
What is the seminal glomus in bird?
Some species of bird have enlarged end of ductus deferens used for sperm storage
Give the 2 insemination methods in birds
- No phallus/no phallus but no intromission = cloacal kiss
- Phallus with intromission
Describe the cloacal kiss in birds
- Method of insemination
- Male everts cloacal wall to everted opening of female oviduct
- Cloaca to cloaca contact
What are the components of the female avian reproductive tract?
- Ovary
- Infundibulum
- Magnum
- Isthmus
- Shell gland
- Vagina
- Oviduct
Describe the ovaries of birds
- Legt ovary function
- Right usually regresses during development and becomes vestigial
- Look like bunch of grapes, yellow
What are the components of avian follicles?
- Oocyte
- Granulosa cells
- Theca cells
Describe the oocytes within follicles in birds
- NO zona pellucida
- Membrana granulosa and cumulus oophorus present, simple structure
- Yellow yolk within each follicle
What is the yellow yolk in birds analogous to?
The oocyte
Describe follicle development in the birds
- Slowly at first, lipids deposited in egg’s yolk
- Small number of oocytes enlarge and deposit white primordial yolk
- Enter rapid growth phase and deposit yellow yolk
- From this point on very rapid enlargement
- Surrounded by granulosa and theca cells, no fluid filled cavity
Describe follicle maturation in birds
- Not in synchrony
- F1 largest, matures first, then F2 then F3
- Smallest white follicles, larger yellow
- Large number of smaller white folicles, will become atretic
What happens at ovulation in brids?
Follicle splits open to release egg (yellow yolk)
Describe the post-ovulatory follicle in birds
- Thin walled sac
- Hypertrophied granulosa cells remain
- Metabolically active for a number of days (8-10)
- Non-steroid hormones being produced
What are the actions of the non-steroid hormones being produced by the granulosa cells in birds following ovulation?
Role in ovipostiion, egg laying and nesting behaviour
What is the function of the granulosa cells in birds (compare this to mammalian)?
- Progesterone production
- In mammals, granulosa cells produce E2
What is the function of the theca cells in birds (compare this to mammals)?
- Production of E2
- In mammals produce progesterone
Where is the progesterone from luteinised cells derived from in birds?
Graulosa and theca cells
Describe the egg laying endocrinology
- E2 rises a couple of weeks prior to egg laying
- E2 linked preparation for egg layinng
- Ovulation preceded by increased LH and progesterone
- Increased LH leads to increased progesterone
- Progesterone positive feedback to hypothalamus to increase LH
What changes occur near ovulation that lead to the hormonal changes seen in birds?
- Follicles mature, enzyme activity in theca cells decreases = less conversion to oestradiol
- Increased activity in granulosa cells = more progesterone produced at time of ovulation
Describe the oestrogen-linked preapartion for egg laying in birds
- Synthesis of calcium ATPase
- Medullary spaces calcified
- VLDL precursors to yolk produced and transferred to yolk
- Oviduct enlarges
- Plumage, comb size and receptivity altered
When is oestrogen highest in the bird?
At start of follicular development
What is the open period in birds?
The window of time for LH release, lasts around 8-10 hours from onset of darkness to around 1 hours after lightonset
Describe ovulation in relation to the open period
- In F1 follicle, enough P4 in open period = LH surge = ovulation
- NO CL formed
What follicles can produce progesterone and what is the function of this?
- Mature follicles only
- Suppress GnRH and LH if high levels
- So only mature produce to avoid suppression
Why is progesterone not needed after ovulation in birds?
In mammals is to maintain foetus, not needed in birds
Give the order of passage of the oocyte through the female tract
- Fertilised in infundibulum
- Into the magnum
- Then isthmus
- Then shell gland/uterus
- Then vagina
Describe the fertilisation of the oocyte in birds
- In infundibulum after ovulation
- ovum capture in infundibulum
- Ciliated epithelium of infundibulum moves ovum into funnel shape and into oviduct
How long does it take from fertilistion to egg production?
~24 hours
Where are the sperm storage tubules?
At the junction of the vagina and the shell gland/uterus
What is the function of the sperm storage tubules?
- Allows storage of sperm for 10-14 days
- Squeezed out of SSTs, fertilise another egg 2 weeks later in abscence of male
Describe the secretory function of the infundibulum
- Produces first egg coat
- Chalazae
- Less than 1 hour here
What is the function of the chalazae?
Anchor yolk in egg, prevent flopping and keep embryo in proper place
Describe the role of the magnum in egg production
- Albumin added here
- Takes 3-4 hours
What stimulates the production and release of albumin?
Physical passge of the egg through the magnum
Where is albumin produced?
Liver and magnum
What is the function of the isthmus?
- Inner and outer shell membranes added
Describe the processes that occur within the shell gland
- Calcium carbonate shell added to the outside of the egg
- Once done, proteins added to form thin cuticle
- May add pigment
What is the function of the thin cuticle of the egg?
Seals and protects against dehydration
What occurs within the vagina?
Ovipostion for egg layiing
What determines clutch size?
- Either determinate or indeterminate
- Determinate: fixed number of eggs in a clutch
- Indeterminate: lay eggs for extended period of time, continue production stimulated by removal of eggs
- Breeding season
- Timing of ovulation and oviposition
Explain how timing of ovulation and oviposition affect clutch size
- In domestic hen, ovulation is 6-8 hours after LH surge
- Egg laid 24-26 hours after ovulation
- Ovulation 15-75 mins after oviposition
- ovulation becomes later each day
- Eventually miss the open period = pause day, clutch formed
What are the hormonal features of brooding?
- High prolactin
- More ovulation inhibited by progesterone
- Decreased LH, oestrogen and progesterone
Why does prolactin increase in brooding period?
- Produced by ruptured follicles
- Gonadal steroids decrease
What is the effect of increased prolactin during the brooding period?
- Increases in males and females when egg laying taking place
- Stimulates nesting activity and incubation
- Accelerates gonadal regression
- Higher in whichever parent is giving parental care
Describe some key features of brooding behaviour
- +/- brood patch (shed or pluck)
- Sit on eggs
- Skin oedematous and highly vascularised
- Increased metabolism to maintain temperature
What triggers the switch from ovulation to the production of prolactin?
Tactile stimulation in brood patch
Why must reproductive processes be primed?
- If not, reproductive activity is lower
- LH also lower
Describe how reproductive processes are primed with regards to a mate
- Full access to mate prior to onset of reproduction
- Ideally full contact
- Auditory
Describe the impact of daylight on breeding
- Increased daylight = increased reproductive activity
- Increase in ovary and testes size
Describe the encephalic photoreceptors
- Deep in brain
- Stimulated by fluorescent, incandescent light
- Through eyes and direct through skull to brain can also stimulate photoreceptors
What is photorefractoriness?
- Observed in some species
- Long day length stimulates gonadal regression
- Become refractory to long day length
- Increase in thyroid hormones
What is the photosensitive phase?
The time in which daylight can have an effect on reproduction
Describe how the photosensitive phase affects reproduction
- Bird checks light twice daily
- At dawn and 13-17 hours later
- In the second period is where light has an effect
- Between these times light is unimportant in reproduction, could have lights off all day and on again in photosensitive period and is same as lights on all day and throughout photosensitive period
Are males or females heterogametic?
Females (ZW), males are ZZ
How can birds be sexed?
- DNA
- Surgical assessment
- Faecal steroids
- Instrument sexing
- Vent sexing
- Auto-sexing
What sexing methods are most commonly used in commercial birds?
- Instrument
- Vent
- Auto
What samples are used for DNA sexing?
- Blood from nail clipping
- Live cells from plucked feather
- Egg shell from hatched bird
- Results 3-4 weeks, accurate, adults or chicks
Describe surgical assessment of sex
- Need to be sexually mature
- See testes or ovaries in abdomen
- Investigate other problems
Give the disadvantages of surgical assement of sex
- Stressful for bird
- Anaesthetic risk
- Post-op complications
Describe sexing using faecal steroids
- Sexually mature and active
- Females: high progesterone and E2
- Males: high androgens
- Fresh faecal sample needed
What are the advantages of faecal steroid sexing?
- Safe
- Cheap
- Accurate
What are the disadvantages of faecal steroid sexing?
- Need to be sexually mature
- Need to be in breeding season
Describe instument sexing (advantages and disadvantages)
- Optical instrument into large intestine
- Visualise gonads through intestinal wall
- Risk of injury
- Good method of discrimination
Describe vent sexing (advantages, disadvantages)
- Look at cloaca for evidence of genital organs
- Water fowl have large cloaca
- Best in 12-24 hour old chicks
- No risk of injury
- Needs lots of experience to be accurate
Describe autosexing
- Phenotypic features different between males and females
- e.g colour, length of wing feathers (longer in females of some species)
